2006 Annual Survey of Juvenile Salmon and Ecologically Related Species and Environmental Factors in the Marine Waters of Southeastern Alaska
September 24, 2006
Juvenile Pacific salmon (Oncorhynchus spp.), ecologically-related species, and associated biophysical data were collected along primary marine migration corridors in the northern and southern regions of southeastern Alaska in 2006. Up to 21 stations were sampled over four time periods (39 sampling days) from May to August. This survey marks 10 consecutive years 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. Typically, 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 during daylight. Surface (3-m) temperatures and salinities ranged from 7.1 to 15.4 ºC and 15.1 to 32.0 PSU from May to August. A total of 10,641 fish and squid, representing 20 taxa, were captured in 94 rope trawl hauls from June to August. Juvenile salmon comprised about 98% of the total fish and squid catch in each region. Juvenile salmon occurred frequently in the trawl hauls, with pink (O. gorbuscha), chum (O. keta), sockeye (O. nerka), and coho salmon (O. kisutch) occurring in 52100% of the trawls in both regions, whereas, juvenile Chinook salmon (O. tshawytscha) occurred in 25% and 28% of the hauls in the southern and northern regions. Of the 10,451 salmonids caught, over 99% were juveniles. In both regions, only two non-salmonid species represented catches of >27 individuals: walleye pollock (Theragra chalcogramma) in the southern region and Pacific herring (Clupea pallasi) in the northern region. 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 in both regions were generally highest in June for all species except Chinook, which had the highest catch rates in July. Size of juvenile salmon increased from June and July; mean fork lengths were: 102 and 121 mm for pink; 112 and 138 mm for chum; 110 and 131 mm for sockeye; 168 and 200 mm for coho; and 202 and 223 mm for Chinook salmon. Coded-wire tags were recovered from 13 juvenile coho salmon, two juvenile and one immature Chinook salmon; all but two were from hatchery and wild stocks of southeastern Alaska origin. The non-Alaska stocks were juvenile Chinook salmon originating from the Similkameen River and the Wells Hatchery within the Columbia River Basin. Alaska enhanced stocks were also identified by thermal otolith marks from 77% of the chum and 7% of the sockeye salmon. Onboard stomach analysis of 95 potential predators, representing 12 species, revealed one predation incident on juvenile salmon by an adult coho salmon. This research suggests that in southeastern Alaska, juvenile salmon exhibit seasonal patterns of habitat use 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.
The Southeast Coastal Monitoring Project (SECM), a coastal monitoring study focused in the northern region of southeastern Alaska, was initiated in 1997 to annually study the early marine ecology of Pacific salmon (Oncorhynchus spp.) and associated epipelagic ichthyofauna and to better understand effects of environmental change on salmon production. Salmon are a keystone species that constitute an important ecological link between marine and terrestrial habitats, and therefore play a significant, yet poorly understood, role in marine ecosystems. Fluctuations in the survival of this important living marine resource have broad ecological and socio-economic implications for coastal localities throughout the Pacific Rim. 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 Niño and La Niña 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.
a time series of synoptic data that combines stock-specific life history characteristics of salmon and their ocean conditions. 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 high levels regional hatchery production of chum salmon (O. keta) and historically high returns of wild pink salmon (O. gorbuscha). For example, in recent years, two private non-profit enhancement facilities in the northern region of southeastern Alaska annually produced more than 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 million fish annually with an exvessel commercial value of 27 million $U.S. (ADFG 2007), including 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. Therefore, 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.
Increased hatchery production of juvenile salmon in southeastern Alaska has raised concern over potential hatchery and wild stock interactions during their early marine residence. A recent study using a bioenergetics approach and SECM data from Icy Strait concluded that hatchery and wild stocks consumed only a small percentage of the available zooplankton (Orsi et al. 2004a); this study also suggested that abundant, vertically-migrating planktivores have a greater impact on the zooplankton standing stock than hatchery stock groups of chum salmon. These findings stress the importance of examining the entire epipelagic community of ichthyofauna in the context of trophic interactions.
To broaden the SECM research scope in southeastern Alaska, sampling was expanded to include strait habitat within the southern region in 2005. This new regional study component was added to the SECM project to support an increased emphasis on forecasting of adult pink salmon returns and to understand regional differences in prey, competitor, and predation dynamics. This study component supplements the core sampling of eight stations in strait habitat of the northern region, and geographically broadens the monitoring to include a southern migration corridor in the opposite end of southeastern Alaska. This study is currently proposed for continued funding over a 3-year period by the Northern Fund of the Pacific Salmon Commission. A primary focus of this study component is to explore the concordance of adult pink salmon harvests in both the southern and northern regions in southeastern Alaska with biophysical parameters such as juvenile abundance, temperature, and zooplankton abundance in each region.