PARENT SESSION
Poster Session #23: Fish, Lakes, Streams, and Wetlands.
Wednesday, August 8, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Selective foraging behavior in pikeperch.

TURESSON, HÅKAN¹, PERSSON, ANDERS¹, BRÖNMARK, CHRISTER¹, ¹

ABSTRACT- Piscivores are typically selective predators. Prey selection can involve active predator choice or be a passive process depending on prey and predator characteristics. Morphological or behavioral differences can result in different encounter rates or capture success for different prey types. Here, we experiment-ally tested if pikeperch (Stizostedion lucioperca), feeding on roach (Rutilus rutilus) and rudd (Scardinius erythrophthalmus) selected prey sizes actively. When given a choice of prey ranging in size between 20-50 % of predator size, pikeperch selected small prey. In behavioral analysis, proportions of approaches towards all prey sizes were equal, but number of attacks was significantly biased towards small prey sizes. The interpretation is that this difference between approach and attack proportions represents an active predator choice. Optimal foraging models, predicting that predators will choose prey sizes giving highest energy return per time spent foraging, are often assumed to explain active choice. We measured handling times for a range of prey sizes and found that the energetically most profitable prey sizes (energy/handling time) were also the actively preferred prey sizes. In a field stomach content analysis, a majority of prey measured between 22 % and 0.36 % of predator size (mean 30%). These prey sizes were also within the range of most profitable sizes obtained from the laboratory experiments, which suggest that active choice might be a component of pikeperch feeding behavior also in the field.

KEY WORDS: predation, piscivory, prey choice, optimal foraging