WORKING GROUP ON FISHERIES, ACOUSTICS, SCIENCE AND TECHNOLOGY (WGFAST) Seattle, WA. USA, March 20–23 2018 Abstracts (alphabetical by topic session) WGFAST 1. Applications of acoustic methods to characterize ecosystems Characterization of sound scattering layers in the Bay of Biscay using broadband acoustics, nets and video Arthur Blanluet 1, Mathieu Doray 1, Laurent Berger 2, Naig Le Bouffant 2, Sigrid Lehuta 1, Jean-Baptiste Romagnan 1, Pierre Petitgas 1 1Unité Écologie et Modèles pour l’Halieutique, Ifremer Nantes, Rue de l’Ile d’Yeu, BP 21105,44300 Nantes Cedex 3, France, [email protected] , [email protected] , [email protected] ; 2Service Acoustique Sous-marine et Traitement de l’Information, Ifremer Brest, Brest, France, [email protected] Sound scattering layers (SSLs) are observed over a broad range of spatio-temporal scales and geographical areas. Yet, the SSLs taxonomic composition remains largely unknown. To improve our comprehension of SSLs, a dedicated study was conducted in Northern Bay of Biscay (France) using broadband acoustic. Four broadband EK80 (i.e. 70, 120, 200 and 333 kHz nominal frequencies) and two narrowband EK60 (i.e. 18 and 38 kHz) echosounders were used to obtain the frequency spectra of SSLs in two contrasted zones. Groundtruthing data were collected by deploying plankton and micronekton nets and in situ video in the SSLs. Measured frequency spectra were compared to forward modeled spectra derived from groundtruthing data to identify organisms contributing to the observed SSLs. The results showed that SSLs were dominated by resonant Gas Bearing organisms, siphonophores and juvenile fishes, especially in the lower range of frequencies (< 90 kHz). Copepods, pteropods and euphausiids contributed to the response at higher frequencies. The usefulness of broadband acoustics to characterize resonant backscatterers and mixed mesozooplankton assemblages is further discussed. Acoustic-Trawl Surveys of Forage Fishes in the California Current Ecosystem David A. Demer 1, Juan P. Zwolinski 2, Kevin L. Stierhoff 1, Josiah S. Renfree 1, Danial Palance 1, Scott Mau 1, David Murfin 1, and Steve Sessions 1 1Southwest Fisheries Science Center, Fisheries Resources Division, Advanced Survey Technologies Group, 8901 La Jolla Shores Drive, La Jolla, CA 92037, [email protected] , [email protected] , [email protected] , [email protected] , [email protected] , [email protected] , [email protected] ; 2Institute of Marine Sciences, University of California, Santa Cruz (Southwest Fisheries Science Center affiliate), Earth and Marine Sciences Building, Room A317, Santa Cruz, California 95064, USA, [email protected] In the California Current, multiple coastal pelagic fish species (CPS; i.e., Pacific sardine Sardinops sagax , northern anchovy Engraulis mordax , jack mackerel Trachurus symmetricus , Pacific mackerel Scomber japonicus , and Pacific herring Clupea pallasii ) comprise the bulk of the forage fish assemblage. These species can attain large biomasses during short periods, comprise prey to marine mammals, birds, and large migratory fishes, and are targets of commercial fisheries. We present the acoustic-trawl method (ATM) as presently used by the Southwest Fisheries Science Center to survey CPS, and example results. Described are some non-standard ATM protocols, e.g., constraining the sampling area by satellite-sensed potential habitat, daytime acoustic sampling with nighttime trawl sampling, industry-collaborative nearshore sampling, post-sampling stratification, and automated data analysis and reporting . A circumnavigation of the Southern Ocean to study the deep scattering layer and krill. Paul G. Fernandes 1, Inigo Everson 2, Roland Proud 3, Camille Le Guen 3, Matteo Bernasconi 4, Joshua Lawrence 1, Linsey Mortimer 1, Katie MacDonald 1, and Andrew S. Brierley 3 1School of Biological Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK. [email protected] ; 2Summer House, Sandy Lane, West Runton, Norfolk NR27 9NB, UK; 3School of Biology, University of St Andrews, Queen's Terrace, St Andrews, Fife KY16 9TS, UK; 4Institute of Marine Research , PO Box 1870, NO-5817 Bergen , Norway Within the mesopelagic zone of the oceans, deep scattering layers (DSLs) of small fish, zooplankton and squids aggregate in distinct layers stretching tens to thousands of kilometres horizontally and tens to hundreds of metres vertically. In the Southern Ocean (SO), DSLs contain prey for apex predators, such as king penguins, and may provide an alternative prey source to krill predators when krill biomass is low, but studies of DSLs in this region are limited. Acoustic data from around the entire SO were collected on the Antarctic Circumnavigation Expedition in the austral summer of 2017. A