Fishes of the Western North Atlantic 193 



reaches a hatching stage {vide supra), it is clear that in nature each female would have 

 to lay more than the maximum observed by us in aquarium experiments (eight) to 

 maintain the stock. If the stock is to be held at the same level, each female must pro- 

 duce two offspring which attain sexual maturity. We suspect that mortality after 

 hatching is relatively low, but if our rough estimate of the percentage of eggs which 

 reach hatching is of the right order of magnitude, this would mean that each female 

 would have to lay a general minimum of 10-20 eggs; actually, each one probably lays 

 20—30 eggs under average conditions. Whether this occurs consecutively, once ma- 

 turity is reached, or whether there is a resting period between successive ovulations, 

 we do not know. However, we strongly favor the latter alternative. We find many 

 large-sized females with reduced shell glands and ovaries, the majority of which are 

 probably in a resting stage prior to another ovulation. Also, the ripe ovary never con- 

 tains at one time more than about three eggs that have reached or are approaching the 

 laying size. We suspect, therefore, that a typical female produces on the order of five 

 to six eggs over a laying period, say the June-July peak, and that the metabolic strain 

 of producing these large-yolked eggs is such that the female requires a number of 

 months to build up to a condition where she can lay another comparable batch of 

 eggs. According to our estimates, each female would have to have at least two or three 

 such laying periods in order to maintain the population, and some may have as many 

 as four. From our knowledge of the age at maturity, the rate of growth of these older 

 fish (roughly 4—5 cm a year as judged from length-frequency and other data), the 

 sharp mortality rate at greater sizes, and from our estimate that there are a number 

 of months between laying periods, we derive a time schedule which would allow for 

 three or four such laying periods in the life of the average female erinacea. Because 

 of the nature of this reproductive pattern, we do not believe that the stock could stand 

 intensive fishing without showing a sharp reduction in the size of the population in a 

 relatively short period and a consequent drop in the catch-per-unit-effort, a situation 

 which has occurred in other elasmobranch fisheries. 



Marking experiments have yielded little information due to the low percentage 

 of return, which we attribute chiefly to the fact that the V2" disc tags we used were not 

 obvious enough to catch the attention of the fishermen as the Skates were shovelled 

 overboard as trash or barrelled in bulk for fish meal or other uses. Out of approximately 

 600 erinacea tagged in June 1946 in the Block Island Sound area, only five fish were 

 returned: one in July 1946; two in August 1946; another in February 1947; and the 

 last in April 1947. All of these recaptures were within five miles or less of the original 

 point of release except the last, which was taken approximately 50 miles to the west, 

 off Herod Point on the north shore of Long Island. If we can judge by such meager 

 returns, it would seem that this species undertakes no extensive migrations in this 

 region, although the specimen captured in Long Island Sound would indicate occasional 

 straying between the Block Island and Long Island Sound populations. However, there 

 does appear to be some evidence of definite seasonal offshore and onshore movements 

 in the Block Island Sound region involving distances of '^—c, miles and upward. This 



