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Bering Sea Integrated Ecosystem Research Program NORTH PACIFIC RESEARCH BOARD BERING SEA INTEGRATED ECOSYSTEM RESEARCH PROGRAM FINAL REPORT Ichthyoplankton: horizontal, vertical, and temporal distribution of larvae and juveniles of Walleye Pollock, Pacific Cod, and Arrowtooth Flounder, and transport pathways between nursery areas NPRB BSIERP Project B53 Final Report Janet Duffy-Anderson1, Franz Mueter2, Nicola Hillgruber2, Ann Matarese1, Jeffrey Napp1, Lisa Eisner3, T. Smart4, 5, Elizabeth Siddon2, 1, Lisa De Forest1, Colleen Petrik2, 6 1Alaska Fisheries Science Center, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115, USA 2University of Alaska Fairbanks, School of Fisheries and Ocean Sciences, 17101 Point Lena Loop Road, Juneau, AK 99801 USA 3Ted Stevens Marine Research Institute, Alaska Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 17109 Pt. Lena Loop Road, Juneau, AK 99801, USA 4School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98195-5020, USA 5Present affiliation: Marine Resources Research Institute, South Carolina Department of Natural Resources, Charleston, South Carolina 29422, USA 6Present affiliation: UC Santa Cruz, Institute of Marine Sciences, 110 Shaffer Rd., Santa Cruz, CA 95060, USA December 2014 1 Table of Contents Page Abstract ........................................................................................................................................................... 3 Study Chronology ........................................................................................................................................... 6 General Introduction ....................................................................................................................................... 8 BSIERP Hypotheses ....................................................................................................................................... 11 Project Objectives ........................................................................................................................................... 12 Chapter 1 ......................................................................................................................................................... 14 Chapter 2 ......................................................................................................................................................... 52 Chapter 3 ......................................................................................................................................................... 88 Chapter 4 ......................................................................................................................................................... 115 Chapter 5 ......................................................................................................................................................... 148 Chapter 6 ......................................................................................................................................................... 189 Chapter 7 ......................................................................................................................................................... 213 Overall Conclusions ........................................................................................................................................ 267 BSIERP and Bering Sea Project Connections ................................................................................................ 270 Management Implications ............................................................................................................................... 272 Publications ..................................................................................................................................................... 273 Poster and Oral Presentations ......................................................................................................................... 275 Outreach .......................................................................................................................................................... 278 Acknowlegements ........................................................................................................................................... 280 2 Abstract This project component (B53) of the Bering Sea Integrated Ecosystem Research Program (BSIERP), a six-year multidisciplinary research effort sponsored by the North Pacific Research Board to study the Bering Sea ecosystem, was designed to examine linkages between physical oceanographic variables, biotic modulators, and distribution and abundance of three target fish species in the eastern Bering Sea (EBS): Walleye Pollock (Gadus chalcogrammus, previously described as Theragra chalcogramma), Pacific Cod (Gadus macrocephalus), and Arrowtooth Flounder (Atheresthes stomias). Effort focused primarily on Walleye Pollock due to limited data availability on Pacific Cod and Arrowtooth Flounder. Studies were based on historical zooplankton, ichthyoplankton, and physical data (1985-2010) collected by the NOAA/Alaska Fisheries Science Center over the Bering Sea shelf as well as on a series of seasonal, collaborative cruises that occurred 2008-2010 which were part of the BSIERP. Data derived from the above investigations were applied to a biophysical model developed to examine interannual patterns in Walleye Pollock distribution and abundance. The model work was funded, in part, with monies from project B53 and with funds provided through the Bering Ecosystem STudy (BEST) Synthesis Program, a Bering Sea research synthesis program sponsored by the National Science Foundation. Cumulative results of this work provide a better understanding of the potential effects of hydrographic variations in rearing conditions, transport, dispersal, and distribution of early life stages of Walleye Pollock in the eastern Bering Sea. In the first part of the project we examined factors affecting distribution, abundance and community composition of larval fish assemblages, which included all three target species, over the Bering Sea shelf and determined: 1) A strong cross-shelf gradient delineates slope and shelf assemblages which is influenced by water masses emanating from the Gulf of Alaska, 2) Larval species assemblages in the Bering Sea differ between warm and cold periods, with larval abundances (including Walleye Pollock) being generally greater in warm years, and 3) Community-level patterns in larval fish composition reflect species-specific responses to climate change. The next part of the project involved a comprehensive suite of studies designed to examine factors influencing distribution and abundance of young Walleye Pollock over the Bering Sea shelf. First, abiotic and biotic variables were examined for effects on distribution and abundance of Walleye Pollock larval stages. From this project it was found that: 1) The influence of temperature on abundances of larval and juvenile Walleye Pollock increases with fish ontogeny, 2) Winds enhance the transport of early life stages from initial spawning locations to shallower depths over the continental shelf, 3) Localized measurements of zooplankton prey are a better indicator of young pollock abundance than 3 broad-scale measurements that are integrated over the shelf, and 4) Temperature is a major driving force structuring variability in abundance of Walleye Pollock in their first year of life. Second, the effects of temperature on young Walleye Pollock were examined in greater detail in a study designed to determine whether early life stages undergo spatial shifts in response to changing temperature conditions, and test whether temperature affects the phenology of developmental events. It was found that: 1) Walleye Pollock early life stages are distributed further east over the continental shelf in warm years compared to cold years, and 2) Differences in the timing of density peaks support the hypothesis that the timing of spawning, hatching, larval development, and juvenile transition are temperature-dependent. Third, a study of the factors affecting vertical distributions was undertaken. Results from this investigation found: 1) Walleye Pollock demonstrate a decrease in the depth of occurrence following hatching, indicating an ontogenetic change in vertical distribution, 2) Walleye Pollock vertical distributions are related to the date of collection, water column depth, and thermocline depth, 3) Non- feeding stages (eggs and yolksac larvae) do not exhibit diel vertical migration, 4) Flexion and postflexion stage larvae, 10.0–24.5 mm SL undergo regular diel migrations (0–20 m, night; 10–40 m, day), 5) Vertical distributions and diel migration a trade-off between prey access and predation risk for postflexion larvae, and 6) Vertical distributions of Walleye Pollock eggs, yolksac larvae, and preflexion larvae in the Bering Sea are different from previously-documented distributions in other ecosystems. Fourth, we sought to determine mechanisms driving the observed spatial shifts in distribution of young Walleye Pollock in warm and cold years. To accomplish this we developed a biophysical model of spawning and dispersal, utilizing the data derived from the above investigations as input data, to examine spawning, drift and connectivity of Walleye Pollock populations over the Bering Sea shelf in warm and cold years. Model results indicate that:
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