Schaefer and Fuller Movements, behavior, and habitat selection of Thunnus obesus 



781 



10°N 



sn 



CN- 



5^- 



ID'S- 



110°W 



105°W 



lOCW 



95°W 



90°W 



85'W 



80°W 



Figure 10 



Geolocation estimates for 22 bigeye tuna at liberty for 30 d or longer (Table 4) classified as unas- 

 sociated (blue dotst or associated with floating objects (red triangles). The yellow solid squares are 

 the release locations and the green crosshairs are the recapture locations. The larger blue and red 

 dots, axes, and elipses are the arithmetic means, major and minor axes, and SS'r probability ellipses, 

 respectively, for the spatial distributions of the geolocation estimates for unassociated behavior and 

 behavior associated with floating objects. 



face temperatures vary little over extremely large areas 

 (Fiedler, 1992); therefore this technique is much less use- 

 ful than in temperate regions. 



The movement paths shown for bigeye tuna in our 

 study (Figs. 9 and 10) derived from the filtered archival 

 tag light data indicated that the area was restricted to 

 the equatorial EPO. No fish traveled further west than 

 about 110°W, and most movements were constrained be- 

 tween about 95° and 100°W and 3°N and 5°S. However, 

 the value of the archival tags in providing fisheries-inde- 

 pendent information on dispersion and movement paths 

 is apparent, especially considering the fact that 16 of the 

 fish were recaptured within 300 nmi of where they were 

 released. Furthermore, the minimum convex polygon for 

 the filtered archival tag data is approximately four times 

 the area of the minimum convex polygon surrounding 

 the release and recapture positions. Movements of big- 

 eye tuna inferred from large-scale conventional tagging 

 programs in the western Pacific (Hampton and Gunn, 

 1998; Hampton et al.''; Kaltongga''! and Hawaii (Itano 

 and Holland, 2000) indicate that, although there are 

 some long-distance movements, most recoveries are near 

 their points of release. Those data appear to indicate, as 



do those of the present study, regional fidelity for bigeye 

 tuna, and that the expected degree of mixing is quite low 

 between the EPO and the central and western Pacific 

 Ocean (CWPO). 



The estimated mean velocity of 117 km/d or 2.6 knots 

 (Table 4) is comparable to the estimate of 130 km/d for 

 Pacific bluefin tuna {Thunnus orientalis) from archival tag 

 data (Tsuji et al.. 1999). Although this estimate should 

 not be interpreted as actual swimming speed through 

 the water, considering the imprecision of the movement 

 paths and the fact that daily vertical movements were not 



Hampton. J., K. Bigelow, and M. Labelle. 1998. A summary 

 of current information on the biolog>', fisheries and stock assess- 

 ment of bigeye tuna [Thunnus obesus) in the Pacific Ocean, with 

 recommendations for data requirements and future research. 

 Secretariat of the Pacific Community. Oceanic Fisheries Pro- 

 gramme. Technical Report 36,46 p. Oceanic Fisheries Pro- 

 gramme. SPC. B.P. D5. 98848 Noumea Cedex. New Caledonia. 

 Kaltongga. B. 1998. Regional tuna tagging project: data 

 summary. Oceanic Fish. Prog. Tech. Rept. 35. 70 p. Secretar- 

 iat of the Pacific Community. Noumea, New Caledonia. Oce- 

 anic Fisheries Programme, SPC. B.P D5. 98848 Noumea Cedex. 

 New Caledonia. 



