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Marine:  Fish/Plankton

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Fisheries researchers, commercial fisherman and regulatory agencies have utilized marine hydroacoustic assessment techniques for decades. Results of detailed hydroacoustic studies are the key component to many important fisheries harvest decisions worldwide. Echo counting and echo integration techniques have been developed to give very accurate fish density and abundance information.


Researchers are able to obtain the spatial, temporal and size distributions within the study area. Scientific hydroacoustic systems can successfully log data from a wide range of targets ranging in size from plankton to whales. Recent advancements in hardware and software technology allow scientists to utilize hydroacoustics for assessment of bottom substrate, aquatic vegetation and aquatic organisms simultaneously in shallow marine and estuary environments to monitor essential habitats.

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Case Studies
Classification of Demersal Capelin Spawning Habitats in Coastal Northeast Newfoundland Using Acoustic Remote Sensing Tools and Techniques
AB: Historically, capelin (Mallotus villosus) spawned on and near gravel beaches in coastal Newfoundland and on the seabed at 40-50 m water depth on the Southeast Shoal of the Grand Banks. Recently, capelin have been observed spawning demersally off the coast of northeast Newfoundland several kilometers from shore at 18-35 m water depth. The spawning sites are dominated by medium sand to pebble dispersed within an area of exposed bedrock. A normal incidence acoustic system (BioSonics DT-X 120 kHz) was used to survey the known demersal spawning sites to map bathymetry and to classify seabed habitats. Unsupervised classification of was carried out using QTC IMPACT software which indicated five to seven classes of seabed. Supervised classification based on ground truthed data from bottom grabs and video distinguished between sand and bedrock habitats as well as habitats characterized by macroalgae (Laminaria sp.) Approximately 33% of the areas surveyed were classified as potential capelin spawning habitats within the coastal region.
 
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Classification of Demersal Capelin Spawning Habitats in Coastal Northeast Newfoundland Using Acoustic Remote Sensing Tools and Techniques 		Product Link:
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Hydroacoustics as a Tool for Assessing Fish Biomass and Size Distribution Associated with Discrete Shallow Water Estuarine Habitats in Louisiana
We developed a relative index of fish biomass and size distribution in ultra-shallow waters (< 2 m) of Barataria Bay, Louisiana, based on the comparison of horizontal hydroacoustic data with gill net and push trawl catches in an effort to understand the role that habitat plays in both fish biomass and distribution. Exclosure net experiments indicated that the contribution of acoustic backscattering from sources other than fishes were negligible. Split-beam transducer, gill net, and push trawl sampling were conducted concurrently in Barataria Bay to provide information on fish composition and length distributions and for comparisons among gear types. Results suggest that acoustic fish biomass was generally higher in the low salinity stations and lower at the high salinity stations, at least in March 2004. We observed a greater mean length of fishes associated with oyster shell habitats when compared to adjacent sand-mud habitats. This paper demonstrates the utility of hydroacoustics as a tool to quantify relative acoustic fish biomass and size distribution associated with common estuarine habitats in ultra-shallow waters. This study also illustrates the potential of using acoustics for augmenting traditional sampling procedures.
 
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Hydroacoustics as a Tool for Assessing Fish Biomass and Size Distribution Associated with Discrete Shallow Water Estuarine Habitats in Louisiana 		Product Link:
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Natural mortality estimates of juvenile Pacific herring (Clupea pallasi) in Prince William Sound, Alaska
The densities of young-of-the-year and 1-year-old Pacific herring, Clupea pallasi, in Prince William Sound, Alaska, were estimated using acoustic surveys from June 1996 to March 1998. Four bays were surveyed with acoustic transects that were repeated three times in 24 h. Species composition and size structure were determined from net collections. Averaging over the 24-h period allowed the best use of all data, as observations between the three replicates were similar but sporadic, possibly resulting from the different seasonal day–night cycle in these northern latitudes. The average instantaneous natural mortality rates for young-of-the-year Pacific herring were 0.009 (standard deviation (SD) = 0.002) and 0.016 (SD = 0.012) for the 1996 and 1997 cohorts, respectively. The average instantaneous natural mortality rates for 1-year-old Pacific herring were 0.003 (SD = 0.007) and 0.008 (SD = 0.005) for the 1995 and 1996 cohorts, respectively. Combining our estimates with those in the primary literature for other life history phases of Pacific herring indicated a progressive decrease in instantaneous natural mortality with age. This study presents the first direct estimates of natural mortality for juvenile herring.
 
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Natural mortality estimates of juvenile Pacific herring (Clupea pallasi) in Prince William Sound, Alaska 		Product Link:
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Shoal behaviour and maturity relations of spawning capelin (Mallotus villosus) off Newfoundland: demersal spawning and diel vertical movement patterns
We investigated shoals of capelin (Mallotus villosus), the focal forage fish species in the Northwest Atlantic, in nearshore Newfoundland during spawning (2000–2003). Large shoals of maturing capelin were observed in warm (>0 °C), deep (>240 m) water. Smaller shoals of maturing fish were located in two specific areas closer to shore in shallower water (100–150 m). Shoals persisted in these staging areas in all years and moved into warm surface water during dark but remained in cold (<0 °C) deep water during daylight. These diel vertical movement patterns may reflect a trade-off between growth and survival, whereby cold, deep water allows reduced predation risk from visual, air-breathing predators while warm, surface water allows increased gonadal development. Shoals of spent capelin, mainly females, were also found in these areas. Sex-specific shoals were observed between staging areas and the coast. Closer to shore, mature, mixed-sex shoals revealed two previously undocumented demersal spawning sites (28–33 m). Suitable habitat for spawning and staging areas resulted in persistent aggregations of capelin shoals, reflecting key foraging areas for top predators and critical areas for conservation.
 
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Shoal behaviour and maturity relations of spawning capelin (Mallotus villosus) off Newfoundland: demersal spawning and diel vertical movement patterns 		Product Link:
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A Floating Device for Stationary Hydroacoustic Sampling in Shallow Waters
A floating device was designed for use in stationary hydroacoustic studies of fish movements and current-speed measurements (Acoustic Doppler Current Profiler ADCP) in the shallow inter- and subtidal zone of mangrove waters (3-10 m depth). The floating device was a stable platform for the hydroacoustic equipment. It features adjustable depth of the transducer below the water surface and adjustable beam direction (horizontal, vertical) of the echosounder. The design is simple, robust, and rapidly bolted together. The results of the ADCP measurements in the mangrove channel at the end of the wet season were unusable even at weak neap tides because bedload transport of fine muddy substrate led to missing bottom echoes that are required for the current-velocity calculation.
 
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A Floating Device for Stationary Hydroacoustic Sampling in Shallow Waters 		Product Link:
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Fish Stock Assessment Using Marine Acoustics Detection and Oceanographic Characteristics In Java Sea
Study on the movements of pelagic fish as a benchmark of pelagic fish stock assessments were investigated by using marine acoustics detection and oceanographical characteristics. Several surveys during 1992 to1994 using a dual-beam BioSonics 120 kHz echo-sounder installed on R/V Bawal Putih (192 GT) were carried out in the middle part of Java Sea. The objective was to verify the importance of seasonal shifting on fish abundance under strong influence of environmental changes. Data were systematically stored using Ines-Movies acquisition and processing system along isobaths 50m to100m. A depth layer was adjusted under 10m stratifications. Descriptions on environmental frame were done through measurements of temperature and salinity by using Seabirds CTD profiler. The result shows higher saline water above 34 ppm is stronger influenced on the east and central of Java Sea during south-east monsoon (September to October 1992 and 1993). This condition is strongly related to the occurrence of higher fish density. The vertical and horizontal distribution of fish density shows that several group of fish populations seasonally occupied in the area. These observations clarified that coldwater intrusion from the Flores Sea and Makassar Strait play an important role in the west-eastward movements of Java Sea pelagic fish stocks.
 
