Currents, predators, and the aggregation of the gastropod Buccinum undatum around bait

Abstract

In the absence of bait, 75.8% of whelks in the N Gulf of St Lawrence were static or buried. In the presence of bait, whelks in a 20-60° downstream sector to a maximum distance of 20 m moved towards the bait. Whelks apparently oriented to the bait by chemotaxis. Average crawling speed towards the bait varied from 7.3-15.1 cm min-1 and was independent of current speed. More whelks arrived at bait per unit time when current direction changed gradually than when current was directionally stable due to exploitation of new grounds and to depletion of the downstream population respectively. Whelk arrival rate is depressed by sudden and marked changes in current direction, because whelks are unable to track the shifting odor plume. Arrival rate was positively correlated with current speed with time lags of up to 3 h, but tended to be negatively correlated with longer time lags. Arrival rate was negatively correlated with the numbers of predators (Cancer irroratus and Hyas araneus) at bait with time lags of up to 1 h, but positively correlated with numbers of H. araneus at bait with longer time lags. -from Authors