502 



Fishery Bulletin 98(3) 



900 



800 



700 



600 



>- 500 - 



LL 400 - 



300 



200 



100 





I 



II 



1 



I I Females, n = 3539 

 V////M Males, n = 3100 



ll 



^ 



,n,n,„, 



60 80 100 120 140 160 180 200 220 240 260 

 Length class (EFL, 10 cm) 



Figure 8 



Size-specific sex ratios of swordfish iXiphiaa gladiiisK used to eval- 

 uate sex and size composition of catch of the Hawaii-based pelagic 

 longline fishery during March 1994-June 1997. For readability, 

 lengths (EFL) have been pooled by 10-cm classes. 



temporal variations in swordfish sex ratios elsewhere in 

 the western Atlantic. The sex ratios of adult-size sword- 

 fish (>125 cm LJFL, but smaller than very large adults 

 [>195 cm], the size at which the numbers of males dimin- 

 ish greatly in Atlantic swordfish stocks) are strongly male- 

 biased only in the subtropical region (19-35°N) in which 

 most spawning occurs (Arocha et al., 1994; Arocha and 

 Lee, 1995). Spatial patterns similar to the latter also have 

 been observed in spawning regions of the tropical western 

 Atlantic iMejuto et al., 1998) and western Indian Ocean 

 (Mejuto et al, 1995). 



Spatial differences in the sex and size composition of 

 swordfish also may be related to sex-specific foraging 

 migrations. Differences in the sex and size composition of 

 swordfish catches have been noted by others in western 

 Atlantic fisheries. Males predominate in catches made at 

 tropical latitudes but females dominate in waters <18°C 

 (Beckett, 1974). Most swordfish caught in the western 

 North Atlantic off New England and the Canadian mari- 

 time provinces are large female fish jTibbo et al., 1961). 



Distributional ecology and energetics of migration 



Limited tag-recapture data"* suggest that some swordfish 

 move great distances within the North Pacific. Swordfish 

 also display marked diel vertical migrations that appear 

 to vary among fish of different sizes and that inhabit conti- 

 nental shelf versus open ocean areas (Carey and Robison, 

 1981; Carey, 1990). As they migrate between warm mixed 

 layer and cold subthermocline waters, swordfish encoun- 

 ter changes in water temperature as great as 19° in 2.5 h 

 (8-27°C: Carey and Robison, 1981). A vascular rete system 

 enables swordfish to dampen the rate of temperature loss 

 in swimming muscles on deep dives, and it is likely that 

 body mass importantly influences this ability (Carey, 1990) 

 and the metabolic costs of inhabiting cold water masses 



^Boggs,C.H. 1998. Unpubl.data. Honolulu Laboratory, South- 

 west fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, Honolulu. HI 

 96822-2396. 



