2009 Annual Survey Of Juvenile Salmon, Ecologically-Related Species, And Environmental Factors In The Marine Waters Of Southeastern Alaska
Juvenile Pacific salmon (Oncorhynchus spp.), ecologically-related species, and associated biophysical data were collected from the marine waters of the northern and southern regions of southeastern Alaska in 2009. This annual survey marks 13 consecutive years of systematically monitoring how juvenile salmon interact in marine ecosystems, and was implemented to identify the relationships among biophysical parameters that influence habitat use, marine growth, predation, stock interactions, and year-class strength of juvenile salmon. This report also contrasts the 2009 findings with selected biophysical parameters from the prior 12 sampling years. Up to 17 stations were sampled in epipelagic waters over four time periods (20 sampling days) from May to August. Typically, at each station, fish, zooplankton, surface water samples, and physical profile data were collected during daylight using a surface rope trawl, conical and bongo nets, a water sampler, and a conductivity-temperature-depth profiler. Surface (3-m) temperatures and salinities ranged from approximately 8 to 15 ºC and 19 to 31 PSU from May to August. Nearly 11,000 fish, representing 12 taxa, were captured in 60 rope trawl hauls in July and August in the two regions. No trawling was conducted in June, in contrast to all other years. Juvenile salmon comprised about 97% of the total fish catch. Juvenile pink (O. gorbuscha), chum (O. keta), sockeye (O. nerka), and coho salmon (O. kisutch) occurred in 5698% of the trawls, while juvenile Chinook salmon (O. tshawytscha) occurred in < 13% of the hauls. All juvenile salmon species occurred more frequently in northern region trawls than in southern region trawls in July. In the northern region, catch rates of juvenile pink, chum, and coho salmon were higher in July than in August, whereas catches of sockeye salmon were higher in August. Coded-wire tags were recovered from 18 juvenile coho salmon from hatchery and wild stocks originating in southeastern Alaska. Alaska enhanced stocks were also identified by thermal otolith marks from 47% of the chum and 18% of the sockeye salmon examined. Onboard stomach analysis of 108 potential predators, representing seven species, did not provide evidence of predation on juvenile salmon. Biophysical measures from 2009 differed from prior years, in many respects. Integrated (20-m) temperature anomalies were all positive and salinity anomalies were negative; in particular, the May temperature anomaly was the 2nd highest on record. Anomalies of zooplankton total density were positive each month, a trend which has persisted for four years. In addition, size anomalies for juvenile salmon were positive, a shift from the previous two years. Condition residual anomalies were unusually high for juvenile salmon species in August. These data, in conjunction with basin-scale biophysical parameters, are currently being used to forecast pink salmon harvest in southeastern Alaska. Long-term monitoring of key stocks of juvenile salmon, on seasonal and interannual time scales, will enable researchers to understand how growth, abundance, and ecological interactions affect year-class strength of salmon and to better understand their roles in North Pacific marine ecosystems.
The Southeast Coastal Monitoring (SECM) project, a coastal monitoring study focused in the northern region of southeastern Alaska (SEAK), 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 (Downton and Miller 1998; Beauchamp et al. 2007; Farley et al. 2007; Taylor 2007). In particular, climate variables such as temperature have been associated with ocean production and survival of salmon; for example, warming trends benefited many wild and hatchery stocks of Alaskan salmon or enhanced their food supplies (Wertheimer et al. 2001; Beauchamp et al. 2007). Biophysical attributes of climate and habitat, such as temperature, salinity, and mixed layer depth (MLD), influence primary and secondary production (Bathen 1972; Kara et al. 2000; Alexander et al. 2001) and therefore may influence the trophic links leading to variable growth and survival of salmon (Mann and Lazier 1991; Francis et al. 1998; Brodeur et al. 2007). However, research is lacking on the links between salmon production and climate variability, intra- and interspecific competition and carrying capacity, and stock composition and biological interactions. In addition, past research has not provided adequate time-series data to explain these links (Pearcy 1997; Beamish et al. 2008). Because regional salmon production has increased over the last few decades, understanding the consequences of these population changes and potential interactions on the growth, distribution, migratory rates, and survival of all salmon stock groups is important.
One goal of the SECM project is to identify mechanisms linking salmon production to climate change using a time series of synoptic data on salmon, their stock-specific life history characteristics, and the ocean conditions they experience. The SECM project obtains stock information from coded-wire tags (CWT; Jefferts et al. 1963) and otolith thermal marks (Hagen and Munk 1994; Courtney et al. 2000) from five Pacific salmon species, including chum (O. keta), pink (O. gorbuscha), sockeye (O. nerka), coho (O. kisutch), and Chinook (O. tshawytscha). Portions of wild and hatchery salmon stocks are tagged or marked prior to ocean entry by enhancement facilities or state and federal agencies in southeastern Alaska, Canada, and the Pacific Northwest. Catches of these marked fish by the SECM project in the northern, southern, and coastal regions of SEAK have provided information on habitat use, migration rates, and timing (e.g., Orsi et al. 2004, 2007a, b); in addition, interceptions in the regional common property fisheries have documented substantial contributions of enhanced fish to commercial harvests (ADFG, 2008). Therefore, examining the early marine ecology of these marked stocks provides an opportunity to study stock-specific abundance, distribution, migration, and species interactions of juvenile salmon that will later recruit to fisheries.
The extent of interactions between hatchery and wild salmon stocks in marine ecosystems is also important to examine with regard to carrying capacity. For example, increased hatchery production of juvenile chum salmon has coincided with declines of some wild chum salmon stocks, suggesting the potential for stock interactions in the marine environment (Seeb et al. 2004; Reese et al. 2009). In SEAK, however, SECM and other studies have shown that growth is not food limited and that stocks interact extensively with little negative impact (Bailey et al., 1975; Orsi et al. 2004; Sturdevant et al. 2002, 2004, 2008; Sturdevant et al. in review). Zooplankton prey fields are more likely to be cropped by the more abundant vertically-migrating planktivores, including walleye pollock (Theragra chalcogramma) and Pacific herring (Clupea pallasi) (Orsi et al. 2004; Sigler and Csepp 2007), than by juvenile salmon. Companion studies in Icy Strait have also suggested that food quantity may be more important to growth and survival of juvenile salmon con-specifics than food type (Weitkamp and Sturdevant 2008) and that predation events can affect salmon year-class strength (Sturdevant et al. 2009). Seasonal and interannual changes in planktivorous jellyfish abundance have been reported by SECM in past years (Orsi et al. 2009; SECM unpublished data). Monitoring their abundance is important because of their potential competition with salmon and forage fish (Purcell and Sturdevant 2001), and their association with environmental change (Brodeur et al. 2008; Cieciel et al. 2009). Similarly, regional differences in composition, abundance, and timing of zooplankton taxa with different life history strategies are important to document because of their dependence on environmental conditions which vary seasonally and interannually (Coyle and Paul 1990; Paul et al. 1990; Park et al. 2004). These findings stress the importance of comparing ecological processes between different areas producing salmon and consistently examining the entire epipelagic community in the context of trophic interactions.
In 2009, the SECM project was supported by the small NOAA research vessels RV Quest and RV Sashin and by a larger charter vessel, FV Chellissa. In addition to sampling in the northern region, sampling in the southern region was reinstated after a year lapse (Orsi et al. 2006, 2007a, 2008) to support forecasting of adult pink salmon returns from juvenile abundance and to explore the concordance of harvests between regions in conjunction with local biophysical parameters.