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Fish Stock Assessment Using Marine Acoustics Detection and Oceanographic Characteristics In Java Sea 		Product Link:
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Target Strength of the Common Jellyfish (Aurelia aurita): A Preliminary Experimental Study with a Dual-Beam Acoustic System
An enclosure was designed for experiments estimating the target strength (TS) of the common jellyfish ( Aurelia aurita ) in the Black Sea. A BioSonics echosounder (Model 102) equipped with 120 and 200 kHz dual-beam transducers was used for the measurements. The average acoustic cross-section for each size class was used in functional regression equations to relate the mean TS (dB) of jellyfish to its disc diameter d (cm) and wet weight W (g). These were found to be as follows: TS=14.72 log d-74.63 and TS=5.71 log W-69.41 at 120 kHz; TS=39.65 log d-104.38 and TS=14.53 log W-88.07 at 200 kHz. The TS values were found to fluctuate periodically with time. The results showed a variation of -54 to -67 dB at 120 kHz for 15.5 cm diameter individuals, with a period of 7.5 to 10 sec; and a variation of -58 to -68 dB for 11.5 cm individuals at 200 kHz, with a period of 6 to 12.5 sec.
 
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Target Strength of the Common Jellyfish (Aurelia aurita): A Preliminary Experimental Study with a Dual-Beam Acoustic System 		Product Link:
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A Comparison of Lidar and Echosounder Measurments of Fish Schools in the Gulf of Mexico
In December 2000 the US National Oceanic and Atmospheric Administration’s Fish Lidar (Light Detection And Ranging) system was operated from an airplane off the west coast of Florida. Schools of fish were located and their volume-backscattering coefficients, (), measured at the lidar wavelength of 532 nm. Concurrently, a 208 kHz echosounder was deployed from a small boat to measure the acoustic volume-backscattering coefficients, sv, of the same schools. Seven schools were characterized with both the lidar and the echosounder. The correlation between these seven pairs of () and sv measurements was 0.994. A linear regression of () versus sv had a negative y-intercept, which supports aerial observations of some degree of avoidance reaction of fish to the passing survey boat. The slope was slightly greater than unity, in agreement with previous calculations that the acoustic backscatter of similar fish is slightly greater than the lidar backscatter. The results of this study indicate that lidar is a suitable tool for surveying rapidly the distributions and abundances of epipelagic fish stocks in the shallow waters off the west coast of Florida. Aerial lidar surveys do not have the biases of fish-avoidance reaction potentially affecting acoustic and trawl surveys.
 
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A Comparison of Lidar and Echosounder Measurments of Fish Schools in the Gulf of Mexico 		Product Link:
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A Comparison of the Contribution of Zooplankton and Nekton Taxa to the Near-Surface Acoustic Structure of Three Turkish Seas
The bioacoustics of upper waters of the Black Sea, the Sea of Marmara, and the Mediterranean Sea were studied in October 1999 with an echosounder with 120 and 200 kHz dual-beam transducers. Net tows were taken to ground-truth the acoustic volume backscattering. A forward solution was applied to determine significant scatterers of the three seas with regard to detection limits of the frequencies and background noise measured in each sea. The noise was 4 dB higher in the Sea of Marmara than in the other two seas. 200 kHz data showed significant correlation between measured and calculated volume backscattering strength, and density (biomass and abundance) of the taxa. Large-sized copepods and chaetognaths in the Black Sea, Aurelia, Beroe, chaetognaths and large-sized and abundant appendicularians in the Sea of Marmara, and fish larvae in the Mediterranean Sea contributed most to the volume backscattering.
 
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A Comparison of the Contribution of Zooplankton and Nekton Taxa to the Near-Surface Acoustic Structure of Three Turkish Seas 		Product Link:
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A Hydroacoustic Assessment of Fish Biomass at the Freeport Sulphur Mine Artificial Reef.
The Freeport Sulphur Mine, located off Grand Isle, LA, is among the world’s largest artificial reefs. It is situated in 15m of water and is composed of more than 29 structures, which range from 4-pile supports to a 35-pile power plant facility and 1.5 miles of bridgework. Hydroacoustic data from bi-monthly mobile surveys have been analyzed to examine differences in fish community structure, biomass and density over artificial reef habitat and surrounding featureless habitats. Preliminary analyses suggest that fish biomass estimates from the artificial reef area are approximately 2 times greater than that of other deeper artificial reefs (toppled and partially removed) surveyed in the Northern Gulf of Mexico (NGOM). However, biomass estimates from standing platforms in the NGOM are approximately 5 times greater than those from the Freeport Sulphur Mine. In addition, fish biomass estimates at the Freeport Sulphur Mine range from 1.5 to 6 times greater than estimates from the West Flower Garden Banks. As anticipated, fish biomass appeared to decrease markedly with range from the structure. We observed a two-fold increase in biomass over the structure when compared to the surrounding featureless environment. Furthermore, we noticed a decline in fish biomass with depth over the structure and an increase in fish biomass with depth away from the structure, perhaps signifying a behavioral response in fish within a featureless habitat. Although these results are preliminary, we anticipate that further analyses will provide a clearer understanding of the role of artificial habitat to fish in shallow water environments, perhaps leading to the development of a successful deployment strategy of artificial reef materials for enhancing fish biomass.
 
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A Hydroacoustic Assessment of Fish Biomass at the Freeport Sulphur Mine Artificial Reef. 		Product Link:
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A lightweight transducer platform for use in stationary shallow water horizontal-aspect acoustic surveys
A robust, remotely controlled transducer platform has been designed for use in stationary shallow water acoustic surveys. The transducer array platform is integrated with a weatherized top-side box allowing for collection of acoustic data at remote stations. The platform allows for vertical placement of the transducer array in the water column and for remotely manipulating the transducer pitch. Both a dual-frequency identification sonar (DIDSON) and a BioSonics split-beam transducer were mounted to the platform for simultaneous data collection over a variety of estuarine habitats. The platform is quickly deployed and retrieved by a single user from a small vessel. Effective water depths for optimal use range from 1 to 3.5 m; however, the equipment can be easily deployed at greater depths. The array platform term has been in service for 2 years and the performance level and data quality remain high.
 
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A lightweight transducer platform for use in stationary shallow water horizontal-aspect acoustic surveys 		Product Link:
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Acoustic Assessment of Squid Stocks
Squid fisheries occur worldwide, but catches are often highly variable, as a result of large interannual fluctuations in squid abundance. Large fluctuations in abundance create difficulties when managers predict stock sizes. Acoustic sampling methods can improve forecasts of stock sizes by providing direct estimates of squid abundance. Acoustic techniques have proven reliable for fish stock assessment, and have been used to a lesser extent for squid stock assessment. The disadvantages of using hydroacoustic equipment include limitations in detecting squid near the surface or bottom, limitations of gear in shallow water, the necessity to ground-truth surveys, and the need to obtain accurate target strength estimates that correspond to the collection of echointegration data. The advantages of using hydroacoustic equipment include the capability to directly measure abundance, survey large areas quickly, sample multiple depth intervals simultaneously, and collect and process large amounts of information in real time with relatively few personnel.
 
