Effects of changing climate on zooplankton and juvenile sockeye salmon growth in southwestern Alaska (original) (raw)
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Marine Ecology Progress Series, 2008
To better understand how densitydependent growth of ocean-dwelling Pacific salmon varied with climate and population dynamics, we examined the marine growth of sockeye salmon Oncorhynchus nerka in relation to an index of sockeye salmon abundances among climate regimes, population abundances, and body sizes under varied lifehistory stages, from 1925 to 1998, using ordinary least squares and multivariate adaptive regression spline threshold models. The annual marine growth and body size during the juvenile, immature, and maturing life stages were estimated from growth pattern increments on the scales of adult age 2.2 sockeye salmon that returned to spawn at Karluk River and Lake on Kodiak Island, Alaska. Intra-specific density-dependent growth was inferred from inverse relationships between growth and sockeye salmon abundance based on commercial harvest. Density-dependent growth occurred in all marine life stages, during the cool regime, at lower abundance levels, and at smaller body sizes at the start of the juvenile life stage. The finding that density dependence occurred during the cool regime and at low population abundances suggests that a shift to a cool regime or extreme warm regime at higher population abundances could further reduce the marine growth of salmon and increase competition for resources.
Linkages between Alaskan sockeye salmon abundance, growth at sea, and climate, 1955–2002
Deep Sea Research Part II: Topical Studies in Oceanography, 2007
We tested the hypothesis that increased growth of salmon during early marine life contributed to greater survival and abundance of salmon following the 1976/1977 climate regime shift and that this, in turn, led to density-dependent reductions in growth during late marine stages. Annual measurements of Bristol Bay (Bering Sea) and Chignik (Gulf of Alaska) sockeye salmon scale growth from 1955 to 2002 were used as indices of body growth. During the first and second years at sea, growth of both stocks tended to be higher after the 1976-1977 climate shift, whereas growth during the third year and homeward migration was often below average. Multiple regression models indicated that return per spawner of Bristol Bay sockeye salmon and adult abundance of western and central Alaska sockeye salmon were positively correlated with growth during the first 2 years at sea and negatively correlated with growth during later life stages. After accounting for competition between Bristol Bay sockeye and Asian pink salmon, age-specific adult length of Bristol Bay salmon increased after the 1976-1977 regime shift, then decreased after the 1989 climate shift. Late marine growth and age-specific adult length of Bristol Bay salmon was exceptionally low after 1989, possibly reducing their reproductive potential. These findings support the hypothesis that greater marine growth during the first 2 years at sea contributed to greater salmon survival and abundance, which in turn led to density-dependent growth during later life stages when size-related mortality was likely lower. Our findings provide new evidence supporting the importance of bottom-up control in marine ecosystems and highlight the complex dynamics of species interactions that continually change as salmon grow and mature in the ocean. r
Variable effects of climate and density on the juvenile ecology of two salmonids in an Alaskan lake
Canadian Journal of Fisheries and Aquatic Sciences, 2014
Despite concerns over rapidly warming temperatures, an empirical understanding of climatic impacts on wild salmonid populations is limited. We tested how temperature and density affected juvenile coho (Oncorhynchus kisutch) and sockeye salmon (Oncorhynchus nerka) using a 31 year census from an Alaskan lake. There were positive effects of temperature on overall salmon biomass, sockeye biomass, and the length of age 2 sockeye smolts. There was, however, little evidence for relationships between temperature or length of growing season and coho biomass, coho length, smolts per spawner (both species), and age structure (both species). In some cases there were temporal changes contrary to what is generally expected in a warming Alaskan lake with longer growing seasons (e.g., increasing proportions of age 2 smolts). Intraspecific density was negatively related to sockeye length at out-migration, but there was no evidence for relationships between density and other response variables. Overall, patterns observed here and in other studies emphasize that responses to climatic variation can vary substantially across locations, between similar species occupying the same habitats, and among alternative life history strategies within populations.
