ESTIMATION OF THE DENSITY OF BUCCINUM-UNDATUM (GASTROPODA) OFF DOUGLAS, ISLE-OF-MAN

The density of the common whelk (Buccinum undatum L.) off Douglas, Isl e of Man, was determined by four methods: (1) pot sampling, (2) diving , (3) mark-recapture experiment, and (4) underwater television. Althou gh the values obtained by these methods were comparable, the last two methods yielded overestimations of Buccinum density. The results from diving survey and from pot sampling showed a good agreement, indicatin g that pot sampling can be used to determine the density of the common whelk, provided a good estimate of the pot attraction area is availab le. The range of whelk density between February 1989 and August 1990 r esulting from pot sampling was between 0.08 and 0.38 individuals m-2. The temporal fluctuations of the whelk densities are discussed in deta il.