Juvenile Pacific salmon (Oncorhynchus spp.), ecologically-related species, and associated biophysical data were collected along a primary marine migration corridor in the northern region of southeastern Alaska. Thirteen stations were sampled over six time periods (31 sampling days) from May to August 2004. This survey marks the eighth consecutive year of systematic monitoring on how juvenile salmon interact in marine ecosystems, and was implemented to identify the relationships among biophysical parameters that influence the habitat use, marine growth, predation, stock interactions, and year-class strength of salmon. Habitats sampled included stations in inshore (Auke Bay and Taku Inlet), strait (four stations each in Chatham Strait and Icy Strait), and coastal (four stations off Icy Point) localities. At each station, fish, zooplankton, surface water samples, and physical profile data were collected using a surface rope trawl, conical and bongo nets, water sampler, and a conductivity-temperature-depth profiler, usually during daylight. Surface (3-m) temperatures and salinities ranged from 6.9 to
17.4 ºC and 9.5 to 31.6 PSU from May to August. A total of 13,460 fish and squid, representing 29 taxa, were captured in 75 rope trawl hauls from June to August. Juvenile salmon comprised 48% of the total catch and occurred frequently in the trawl hauls, with pink (O. gorbuscha) occurring in 75% of the trawls, sockeye (O. nerka) in 73%, chum (O. keta) in 72%, coho (O. kisutch) in 51%, and chinook salmon (O. tshawytscha) in 19%. Of the 6,552 salmonids caught, over 99% were juveniles. Walleye pollock (Theragra chalcogramma) and Pacific herring (Clupea pallasi) were the only non-salmonid species that comprised more than 1% of the total catch. Temporal and spatial differences were observed in the catch rates, size, condition, and stock of origin of juvenile salmon species. Catch rates of juvenile salmon were generally highest in June for all species except coho that had catch rates highest in August. Between habitat types, juvenile salmon catch rates were almost always highest in the strait habitat for each species and in each time period. Size of juvenile salmon increased steadily throughout the season; mean fork lengths in June, July, and August were, respectively: 98, 129, and 163 mm for pink; 104, 139, and 166 mm for chum; 111, 137, and 165 mm for sockeye; 170, 203, and 246 mm for coho; and 199, 228, and 279 for chinook salmon. Coded-wire tags were recovered from 14 juvenile coho, three juvenile and six immature chinook salmon; all but one were from hatchery and wild stocks of southeastern Alaska origin. The non-Alaska stock was a juvenile chinook originating from Oregon. Alaska hatchery stocks were also identified by thermal otolith marks from 74% of the chum, 18% of the sockeye, 9% of the coho, and 45% of the chinook salmon. Onboard stomach analysis of 199 potential predators, representing 10 species, revealed four predation instances on juvenile salmon: three by adult coho salmon and one by an immature chinook salmon. This research suggests that in southeastern Alaska, juvenile salmon exhibit seasonal patterns of habitat use synchronous with environmental change, and display species- and stock-dependent migration patterns. Long-term monitoring of key stocks of juvenile salmon, on both intra- and interannual bases, will enable researchers to understand how growth, abundance, and ecological interactions affect year-class strength and to better understand the role salmon play in North Pacific marine ecosystems.