NOTES 



ENERGY FOR MIGRATION IN 

 ALBACORE, THUNNUS ALALUNGA 



The relations between immigrants and residents 

 of a specific fishing ground can likely be evaluated 

 from examination of the relative fat content of 

 individuals from a time sequenced sampling of the 

 fishery. These kinds of information are not yet 

 estimable for pelagic populations. 



The problem of energy availability and utiliza- 

 tion in migrations offish is a perplexing one. Mi- 

 grations are energetically quite expensive unless 

 a fish is passively carried by currents. Recently 

 recorded migrations of two tagged albacore, 

 Thunnus alalunga (Bonnaterre), across the 

 Pacific Ocean indicate that they traveled an aver- 

 age of 48 km/day (Japanese Fisheries Agency 

 1975). As these fish were approximately 80 cm 

 long on release, the average migration speed was 

 about 0.65 body lengths/s (55.6 cm/s). This is well 

 within the range of observed swimming speeds for 

 this species. These albacore were reported to have 



traveled from lat. 35°44'N, long. 171°37'E (Figure 

 1, point E) to lat. 47°00'N, long. 125°30'W (Figure 

 1, point F), a distance of 5,239 km in 110 days. The 

 caloric equivalent, in grams of fat, 1 utilized by 

 these two fish at the estimated rate of travel of 

 about 55 cm/s would be about 1,450 g or 14.5% of 

 their expected weight at the onset of migration. 

 Although great amounts of feed would not be 

 necessary for this migration given the 1 kcal/g 

 average available caloric content for forage (Sharp 

 and Francis 1976), the albacore has been reported 

 to have up to 18.2% fat in the edible flesh portions 

 (Sidwell et al. 1974). Muscle tissue constitutes 

 58.2% of the total body weight of albacore (Dotson 

 unpubl. data) which means up to 10.6% body 

 weight in fat has been observed, a value approach- 

 ing that necessary to provide the caloric energy for 

 these migrations. 



There is little doubt that albacore do not mi- 

 grate directly, that feeding does occur, and that 

 the fish probably do grow in overall length and 



*9.4 kcal/g fat. 



160° 170° 180" 170° 160° 



EAST - LONGITUDE - WEST 



150° 



140° 



130° 



FIGURE 1. — A great circle plotting chart is shown and the quantity and location of albacore samples is indicated by the numerals. A 

 length-mass equation was developed for the 477 albacore caught west of long. 130°W during June 1974. The numbers 14 and 37 near 

 San Diego represent the samples collected in July and September 1975, respectively. Using ▲ as the origin the letters A and B along the 

 line represent the distances which a 63-cm albacore could swim utilizing 404 g of fat at A, its minimum speed; B, the observed 

 diurnal-nocturnal activity level. Points C and D on the same line represent the distance that the 65-cm fish with the greatest observed 

 mass deficit (999 g) could have traveled utilizing the energy of this quantity of fat at the two respective activity levels described above. 

 Points E and F are the release and recapture positions of two albacore tagged by Japanese researchers. The minimum temperature 

 habitat limit of albacore (14.5°C) is depicted by a dashed line. The great circle route does not differ markedly from this boundary but 

 likely represents a conservative estimate of the total distance traveled between points E and F. 



447 



