in laboratory experiments, are stout tagelus 

 ( Tagelus gibbus ) , cross-barred venus ( Chione 

 cancellata ), and quahaugs ( Mercenaria ( Venus ) 

 mercenaria ) . The whelks in Oyster Pond River 

 appeared to prefer oysters ( Crassostrea vir - 

 ginica ) , but were also observed feeding on 

 quahaugs and blue mussels ( Mytilus edulis). 



The manner in which Busycon attacks 

 oysters is of interest. According to Colton 

 (1908), the whelk crawls on top of the oys- 

 ter; then when the oyster opens, the snail 

 thrusts the edge of its shell between the 

 valves and introduces the proboscis. The 

 oyster is eaten in 40 minutes. According 

 to Warren (1916), the whelk opens an oyster 

 by grasping the bivalve in its foot and 

 chipping away the shell with the edge of its 

 outer lip. When enough shell is chipped 

 away, the whelk inserts its proboscis and 

 consumes the oyster. 



We do not know the feeding rate of 

 channeled and knobbed whelks in nature. In 

 laboratory experiments conducted by Carriker 

 (1951) with a mixed group of whelks, each 

 snail consumed from 0.8 to 2.7 oysters a 

 week. Fifty percent of the oysters eaten 

 were less than three-quarters of an inch in 

 height; all others were larger but did not 

 exceed 3 inches. 



In 1957 studies of the feeding rate 

 of whelks on oysters were undertaken. As 

 knobbed whelks were practically never taken 

 in any trap that had yet been devised, the 

 study consequently was limited to the chan- 

 neled whelk. Since most oysters on the 

 leases in Oyster Pond River are greater than 

 3 inches in height, the following observa- 

 tion was made on the rate of feeding of 

 channeled whelks on large oysters: 



A lath box, 24 x 18 x 18 inches, con- 

 taining 6 large channeled whelks, 12 oysters 

 (each over 3 inches in height), and 6 large 

 quahaugs was placed in Oyster Pond River on 

 June 3, 1957. On July 1, 1957, 8 of the oys- 

 ters with their shells showing signs of be- 

 ing chipped by whelks were dead and without 

 meats. Four oysters and all whelks and qua- 

 haugs were alive, though 1 quahaug had marks 

 on the edge of its shell indicating that a 

 whelk had tried unsuccessfully to open it. 



The observed rate of feeding during 

 this experiment was 0.3 oyster per whelk per 

 week. This rate probably is lower than that 

 which occurs under natural conditions be- 

 cause on several occasions the experimental 



box was out of water at low tides and 

 presumably feeding was interrupted. The 

 oyster bottoms of this area are never ex- 

 posed at low water. Reduced circulation 

 inside the lath box may also have affected 

 the whelks' feeding rate. Thus it is rea- 

 sonable to assume that the results of this 

 experiment yielded a minimum estimate of 

 the natural feeding rate. 



Channeled whelks are known to feed 

 in temperatures ranging from 60" to 72° F. 

 This range of temperature in Oyster Pond 

 River occurs at least during 5 months, June 

 through October, of each year. It is, 

 therefore, probable that the feeding of 

 whelks in the river continues throughout 

 this period. 



ESTIMATES OF CHANNELED WHEIX 

 PREDATION 



Oyster growers estimate their losses 

 by counting the numbers of dead oysters, 

 known as clappers or boxes, they find when 

 culling; but the percentage of these deaths 

 that result from whelk predation is not 

 known. By assuming that the consumption of 

 0.3 oysters per week per whelk is near the 

 minimum feeding rate, and that 1.8 oysters 

 per week per whelk (an average of Carriker's 

 observations) approaches the maximum feeding 

 rate, the following estimates of probably 

 whelk damage can be made for Oyster Pond 

 River . 



Since more than 1,000 snails were 

 trapped annually in both 1957 and 1958 from 

 a 2-acre lease, we assume in the absence of 

 any control a minimum of 1,000 snails on 

 each of the 2-acre leases. At a feeding 

 rate ranging from 0.3 to 1.8 oysters per 

 week per whelk, 1,000 snails could consume 

 from 300 to 1,800 oysters in 1 week, or from 

 6,000 to 36,000 oysters during the 5-month 

 period. At approximately 250 oysters to the 

 bushel, the estimated loss of each oysterman 

 varied from 24 bushels to 144 bushels. We 

 may assume that his actual loss is near the 

 midpoint of the two extremes, i.e., about 

 80 bushels. 



At the present wholesale price of 

 $11.50 a bushel for Chatham oysters, the 

 annual losses from channeled whelk predation 

 can be estimated at $920 for each of the 

 2-acre leases. This amount may appear in- 

 significant to large oyster compani,es, but 

 the loss is considerable to the oyster 



