In the 2 years of trapping, 2,174 

 channeled whelks were caught, 1,122 in 1957 

 and 1,052 in 1958. The cumulative curves 

 for total numbers of channeled whelks caught 

 in 1957 and in 1958 (figs. 4 and 5) indicate 

 that after 50 percent of the total catch 

 was taken, the rate of trapping gradually 

 declined. In 1957, more than 80 percent of 

 the total catch was attained during the 

 first 2 weeks of trapping; in 1958 a month 

 passed before the same percentage was 

 reached. 



Because almost equal numbers of 

 snails were caught in 1957 and in 1958 from 

 the same oyster bed, it appeared that whelks 

 were moving to the oyster bed from other 

 localities. When trapping was terminated in 

 1957, the rate of capture was less than 2 

 snails per trap per day (fig. 6), yet during 

 the first 10 days of trapping in 1958, the 

 rate was as high as 6 snails per trap per 

 day (fig. 7). It is probable the high ini- 

 tial rate in 1958 was due to an influx of 

 snails from other localities. When trapping 

 was terminated in 1957, very few channeled 

 whelks were observed on the study area. 

 This suggests that the success in trapping 

 in 1958 is related to snail movement; there- 

 fore, it is advisable for oyster growers to 

 undertake trapping operations each spring 

 to minimize whelk predation. 



FIGURE 6. --THE NUMBER OF CHANNELED WHELKS CAUGHT 

 PER DAY PER TRAP IN 1957. {SURFACE TEMPERA- 

 TURE WAS TAKEN WHEN TRAPS WERE FISH.) 



JUNE 



FIGURE 7. --THE NUMBER OF CHANNELED WHELKS CAUGHT 

 PER DAr PES TRAP I:J 1358. (SURFACE TEMPERA- 

 TURE WAS TAKEN WHEN TRAPS WERE FISHED.) 



Trapping was initiated when the 

 rising water temperature reached a 50° F. 

 level. There is some indication that as 

 the temperature rises the number of whelks 

 per day per trap decline (figs. 6 and 7). 

 Generally, the greatest number of whelks 

 were caught when the traps were first placed 

 on the beds, after which a slow decline oc- 

 curred. Although temperature may have some 

 effect on the behavior of snails, a more 

 logical explanation is that the decline in 

 catch rate resulted from a decrease in the 

 abundance of snails. Trapping was termi- 

 nated for the year when the rate fell below 



1 snail per trap per day or when the rate 

 was below 2 snails per trap per day for more 

 than 2 consecutive weeks. 



During the 2 years of trapping only 



2 knobbed whelks were caught, although from 

 visual observations the beds were heavily 

 populated with this species. Hence there 

 is no known method for trapping knobbed 

 whelks, they must be controlled by mechani- 

 cal methods, such as dredging and tonging, 

 or be picked up by skin divers. 



CONCLUSION 



The damage caused by whelk predation 

 is often overlooked by many oyster growers. 

 When drills and starfish are present on 

 oyster beds, little concern is given to the 

 whelk as a serious predator. From labora- 

 tory and field observations it is apparent 