Fishery Bulletin- National Oceanic and Atmospheric Administration
Fish stocks and fisheries in the Gulf of Alaska are strongly influenced by climatic and oceanic (C-O) conditions (Francis and Hare, 1994; Hare and Francis, 1995). In the past century C-O conditions in the North Pacific Ocean and Gulf of Alaska (GOA) have shifted from a warm regime and higher salmon (Oncorhynchus spp.) produc-tion (1927–46) to a cool regime and low salmon production (1947–76) and back to a warm regime and higher salmon production (1977–2000) (Francis and Hare, 1994; Hare and Francis, 1995). Changes in C-O conditions, either annually or over longer regime peri-ods, may affect salmon smolt-to-adult survival rates by affecting the growth rate of smolts after they enter the ocean. For example, higher survival rates of Alaska sockeye (O. nerka), pink (O. gorbuscha), and chum (O. keta) salmon have been associated with warmer coastal sea-surface tem-peratures (SST) during the first year that young salmon spend in the ocean (Mueter et al., 2002a). Relationships have been fou...
Canadian Journal of Fisheries and Aquatic Sciences, 2009
Recent climate changes have had marked effects on the ice-free season and thermal conditions in many highlatitude lakes, but their ecological effects combine with density-dependent processes to affect fish growth and life history. To better understand the relative roles of climate and intraspecific density, we applied Gaussian state-space models to long-term data on growth of juvenile sockeye salmon (Oncorhynchus nerka) in Iliamna Lake, Alaska, USA. Both temperature and density influenced fry size at the end of their first growing season, but the positive effect of temperature exceeded the negative effects of density. Fry growth was affected by the magnitude of their own cohort more strongly than by the previous brood (i.e., yearlings). In contrast, density was more important than temperature in Lake Aleknagik, also in Bristol Bay, over the same period of record, probably because Iliamna Lake is cooler and has generally lower densities of juvenile sockeye salmon than Lake Aleknagik. In both lakes, the size of the fish at the end of the first growing season affects smolt size and age at seaward migration, hence survival at sea and age at maturity, so the relative effects of climate and density depend on the ecological context.
Climate , Growth and Population Dynamics of Yukon River Chinook Salmon
2009
Harvests of Yukon Chinook salmon increased in the mid-1970s, then declined during 1998 to 2007 in response to fewer returning salmon. We examined annual growth of age-1.3 and age-1.4 Yukon Chinook salmon scales, 1965–2004, and tested the hypothesis that shifts in Chinook salmon abundance were related to annual growth at sea. Annual scale growth trends were not significantly correlated with salmon abundance indices, sea surface temperature, or climate indices, although growth during the first year at sea appeared to have been affected by the 1977 and 1989 ocean regime shifts. Chinook salmon scale growth was dependent on growth during the previous year, a factor that may have confounded detection of relationships among growth, environmental conditions, and abundance. Scale growth during the second year at sea was greater in oddnumbered years compared with even-numbered years, leading to greater adult length of age-1.3 salmon in oddnumbered years. The alternating-year pattern in Chinoo...
Climatic Change, 2009
General circulation models predict increases in air temperatures from 1 • C to 5 • C as atmospheric CO 2 continues to rise during the next 100 years. Thermal regimes in freshwater ecosystems will change as air temperatures increase regionally. As air temperatures increase, the distribution and intensity of precipitation will change which will in turn alter freshwater hydrology. Low elevation floodplains and wetlands will flood as continental ice sheets melt, increasing sea-levels. Although anadromous salmonids exist over a wide range of climatic conditions along the Pacific coast, individual stocks have adapted life history strategies-time of emergence, run timing, and residence time in freshwater-that are often unique to regions and watersheds. The response of anadromous salmonids will differ among species depending on their life cycle in freshwater. For pink and chum salmon that migrate to the ocean shortly after they emerge from the gravel, higher temperatures during spawning and incubation may result in earlier entry into the ocean when food resources are low. Shifts in thermal regimes in lakes will change trophic conditions that will affect juvenile sockeye salmon growth and survival. Decreased summer stream flows and higher water temperatures will affect growth and survival of juvenile coho salmon. Rising sea-levels will inundate low elevation spawning areas for pink salmon and floodplain rearing habitats for juvenile coho salmon. Rapid changes in climatic conditions may not extirpate anadromous salmonids in the region, but they will impose greater stress on many stocks that are adapted to present climatic conditions. Survival of sustainable populations will depend on the existing genetic diversity within and among stocks, conservative harvest management, and habitat conservation.
