2010 Annual Survey of Juvenile Salmon, Ecologically-Related Species, and Environmental Factors in the Marine Waters of Southeastern Alaska
September 25, 2010
Juvenile Pacific salmon (Oncorhynchus spp.), ecologically-related species, and associated environmental (biophysical) data were collected from the marine waters of the northern region of southeastern Alaska in 2010. This annual survey, conducted by the Southeast Coastal Monitoring (SECM) project, marks 14 consecutive years of systematically monitoring how juvenile salmon utilize 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 2010 findings with selected biophysical parameters from the prior 13 sampling years. Up to 13 stations were sampled in epipelagic waters monthly, totaling 21 sampling days, from May to August. Fish, zooplankton, surface water samples, and physical profile data were typically collected during daylight at each station 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 9 to 14 ºC and 17 to 32 PSU from May to August. More than 39,000 fish, representing 26 taxa, were captured in 67 rope trawl hauls fished from June to August. Juvenile salmon comprised about 97% of the total fish catch. Juvenile pink (O. gorbuscha), chum (O. keta), sockeye (O. nerka), and coho (O. kisutch) salmon occurred in 71-87% of the trawls, while juvenile Chinook salmon (O. tshawytscha) occurred in 9% of the hauls. Unusually high numbers of juvenile salmon were captured in strait habitat in both June and July, although CPUE was greatest in June for all species except sockeye salmon. Coded-wire tags were recovered from 15 juvenile coho salmon and one juvenile Chinook salmon from hatchery and wild stocks originating in southeastern Alaska and Washington. Alaska enhanced stocks were also identified by thermal otolith marks from 67% of the chum and 16% of the sockeye salmon examined. Onboard stomach analysis revealed predation on highly abundant juvenile salmon by adult coho salmon, a common predator, and adult pink salmon, a rare predator. Biophysical measures from 2010 differed from prior years, in many respects. May integrated (20-m) temperature anomalies were generally positive and salinity anomalies were generally negative; in particular, the positive May temperature anomaly was the highest on record. Zooplankton monthly total densities were near longterm averages, reversing the trend for strongly positive anomalies over the past four years. For juvenile pink, chum, and sockeye salmon, low condition residuals in June were followed by small size and low energy density in July. Regional biophysical data from SECM are used in conjunction with basin-scale biophysical parameters to forecast pink salmon harvest in southeastern Alaska. Longterm 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, an ecosystem 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, affect 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 biological interactions among stock groups. In addition, past research has not provided adequate time series data to explain these links (Pearcy 1997; Beamish et al. 2008). Regional salmon production has increased over the last few decades, emphasizing the importance of understanding the consequences of population changes and potential interactions on the growth, distribution, migratory rates, and survival of all salmon stock groups.
A goal of the SECM project is to identify mechanisms linking salmon production to climate change using a time series of synoptic data on salmon and the ocean conditions they experience, including salmon stock-specific life history characteristics. 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: pink (O. gorbuscha), chum (O. keta), 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 trends in early marine ecology of these marked stock groups provides an opportunity to link increasing salmon production to climate change, particularly in the context of increased enhancement.
The extent of interactions between stock groups 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. 2004, 2011). Zooplankton prey fields are more likely to be cropped by the more abundant planktivores forage fish, 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 than food type for growth and survival of juvenile salmon con-specifics (Weitkamp and Sturdevant 2008) and that predation events can affect salmon year-class strength (Sturdevant et al. 2009). Monitoring jellyfish abundance is also 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). Seasonal and interannual changes in planktivorous jellyfish abundance have been reported by SECM (Orsi 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 that produce salmon and consistently examining the entire epipelagic community in the context of trophic interactions.
In 2010, SECM sampling was conducted in the northern region of SEAK for the 14th consecutive year to continue annual monitoring, explore juvenile salmon abundance relationships with biophysical parameters, and support models to forecast adult pink salmon returns. This document summarizes data on juvenile salmon, ecologically-related species, and associated biophysical parameters collected by the SECM project in 2010, and contrasts key parameters from 2010 with the entire 14-yr time series.