1997 Survey of Juvenile Salmon in the Marine Waters of Southeastern Alaska
Twenty 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 ofjuvenile (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 and Icy Point)-and sampled aboard the NOAA ship John N. Cobb from May to August 1997. At each station, fish, zooplankton, temperature, and salinity data were collected during daylight with a surface rope trawl, conical nets, bongo nets, and a CTD (conductivity, temperature, and depth profiler). A total of 6,252 fish and squid were captured with· the rope trawl, representing 31 taxa. All five species ofjuvenile Pacific salmon and steelhead (0. mykiss) were captured and made up 80% of the total catch. Of the 5,000 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), squid (Gonatidae), capelin (Ma/lotus villosus), walleye pollock ( Theragra cha/cogramma ), and sablefish (Anop/opoma .fimbria). Chum ( 0. keta), coho (0. kisutch), pink (0. gorbuscha), sockeye (0. nerka), and chinook (0. tshawytscha) salmon and crested sculpin (Blepsias bilobus) occurred most frequently (~30%) in the trawl catches. Overall catches of juvenile salmon were highest in July and zero in May. Catch rates of coho and sockeye salmon were highest in June, whereas catch rates of chum, pink, 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 within 25 km of shore, and no juvenile salmon was found beyond 40 km. Mean fork lengths of juvenile salmon in JuneJuly-August were: chum (97-137-162 mm), pink (96-136-156 mm), sockeye (110-146-154 mm), coho (148-207-247 mm), and chinook salmon (143-172-222 mm). Twenty-three juvenile and immature salmon containing internally planted coded-wire tags (CWTs) were recovered; 21 originated in Alaska and two in Oregon (one chinook and one coho salmon). The Oregon chinook salmon is the earliest recorded recovery of a stream-type chinook salmon of the Columbia River stock in Alaska during its first summer at sea. Onboard stomach analysis of potential predators ofjuvenile salmon did not indicate a high level of salmon predation; however, few predators were present during high levels of juvenile salmon abundance, and fish remains in stomachs were often too far digested to identify. Results from this study and further laboratory analysis of otolith-marked fish will be used to assess competitive interactions between wild and hatchery stocks and stock-specific 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 otolith thermal marks (Hagen and Munk 1996) now offer an opportunity to examine growth, survival, distribution, and migratory rates of specific stocks.
Approximately 123 million thermally-marked juvenile chum salmon (0. keta) were released in the spring of 1997 from two major enhancement facilities in the northern region of southeastern Alaska. Samples of these fish were collected 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. Oceanographic data were also collected to expand existing time senes.