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1998 Survey of Juvenile Salmon in the Marine Waters of Southeastern Alaska

September 24, 1998

Twenty four stations were sampled monthly along a primary marine migration corridor in the northern region of southeastern Alaska to assess the distribution, growth, mortality, and diet of wild and hatchery stocks of juvenile (age -.0) Pacific salmon ( 0ncorhynchus spp.). Stations were stratified into three different habitats-inshore (Taku Inlet and near Auke Bay), strait (Chatham Strait and Icy Strait), and coastal (Cross Sound, Icy Point, and Cape Edward)-and sampled aboard the NOAA ship John N. Cobb from May to August 1998. At each station, fish, zooplankton, temperature, and salinity data were collected during daylight with a surface rope trawl, conical nets, bongo nets, and a conductivity, temperature, and depth profiler. Surface (2-m) temperatures and salinities during the survey ranged from 7.6 to 14.2°C and 16.4 to 32.0%0. A total of 12,814 fish and squid were captured with the rope trawl, representing 30 taxa. All five species of juvenile Pacific salmon and steelhead (0. mykiss) were captured and comprised 85% of the total catch. Of the 10,895 salmonids caught, over 99% were juveniles, and less than 1 % were immatures or adults. Non-salmonid species making up>1 % of the catch included Pacific herring (Clupea harengus), capelin (Mallotus villosus), squid (Gonatidae), and sablefish (Anoplopomafimbria). The highest frequency of occurrence (>25%) in the trawl catches was observed for chum (0. keta), coho (0. kisutch), sockeye (0. nerka), pink (0. gorbuscha), and chinook (0. tshawytscha) salmon, and wolf-eels (Anarrhichthys ocellatus). Overall catch rates of juvenile salmon were highest in June and July, intermediate in August, and zero in May. Catch rates of pink and chum salmon were highest in June, whereas catch rates of sockeye, coho, and chinook salmon were highest in July. Catch rates of juvenile salmon except chinook salmon were highest in strait habitat and lowest in inshore habitat; chinook salmon catch rates were highest in inshore habitat. Overall catch rates for juvenile salmon along the offshore transect declined with distance offshore: most juveniles were captured within 25 km of shore, and only one juvenile salmon was found beyond 40 km. Mean fork lengths ofjuvenile salmon in JuneJuly-August were: pink (94-127-162 mm), chum (102-134-164 mm), sockeye (112-139-153 mm), coho (166-213-253 mrri), and chinook salmon (160-166-190 mm). Twenty-four juvenile and immature salmon ( 13 chinook and 11 coho) containing internally planted coded-wire tags were recovered; 20 originated from Alaska, 3 from the Columbia River Basin, and l from Washington. Recoveries of juvenile chinook salmon from the Columbia River Basin are some of the earliest documented recoveries of these stream-type stocks in Alaska during their first summer at sea. Onboard stomach analysis of potential predators of juvenile salmon indicated a low level of salmon predation by sablefish, spiny dogfish (Squalus acanthias), and adult coho salmon. Results from this study and further laboratory analysis of otolith-marked fish will be used to assess potential competitive interactions between wild and hatchery stocks and stockspecific life history characteristics.

Increasing evidence for relationships between Pacific salmon (Oncorhynchus spp.) production and shifts in climate conditions has renewed interest in processes governing yearclass strength in salmon (Beamish 1995). However, actual links tying salmon production to climate variability are understood poorly due to a lack of adequate time-series data (Pearcy 1997). In addition, mixed stocks with different life history characteristics confound attempts to accurately assess growth, survival, distribution, and migratory rates of specific stocks. Synoptic time series of ocean conditions and stock-specific life history characteristics of salmon are needed to adequately identify mechanisms linking salmon production to climate change. Until recently, stock-specific information relied on labor-intensive methods such as coded-wire tagging (CWT; Jefferts 1963). However, advances in mass-marking methods using thermally induced otolith marks (Hagen and Munk 1994) offer an opportunity to examine growth, survival, distribution, and migratory rates of specific stocks.

In 1997, we initiated a survey along sampling stations in marine waters of the northern region of southeastern Alaska to build time series data on specific stocks of salmon and oceanographic conditions (Orsi et al. 1997). In 1998, our object was to repetitively sample the same stations as 1997, including an additional coastal transect. As in 1997, juvenile chum salmon (0. keta) were a primary focus in 1998 because each year over 100 million otolithmarked juveniles were released from two major enhancement facilities in the northern region of southeastern Alaska. In our survey we sampled juvenile salmon seasonally along a seaward migration corridor to determine whether competitive interactions between hatchery and wild stocks exist and to obtain stock-specific life history characteristics such as growth, migration, diet, condition, and size-selective mortality.

Last updated by Alaska Fisheries Science Center on 04/23/2019