2003 Survey of Juvenile Salmon in the Marine Waters of Southeastern Alaska

September 24, 2003

Juvenile Pacific salmon (Oncorhynchus spp.) 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 (32 sampling days) from May to August 2003. This survey marks the seventh consecutive year of systematic monitoring, and was implemented to identify the relationships among biophysical parameters that influence the habitat use, marine growth, predation, stock interactions, year-class strength, and ocean carrying capacity of juvenile salmon. Habitats sampled included stations in inshore (Auke Bay), 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 (fish), conical and bongo nets (zooplankton), and a conductivity-temperature-depth profiler (physical data), usually during daylight. Surface (2-m) temperatures and salinities ranged from 7.6 to 15.8ΕC and 15.5 to 32.0 PSU from May to August. A total of 10,724 fish and squid, representing 23 taxa, were captured in 64 rope trawl hauls from June to August. Juvenile salmon comprised 29% of the total catch and occurred frequently in the trawl hauls, with chum (O. keta) occurring in 66% of the trawls, pink (O. gorbuscha) in 56%, coho (O. kisutch) in 55%, sockeye (O. nerka) in 50%, and chinook salmon
(O. tshawytscha) in 2%. Of the 3,254 salmonids caught, 98% 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 highest for chinook and sockeye salmon in June, highest for chum and pink salmon in July, and highest for coho salmon in August. By habitat type, juvenile salmon catch rates for pink, chum and sockeye were highest in the coastal habitat, whereas catch rates of coho and chinook were highest in the strait habitat. Size of juvenile salmon increased steadily throughout the season; mean fork lengths in June and early August were, respectively: 105 and 133 mm for pink, 116 and 138 mm for chum, 120 and 145 mm for sockeye, 173 and 215 mm for coho, and 169 mm (June only) for chinook salmon. Coded-wire tags were recovered from two juvenile coho and one immature chinook salmon; all were from hatchery and wild stocks of southeastern Alaska origin. Alaska hatchery stocks were also identified by thermal otolith marks from 32% of the chum, 45% of the sockeye, 11% of the coho, and 100% of the chinook salmon. Onboard stomach analysis of 248 potential predators, representing 10 species, indicated one predation instance on juvenile salmon by a spiny dogfish (Squalus acanthias) in the coastal habitat in July. 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 ocean carrying capacity for salmon.

Studies of the early marine ecology of Pacific salmon (Oncorhynchus spp.) in Alaska require adequate time series of biophysical data to relate climate fluctuations to the distribution, abundance, and production of salmon. Because salmon are keystone species and constitute important ecological links between marine and terrestrial habitats, fluctuations in the survival of this important living marine resource have broad ecological and socio-economic implications for coastal localities throughout the Pacific Rim. Increasing evidence for relationships between production of Pacific salmon and shifts in climate conditions has renewed interest in processes governing salmon year-class strength (Beamish 1995). In particular, climate variation has been associated with ocean production of salmon during El NiΖo and La NiΖa events, such as the recent warming trends that benefited many wild and hatchery stocks of Alaskan salmon (Wertheimer et al. 2001). However, research is lacking in areas such as the links between salmon production and climate variability, between intra- and interspecific competition and carrying capacity, and between stock composition and biological interactions. Past research has not provided adequate time-series data to explain such links (Pearcy 1997). Because the numbers of salmonids produced in the region have increased over the last few decades (Wertheimer et al. 2001), mixing between stocks with different life history characteristics has also increased. The consequences of such changes on the growth, survival, distribution, and migratory rates of salmonids remain unknown.

To adequately identify mechanisms linking salmon production to climate change, a time series of synoptic data that combines stock-specific life history characteristics of salmon and their ocean conditions is needed. Until recently, stock-specific information relied on labor-intensive methods of marking individual fish, such as coded-wire tagging (CWT; Jefferts et al. 1963), which could not practically be applied to all of the fish released by enhancement facilities. However, mass-marking with thermally induced otolith marks (Hagen and Munk 1994) is a technological advance implemented in many parts of Alaska. The high incidence of these marking programs in southeastern Alaska (Courtney et al. 2000) offers an opportunity to examine growth, survival, and migratory rates of specific salmon stocks during the current record production of hatchery chum salmon (O. keta) and wild pink salmon (O. gorbuscha) in the region. For example, in recent years, two private non-profit enhancement facilities in the northern region of southeastern Alaska have annually produced more thana total of 150 million otolith-marked juvenile chum salmon. Consequently, since the mid-1990s, commercial harvests of adult chum salmon in the common property fishery in the region have averaged about 12.5 million fish annually (ADFG 2003), supplemented by a high proportion of otolith-marked fish from regional enhancement facilities. In addition, sockeye salmon (O. nerka), coho salmon (O. kisutch), and chinook salmon (O. tshawytscha) are otolith-marked by some enhancement facilities. Examining the early marine ecology of these marked stocks provides an opportunity to study stock-specific abundance, distribution, and species interactions of juvenile salmon that will later recruit to the fishery.

A coastal monitoring study in the northern region of southeastern Alaska, known as the Southeast Coastal Monitoring Project (SECM), was initiated in 1997 and has been repeated annually to understand the relationships between annual time series of biophysical data and stock-specific information. This document summarizes juvenile salmon catches and associated biophysical data collected by SECM scientists in 2003.

 

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

Salmon