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Fishery Bulletin 104(4) 



waters, Norcross et al. (1974) did not collect bluefish 

 >22 mm total length in near-surface waters and at- 

 tributed the absence of this fish to a lack of samples 

 at depths where larger bluefish were presumably con- 

 centrated. In our study, continental shelf bottom waters 

 were sampled with otter trawls (trawl vertical opening 

 ~2 m), and the size of first occurrence was 30 mm SL. 

 This finding indicates that juveniles may seek deeper 

 water as body size increases and swimming ability 

 improves (Norcross et al., 1974). Alternatively, small 

 bluefish collected with otter trawl tows may have been 

 concentrated in surface waters and were incidentally 

 captured during initial gear deployment and final re- 

 trieval (i.e., under conditions when the otter trawl was 

 inadvertently fishing the upper water column). Third, 

 recruitment of juvenile bluefish >50 mm SL to estua- 

 rine or coastal habitats is another plausible explanation 

 for their absence in continental shelf waters. As previ- 

 ously mentioned, bluefish actively or passively migrate 

 inshore at 40-80 mm FL (McBride and Conover, 1991; 

 Able et al., 2003). The size at which bluefish enter 

 inshore habitats may be the result of biological tim- 

 ing and morphological constraints. These two factors 

 are consistent with the fact that inshore recruitment 

 co-occurs with a switch in diet from copepods to avail- 

 able piscine prey (Marks and Conover, 1993; Juanes 

 and Conover, 1995). Correspondingly, bluefish may not 

 enter estuaries until swimming ability improves and 

 morphological development is complete, i.e., when fin 

 ray development and scale formation (between 34 and 

 37 mm SL) are complete (Silverman, 1975). Swimming 

 ability in many fish species dramatically improves af- 

 ter the transformation from larval to juvenile stages 

 (Hunter, 1981; Stobutzki and Bellwood. 1994). If mor- 

 phological development is coupled with improved swim- 

 ming ability in bluefish, juveniles most likely have the 

 physical ability to actively recruit to estuarine habitats 

 from inner continental shelf waters (Shima, 1989; Hare 

 and Cowen, 1993, 1996). This study provides cursory 

 evidence that summer-spawned juveniles move inshore 

 during August and early September. Furthermore, 

 the disappearance of bluefish of 25-50 mm SL from 

 continental shelf surface waters coincided with the ap- 

 pearance of somewhat larger fish (-50-60 mm SL) at 

 estuarine and coastal ocean sites in late August and 

 early September. 



Along the northeastern coast of the United States 

 (Cape May, New Jersey, to Long Island, New York), in- 

 gress of juvenile bluefish to inshore habitats presumably 

 occurs as two distinct episodes (McBride and Conover, 

 1991 and references therein); which are consistent with 

 intra-annual and bimodal length-frequency distribu- 

 tions. This bimodality in bluefish size-composition is 

 a result of a first cohort recruiting inshore from late 

 May to early June (spring-spawned cohort), and a sec- 

 ond cohort entering the same geographic region from 

 July to October (summer-spawned cohort) (Nyman and 

 Conover, 1988; McBride and Conover, 1991; McBride et 

 al., 1993). In our study, the size-composition of bluefish 

 across habitats was multimodal, yet length-based in- 



formation indicated that the overwhelming majority of 

 YOY bluefish had been summer-spawned. Similarly, re- 

 cent investigations of the inshore and continental shelf 

 regions of the MAB also documented the numerical 

 dominance of summer-spawned bluefish in late summer 

 and early fall (Able et al., 2003; Conover et al., 2003; 

 Wilber et al., 2003). 



Although summer-spawned bluefish presumedly domi- 

 nated the catches of YOY across all habitats and tem- 

 poral scales examined in our study, the recruitment 

 success and contribution of these cohorts to year-class 

 strength is unknown. The abundance of these fish, 

 compared to that of spring-spawned individuals, implies 

 that they potentially make important contributions to 

 bluefish year-class strength (Able et al., 2003); yet it is 

 unknown whether the area sampled in this survey is 

 indicative of bluefish abundance along other portions 

 of the U.S. northeastern coast or whether this sur- 

 vey is representative of other years. Moreover, bluefish 

 spawned later in the season (e.g., those encountered 

 on the shelf in late September and October) may not 

 achieve a size permitting either movement into estuar- 

 ies or successful seasonal migrations. These bluefish, 

 along with relatively small juveniles, may fail to con- 

 tribute to the adult population because of size-selective 

 mortality and decreased survival during overwintering 

 periods (Hare and Cowen, 1997; Sogard, 1997; Hales 

 and Able, 2001). There is also a consensus that spring- 

 spawned juveniles frequently dominate the emigrating 

 population in the fall, and therefore, are the key con- 

 tributors to year-class strength (Nyman and Conover, 

 1988; Chiarella and Conover, 1990; Munch and Conover. 

 2000). This assertion has been recently contested, how- 

 ever, because other studies have indicated that summer- 

 spawned bluefish contribute equally, if not exceedingly, 

 to the YOY population (Able et al., 2003; Conover et al., 

 2003; Wilber et al., 2003). It is probable that bluefish 

 population dynamics along the coastal United States 

 are a function of the combined recruitment success of 

 spring- and summer-spawned cohorts and that contri- 

 butions vary annually or over decadal scales (McBride 

 and Conover, 1991; Munch and Conover, 2000). As a 

 result, future research must focus on broad geographi- 

 cal areas over sufficiently long temporal periods in order 

 to adequately resolve the contribution of the different 

 bluefish cohorts. 



Acknowledgments 



We are grateful to the staff of the Rutgers University 

 Marine Field Station for assistance in field collections 

 and processing of bluefish samples, particularly Geoff 

 Bell, David Bottinelli, Ryan Nichols, and Rob Rinaldi. 

 We also thank Doug Clarke (U.S. Army Corps of Engi- 

 neers) for access to bluefish data from nearshore ich- 

 thyoplankton surveys. This study was funded through 

 the Bluefish/Striped Bass Research Program, Rutgers 

 University and National Marine Fisheries Service col- 

 laborative program. 



