180 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Fortunately, our difficulties with the tags and 

 pins were not nearly as serious as those reported 

 by Calhoun, Fry, and Hughes (1951, p. 310). 

 They reported that at the end of 7 months in an 

 aquarium "19 of the 20 tags in which the nickel 

 pins had been used had fallen off as a direct re- 

 sult of pin corrosion." In our experiments with 

 yellowtail we recovered 1 tagged specimen after 

 it had been out 5 years and 11 months, and 58 of 

 our 377 recaptures were made after a year at sea. 

 Of 52 of the tags that had been out more than 1 

 year (all of which were available for examina- 

 tion), pin corrosion was evident in only 2, which 

 were out 3 years and 5 months, and 2 years and 8 

 months. Of course, flounders that had lost their 

 tags could not. be distinguished in the commercial 

 catch, but if corrosion had been a serious problem 

 many more partly corroded pins should have been 

 recovered. However, the finding of even 2 cor- 

 roded pins indicates that some tags probably were 

 lost and this probability must be considered in 

 estimates of mortality from the tagging data. 



The yellowtail collected for tagging were 

 caught with otter-trawl nets from commercial ves- 

 sels prior to June 1946, and subsequently from the 

 Fish and Wildlife Service vessels Skimmer and 

 Albatross III (except lot No. 11 released in Au- 

 gust 1946). Naturally, only lively fish were se- 

 lected for release, although with the Service ves- 

 sels it was possible to make short tows and give 

 the fish much better handling. Even when the 

 fish were given the best of handling and appeared 

 to be in good condition, many were slightly in- 

 jured and probably some mortality occurred. 

 Manzer (1952), who tagged Pacific coast flounder 

 with the Petersen disk tag, found considerable 

 mortality even under the best conditions. 



Most of the yellowtail released from the Service 

 vessels were classified in three groups according to 

 the degree of visible injury (table 5) : those with 

 no injury apparent under casual examination (0) ; 

 those with marks less severe than the following 

 (1) ; those with more than three splits in fins, or 

 with any part of a fin missing, or with red marks 

 on the white side more than 2 millimeters wide, 

 or with more than 2 square centimeters of scales 

 missing from the dark side (2). All fish showing 

 severe injury or any lethargy were rejected. 



Large differences were found in the recovery 

 rates of the three groups. Fish from the 



Table 5. 



-Recaptured yellowtail classified by degree of 

 injury at time of tagging 



[Based on lot Nos. 9, 10, 12, 13, and 14] 



group, not noticeably injured, were recovered at 

 a rate of 19.7 percent, from the 1 group, 13.1 per- 

 cent and the 2 group, only 3 percent. The chi- 

 square value of the smaller difference between 

 groups and 1 is 4.32, a statistically significant 

 value. In addition to such direct evidence, the 

 low returns from one release off Cape Cod (lot 

 No. 3, 5.9 percent), which was tagged under se- 

 vere weather conditions in a heavily fished area, 

 suggest that considerable mortality due to tag- 

 ging occurred. Obviously, our methods of han- 

 dling killed some of the tagged fish and, equally 

 obvious, in future experiments only completely 

 uninjured fish should be used even though others 

 may be lively. 



Evidence of a regular seasonal migration is 

 provided by the recovery of yellowtail (lot No. 1) 

 released off Jones Beach, N. Y., in February 1942 

 (table 4). These fish were recaptured on the 

 principal fishing grounds off No Mans Land and 

 Nantucket (fig. 4) in the summers of 1942, 1943, 

 and 1945, and back near the point of their release 

 in the winters of 1943, 1944, and 1946. These win- 

 ter recaptures are especially significant because 

 the majority of the landings in the winter fishery 

 originated from the grounds off No Mans Land 

 and Nantucket Shoals (table 3). This indicates 

 that the fish tagged off Jones Beach are not a 

 part of the stock found off Nantucket Shoals and 

 No Mans Land in the winter, and suggests that the 

 population found off Nantucket and No Mans 

 Land in the summer differs from the winter pop- 

 ulation of the same place. 



A similar pattern of migration is evident from 

 the recaptures of yellowtail released off Montauk 

 Point (fig. 4). These tagged fish were taken to 

 the east of No Mans Land and Nantucket Shoals 

 during the summer of 1942 and back off Montauk 

 Point in the winters of 1943 and 1944. It may 

 be significant that no fish released off Montauk 

 Point were recaptured off Jones Beach. It appears 



