Capture Probabilities of Lake Superior Zooplankton by an Obligate Planktivorous Fish—The Lake Herring

Abstract

–Lake herring Coregonus artedi were videotaped while feeding separately on seven different zooplankton taxa. If a fish reacted to a prey item, I observed whether the prey item entered the buccal cavity of the fish. Copepods were captured at a lower percentage of the time (mean = 48.9%) than were cladocerans (mean = 86.7%). Limnocalanus macrurus, a large copepod, was captured less frequently (30%) than smaller copepods such as Diaptomus sicilis (42.5%), Cyclops vernalis (57.5%), and diaptomid copepodids (65%). Daphnia galeata mendotae were captured less frequently (80%) than smaller cladocerans such as juvenile daphnids (87.5%) or Bosmina longirostris (92.5%). The differences between copepods and cladocerans and sizes of each likely result from differential swimming strengths and behaviors of these various taxa. These results confirm observations from other planktivores that the evasive ability of zooplankton greatly reduces the successful completion of the planktivory process (encounter, attack, capture, ingestion). Additionally, the planktivory process should be examined in its entirety because my results are counterintuitive to those expected from classical size-selective planktivory.