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Acoustic assessment of squid stocks


Acoustic Characteristics of Forage Fish Species in Gulf of Alaska and Bering Sea Based on Kirchhoff-Approximation Models
Acoustic surveys are routinely used to assess fish abundance. To ensure accurate population estimates, the characteristics of echoes from constituent species must be quantified. Kirchhoff-ray mode (KRM) backscatter models were used to quantify acoustic characteristics of Bering Sea and Gulf of Alaska pelagic fish species: capelin (Mallotus villosus), Pacific herring (Clupea pallasii), walleye pollock (Theragra chalcogramma), Atka mackerel (Pleurogrammus monopterygius), and eulachon (Thaleichthys pacificus). Atka mackerel and eulachon do not have swimbladders. Acoustic backscatter was estimated as a function of insonifying frequency, fish length, and body orientation relative to the incident wave front. Backscatter intensity and variance estimates were compared to examine the potential to discriminate among species. Based on relative intensity differences, species could be separated in two major groups: fish with gas-filled swimbladders and fish without swimbladders. The effects of length and tilt angle on echo intensity depended on frequency. Variability in target strength (TS) resulting from morphometric differences was high for species without swimbladders. Based on our model predictions, a series of TS to length equations were developed for each species at the common frequencies used by fisheries acousticians.
 
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Acoustic Characteristics of Forage Fish Species in Gulf of Alaska and Bering Sea Based on Kirchhoff-Approximation Models 		Product Link:
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Acoustic evaluation of anchovy larvae distribution in relation to oceanography in the Cape Passero area (Strait of Sicily)
The aim of the paper is to present the results of a study on the relationship between ichthyoplanktonic distribution and the hydrographic features in the Cape Passero area (Strait of Sicily). Acoustic, physical, and biological data were collected during two multidisciplinary research surveys performed during the summer in 2002 and 2003 in the Strait of Sicily. The oceanographic surveys ‘Ansic 02’ and ‘Ansic 03’ were carried out on board the RV Urania in the framework of the work programme of the ASTAMAR research project. An accurate post-processing procedure was adopted to estimate anchovy larvae distribution in a sea area around Cape Passero, also taking into account the results of biological sampling. The analysis of acquired data has singled out a relationship between the acoustic-based ichthyoplanktonic distribution and the presence in both surveys of a thermohaline front positioned in the south-eastern part of the study area, which appears to be able to promote concentration processes.
 
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Acoustic evaluation of anchovy larvae distribution in relation to oceanography in the Cape Passero area (Strait of Sicily) 		Product Link:
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Acoustical Identification of the Concentration Layer of a Copepod Species, Calanus Euxinus
Swimming trajectories of Calanus euxinus Hulsemann in the Black Sea were studied using an echosounder at 120 and 200 kHz. C. euxinus were acoustically discriminated with respect to vertical migration and swimming speed, according to dissolved oxygen (DO) concentration and the timing of migrations. Species became torpid in water with DO values <0.5 mg lm1. The time spent swimming under DO conditions between 2 and 5 mg lm1 was insignificant, and varied greatly from the 10% to 25% of total time spent swimming under normoxic conditions (5-10 mg lm1). C. euxinus formed a concentration layer in the water of 1-3 m thickness. Upward migration was completed in about 3.5 h, starting 2.5 h before and ending 1 h after sunset (average rate: 0.95 cm sm1) in summer. Species ascended discretely from the suboxic to the lower boundry of the cold intermediate layer (CIL) at 0.82 cm sm1, and passed up the CIL and thermocline fast (2.3 cm sm1). Downward migration took less time (2 h), starting ~1 h before and ending ~1 h after sunrise. Swimming speed within the thermocline and CIL was 2.7 cm sm1; copepods subsequently returned to daylight depth at a sinking speed of 0.57 cm sm1. Total time for C. euxinus to settle to their nocturnal depth layer was about 5 h.
 
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Acoustical Identification of the Concentration Layer of a Copepod Species, Calanus Euxinus 		Product Link:
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Campagne comparaison de sondeurs
Suite à la campagne CALIB et à des expérimentations faites au bassin de Brest avec nos deux équipements portables : EY500 (Simrad) et DT5000 (Biosonics), le besoin est apparu de compléter les comparaisons. Ces deux sondeurs sont de constructeurs et de technologies différentes (un splitbeam et un dual-beam), les logiciels diffèrent donc également, et ils fonctionnent à des fréquences voisines mais non identiques (120 et 129 kHz). Les traitements effectués sur quelques données issues des expérimentations mentionnées ci-dessus ont montré un écart de plusieurs dB au niveau des résultats d'échointégration, qui reste pour le moment inexpliqué. Le but initial de cette mission était donc de vérifier l'existence de cette différence sur un jeu de données beaucoup plus consistant. Le site du Lac d'Annecy présentait de nombreux avantages. Depuis de nombreuses années le laboratoire INRA de Thonon-les-bains étudie ce lac, son peuplement pisciaire est bien connu et à cette époque de l’année on sait qu’il est possible de détecter aisément des poissons en banc (juvéniles de perches) et de les capturer par un petit chalut pélagique. Ce site associait donc un environnement naturel et un milieu relativement contrôlé. La station INRA a mis à notre disposition un bateau équipé spécialement
 
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Campagne comparaison de sondeurs 		Product Link:
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Density-dependent distribution of demersal juvenile Atlantic cod (Gadus morhua) in Placentia Bay, Newfoundland
Age 0 cod (Gadus morhua) were surveyed with beach-seines monthly from September to December, 1997–1999, at sites located throughout Placentia Bay, Newfoundland. Catch rates (densities) varied annually, being highest in 1998 (7 fish per sample) and lowest in 1997 (<1). Each year, fish size and density increased from September to November, as expected from a stock that tends to produce a single cohort spawned in April/May. However, in December the expected larger fish were absent, and the presence of smaller cod suggested a later cohort (July spawning). Large-scale spatial patterns also persisted among years, with densities consistently higher in the inner bay and on the western side, and lower on the eastern side. The rank of the sites from greatest to lowest density of age 0 cod remained fairly consistent among years. In a comparison of all 12 sampling events, the proportion of sites occupied by cod was strongly and positively correlated with the total number caught (r2 = 0.95). These observations suggested a density-dependent range expansion not previously reported for age 0 cod.
 
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Density-dependent distribution of demersal juvenile Atlantic cod (Gadus morhua) in Placentia Bay, Newfoundland 		Product Link:
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Design and Deployment of the Bonne Bay Observatory
We have deployed the Bonne Bay Observatory (B20) in Bonne Bay, a fjord on the west coast of Newfoundland, in the spring of 2004. The scientific goal of this system is to provide continuous, year-round, real-time data to enhance our understanding of the coupling between the physical and biological environment in this sub-Arctic fjord, which is ice covered for several months each year. The Observatory permits investigators to schedule and interactively manage real time data acquisition and control of the network of sensors. Serving a multidisciplinary team, the instrument array is diverse, including acoustic sensors to determine currents, bubble distribution and plankton abundance, video to determine plankton and benthos species abundance, and sensors for temperature, salinity, chlorophyll fluorescence, carbon dioxide, oxygen, inorganic nutrient concentrations and spectral irradiance. Instruments are deployed on fixed and moveable structures and on an underwater profiling winch. The control and telemetry system includes a power distribution sub-system and TCP/IP based network consisting of two local area networks, one on shore linking data acquisition and control computers and one underwater connecting the sensors, joined by an armored 1.4 km electro-optic cable. The cable provides up to two 100BASE-FX network connections and 2 kW of power to the underwater systems. The system is designed to operate autonomously, and to be controlled remotely by the DACNet ocean observatory operating system. The underwater hardware elements are modular, accommodating guest instruments at spare Ethernet and serial ports. The paper describes the system design with description of instrumentation deployed underwater for the first time, lessons learned during design and deployment and presents preliminary samples of the data collected.
 
