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NOAA Technical Memorandum NMFS-AFSC-236

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A refined description of essential fish habitat for Pacific salmon within the U.S. Exclusive Economic Zone in Alaska


In 2005 the North Pacific Fishery Management Council used an improved analytical approach to identify essential fish habitat (EFH) for most species of groundfish and crab, however, due to the lack of available information, the entire U.S. Exclusive Economic Zone (EEZ; 200-nautical miles (nmi) from shore) for each of the five species of Pacific salmon was left intact as EFH.  In order to better define EFH within the U.S. EEZ for Pacific salmon found in Alaska (Oncorhynchus spp.), we acquired catch, maturity, salinity, temperature, and station depth data for the Bering Sea and Gulf of Alaska from multiple data sources.  We analyzed the influence of sea surface salinity (SSS), sea surface temperature (SST), and bottom depth on the distribution of Pacific salmon. Very few significant associations between catch and the three tested environmental variables were found to exist, indicating little to no relationship between species distribution and the three measures of habitat condition; however, many patterns were still evident. By calculating and mapping the coincidence of the 95% range of each environmental variable (SSS, SST, depth) for each of the five species at each maturity stage, our updated EFH descriptions reduce the area of designated EFH for Pacific salmon by 71.3% on average. Juvenile salmon EFH generally consists of the water over the continental shelf within the Bering Sea extending north to the Chukchi Sea, and over the continental shelf throughout the Gulf of Alaska and within the inside waters of the Alexander Archipelago. Immature and mature Pacific salmon EFH includes nearshore and oceanic waters, often extending well beyond the shelf break, with fewer areas within the inside waters of the Alexander Archipelago and Prince William Sound. This has been the first time that salmon data sets from multiple surveys, agencies, and years have been accumulated and formatted for Pacific salmon distribution and habitat analysis.  This study summarizes catches > 420,000 Pacific salmon sampled during 5,280 surface trawl and purse seine events in the Alaska EEZ from 1964 to 2009.  Distribution was plotted for each salmon species and life history within the Alaska EEZ.   To better describe salmon EFH, additional detailed habitat preference analysis was performed with available biophysical data from approximately 84% of the events. Not only will the database resulting from this project be of invaluable use for future research, but a much greater understanding of Pacific salmon distribution in the marine environment has been gained. 

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