Simrad EK80 12.5 kHz broadband scientific echosounder linked to the ships own transducer was used to study the circumpolar distribution of DSLs, and an EK60 200 kHz for krill distributions. DSL density varied significantly across the survey; density was lowest at high latitudes and increased across the frontal zones, peaking around the island of Tasmania. Krill was distributed as expected, with much higher densities around South Georgia. This study forms part of an international interdisciplinary effort, and ongoing work will link these data to simultaneous oceanographic and atmospheric measurements, providing new information to understand the SO marine ecosystem and the effects of climate change. Distribution of pelagic fish in the Hoburgs bank Ronny Fredriksson, Olavi Kaljuste, Ulf Bergström Swedish University of Agricultural Sciences, Department of Aquatic Resources, Institute of Coastal Research, Skolgatan 6, Öregrund, Uppland, Sweden [email protected] In the autumn of 2016, a cooperation project was initiated between Geological Survey of Sweden (SGU), the Department of Aquatic Resources at the Swedish University of Agricultural Sciences (SLU Aqua) and Aquabiota AB, with the intention of carrying out a comprehensive marine mapping of Hoburgs bank (Hoburg Shoal), a shoal located in the Baltic Sea, in the southern zone of the Gotland shelf. The mapping covered bathymetry, geology, oceanography and biology. This study presents the results of the hydroacoustic data analyzes. The data for the analysis were collected in August and September 2016. The acoustic measurements were performed by SGU aboard their survey vessel Ocean Surveyor with a Kongsberg EM2040 multi-beam echo sounder. The purpose of the acoustic investigation was to map the bottom topography, but within the framework of this study, these data are also used for mapping of pelagic fish. These analyzes have been performed by SLU Aqua and an important part of the study was to evaluate the possibility of collecting information about pelagic fish in the water column with SGU's equipment while collecting bathymetric information. The result of the interpolation of acoustic data shows that the core areas of the pelagic fish are similar during the day and night. However, the fish is distributed over a larger area at night compared to daytime. Common to these two analyzes is that they both show that the highest relative biomasses were presented at the shallowest area and the nearby slopes in the northern part of the study area. The most common pelagic species in the area are Baltic herring, sprat and 3-spine stickleback, but since no trawling was performed in connection to the acoustic sampling, we do not know how the species or size distribution of pelagic fish looked like in the study area. Habitat modeling was performed using Generalizable Additive Models (GAM). During the modeling, different options of spatial resolution were tested for the depth and depth range variables. The tests showed that the roughest resolution of 500 meters gave models the highest degree of explanation. This was true for both models based on data from night and day time. The variable depth range was not significant in any of the final models. For the variables temperature and salinity, both the temperature and salinity at the bottom and in the entire water column were tested. In the final models, salinity and temperature at the bottom were used for data from daytime, because the fish was to a greater extent close to the bottom then. During nighttime, when the fish is more evenly distributed in the water column, temperature and salinity of the entire water column was used instead. Although statistically significant relationships could be demonstrated between the tested variables and the distribution of pelagic fish, the degree of explanation of the models was low. For the model based on data from night, about 14% of the variation could be explained by the included variables, while the corresponding figure for the day models was just over 6%. The models showed that the fish during the night preferred areas deeper than 20 m, while the fish during daytime were found in the shallower parts of the survey area. For the night model, the response to temperature showed that the optimum was between ca. 10-14 degrees. During the daytime, there was more fish in the colder waters. For both models, the response was negative for salinity. The attempt to model the distribution of pelagic fish with the help of a few environmental variables showed then that it is difficult to obtain good models. This is due to the fact that it is generally difficult to model the occurrence of pelagic, shoal-forming species, but probably to a large extent that species and size