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Design and Deployment of the Bonne Bay Observatory 		Product Link:
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Developing Acoustic Methods for Surveying Groundfish
The Alliance for Coastal Technologies (ACT) is a NOAA-funded partnership of research institutions, state and regional resource managers, and private sector companies interested in developing and applying sensor/ sensor platform technologies for monitoring and studying coastal environments. At the “Developing Acoustic Methods for Surveying Groundfish” sponsored by the Alliance for Coastal Technology, the goals were to advance understanding of operational survey applications of acoustics for estimating fish stock abundance, to gain acceptance and support for the broad application of acoustic survey techniques in coastal waters, to define specific mechanisms, funding requirements, and research priorities to foster the development and application of acoustic methods to benefit coastal fisheries.
 
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Developing Acoustic Methods for Surveying Groundfish 		Product Link:
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Diagnostic Tools for Unbiased In Situ Target Strength Estimation
In situ target strength (TS) is theoretically the optimal measure to scale echo-integration values to fish density. In practice, in situ TS is often biased. The number of fish per sample volume (Nv) has been used to set a threshold density to reduce the bias attributable to multiple targets. However, order of magnitude differences in the Nv threshold have been reported within the theoretical range 0 < Nv £ 1. To investigate the use and scale-dependence of the Nv index, with the objective of achieving unbiased estimates of in situ TS, redfish (Sebastes spp.) aggregations were measured in Newfoundland waters. When averaged over large horizontal distances (large scale), TS was biased upwards if Nv exceeded 0.04. However, TS could be estimated at higher densities without bias using smaller measurement scales. To deal with these scale-dependent variations, we develop diagnostic tools based on Nv and an echo-count index (Tv), which enable unbiased estimates of the Nv threshold and in situ TS.
 
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Diagnostic Tools for Unbiased In Situ Target Strength Estimation 		Product Link:
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Diel variability of school structure with special reference to transition periods
Pelagic fishes generally disperse at dusk and aggregate in schools at dawn. The dynamics (duration, variation in school number, and characteristics) of these two behavioural processes have been studied during a 26 h survey in a small area of high fish abundance in the Catalan Sea (Spain). The dynamics of aggregation and dispersion were investigated using a dual-beam vertical echo-sounder (BioSonics) connected to a special school integrator software package (INES-MOVIES-B) which estimates school parameters in terms of size, geometry, and density. This study shows that, during the night, fish dispersion is limited and schools can still be observed. They are characterized by a highly skewed distribution of the cross-sectional area (many small schools plus a few medium and large schools), low values of packing density and biomass, and irregular shape, while during the day there are only a few schools which have a lower variability of the area, high values of packing density, and a more regular shape. The dynamics of schooling are different between dawn (fast aggregation) and dusk (slower dispersion).
 
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Diel variability of school structure with special reference to transition periods 		Product Link:
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Diel vertical migration and shoaling heterogeneity in Atlantic redfish: effects on acoustic and bottom-trawl surveys
A series of experiments comparing acoustic and bottom-trawl surveys was conducted on Atlantic redfish (Sebastes spp.) on the edge of the Green and Grand Banks of Newfoundland, Canada. Redfish were on or near bottom by day and migrated vertically in the water column at night. In an attempt to account for biases attributable to the presence of fish in the near-bottom dead zone (DZ), a correction factor was applied based on density values measured within the first few metres above the detected bottom. Acoustic densities within increasing range increments above the bottom were compared with densities estimated from the trawl catch. Swept area was calculated using both the trawl's wing spread and door spread as proxies for the minimum and maximum fishing widths. Uncorrected acoustic densities were significantly higher during the night than during the day. No significant day/night differences for the entire water column were observed after DZ corrections. Close agreement between acoustic and trawl densities was obtained by integrating within the first 10 to 20 m off the bottom, with or without the DZ corrections, for both day and night experiments, but regression slopes differed. Trawl catchability appeared to be density-dependent at night, being higher at lower fish densities. Daytime acoustic estimates were more variable than those made at night, as indicated by consecutive passes of several transects and CVs of density (means of 131% during day, 35% at night). We conclude that acoustic measurements made at night provide the most reliable and least variable density estimates, and make recommendations for surveys.
 
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Diel vertical migration and shoaling heterogeneity in Atlantic redfish: effects on acoustic and bottom-trawl surveys 		Product Link:
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Diel Vertical Migration of Sagitta Setosa as Inferrred Acoustically in the Black Sea
Abstract Swimming trajectories of chaetognaths Müller in the Black Sea were studied using an echosounder operating at 120 and 200 kHz and an acoustic Doppler current profiler (ADCP) operating at 150 kHz. S. setosa were acoustically discriminated with respect to vertical migration and swimming speed, according to dissolved oxygen (DO) concentration and the timing of migrations. S. setosa formed a concentration layer thicker than Calanus euxinus did (1–3 m). The migration was completed in about 2.5–4 h, upward migration starting before C. euxinus and downward migration after C. euxinus. Adult Sagitta swam fast only in the well-oxygenated layer (subsurface maximum DO). The DO was found to be a significant (p<0.05) variable by partial correlation between the speed and hydrographical parameters. This feature constituted an oxygen-dependent influence on S. setosa’s vertical swimming and distinguished S. setosa from C. euxinus. Chaetognaths migrated daily between the nearsurface and the oxycline or the suboxic zone (OMZ, see Fig. 3b for the layers characterized by DO). Whether the deepest depth limit of migration was the oxycline or the OMZ depended on the relative abundance of adult and immature (young) individuals in the concentration layer. In July and September, individuals belonging to a new generation did not migrate but stayed in subsurface water day and night.
 
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Diel Vertical Migration of Sagitta Setosa as Inferrred Acoustically in the Black Sea 		Product Link:
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Echohydrology and Physical Habitat Modification for Fish - the Integrative Approach for Reversing Decline of Fish Communities and Good Ecological Status of Freshwater Ecosystems
Hydroacoustics offers a great variety of applications for studying fish in a changing environment, as well as aspects of their habitats (e.g. water depth, bottom type, macrophytes). Echo-sounding techniques, due to their high resolution in time and space, enable the observation of both short-term and long-term effects of habitat modification on fish populations. A number of examples of such studies are presented illustrating the effects of environmental stressors including eutrophication, water level fluctuations, temperature gradients and water heating. In addition, an example is presented of a hydroacoustic survey of macrophytes using a newly developed system, with estimations of their coverage and heights. Since hydroacoustic methods provide high resolution, area-based, synoptic, spatiallyintegrated data, they are particularly suitable for monitoring the dynamic changes of aquatic ecosystems and so can make a significant contribution to ecohydrology.
 
