THE ROLE OF CHEMORECEPTION IN SALMON-EGG PREDATION BY COASTRANGE (COTTUS-ALEUTICUS) AND SLIMY (C-COGNATUS) SCULPINS IN ILIAMNA-LAKE, ALASKA

Egg predation by coastrange sculpins (Cottus aleuticus) and slimy scul pins (C. cognatus) may be a major factor affecting sockeye salmon (Onc orhynchus nerka) production in Iliamna Lake, Alaska. In this study, we examined the potential roles of visual and chemosensory cues in egg p redation by sculpins. A field study tested whether sculpins were diffe rentially attracted to minnow traps baited with eggs that were (i) vis ible 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 eg: However, attracti on 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-ch oice maze. Test odours were prepared by soaking eggs in lake water. Sc ulpins preferred egg wash to lake water but demonstrated no attraction to ovarian fluid versus lake water, suggesting that the attractive su bstances are derived directly from egg material. These results are dis cussed in relation to the known sensory mechanisms involved in feeding by sculpins as well as to the ecological relationship between spawnin g sockeye salmon and sculpins.