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Fishery Bulletin 103(4) 



nmi/day for Punta Cana; 9.4 nmi/day for the U.S. Mid- 

 Atlantic region; and 8.2 nmi/day for La Guaira Bank 

 (Fig. 7). Thus, the average white marlin displacements 

 found by Graves and Horodysky were 2 to 3-fold higher 

 than those reported in the present study. Black marlin 

 (Makaira indica, Gunn et al., 2003) and striped marlin 

 (Tetrapturus audax, Domeier et al., 2003) monitored 

 mostly outside of spawning times and areas had displace- 

 ments per day 2 to 4-fold higher than those in the pres- 

 ent study. Therefore, reproductively active white marlin 

 and blue marlin monitored in our study (30- or 40-day 

 deployments) appeared to have more constrained average 

 displacements per day than those in other studies where 

 similar PSAT technology was used to monitor marlin in 

 and outside of their respective spawning seasons. 



Further PSAT-based research, with extended monitor- 

 ing durations (i.e. at least s3-4 months) on white mar- 

 lin and other billfish species in their spawning areas, 

 will be necessary to clarify the causative factors for 

 these findings. Interpretation of our findings also needs 

 to be tempered by the fact that the displacement vectors 

 (minimum straight line distances) used to characterize 

 movements in this study were limited to beginning and 

 end points. In theory, daily estimates of light-based 

 geolocation would provide improved resolution of small- 

 scale movement patterns. However, there is little sci- 

 entific agreement (Musyl et al., 2001; Hill and Braun, 

 2001) as to the methods and validity of daily tracks 

 generated from highly variable light levels, particularly 

 for wide ranging species near the equator. 



Although we present no evidence that the horizontal 

 movement patterns of blue marlin (other than possi- 

 bly constrained displacements) reported in our study 

 are directly related to spawning activity, the possibil- 

 ity that white marlin could show fidelity to a spawn- 

 ing area cannot be ruled out. For example, Pepperell 

 (1990) examined conventional tagging results off east- 

 ern Australia and reported that the periodic peaks in 

 return frequency were possibly indicative of black mar- 

 lin returning to the spawning ground as part of their 

 annual migration cycle. The multidirectional pattern 

 of blue and white marlin displacements found in the 



present study was very similar to the pattern reported 

 by Graves et al. (2002) for blue marlin monitored with 

 PSAT tags for five days off Bermuda. The relatively 

 short-term duration of PSAT tags in both studies (5-40 

 days) generally precludes detection of directed seasonal 

 horizontal movement patterns (including potential an- 

 nual fidelity to a spawning area) as described by Mather 

 et al. (1975), Pepperell (1990), and Ortiz et al. (2003). 

 Detailed accounts of temperature and depth prefer- 

 ences of electronically monitored white marlin have 

 been rare and those that do exist are limited to very 

 short (<;ten days) monitoring durations (Block et al., 

 1990; Horodysky et al., 2003; Graves and Horodysky 4 ). 

 We found that white marlin monitored with PSATs for 

 periods of 28-40 days spent the majority of time in the 

 upper 25 m of the water column at temperatures of 

 28-30°C. Similar findings were found for this species by 

 Graves and Horodysky 4 and Horodysky et al. (2003), as 

 well as for blue marlin, black marlin, and striped mar- 

 lin reported by Graves et al. (2002); Kerstetter et al. 

 (2003); Gunn et al. (2003); and Domeier et al. (2003). 

 However, we could not directly address the depth at 

 which spawning occurs in our study from PSAT results, 

 other than to note the preference of adults for, and 

 capture of larvae in, surface waters. Empirical data on 

 the depth of spawning for istiophorids are not available, 

 although anecdotal evidence indicates that some species 

 may spawn in surface waters (black marlin observations 

 by Harvey, personal commun. 5 ). 



Spawning 



Prior studies of gonads have indicated that white marlin 

 spawn in the northwest Atlantic during the spring 

 (Baglin, 1977, 1979; de Sylva and Breder, 1997). Spring 

 aggregations of white marlin have been the target of the 

 Cabeza de Toro billfish tournament off Punta Cana for 

 over 40 years (Casilla 3 ), and the sampling of larvae in 



s Harvey, G. C. McN. 2004. Personal commun. 102 Webster 

 Drive, P.O. Box 10499 APO, Grand Cayman Island, Cayman 

 Islands, British West Indies. 



