Through the School of Aquatic and Fishery Sciences, Sarah Schooler, ’15, spent six weeks in the Alaskan bush, collecting the same data in the field she’d been studying in the classroom: salmon and the hungry habits of grizzly bears.
Sarah Schooler and UW staff and students placing a fishing net on lake Aleknagik.
Curry J. Cunningham, Gregory T. Ruggerone, and Thomas P. Quinn
How does the availability of food affect the selectivity of the consumer? It has long been known that survival of prey can depend on their density, as predators become satiated or cannot catch them all. In addition, many studies have shown that predators are selective, tending to kill and consume some species or sizes of prey over others, but very few are examples of prey density driving patterns of selection by predators. Brown bears inhabiting coastal ecosystems of the Pacific Rim obtain much of their annual protein and fat supply by consuming the Pacific salmon that return annually to streams to spawn, and they tend to kill the larger salmon among those available to them. However, this is a world of feast and famine; the number of returning salmon can vary greatly from one year to the next.
Utilizing 20 years of data including individual 41,240 salmon measurements from a small tributary of Bristol Bay, Alaska, scientists at the University of Washington have found that the strength of predatory selection by bears is inversely related to the density of their sockeye salmon prey. That is, contrary to the expectation that when the salmon are abundant the bears can choose the largest fish, the bears were more selective, tending to kill especially large fish, when salmon were scarce. This finding is especially interesting and important because these salmon populations are also exposed to a commercial fishery that is itself selective, tending to catch the large fish. The fishery has, therefore, both the direct form of selection and also intensifies size-selective predation by bears through the reduction in salmon density.
Summer emigration and resource acquisition within a shared nursery lake by sockeye salmon (Oncorhynchus nerka) from historically discrete rearing environments
R.K. Simmons,* T.P. Quinn, L.W. Seeb, D.E. Schindler, and R. Hilborn. School of Aquatic and Fishery Sciences, Box 355020, University of Washington, Seattle, WA 98195, USA.
Abstract
Many fish species disperse broadly during juvenile life history stages. While this may enable persistence in variable environments, it may also produce novel competitive interactions in recipient habitats that contain conspecifics from other populations. Here we used genetics techniques to study the stock-specific movement and performance of juvenile sockeye salmon (Oncorhynchus nerka) between July and August of 2008 in an ecosystem characterized by extensive juvenile migration and environmental change: the Chignik Lake system, Alaska. Genetic composition of juvenile sockeye salmon in the lower nursery lake based on 45 single nucleotide polymorphism markers indicated that 2008 was characterized by earlier timing and larger magnitude of emigrations from the upper lake, where rearing conditions have become increasingly unstable in recent decades. However, the larger size of emigrants did not confer a clear advantage in foraging based on comparisons of growth and body condition with juveniles native to the lower lake. These results highlight how shifting environmental conditions may exert pressures on evolved behavior patterns and increase interactions between sympatric populations, a theme of increasing importance where ecological uncertainty is high.
Can. J. Fish. Aquat. Sci. 70: 57–63 (2013) dx.doi.org/10.1139/cjfas-2012-0159 Published at www.nrcresearchpress.com/cjfas on 8 November 2012.