MATHER ET AL.: TAGGED BLUEFIN TUNA 

 Table 2. — Continued 



'Positive values signify northward movement. Negative values signify southward movement. 

 ^Positive values signify eastward movement. Negative values signify westward movement. 

 ^New Jersey. 

 *Long Island. 

 ^Southern New England. 



Jersey or that the intensity of the southern New 

 England fishery was greater than that off New 

 Jersey. While the latter may be true, there may be 

 alternative interpretations and additional 

 analysis is required. It is also suggested that 

 analysis be undertaken for tags returned after the 

 season of release. 



MORTALITY ESTIMATION 



The number of recoveries per year from releases 

 by year, months within years, and various group- 

 ings of years, months, and release locations were 

 employed to estimate the survival rates for young 

 bluefin in the middle Atlantic bight of North 

 America. The first analyses were run using only 

 the data employed to form the basic groups as 

 defined in the migration analysis, thus eliminat- 

 ing some releases which were substantially differ- 

 ent with respect to their location and/or time of 

 release than for most of the fish tagged. Although 

 this reduced the numbers of returns used, it prob- 

 ably did not greatly affect the estimates of mortal- 

 ity rates. 



Method of Release 



In all years since 1961, with the exception of 

 1963, tuna were captured for tagging by both sport 

 and commercial gear (purse seine). In Table 3 the 



TIME AT LIBERTY IN DAYS 



< 



q: 



UJ 



NEW 

 JERSEY 

 COAST 



LONG 

 ISLAND 

 COAST 



SOUTHERN 



NEW 



ENGLAND 



COAST 



4e5(5Al 

 .. ■'7 914CI 



29 6(2C) 

 27 4(93 



46 4(46) 

 33 6(4 A) 



31 6(28) " 



32 6(1161 

 26.6(76] 

 326(3) ^ 



, 24.0(96! 



393(96) 

 69 I (9A) 

 20.7(6D) 

 76 7(66) 

 60-4(5A) 

 64.6(4(3 

 74 6(48) 

 I02.0(4A) 

 897^8) 



897(2' 



i<.oS 



766(9A) 

 64 7(60) 

 112 0(681 

 66 4(6AI, 



22B(IIA) 



53 I (60 



46 7(6C) 



., 5e6(6A) 



39.911161 

 824(6E)^ 



. 360(7F1 



' 32 2(76) 



28 3(161 



I7 9(7cr 

 29.3(7E) 



269(7F) 

 .. ■'6.5(701 



'50,3(7E) 

 299(761 

 28.1(151 

 67 7(16) 



28 9(7C) ^ * 



4e0(7n 

 4eof7G) 

 282(15) 

 57 1(17) 



Figure 2. — Summary of mean distance and direction of migra- 

 tion of tagged bluefin tuna stratified by time at liberty and by 

 general area of release. Distances are in nautical miles. Release 

 group numbers are given in parentheses. 



proportions of tagged fish returned were compared 

 for the two methods of original capture. Five of the 

 nine chi-square tests of the hypotheses of 

 homogeneity indicate highly significant differ- 

 ences in the return percentages between the types 

 of gear used to capture the tuna for tagging. When 

 only the 5 yr with significantly different return 

 rates for the types of gear, i.e., 1965, 1966, 1968, 

 1969, and 1970 are considered, higher return per- 

 centages were obtained for sport tagged fish in 4 of 



905 



