For decades ecologists have recognized the potential importance of marine‐derived nutrients (MDN) deposited in freshwater ecosystems by spawning anadromous salmon. Previous studies have shown that some MDN are retained in freshwater ecosystems. A popular hypothesis linking MDN to salmon population productivity posits that MDN provided by post‐spawning mortality of salmon are critical for salmon population dynamics because they enhance prey populations in the freshwater ecosystems used as nursery habitats. We tested this hypothesis by reconstructing historical sockeye salmon populations for the last 300 years in Bristol Bay, Alaska. Stable nitrogen isotope chronologies in lake sediments and sockeye catch and escapement histories show that commercial fisheries intercepted about two‐thirds of MDN bound for freshwater spawning grounds since about 1900. Reconstruction of lake algal production using fossil pigments shows that this loss of MDN has reduced lake algal productivity to about one‐third of its level before commercial fishing. However, contrary to expectation, recent sockeye population sizes (sum of spawning escapement and fishery catch) in the last century were equivalent to those before the advent of commercial fishing. These data demonstrate that the MDN subsidy is important for the productivity of coastal lakes but that some sockeye salmon populations are limited by other features of ecosystems such as the amount of suitable spawning habitat.
Increasing interest in the marine trophic dynamics of Pacific salmon has been motivated by the recognition of their sensitivity to changing climate and to the competitive effects of hatchery fish on wild stocks. It has become more common to use stable isotopes to supplement traditional diet studies of salmon in the ocean; however, there have been no integrated syntheses of these data to determine whether stable isotope analyses support the existing conventional wisdom of feeding strategies of the Pacific salmon. We performed a metaanalysis of stable isotope data to examine the extent of trophic partitioning among five species of Pacific salmon during their marine lives. Pink, sockeye, and chum salmon showed very high overlap in resource use and there was no consistent evidence for chum relying on alternative food webs dominated by gelatinous zooplankton. d 15 N showed that Chinook and coho salmon fed at trophic levels higher than the other three species. In addition, these two species were distinctly enriched in 13 C, suggesting more extensive use of coastal food webs compared to the more depleted (pelagic) signatures of pink, sockeye, and chum salmon. This paper presents the first synthesis of stable isotope work on Pacific salmon and provides d 15 N and d 13 C values applicable to research on the fate of the marine derived nutrients these organisms transport to freshwater and riparian ecosystems.
This study explored battered mothers' perceptions of their interactions with child protectiv services (CPS) workers to increase understanding about how child welfare workers and pol cies can have negative as well as positive impacts on women's and children's lives. Th research was guided by two feminist frameworks: structured action theory and social entrap ment theory. Twenty women participated in the in-depth, qualitative interviews. Most felt mi understood and unsupported by their CPS workers and thought that this treatment directl harmed them and their children. Many batterers manipulated caseworkers and escaped sanc tions, which contributed to negative consequences. Some women received helpful response from their caseworkers and viewed such support as invaluable. Implications for social wor practice are discussed.
We quantified spatial patterns of stable isotopes of N and C (d 15 N, d 13 C) and fossil pigment concentrations in the uppermost 10 mm of sediment (,10 yr) from 74 profundal locations and three spawning-stream discharge areas in Lake Nerka, southwest Alaska. Sediment d 15 N (4.3% 6 0.7%) and d 13 C (226.3% 61.2%) varied directly (d 15 N ) or inversely (d 13 C) with water column depth, whereas concentrations of most fossil pigments from algae were negatively correlated with depth. Sediment d 15 N and d 13 C were poorly correlated with either fossil pigment abundance or the local densities of spawning salmon. Instead, coastal nursery lakes appeared to integrate marine-derived nutrients rapidly into lakewide nutrient pools, suggesting that while individual cores may be used to reconstruct whole-lake salmon densities, habitat-specific variations of past fish populations cannot be quantified reliably from sedimentary analyses.
In coastal areas of the Pacific Northwest bears (Ursus spp.) prey heavily on spawning Pacific salmon (Oncorhynchus spp.) and selectively kill energy-rich individuals that are the most recent arrivals on spawning grounds. Pacific salmon eventually die in spawning habitats anyway, albeit with considerably lower energetic content. We investigated whether foraging activities of bears facilitate growth of stream invertebrates by increasing the duration of salmon carcass availability and the nutritional value of carcasses for scavengers. Our survey in southwest Alaska showed that carcasses are highly colonized by caddisfly (Trichoptera) larvae. Caddisflies show a strong preference for bear-killed over senescent carcasses, which may be a result of extended temporal availability, improved accessibility of consumable tissue, and higher energetic content of bear-killed fish. Isotope analyses further indicate uptake of marine-derived nutrients in caddisflies during the salmon run, which, however, does not extend into subsequent generations. Thus, species with life histories linked to the annual marine derived nutrient pulse gain the biggest advantage from the salmon resource subsidy. A long-term survey in several creeks in this region showed that bear predation intensity varied greatly among creeks and years, therefore indirect effects of bear predation on aquatic scavengers are likely highly patchy in time and space.
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