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Effect of external factors (environment and survey vessel) on fish school characteristics observed by echosounder and multibeam sonar in the Mediterranean Sea
Spatial dynamics are of paramount importance to the understanding of the forces governing population dynamics. In the particular case of fish stocks, studying the factors inducing and maintaining the aggregation of fish within schools could be helpful to better understand the spatial heterogeneity of small pelagic fish populations and the mechanisms that lead to the particular mode of distribution of schools.
 
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Effect of external factors (environment and survey vessel) on fish school characteristics observed by echosounder and multibeam sonar in the Mediterranean Sea 		Product Link:
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Effectiveness of Protection of Seagrass (Posidonia oceanica) Populations in Cabrera National Park (Spain)
Posidonia oceanica, the dominant seagrass species in the Mediterranean, appears to be experiencing widespread loss. Efforts to conserve Posidonia oceanica are increasing, as reflected in the increase in the number of marine protected areas in the Mediterranean. However, the effectiveness of these measures to conserve seagrass meadows is unknown. In this study, the present status of the Posidonia oceanica meadows in the Cabrera National Park (Mediterranean), the only marine national park in Spain, was assessed, and the effectiveness of the conservation measures adopted was tested. This was done by reconstruction of past and present growth, quantification of the demographic status of the established meadows, and quantification of patch formation and growth rates in areas where recolonization is occurring.
 
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Effectiveness of Protection of Seagrass (Posidonia Oceanica,) Populations in Cabrera National Park (Spain) 		Product Link:
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Ex situ target strength of rockfish (Sebastes schlegeli) and red sea bream (Pagrus major) in the Northwest Pacific
This study determined the ex situ target strength (TS) of rockfish (Sebastes schlegeli) and red sea bream (Pagrus major) in an artificial seawater tank as a means of helping to estimate fishery resources in coastal areas. TS experiments were conducted at frequencies of 38 kHz (split beam), 120 kHz (split beam), and 200 kHz (dual beam). The species were examined under two conditions: first, live fish confined to a small, net cage; and, second, as free-swimming fish inside a large tank. The study examined 21 rockfish and 20 red sea bream. The data were used to obtain expressions for TS against length and weight for the two species. The relationships between TS and fish length were as follows: for rockfish, TS38 kHz = 20 log10(L)  67.7 (r = 0.80), TS120 kHz = 20 log10(L)  74.3 (r = 0.61), TS200 kHz = 20 log10(L)  72.8 (r = 0.41); and for red sea bream, TS38 kHz = 20 log10(L)  66.8 (r = 0.86), TS120 kHz = 20 log10(L)  74.0 (r = 0.65), TS200 kHz = 20 log10(L)  74.1 (r = 0.83). The TS equations for rockfish and red sea bream as a function of fish weight at 38 kHz were TS38 kHz = 6.75 log10(W)  56.0 (r = 0.78) and TS38 kHz = 4.08 log10(W)  49.9 (r = 0.89), respectively. For comparison, calculations using the HelmholtzKirchhoff ray-approximation model based on swimbladder morphology were compared with the measured TS. When the tilt angle of the fish is zero, the mean TS from the model is 310 dB higher than the experimental results, although the maximum TS values were only 34 dB different.
 
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Ex situ target strength of rockfish (Sebastes schlegeli) and red sea bream (Pagrus major) in the Northwest Pacific 		Product Link:
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Fish School Selection by Marbled Murrelets in Prince William Sound, Alaska: Responses to Changes in Availability
Foraging theory for central place foragers suggests that the energy return expected from a food item is weighed against the cost of obtaining that item when choosing which food source to pursue. Within Prince William Sound (PWS), Alaska, seabirds consume several different food items, which vary in energy content.
 
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Fish School Selection by Marbled Murrelets in Prince William Sound, Alaska: Responses to Changes in Availability 		Product Link:
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Forecasting Annual Harvests of Atlantic and Gulf Menhaden
Continuous records of annual landings and fishing effort exist in the Atlantic purse-seine fishery for Atlantic menhaden Brevoortia tyrannus since 1940 and the Gulf of Mexico fishery for Gulf menhaden B. patronus since 1946. Currently, year-ahead forecasts of landings from these species-specific fisheries separated by the Florida peninsula are provided to the industry by means of multiple-linear-regression models that relate landings and effort over the data series. Here, we compare three methods for this purpose—multiple regression, time series, and artificial neural networks—to determine whether forecast accuracy can be increased. Best-fit models were developed with each method for each fishery, and then 10-year retrospective analyses of 1-year-ahead catch forecasts were compared among the three methods. In general, multipleregression and artificial neural network models were similar in their fit to the data series and both were better than time series models, judging from the Akaike information criterion, the correlation between observed and predicted catches, the mean prediction error, and the root mean square error of prediction. A 10-year retrospective analysis (1993–2002) of 1-year-ahead catch forecasts indicates that the three methods provided similar within-stock mean absolute forecast errors (19–21% in the Atlantic and 15–20% in the Gulf), with generally better forecasts for the Gulf fishery. Overall, multiple-regression and artificial neural network models provide lower average catch forecast errors and better fits to the fishery data, whereas similar forecast errors are provided by a univariate time series model (autoregressive integrated moving average model) in the Atlantic and a multivariate time series model (state space model) in the Gulf.
 
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Forecasting Annual Harvests of Atlantic and Gulf Menhaden 		Product Link:
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Habitat Selection Models for Pacific Sand Lance (Ammodytes Hexapterus) in Prince William Sound, Alaska
We modeled habitat selection by Pacific sand lance (Ammodytes hexapterus) by examining their distribution in relation to water depth, distance to shore, bottom slope, bottom type, distance from sand bottom, and shoreline type. Through both logistic regression and classification tree models, we compared the characteristics of 29 known sand lance locations to 58 randomly selected sites. The best models indicated a strong selection of shallow water by sand lance, with weaker association between sand lance distribution and beach shorelines, sand bottoms, distance to shore, bottom slope, and distance to the nearest sand bottom. We applied an information-theoretic approach to the interpretation of the logistic regression analysis and determined importance values of 0.99, 0.54, 0.52, 0.44, 0.39, and 0.25 for depth, beach shorelines, sand bottom, distance to shore, gradual bottom slope, and distance to the nearest sand bottom, respectively. The classification tree model indicated that sand lance selected shallow-water habitats and remained near sand bottoms when located in habitats with depths between 40 and 60 m. All sand lance locations were at depths <60 m and 93% occurred at depths <40 m. Probable reasons for the modeled relationships between the distribution of sand lance and the independent variables are discussed.
 
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Habitat Selection Models for Pacific Sand Lance (Ammodytes Hexapterus) in Prince William Sound, Alaska 		Product Link:
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Hydroacoustic Assessment of the Fish Stock in Theodorushaven, a Small Dutch Harbour
Assessment of the fish stock in the Theodorushaven was conducted with a dual-beam hydroacoustic system. Species composition determined by a seine and trawl fishery showed large concentrations of fish in the harbour during winter. The hydroacoustic survey showed that the distribution of fish in the harbour area was stratified with fish near the bottom. The overall density in the harbour area was 0.67 fish m-3. The density in the associated channel area was estimated at 0.1 fish m-3. The coefficient of variation for the estimated total fish abundance was >25%.Fish >25 cm were not caught in the Theodorushaven fishery, although analysis of the sonar data indicated their presence. Fishery data from the adjacent Volkerak-Zoommeer showed that bream was the dominant species. Therefore, the biomass estimate of the stock >25 cm in the Theodorushaven was based on the standard length–weight relationship of bream. This resulted in maximum biomass estimates of 5800 kg ha-1 for the harbour area and 1100 kg ha-1 in the channel area. The minimum biomass estimate, based on the assumption that the more slender zander was the dominant species >25 cm, gave values of 4100 kg ha-1 in the harbour area and 780 kg ha-1 in the channel area.
 
