MINNOW PREDATION ON VENDACE LARVAE - INTERSECTION OF ALTERNATIVE PREYPHENOLOGIES AND SIZE-BASED VULNERABILITY

Time-intensive sampling was used to study minnow Phoxinus phoximus den sity and foraging activity in the littoral area of Lake Lentua at a ti me of high vendace Coregonus albula larval abundance. Minnow activity and foraging during the late spring-early summer period at low tempera tures was found to be mainly nocturnal and quite consistent with featu res reported in the literature, with the exception of feeding on venda ce larvae. The absence of the latter finding from previous studies may be due to previous seasonally limited daytime samplings. The temporal or spatial scale of sampling is decisive when studying foraging on fo od animals with a brief period of vulnerability and seasonal phenology . However, minnows in Lake Lentua seemed to prefer Bosmina longispina whenever available and low B. longispina density during the first week s after the break-up of ice directed minnow predation towards the vend ace larvae. Estimated gross predation values showed that the minnow ha s the potential to become a remarkable predator on fish larvae. Slight variations in the vernal timing of the vendace hatching and larval de velopment with respect to minnow activity, both of which are obviously temperature related, may be critical to vendace larval survival in th e nearshore zone. However, the predation on the larvae is probably a s trong factor only for a short period and the survival of the vendace l arvae may be more related to the availability of suitably sized food r esources than to predation by the minnow. (C) 1997 The Fisheries Socie ty of the British Isles.