FISHERY BULLETIN: VOL. 74, NO. 3 



measured on a Naugahyde-covered foam measur- 

 ing pad and tagged by a technician while it was on 

 the pad. In order to tag an albacore on each side, 

 using this method, the fish had to be turned from 

 side-to-side. 



Spaghetti-dart type Floy^ tags are being used in 

 the tagging program. The tags are made of yellow 

 Resinite tubing, 12 to 13 cm long and similar in 

 structure to those described by Yamashita and 

 Waldron (1958) and identical to those used by Fink 

 (1965). The tags were inserted on both sides of the 

 fish below the second dorsal fin with the aid of a 

 beveled stainless steel piece of tubing, 14 to 16 cm 

 long and 0.135- or 0.156-inch inside diameter. The 

 tags were inserted so that the barb of the tag was 

 lodged around the pterygiophores of the second 

 dorsal fin. 



We estimated rates of tag shedding using the 

 notation and methodology of Bayliff and Mol)rand 

 (1972) for yellowfin tuna as did Lenarz et al. (1973) 

 in a similar study on bluefin tuna. Bayliff and 

 Mobrand's equations for returns of tags are: 



(1) 



ndrffc=FTiVD7rp''e-(^+A' + 2LK. 



and 



nd,k = 2FtN^7tp (1 - pe-^'k)e-^^ + ^ + ^". 



(2) 



where 



No 

 77 



time at the middle of the kth recovery 



period of length t days {k = 1, 2); 



number of returns of double-tagged 



fish retaining both tags during the 



period centered at t^ ; 



number of returns of double-tagged 



fish retaining only one tag during the 



period centered at 4; 



number fish released with double tags; 



portion of tagged fish which remain 

 alive after the immediate mortality, 

 including Type Itagging mortality, has 

 taken place; 



= portion of the tags which are retained 

 after Type-I (immediate) shedding 

 has taken place; 



= instantaneous rate of fishing mor- 

 tality; 



••Floy Manufacturing Company, Seattle, Wash. Reference to 

 trade names does not imply endorsement by the National Marine 

 Fisheries Service, NOAA. 



X = instantaneous rate of other mortality 

 (other included natural mortality, 

 Type-II (long-term) tagging mortali- 

 ty, and apparent mortality due to 

 migrations from the fishery); and 



L = instantaneous rate of tag shedding 

 (Type-II shedding). 



Bayliff and Mobrand (1972), using Equations (1) 

 and (2), showed that 



In 



27id, 



dk 



Odsfc '^^^idk 



= -L4 -h In p = ^^ 



(3) 



where //,, is an estimate of the natural logarithm of 

 the proportion of tags retained up to time ^;^. Note 

 that the first factor of the right-hand side of 

 Equation (2) is the integer 2. Both Bayliff and 

 Mobrand (1972) and Lenarz et al. (1973) mis- 

 takenly left this multiplier out of the equation in 

 their papers. However, the error was typo- 

 graphical and did not affect their derivations or 

 results. Given n,,,,^, n,,,,,^, and f,. , L and p are 

 estimated using simple linear regression; or as in 

 the case of this study when only two recovery 

 periods are used, the solution of two simultaneous 

 equations. Equations (1) and (2) assume that L and 

 the total of F and X are constant over t,^ . Since the 

 albacore fishery is seasonal, the assumption is 

 likely to be violated. The effect of the violation has 

 not been examined. 



RESULTS 



Release and return data through 1973 are shown 

 in Table 1. The number of returns in 1974 was 

 insufficient for analysis. A chi-square test indicat- 

 ed that gear type did not have a significant effect 

 on the proportions of single- and double-tag returns 

 in 1972 (x- = 1.117, df = 1). Data from both gears 

 were combined for the remainder of the analysis. 



Estimates of p and L are shown in Table 2. Only 

 returns that could be specified to the nearest week 

 are included in Table 1. Precise dates of recovery 



Table l.-Tag releases and returns with information on date of 

 recovery for North Pacific albacore and double-tag study. 



1972 

 double- 



1972 returns 



1973 returns 



Gear 

 type 



Average Average 



tag Double Single days out Double Single days out 



releases In^^,) (n^J 



(',) 



("..2) ("ds) 



('2) 



Jig 330 



Bait 448 



Total 778 



10 

 22 

 32 



5 



5 



10 



— 12 



— 2 

 54.71 14 



451.55 



676 



