DeMartini et al.: Maturity, size, and sex composition oi Xiphias gladius 



499 



40° 



30° 



20° 



■o 



3 10° 



30° - 



20° - 



10° 



180° 170° W 160° W 150° W 



180° 



170° W 160° W 150° W 



Longitude W 



Figure 6 



Capture locations of imminent spawners (stages 5-6; solid triangles) overlaid on locations of all repro- 

 ductively active females (stages 4-6; shaded circles), for swordfish [Xiphias gladius) caught by the 

 Hawaii-based pelagic longline fishery during March 1994^une 1997. Monthly plots from March, April, 

 May, and June depict the increasing proximity of imminent spawners to the Hawaiian Archipelago as 

 the spawning season progresses. 



ation of gi-eater numbers of females by using only a single 

 ovary section offsets the rare failure to detect maturity in 

 mature but inactive females. 



Histological examination of gonadal developmental stage 

 is the most accurate and expensive method of character- 

 izing sexual maturity, and cost-effective alternatives are 

 desirable (West, 1990). Gonad indices (GIs) represent one 

 such general (West, 1990) and specific (Hinton et al., 1997) 

 option. Our findings indicate that swordfish body weight 

 plus ovary weight together can predict reproductive activ- 

 ity with >90''/f accuracy in swordfish caught by the Hawaii- 

 based fishery. Our observations support the conclusion of 

 Hinton et al. (1997) that GIs can provide useful proxies 

 of reproductive activity in swordfish. We reiterate, how- 

 ever, that GIs alone are limited to detection of reproduc- 

 tive activity (Hinton et al., 1997); without ancillary data 

 such as gonad development or oocyte size, GIs are often 

 not reliable measures to distinguish reproductively inac- 

 tive but mature females from immature females during 

 the nonspawning season (West, 1990; Mejuto and Garcia, 

 1997 ). GIs are most often used for determining spawning 

 seasons; if nonspawning season fish are to be included in a 



Table 4 



Results of 2x3 x~ test comparing relative frequency with 

 which imminently spawning (stages 5-6 1 female swordfish, 

 Xiphias gladius. were caught, among all reproductively 

 active females (stages 4-6 1 caught during new, quarter, and 

 full moon periods by the Hawaii-based pelagic longline 

 fishery during March 1994-.June 1997. X" = 3.28, df = 2, 

 P = 0.20. 



size-at-maturity evaluation, a relatively inexpensive alter- 

 native to histological staging (such as oocyte size) should 

 be used for deducing maturation stages. Oocyte size can 

 provide an accurate proxy for gonadal developmental stage 