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Hydroacoustic assessment of the fish stock in Theodorushaven, a small Dutch harbour 		Product Link:
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Hydroacoustic estimation of fish biomass in the Gulf of Nicoya, Costa Rica
A stratified sampling design was used for a hydroacoustic survey of the inner parts of the Gulf of Nicoya in 1987 and 1988. The bottom topography of the inner Gulf was modeled by introducing the concept of a topographical basin model, as the basis for the projection of the sample survey estimates to the entire inner gulf. The bottom depth contours and volumes for the basin model were constructed from nautical charts. The estimates of sample abundance were made for the fish in the inner Gulf using the acoustic methods, EMS (Expectation Maximization and Smoothing) and echo integration. The estimates of population were made by the multiplication of the topographic model's estimate of water volume and a model of fish density dependent on bottom depth. The results showed a general decrease in fish density biomass with bottom depth, and a simultaneous tendency for maximum concentrations over bottom depths of about four meters. The four meter bottom depth includes a broad expanse of the inner Gulf located south of Isla Chira. Overall estimates of volumetric density (0.269 fish/m3) and of areal densities (1.88 fish/m2) are comparable to other estuarine shallow water environments.
 
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In Situ Acoustic Target Strength of Juvenile Capelin
A dispersed, monospecific aggregation of juvenile (0+) capelin was detected acoustically in shallow (20–70 m) water in Bonavista Bay, northeastern Newfoundland in January 2000. This provided a rare opportunity to measure acoustic target strength (TS) of very small (mean LENGTH=51 mm) capelin in situ. Mean observed TS at 38 kHz was −61.0 dB. Observed TS was similar to TS predicted by the Norwegian-Icelandic capelin TS-length relationship (TS=19.1 log L (cm)−74), but not, vert, similar2 dB lower than predicted by the existing TS-length relationship for capelin in Newfoundland waters at 38 and 49 kHz (TS=20 log L (cm)−73.1). Combining present data with previous 38 kHz data indicates the relationship TS=23.3 log L (cm)−77.1 (r2=0.95, N=6) for capelin of lengths 5–14 cm in Newfoundland waters.
 
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In Situ Acoustic Target Strength of Juvenile Capelin 		Product Link:
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Modeling rockfish distributions using hydroacoustics and high resolution bathymetry
Advances in multibeam hydroacoustics have allowed mapping of the marine bottom terrain with increasingly high resolution. At the same time advances in fisheries acoustics have made it possible to plot individual fish in three dimensional space. When a fish species has an affinity for certain bottom structures, the high resolution bathymetry can be used to predict where fish will be located and then these predictions can be used to more efficiently plan hydroacoustic surveys.
 
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Modeling rockfish distributions using hydroacoustics and high resolution bathymetry 		Product Link:
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Monitoring coastal northern cod: towards an optimal survey of Smith Sound, Newfoundland
The extant, coastal northern cod (Gadus morhua) have over-wintered and spawned in Smith Sound, Newfoundland, since 1995, and acoustic surveys have been conducted in several seasons since then. Cod move into the Sound in late fall, over-winter in a dense, size- and age-structured aggregation, spawn between late March and early June and then disperse into and beyond Trinity Bay during summer to feed. The optimal survey time for biomass estimation is JanuaryFebruary, when the waters are ice-free and the cod are in mono-specific, relatively stationary, and well-defined aggregations with the highest densities and are typically clear of "bottom returns". Biomass surveys have been conducted in mid-January since 1999. An error analysis indicated the main sources of uncertainty to be density variability and target strength (TS). Repeated quasi-synoptic (10 h) surveys were the optimal means of producing an estimate of uncertainty about population size. Some vertical movement led to night-time surveys consistently having higher estimates than day-time surveys by approximately 15%. Detectability ranged from 73 to 86% and deadzone-corrected, acoustic measures did not differ from swept-area densities found by bottom trawling. Biomass scaling by TS used length-dependant dB/kg to reduce the size-sampling error. Overall, population biomass doubled in approximately 7 years, consistent with a rate of increase around 0.2, largely through recruitment. The surveys are internally consistent and indicate instantaneous rates of mortality among year classes of 0.3 to >2 (very high on older fish) and provide a method for monitoring the annual biomass (cv<40%).
 
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Monitoring coastal northern cod: towards an optimal survey of Smith Sound, Newfoundland 		Product Link:
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Oceanographic Conditions Structure Forage Fishes into Lipid-Rich and Lipid-Poor Communities in Lower Cook Inlet, Alaska, USA
Forage fish populations1 in the Gulf of Alaska fluctuate in abundance over a range of temporal and spatial scales (Bechtol 1997, Anderson & Piatt 1999, Mueter & Norcross 2000). After a climatic regime shift occurred in the North Pacific during the late 1970s (Francis et al. 1998, Hare & Mantua 2000), gadid and flatfish populations increased dramatically while shrimp and capelin Mallotus villosus populations virtually disappeared (Anderson et al. 1997, Anderson & Piatt 1999, Mueter & Norcross 2000). This trophic reorganization is hypothesized to be an important contributor to declines in populations of seabirds (Piatt & Anderson 1996) and marine mammals (Merrick et al. 1987), because lipidpoor gadids and flatfishes generally replaced lipid-rich fish species in the Gulf of Alaska food web. On a smaller temporal scale, El Niño Southern Oscillation (ENSO) events in the northern Gulf of Alaska may be associated with changes in the distribution and recruitment of pelagic juvenile stages of Pacific herring Clupea pallasi (hereafter referred to as herring) and groundfishes (Mysak 1986, Bailey et al. 1995, Piatt et al. 1999). Understanding the response of fish populations to changes in physical oceanography is an important step toward understanding the effects of climatic shifts on marine piscivores (McGowan et al. 1998, Kitaysky & Golubova 2000, Stenseth et al. 2002, Chavez et al. 2003).
 
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Oceanographic Conditions Structure Forage Fishes into Lipid-Rich and Lipid-Poor Communities in Lower Cook Inlet, Alaska, USA 		Product Link:
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Potential Acoustic Discrimination Within a Boreal Fish Assemblage
Differences in the acoustic characteristics of forage fish species in the Gulf of Alaska and the Bering Sea were examined using Kirchhoff ray-mode (KRM) backscatter models. Our goal was to identify species-specific characteristics and metrics that facilitate the discrimination of species using acoustic techniques. Five fish species were analyzed: capelin (Mallotus villosus), Pacific herring (Clupea pallasii), walleye pollock (Theragra chalcogramma), Atka mackerel (Pleurogrammus monopterygius), and eulachon (Thaleichthys pacificus). Backscatter amplitude differences exist among these species, especially between swimbladdered and non-swimbladdered fish. Echo intensities were variable within and among species. The effect of morphological variability was indexed using the ratio of the Reducedscattering length (RSL) standard deviation over its mean. Morphological variability was low only at fish length to acoustic wavelength ratios less than eight. Target strength differences between pairs of carrier frequencies (ranging from 12 kHz to 200 kHz) differed among species, and were dependent on fish size and body orientation. Frequency differencing successfully discriminated between fish species but the choice of frequency to maximize target strength differences was not consistent among species pairs. Frequencydependent, backscatter model predictions facilitate comparison of target strength differences prior to acoustic data collection.
 
