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Rubidium and cesium as indicators of diet in freshwater fish with particular emphasis on overlap in diet between juvenile sockeye salmon (Oncorhynchus nerka), and threespine stickleback (Gasterosteus aculeatus)

University of British Columbia

Body burdens of rubidium and cesium were used to assess overlap in diets of sockeye salmon (Oncorhynchus nerka) and threespine stickleback (Gasterosteus aculeatus) in Kennedy, Cultus, and Great Central Lakes, British Columbia and Lake Aleknagik, Alaska, lakes in which competition between sockeye salmon and threespine stickleback has been suggested. Differences in uptake patterns of Cs in juvenile . coho (Oncorhynchus kisutch) and threespine stickleback were attributable to differences in diet and not physiology. Tissue concentrations of Rb and Cs were examined in threespine stickleback and juvenile sockeye held in wire cages in both the littoral and limnetic zones of Kennedy Lake. Concentrations of Rb were dependent on type of substrate over which fish had fed. When significant differences in concentrations were detected, higher concentrations were associated with the littoral zone. In late May, Cs concentration in fish captured offshore were higher in threespine stickleback than in juvenile sockeye but not in June or July. Neither species tracked Rb and Cs concentrations in zooplankton. In Kennedy, Cultus, Great Central, and Lake Aleknagik, higher concentrations of Cs were found in threespine stickleback captured onshore than in juvenile sockeye captured offshore. In Enos Lake, were there are two varieties of sticklebacks, rubidium concentrations appeared to be modified by feeding over different substrates. In a comparison of squawfish (Ptychocheilus oreqonensis), redside shiners (Richardsonius balteatus), cottids (Cottus asper), and peamouth chub (Mylocheilus caurinus), from Cultus Lake, higher concentrations of Cs were observed in squawfish, in agreement with higher concentrations of Cs reported in piscivores. It was concluded that Rb and Cs concentrations may reflect the extent to which sockeye, stickleback or other species have been feeding onshore or offshore but does not provide a readily quantified measure of the degree of overlap in diet. Present understanding of Rb and Cs in both fish and their prey is insufficient for use of this technique to assess similarity in diet. The method would appear best suited for small lakes with few species.

Text

2010-07-30

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http://hdl.handle.net/2429/27042

Zoology

University of British Columbia

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