14 UNUTILIZED FISHES. 



ESTIMATE OF DESTRUCTIVENESS. 



The significance of the foregoing results is made apparent upon 

 the reduction to figures of the damage resulting to the lobster fish- 

 eries from the presence of 100,000 smooth dogfish in a locality like 

 Buzzards Bay during a single season. It is, of course, impossible to 

 make even an approximate estimate of the number of any kind of 

 fish that are present in a given area of considerable extent. But 

 judging from the great numbers that are taken in the traps and from 

 the fact that smooth dogfish can be caught in almost any part of 

 Buzzards Bay where a baited hook is let down, it may be assumed 

 that the number of smooth dogfish in that region is not less than 

 100,000, and this, to my mind, is a very conservative estimate. By a 

 series of experiments it was found that a smooth dogfish can com- 

 pletely digest and pass off from the stomach a rock crab or lobster in 

 from 65 to 84 hours. Several medium-sized smooth dogfish were 

 kept in a large cod car for five days to make sure that their alimen- 

 tary tracts were clean. Rock crabs and large pieces of lobster were 

 then forced down their throats, and at intervals of from 12 to 20 

 hours fish were caught and killed and the digestive tract contents 

 examined. After about 65 hours the shells of crabs or lobsters were 

 soft and flaky and could be mashed and molded by the fingers. After 

 about 84 hours, or half a week, nearly all traces of the stomach con- 

 tents had passed into the intestine. Judging from these facts, in 

 order for 16 per cent of the smooth dogfish constantly to contain 

 lobster material, that number would have to take, on the average, a 

 lobster twice each week. Sixteen per cent of 100,000X2=32,000, 

 which would represent the number of lobsters per week consumed by 

 100,000 smooth dogfish. Since these fish are common in Buzzards 

 Bay for not less than twenty weeks of each year, we would then have 

 20X^2,000=640,000, the minimum number of lobsters probably de- 

 stroyed in Buzzards Bay during one season by this agency. 



From data collected, and by this same method of calculation, there 

 is obtained for the principal species eaten the following estimate of 

 the number of individuals of each destroyed each year in the region 

 of Buzzards Bay by every 100,000 smooth dogfish : 