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Quantifying Changes in Fish Habitat Use in Coastal Waters of Louisiana, USA: A Hydroacoustic Approach
The development of reliable tools for identifying essential fish habitat (EFH) has proven problematic. Knowledge of the distribution and biomass of fishes over discrete habitat types is a prerequisite for effective use of EFH in the management of important commercial and recreational fish species. Resolution of the influence of habitat type and environmental factors on the distribution of fishes is confounded by limitations of traditional sampling gears. To date, hydroacoustic technology has been widely accepted as a tool for surveying fishery resources; however few studies have implemented acoustics in ultra shallow (<2 m) coastal waters. Efforts should be made to utilize hydroacoustics for quantifying changes in fish distributions within estuarine environments given the benefits provided through acoustic technology (e.g. ease of deployment, reduced sampling effort, and non-invasive sampling attributes).
 
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Quantifying Changes in Fish Habitat Use in Coastal Waters of Louisiana, USA: A Hydroacoustic Approach 		Product Link:
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Report of the Planning Group on Aerial and Acoustic Surveys for Mackerel
The Planning Group on Aerial and Acoustic Surveys for Mackerel [PGAAM] (Chair E. Shamray, Russia) met in Aberdeen, Scotland UK from 23–26 February 2004. The main objectives of PGAAM are to provide distributions of mackerel and biomass/number indices that may be used by WGMHSA in future assessments. Furthermore, it aims to collate information on the hydrographic and planktonic conditions of the Norwegian Sea and adjacent waters and to describe how feeding and migration of mackerel are influenced by this.
 
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Aerial and Acoustic Surveys for Mackerel 		Product Link:
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Response of Seabirds to Fluctuations in Forage Fish Density
Following the Exxon Valdez Oil Spill (EVOS), one concern was that prevailing ecological conditions in the Gulf of Alaska (GOA) would not favor recovery of damaged seabird populations. To address this issue, we examined relationships between oceanography, forage fish and seabirds near three seabird colonies in lower Cook Inlet (LCI) in 1995-1999. Upwelling of cold, nutrient-rich GOA waters at the entrance to the shallow LCI estuary supports a high density of juvenile pollock, sand lance, and capelin; which in turn are exploited by high densities of breeding seabirds (murres, kittiwakes, puffins, etc.) on the east side of LCI. Waters on the west side of LCI are oceanographically distinct (warmer, less saline, outflowing), and much less productive for forage fish and seabirds. Patterns of seabird foraging behavior, productivity and population change reflected patterns of forage fish abundance and distribution, which in turn depended on local oceanography. Most seabird parameters varied with forage fish density in a non-linear (e.g., sigmoidal, exponential) fashion, and in some areas and years, productivity was limited by food availability. Current and projected ecological conditions favor recovery of seabirds from the EVOS at some colonies. In 14 chapters, this report summarizes data and compiles it into 247 tables, figures and appendices. Chapter 14 iv provides a thorough synthesis of overall project findings. Final analyses and interpretations of data will be published later in peer-reviewed journals (in addition to 51 articles already completed).
 
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Response of Seabirds to Fluctuations in Forage Fish Density 		Product Link:
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Seabird, Fisheries, Marine Mammal, and Oceanographic Investigations Around Kasatochi, Koniuji, and Ulak Islands, August, 1996
Although islands in the Aleutians are known to support some of the highest densities of seabirds in the world, their remoteness has limited systematic research on the at-sea distribution of seabirds near these colonies. Kasatochi, Koniuji, and Ulak islands, in the central Aleutian Islands, together comprise one of nine ecological sites monitored once every 5 years on an annual rotation since 1996 by the Alaska Maritime National Wildlife Refuge (AMNWR). To supplement annual colony monitoring and examine seabird distribution away from colony sites, the AMNWR personnel in conjunction with U.S. Geological Survey (USGS) researchers, conducted a pelagic survey of the waters around these 3 islands in 1996.
 
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Seabird, Fisheries, Marine Mammal, and Oceanographic Investigations Around Kasatochi, Koniuji, and Ulak Islands, August, 1996 		Product Link:
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SEARCH STRATEGIES OF A PURSUIT-DIVING MARINE BIRD AND THE PERSISTENCE OF PREY PATCHES
We explored foraging strategies used by marine animals to search for prey by examining the relative importance of information exchange and memory in a cold ocean environment from 1998 to 2000. Recent technological advances have increased our knowledge of the foraging patterns of marine predators, but few of these studies have concurrently measured prey distribution and behavior. We quantified the arrival and departure behavior of a pursuit-diving, colonial seabird, the Common Murre, Uria aalge, at two colonies on the eastern Newfoundland Shelf through observational techniques. We also measured the distribution, abundance, and behavior of the capelin, Mallotus villosus, the main prey species of murres, within foraging ranges of each colony, using hydroacoustic, vessel-based techniques. Return and departure flight directions of murres did not match at either colony during the same period. This indicated that murres departing colonies did not use information on prey distributions outside of visual range of the colony provided by the flight paths of returning flocks of birds to the colony carrying fish. High-abundance aggregations of capelin were reliably found within specific 2.25-km areas (“hot spots”) for up to two weeks within the foraging ranges of murres from both colonies (100 km). This circumstance suggests that murres could use memory to locate hot spots on the coarse scale (1–100 km) of foraging ranges from both colonies. Specific commuting routes (regular flight paths) of murres toward and away from hot spots were obvious at sea, and feeding murres consistently marked the location of capelin schools within hot spots. These distributions provided excellent conditions for murres to locate capelin schools on both coarse and fine (1–1000 m) scales by cueing to the activities of conspecifics, known as local enhancement. While central-place foraging from breeding colonies, murres likely use a mixture of memory and local enhancement to locate prey, depending on the spatial and temporal resolution of search and current prey conditions. Uncovering such behavioral mechanisms responsible for predator–prey interactions increases our understanding of linkages among trophic levels and, ultimately, ecosystem dynamics.
 
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SEARCH STRATEGIES OF A PURSUIT-DIVING MARINE BIRD AND THE PERSISTENCE OF PREY PATCHES


Seasonal growth of Atlantic cod: effects of temperature, feeding and reproduction
Growth of 2659 Atlantic cod Gadus morhua aged 4 to 9 years examined in Placentia Bay, Newfoundland, peaked in most cases in June and was at a minimum in October or November. Water temperature, partial fullness index (IP) and gonado-somatic index (IG) explained between 31 and 52% of the monthly variability in growth. Temperature and IP of capelin Mallotus villosus had significant effects on growth of all age groups and explained most of the variance for ages 6–8 and 4–5 years, respectively. The IP of large invertebrates (ages 4 to 7 years), sandlance (Ammodytes sp. age 6 years) and demersal fishes (age 9 years) had age-specific effects in the model. Overall, amphipods, decapods and echinoderms dominated the Atlantic cod diet in most seasons, but fish consumption by Atlantic cod was high in June and July, particularly on capelin. The rapid increase in somatic mass during June and July occurred despite cold water temperatures ( < 3° C at 50 m) and moderate to high gonado-somatic index. The findings of this study suggest that when food was not a limiting factor, growth tended to increase even when Atlantic cod occupied colder waters, but when food was limiting, the opposite may have occured.
 
