ESTIMATES OF RATES OF TAG SHEDDING BY 

 NORTH PACIFIC ALBACORE, THUNNUS ALALUNGA 



R. Michael Laurs, William H. Lenarz, and Robert N. Nishimoto ' 



ABSTRACT 



Type-I (immediate) and Type-II (instantaneous) rates of tag shedding by North Pacific albacore, 

 Thunnus alalunga, are estimated using data from a double-tagging experiment. Type-I shedding is 

 estimated to be about 0.12 and Type-II to be between 0.086 and 0.098 on an annual basis. The paper also 

 contains a discussion on the accuracy of the estimates, and a method is developed to estimate possible 

 bias due to fishermen reporting double tag recoveries as single tag recoveries. The possible bias is 

 estimated to be low. 



A tagging program was initiated in 1971, and is 

 continuing, on Nortli Pacific albacore, Thunnus 

 alalunga (Bonnaterre), to examine their migra- 

 tion patterns, to obtain information for use in 

 population studies, and to estimate rates of mor- 

 tality. Because loss of tags through shedding can 

 cause estimates of mortality to be biased upwards 

 unless corrected for, part of the tagging program 

 in 1972 consisted of an experiment in which 788 

 albacore were double-tagged to evaluate tag 

 shedding by this species. 



Chapman et al. (1965) developed a formulation 

 of the return of single- and double-tagged fish 

 which includes instantaneous loss rates due to 

 fishing mortality, other mortality, and tag shed- 

 ding. They then solved for the instantaneous rate 

 of tag shedding given data from double-tagging 

 experiments. Bayliff and Mobrand (1972) e.xtended 

 the work of Chapman et al. to provide estimates of 

 the portion of tags which are retained after 

 immediate shedding occurs. Results of the use of 

 the Bayliff and Mobrand procedure to estimate 

 rates of tag shedding from the double-tagging 

 experiment on North Pacific albacore are pre- 

 sented in this paper. 



METHODS 



The tagging program is being conducted jointly 

 by the National Marine Fisheries Service- 



' Southwest Fisheries Center La Jolla Laboratory, National 

 Marine Fisheries Service, NOAA, La Jolla, CA 92038. Authorship 

 is alphabetical. Laurs was the investigation leader and responsi- 

 ble for the overall tagging program and was aided by Nishimoto. 

 Lenarz was responsible for the analytical aspects of the study. 



 Southwest Fisheries Center, La Jolla, CA 92038. 



(NMFS), NOAA, and the albacore fishing industry 

 through the American Fishermen's Research 

 Foundation' (AFRF). 



Albacore were caught by commercial jig boats 

 and a bait boat on charter to the AFRF. Fishing 

 operations on jig boats were conducted with 

 standard commercial albacore feathered jig- 

 fishing equipment and commercial trolling meth- 

 ods. Most of the fish that were tagged and released 

 from the bait boat were caught by the "winging" 

 method of live-bait, pole-and-line fishing, whereby 

 a fish is caught on an anchovy-baited barbless hook 

 on the end of a short line attached to a stout pole. 

 Immediately after hooking, the fish is lifted out of 

 the water, swung toward the fisher, and caught 

 under the arm of the fisher, who then removes the 

 hook. A small number of the fish tagged from the 

 bait boat were taken by trolling feathered jigs and 

 on rod-and-reel using live anchovy as bait. 



Special care was exercised to tag and release 

 only fish judged to be in very good condition. Fish 

 which showed signs of severe bleeding, which were 

 hooked through the roof of the mouth or which 

 showed signs of extreme exhaustion, were not 

 tagged. For each tagged and released fish records 

 were kept of the number of the tag, the date and 

 time of tagging, the length of fish to the nearest 

 lower centimeter, condition of fish, and sea surface 

 temperature. A fish caught by pole and line was 

 measured with a large caliper and tagged with two 

 tags inserted almost simultaneously by a tech- 

 nician while the fisher held the fish under his arm. 

 A fish caught on trolling gear and rod-and-reel was 



Manuscript accepted January 1976. 

 FISHERY BULLETIN: VOL. 74, NO. 3, 1976. 



^AFRF administers revenues derived from an assessment paid 

 on U.S. - landed albacore. 



675 



