The role of chemoreception in salmon-egg predation by coastrange (Cottus aleuticus) and slimy (C. cognatus) sculpins in Iliamna Lake, Alaska

Abstract

Egg predation by coastrange sculpins (Cottus aleuticus) and slimy sculpins (C. cognatus) may be a major factor affecting sockeye salmon (Oncorhynchus nerka) production in Iliamna Lake, Alaska. In this study, we examined the potential roles of visual and chemosensory cues in egg predation by sculpins. A field study tested whether sculpins were differentially attracted to minnow traps baited with eggs that were (i) visible with no odours present, (ii) visible with odours present, or (iii) not visible with odours present. Our results indicated that sculpins do not require visual cues for detecting salmon eggs. However, attraction to sockeye eggs did require chemical cues emanating from the eggs. To characterize the chemical attractants that emanate from salmon eggs, we tested whether sculpins were attracted to test odours in a two-choice maze. Test odours were prepared by soaking eggs in lake water. Sculpins preferred egg wash to lake water but demonstrated no attraction to ovarian fluid versus lake water, suggesting that the attractive substances are derived directly from egg material. These results are discussed in relation to the known sensory mechanisms involved in feeding by sculpins as well as to the ecological relationship between spawning sockeye salmon and sculpins.