802 



Fishery Bulletin 91(4), 1993 



16 



14 -- 



12 



w 10 



>- 



o 



3 

 Or 

 UJ o  - 



UNSCARRED 

 SCARRED 



| I . . . ~N  



45 50 55 



60 65 70 75 80 

 FORK LENGTH (cm) 



95 



10 



>- 



<-> 6 



Z 

 LJ 

 Z> 



S 4 



UNSCARRED 



SCARRED 



B 



i i t' i i 



45 50 55 60 65 70 75 80 85 90 95 

 FORK LENGTH (cm) 



Figure 3 



Size-frequency distribution of the unmarked and net-marked 

 albacore sampled for our study (A) (215 unmarked and 114 

 net-marked fish) and much larger data set (B) (12085 un- 

 marked and 318 net-marked fish I from which the fish used in 

 our study are a subset (N. Bartoo, D. Holts, C. Brown, and L. 

 Halko, SWFSC, La Jolla Laboratory, unpubl. data). 



drift net. It is unknown if this is sufficient time for 

 differences in relative otolith weight to become mea- 

 surable. Boggs and Kitchell (1991) showed that sig- 

 nificant weight loss occurs in tunas within one week of 

 starvation. Therefore, it was likely that net-marked 

 fish were at liberty long enough for measures of physi- 

 ological fitness to become apparent, assuming net- 

 marked albacore had not been feeding prior to recap- 

 ture. The rate at which relative leukocyte abundance 

 changes in albacore following stress or infection is not 

 known, but in coho salmon (Oncorhynchus kisutch) and 

 rainbow trout (O. mykiss) leukocyte abundance changes 

 within 96 hours of imposition of stressful conditions 

 (McLeay and Gordon, 1977). Leukocyte abundance 

 should be a good measure of differences in the health 

 of net-marked and unmarked albacore, but the large 

 standard deviation (Table 2) may limit its usefulness 

 in this species. 



Failure to detect differences (Table 2) between un- 

 marked and net-marked albacore suggests that the 

 fish escaping from drift nets, and living long enough to 

 become vulnerable to recapture by U.S. trailers, do not 

 suffer increased natural mortality. Most of the fish 

 however, recaptured by trailers are found to be only 

 minimally damaged or to have healed scars (Table 1), 

 which may explain the lack of differences between net- 

 marked and unmarked fish. As shown in Figure 2, 

 there is most likely a spectrum of damage caused dur- 

 ing encounters with drift nets. We do not know if the 

 distribution of damage severity in the population of 

 albacore vulnerable to the troll fishery is the same as 

 that of all the albacore that escape drift nets alive. 

 Also, the number of albacore falling out dead, or es- 

 caping so badly injured that they succumb before be- 

 coming vulnerable to recapture by troll vessels, may 

 well be significant but remains to be determined. 



Literature cited 



Alexander, N., R. M. Laurs, A. Mcintosh, and S. W. Russell. 



1980. Haematological characteristics of albacore, 



Thunnus alalunga (Bonnaterre), and skipjack tuna, 



Katsuwonus pelamis Linnaeus. J. Fish. Biol. 16:383- 



395. 



Anderson, D. P. 



1990. Immunological indicators: effects of environmen- 

 tal stress on immune protection and disease 

 outbreaks. Am. Fish. Soc. Symp. 8:38-50. 



Blaxhall, P. C. 



1972. The haematological assessment of the health of 

 freshwater fish. J. Fish. Biol. 4:593-604. 

 Boehlert, G. W. 



1985. Using objective criteria and multiple regression 

 models for age determination in fishes. Fish. Bull. 

 83:103-117. 

 Boggs, C. H., and J. F. Kitchell. 



1991. Tuna metabolic rates estimated from energy 

 losses during starvation. Physiol. Zool. 64:502-524. 



Bolger, T., and P. L. Connolly. 



1989. The selection of suitable indices for the mea- 

 surement and analysis offish condition. J. Fish. Biol. 

 34:171-182. 



Brill, R. W. 



1992. The Kewalo Research Facility, 1958-1992: over 30 

 years of progress. Southwest Fish. Sci. Cent., NMFS, 

 NOAA, Honlulu, HI, Tech. Mem. TM 171, 41 p. 



Brill, R. W., R. Bourke, J. A. Brock, and M. D. Daily. 



1987. Prevalence and effects of infection of the dorsal 

 aorta in yellowfin tuna, Thunnus albacares, by the 

 larval cestode, Dasyrhynchus talismani. Fish. Bull. 

 83:767-776. 

 Bulow, F. J. 



1970. RNA-DNA ratios as indicators of recent growth 

 rates of a fish. J. Fish. Res. Board Can. 27:2343- 

 2349. 