Detecting the biological impacts of climate change is a current focus of ecological research and has important applications in conservation and resource management. Owing to a lack of suitable control systems, measuring correlations between time series of biological attributes and hypothesized environmental covariates is a common method for detecting such impacts. These correlative approaches are particularly common in studies of exploited fish species because rich biological time-series data are often available. However, the utility of species-environment relationships for identifying or predicting biological responses to climate change has been questioned because strong correlations often deteriorate as new data are collected. Specifically stating and critically evaluating the mechanistic relationship (s) linking an environmental driver to a biological response may help to address this problem. Using nearly 60 years of data on sockeye salmon from the Kvichak River, Alaska we tested a mechanistic hypothesis linking water temperatures experienced during freshwater rearing to population productivity by modeling a series of intermediate, deterministic relationships and evaluating temporal trends in biological and environmental time-series. We found that warming waters during freshwater rearing have profoundly altered patterns of growth and life history in this population complex yet there has been no significant correlation between water temperature and metrics of productivity commonly used in fisheries management. These findings demonstrate that pairing correlative approaches with careful consideration of the mechanistic links between populations and their environments can help to both avoid spurious correlations and identify biologically important, but not statistically significant relationships, and ultimately producing more robust conclusions about the biological impacts of climate change.
Seasonal and annual marine growth of chum salmon (Oncorhynchus keta) from Fish Creek, Alaska, during 1972–2004 and from Quilcene River, Washington, during 1973–2004 were examined in relation to abundances of chum salmon and pink salmon (O. gorbuscha) and climate indices from that period. Pink salmon abundance indices were included in the analysis because of evidence for density-dependent effects on chum salmon growth and survival. In linear regression models, growth was negatively related to abundance of chum salmon or to the combined abundance of pink and chum salmon during the middle juvenile (July–Sept), 1st immature, 2nd immature, and maturing stages for the Fish Creek chum salmon and the 1st immature, 2nd immature, and maturing stages for Quilcene River chum salmon, indicating possible density-dependent effects on growth. Mid-juvenile and maturing growth models for the Fish Creek chum salmon and the maturing growth model for Quilcene River chum salmon performed well in model validation, when model predictions were tested against 20% of the data that were not used for model specification, and provided insight into the effects of climate and abundance on growth of chum salmon from 1972 to 2004.
Temporal and Spatial Variation in Growth Condition of Pacific Salmon
North Pacific Anadromous Fish Commission Bulletin, 2016
Temporal and spatial variation in the growth condition of Pacifi c salmon (Oncorhynchus spp.) were investigated using the prey-density function for consumption. Zooplankton prey density was estimated from an ecosystem model, NEMURO, embedded in a 3D physical model for the years 1948-2007. This study focused on three species of Pacifi c salmon (chum (O. keta), pink (O. gorbuscha), and sockeye (O. nerka)), all of which are zooplankton feeders. The prey dependence function for consumption of Pacifi c salmon varies on a decadal time scale, and its empirical orthogonal function fi rst mode was correlated with the Pacifi c Decadal Oscillation. The variation in the prey dependence function for consumption in the Bering Sea and the Western Subarctic Gyre was correlated with the variation in the carrying capacity of chum, pink, and sockeye salmon, indicating that these are key areas for connecting climate variability to the carrying capacity of Pacifi c salmon. In these areas, prey density increased after the 1976/77 regime shift, in synchrony with the increase in primary production due to enhanced nutrient supply through deepening of the mixed layer and/or stronger Ekman upwelling.