Taylor et al Habitat use by summer-spawned Pomatomus saltatrix on the inner continental shelf off southern New Jersey 



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Sampling of bottom waters on the inner continental 

 shelf during the same time period collected 179 and 367 

 bluefish in August and October-November, respectively 

 (Table 1; Fig. 5). The size composition of bluefish col- 

 lected from otter trawl tows was comparable to that 

 observed at inshore sites (particularly ocean beaches), 

 but distinctly different from that of fish captured in 

 continental shelf surface waters. For example, 96.5% of 

 the bluefish captured during sampling of shelf bottom 

 waters were >50 mm SL (mean size = 63.8 and 125.6 

 mm SL in August and October-November, respectively). 

 Of the remaining individuals that were <50 mm SL. 

 all were collected during the August otter trawl sur- 

 vey. Spring-spawned bluefish were collected in August 

 and October-November by otter trawl tows, but again 

 these bluefish represented a small portion of the total 

 sampled population (5.1%). 



Discussion 



In our study, summer-spawned larval, transitional, and 

 juvenile bluefish used the inner continental shelf exten- 

 sively and represented a major portion of the entire fish 

 assemblage collected in surface waters off the southern 

 coast of New Jersey. For example, summer-spawned 

 bluefish were the most frequently encountered species 

 within the surface fish assemblage and ranked fourth 

 in numerical dominance during the summer and early 

 fall. Moreover, patterns of bluefish density observed 

 in this study are consistent with those seen in other 

 ichthyoplankton surveys in the MAB. Kendall and Wal- 

 ford (1979) found that bluefish larvae <4 mm SL were 

 widely distributed in the MAB in August (Long Island, 

 New York, to Virginia) and that peak concentrations 

 occurred on the inner continental shelf in the vicinity of 

 New Jersey and Delaware. Similarly, Smith et al. (1994) 

 observed high densities of bluefish eggs in June and July 

 and that centers of abundance occurred in mid-shelf 

 waters off Delaware Bay and New Jersey (Berrien and 

 Sibunka, 1999). Subsequent months were character- 

 ized by relatively broad spatial distributions of bluefish 

 larvae from the central MAB to southern New England 

 and by dense concentrations off New Jersey in July and 

 August, followed by decreased abundance over the entire 

 continental shelf in October (Kendall and Walford, 1979; 

 Smith et al., 1994). These observations from the inner 

 continental shelf, in conjunction with the reported use of 

 inshore habitats by summer-spawned juveniles (McBride 

 and Conover, 1991; Able et al., 2003; Wilber et al, 2003), 

 indicate that coastal regions of New Jersey and adjacent 

 areas are important summer-spawning sites for bluefish 

 and, moreover, represent an appropriate location for 

 synoptic comparisons of bluefish abundance and size- 

 structure across habitats. 



Empirical observations indicate that summer-spawned 

 bluefish may use inner continental shelf habitats and, 

 to a lesser extent, ocean beaches during their earliest 

 life history stages (larval, transitional, and small ju- 

 veniles). As surmised from this and previous studies. 



bluefish <50 mm SL are prominent constituents of the 

 ichthyoplankton assemblage in the MAB (Kendall and 

 Walford, 1979; Hare et al., 2001), but the these life 

 stages are found rarely in estuaries and inlets. Field 

 collections from our study indicated an abundant sup- 

 ply of larval to small juvenile bluefish in the vicinity 

 of Little Egg Inlet from August to October, yet these 

 particular life stages were not observed during concur- 

 rent sampling at estuarine sites. Moreover, larval fish 

 assemblages were monitored over 16 years (1989-2004) 

 inside Little Egg Inlet (Fig. 1), and bluefish were found 

 in only 0.8% of the total 640 plankton tows performed 

 between July and September (25 total bluefish, size 

 range: 7.6-57.0 mm SL) (Witting et al., 1999; K. W. 

 Able, unpubl. data). 



In another study, juvenile bluefish were conspicuous 

 members of the pelagic fish assemblage in Great Bay 

 (Fig. 1), ranking fifth in frequency of occurrence and 

 tenth in numerical dominance (Hagan and Able, 2003). 

 The mean body size of bluefish collected in Great Bay, 

 however, was 87.4 mm FL — a size that indicates that 

 bluefish may not use estuaries during the earliest life 

 history stages. More likely, YOY bluefish recruit to 

 estuarine and ocean beach habitats as small juveniles 

 (40-80 njm FL), as has previously been reported (Mc- 

 Bride and Conover, 1991; Hare and Cowen, 1993; Able 

 et al., 2003). This assertion was reconfirmed in our 

 study by the synoptic examination of summer-spawned 

 bluefish across multiple habitats, where the smallest 

 bluefish collected in estuarine, inlet, and ocean beaches 

 averaged 47.3 mm SL. 



In contrast to the size-composition of bluefish inhab- 

 iting estuarine and coastal ocean sites, bluefish in sur- 

 face waters on the inner continental shelf were strictly 

 larval, transitional, and small juveniles <50 mm SL 

 (Fig. 5). The paucity of juvenile bluefish >50 mm SL 

 off the southern coast of New Jersey may be attributed 

 to several factors including gear avoidance, size-de- 

 pendent depth and habitat distributions, and active or 

 passive emigration. First, gear avoidance appears un- 

 likely because of the speed (-2.5-3.5 knots), duration (4 

 minutes), and frequency (140 tows) at which tows were 

 performed (Norcross et al., 1974). For example, the ap- 

 proximate swimming speed of a 50-mm bluefish is 10 

 cm/s (011a et al., 1985; Hare and Cowen, 1993) under 

 the assumption that the fish swims at 2 body length/s 

 (Hunter, 1981). At this rate, it is improbable that juve- 

 nile bluefish could actively avoid a Methot trawl being 

 towed at 128-180 cm/s (1 knot=51.44 cm/s). Secondly, 

 larval-to-juvenile bluefish are surface oriented (0-6 

 m), as indicated by collection efforts across different 

 water depths (Norcross et al., 1974; Kendall and Wal- 

 ford, 1979; Kendall and Naplin, 1981; Shima, 1989) 

 and by morphometric characteristics (e.g., silver and 

 dark blue counter-coloration) of pelagic juveniles that 

 indicate that they are adapted for a surface oceanic 

 existence. Sampling in our study, however, was limited 

 to the immediate surface layer (0-2 m), and therefore 

 the current sampling design would not detect size-de- 

 pendent depth distributions >2 m. In Virginian coastal 



