Auke Bay Laboratory (ABL)

Ocean Carrying Capacity Program

Functional Response of Juvenile Pink Salmon and Chum Salmon to Two Types of Zooplankton Prey

Models that predict the feeding behavior of planktivorous fish based on environmental conditions can advance our understanding of trophic dynamics in the marine environment by offering insight into the mechanistic controls limiting prey consumption. The functional response model, which is among the most simplistic models of feeding behavior, predicts the consumption rate of a predator as a function of prey density and is considered a fundamental framework for studying predator-prey interactions.

We conducted feeding rate experiments with juvenile pink (Oncorhynchus gorbuscha) and chum (O. keta) salmon by presenting them with varying densities of small copepods (Tisbi sp.) and large mysid shrimp (Mysidopsis bahia) under high light and low turbidity conditions. Prey densities ranged from 1 to 235 prey/L, and water temperatures ranged from 10.5° to 12.0°C. Both species of salmon demonstrated a type II functional response to zooplankton prey, where the rate of prey consumption by the predator rises as prey density increases, then levels off and remains constant.

Estimates of maximum feeding rate for juvenile pink (12.3 prey/min) and chum (11.5 prey/min) salmon foraging on mysid prey were similar, and were higher than feeding rates estimated from experiments where copepods were presented (0.4 prey/min for pink salmon, 3.8 prey/min for chum salmon), indicating that copepods were more difficult to capture than mysids. Smaller pink salmon fry demonstrated a type II functional response to copepod prey and consumed the relatively smaller prey more readily than did the larger juvenile pink salmon. These results indicate that smaller-bodied juvenile salmon have a competitive advantage in prey capture ability over larger-bodied conspecifics when feeding in overlapping areas dominated by smaller-bodied zooplankton species.

By Jamal Moss

Southeast Alaska Synthesis of Marine Biology and Oceanography Workshop

Ginny Eckert of the University of Alaska Southeast (UAS) and Lisa Eisner of ABL organized a workshop on the state of marine biology and oceanography in Southeast Alaska, held in Juneau in March 2005. The workshop was funded by the North Pacific Research Board (NPRB).

The goals of the workshop were to 1) summarize past and present research in marine biology and oceanography in Southeast Alaska from Dixon Entrance to Cape Fairweather, including the outer coast, and 2) identify data gaps and future research needs.

Overviews were presented on physical oceanography (Tom Weingartner of the University of Alaska Fairbanks (UAF)), biological oceanography (Lisa Eisner), fisheries (Gordon Kruse of UAF), seabirds (John Piatt of the U.S. Geological Survey), nearshore ecology (Ginny Eckert of UAS) and marine mammals (Jan Straley of UAS). The meeting had approximately 40 participants from universities and state and federal agencies. The presenters will be submitting their findings to peer-reviewed journals and are preparing a workshop report for the NPRB.

By Lisa Eisner

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AFSC Quarterly Research Reports Jan-Mar 2005