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Spatiotemporal Predictability of Schooling and Nonschooling Prey of Pigeon Guillemots
Low spatiotemporal variability in the abundance of nonschooling prey might allow Pigeon Guillemots (Cepphus columba) to maintain the high chick provisioning rates that are characteristic of the species. We tested predictions of this hypothesis with data collected with beach seines and scuba and hydroacoustic surveys in Kachemak Bay, Alaska, during 1996–1999. Coefficients of variability were 20–211% greater for schooling than nonschooling prey on day, seasonal, and km scales. However, the proportion of schooling prey in chick diets explained relatively little variability in Pigeon Guillemot meal delivery rates at the scale of hours (r2 5 0.07) and weeks (r2 5 0.19). Behavioral adaptations such as flexible time budgets likely ameliorate the negative effects of high resource variability, but we propose that these adaptations are only effective when schooling prey are available at distances well below the maximum foraging range of the species.
 
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Spatiotemporal Predictability of Schooling and Nonschooling Prey of Pigeon Guillemots 		Product Link:
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Surveys to Locate Eulachon Aggregations in the Lower Fraser River, British Columbia
Eulachon, sometimes known as candlefish, are a small (<25 cm) smelt native to the west coast of North America, where they spawn in only 30–40 streams throughout their range. Information about their fine-scale spatial distribution patterns is difficult to obtain with conventional netting and trapping methods in the deeper habitats of large, powerful streams, such as the Fraser River in British Columbia, Canada. As part of a study of dredging impacts on the local aquatic community of this stream, coordinated acoustic and trawl surveys were conducted to measure where eulachon occurred in habitats more than 2 meters deep within a 9 km long freshwater reach of the lower Fraser River during the 2001 and 2002 spring spawning periods.
 
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Surveys to Locate Eulachon Aggregations in the Lower Fraser River, British Columbia 		Product Link:
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The Bahamas’ Nassau grouper (Epinephelus striatus) fishery – two assessment methods applied to a data – deficient coastal population
The Nassau grouper is an important fish species in the reef ecosystem of the Bahamas. It is subjected to intense exploitation by small-scale fisheries and is harvested with different fishing gears, primarily during the winter spawning season. The piecemeal nature of the fishing operations precludes an economically feasible way to compile data to assess the status of exploitation of the resource. There is public and governmental concern regarding over-exploitation of the Nassau grouper due to the numerous extinctions of spawning aggregations in the greater Caribbean. Due to the large size of the Bahamas archipelago, where many Nassau grouper spawning aggregations still occur, the collection of appropriate data for stock assessments is very difficult. In addition, stock assessment algorithms that are applicable to tropical, seasonally aggregating species are noticeably lacking. In this paper we present applications of analytical and hydroacoustic assessment algorithms to the Nassau grouper fishery in the Bahamas that could be implemented under data-limited conditions. The results of the analyses indicate that the methods generate consistent abundance and mortality rate estimates that are commensurable with a stock subjected to full exploitation.
 
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The Bahamas’ Nassau grouper (Epinephelus striatus) fishery – two assessment methods applied to a data – deficient coastal population 		Product Link:
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Thoms, Salmon Bay, and Luck Lakes Sockeye Salmon Stock Assessment Project 2002 Annual Report
Sockeye salmon (Oncorhynchus nerka) returning to Thoms, Salmon Bay, and Luck lakes are an important subsistence resource for the people of Wrangell, Petersburg, and Prince of Wales Island. The Thoms, Salmon Bay, and Luck Lakes Sockeye Salmon Stock Assessment Project was initiated because of concerns about the potential increase in harvest of sockeye salmon returning to these lake systems. Unfortunately, not much was known about these sockeye stocks until this project was initiated. In this report, we summarize work conducted during the second year of project operations, 2002.
 
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Three-dimensional acoustic mapping and simulation of krill distribution in the Saguenay—St. Lawrence Marine Park whale feeding ground
Oceans are three-dimensional (3D) spaces. Many properties measured in these ecosystems exhibit a structure over a range of scales in space and time (Haury et al., 1978; Mackas et al., 1985). Such structuring plays a fundamental role in ecosystem function from plankton (Steele, 1978) to whales (e.g. Simard et al., 2002).Vertical gradients tend to be several times larger than the horizontal ones. Oceans are also in motion and sampling effectively in time and space can be difficult. Acoustics tools can sample these huge 3D-environments remotely, rapidly and continuously.
 
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Three-Dimensional Acoustic Mapping and Simulation of Krill Distribution in the Saguenay-St. Lawrence Marine Park Whale Feeding Ground 		Product Link:
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Using geostatistics to quantify seasonal distribution and aggregation patterns of fishes: an example of Atlantic cod (Gadus morhua)
Geostatistical methods were used to (i) quantify fish aggregation patterns over a range of scales (100 m to 67 km) using both simulated and acoustic density data of Atlantic cod (Gadus morhua) and (ii) examine how changes in aggregation patterns influenced the precision of geostatistical density indices. Variogram parameters (range, sill, and nugget) reflected changes in distribution patterns. Variograms of dispersed and low-density aggregations had large range and small sill and nugget values. In contrast, when fish were aggregated in a small portion of the study area, the range was low and the sill and nugget large. The precision of density indices (coefficient of variation) was below 20% in all cases but at a maximum during summer when cod were broadly distributed in small, moderate to dense aggregations. Geostatistical modeling allowed us to describe and quantify distribution patterns of fish density over different scales of observation, comparisons of spatiotemporal changes in density distribution, and estimations of the precision of density indices while accounting for the effects of heterogeneous distributions, outliers and the typically large number of zero and low-density observations. Geostatistical methods have particular applicability to fishes exhibiting gregarious behaviour and seasonally variable distributions, which include many temperate and high-latitude fish species.

Nous avons utilisé des méthodes géostatistiques afin de (i) quantifier les patterns de répartition contagieuse des poissons à différentes échelles (100 m à 67 km) à l'aide de données de densité simulées et de données d'inventaires acoustiques chez la morue franche (Gadus morhua) et (ii) examiner comment les changements dans les patterns de contagion influencent la précision des indices géostatistiques de densité. Les paramètres des variogrammes (portée, palier et pépite) reflètent les changements dans les patterns de répartition. Les variogrammes des contagions dispersées et de faible densité ont une grande portée, mais des valeurs faible de palier et de pépite. En revanche, quand les poissons se rassemblent dans une petite portion de la zone d'étude, la portée est faible et le palier et la pépite sont élevés. La précision des indices de densité est inférieure à 20 % dans tous les cas, mais elle atteint un sommet en été quand les morues sont largement réparties dans de petites contagions de densité moyenne à grande. La modélisation géo statistique nous a permis de décrire et de quantifier les patterns de répartition de la densité des poissons à différentes échelles d'observation, les comparaisons des changements spatio-temporels de répartition de la densité, ainsi que les estimations de la précision des indices de densité, tout en tenant compte des distributions hétérogènes, des valeurs aberrantes et du nombre généralement élevé d'observations de densité faible ou nulle. Les méthodes géostatistiques s'appliquent particulièrement bien aux poissons qui possèdent un comportement grégaire et qui ont des répartitions variables au cours des saisons, ce qui inclut plusieurs espèces de poissons des régions tempérées et des zones de haute latitude.[Traduit par la Rédaction]
 
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Using geostatistics to quantify seasonal distribution and aggregation patterns of fishes: an example of Atlantic cod (Gadus morhua) 		Product Link:
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