594 



Fishery Bulletin 104(4) 



onset of the juvenile stage at 34-37 mm SL (Silverman, 

 1975). Juveniles remain oceanic for an additional 15-45 

 days before passively or actively recruiting to estuarine 

 habitats at 40-80 mm fork length (FL) (Nyman and 

 Conover, 1988; McBride and Conover, 1991; Hare and 

 Cowen, 1993). 



Along the U.S. northeastern coast, juvenile bluefish 

 recruit to estuaries and have a consistent intra-annual 

 and bimodal length-frequency distribution: the first 

 cohort enters estuaries from late May to early June 

 (spring-spawned cohort), and a second cohort enters 

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

 and Conover, 1988; McBride and Conover, 1991; Mc- 

 Bride et al., 1993; Creaser and Perkins, 1994). This is 

 consistent with previous studies that indicate that juve- 

 niles of both spring and summer cohorts are estuarine 

 dependent (Juanes et al., 1996; Able and Fahay. 1998). 

 There is recent evidence, however, that select cohorts of 

 bluefish may exclusively use alternative habitats, such 

 as ocean beaches, during the juvenile stage (Able et al., 

 2003; Wilber et al., 2003), In addition, samples of larval 

 and juvenile bluefish from surface waters on the inner 

 continental shelf have indicated at least two cohorts of 

 presumably summer-spawned fish that may not recruit 

 to estuaries (Kendall and Walford, 1979; Rowe et al.'; 

 Taylor and Able, in press). 



Spring-spawned bluefish historically dominate juve- 

 nile year-class strength and were therefore assumed 

 to determine adult population dynamics (Nyman and 

 Conover, 1988; McBride and Conover, 1991; Munch and 

 Conover, 2000). This assertion, however, is based pri- 

 marily on estimates of juvenile abundance in MAB 

 estuaries (Nyman and Conover, 1988; McBride and 

 Conover, 1991) and failed to consider contributions from 

 alternative habitats, including the inner continental 

 shelf. A more recent evaluation of bluefish collected 

 from the MAB also has indicated a shift in the cohort- 

 specific production of juveniles over the last decade 

 (Conover et al., 2003), such that summer-spawned fish 

 numerically dominate recent year classes. Despite the 

 apparent switch in the relative dominance of the two co- 

 horts, bluefish successfully recruiting to the adult popu- 

 lation remain the products of spring-spawning events 

 (Chiarella and Conover, 1990; Conover et al., 2003). The 

 factors underlying the apparent failure of the summer- 

 spawned cohort to contribute substantially to the adult 

 population are unknown. This failure is due, in part, 

 to insufficient information that would otherwise enable 

 a critical evaluation of each cohort's role in regulating 

 year-class strength. Attempts to determine factors af- 

 fecting recruitment patterns should include an evalua- 



1 Rowe, P. M., K. W. Able, and M. J. Miller. 2002. Distri- 

 bution, abundance, and size of young-of-the-year bluefish 

 (Pomatomus saltatrix) in ocean and estuarine habitats in 

 southern New Jersey during 1999-2000, .54 p. Jacques 

 Cousteau Technical Report no. 100-16. Rutgers Univer- 

 sity, Institute of Marine and Coastal Sciences, Marine Field 

 Station, 800 c/o 132 Great Bay Boulevard, Tuckerton, NJ 

 08087-2004. 



tion of the cohort dynamics of summer-spawned bluefish 

 that utilize inner continental shelf habitats. 



The goal of our study was to provide greater insight 

 into the habitat use by summer-spawned bluefish in a 

 localized area in the MAB. In 1998, young-of-the-year 

 (YOY) bluefish were sampled during the summer and 

 fall on the inner continental shelf off southern New Jer- 

 sey. Spatial and temporal abundance and distribution 

 patterns were used to evaluate the potential importance 

 of continental shelf waters as habitats for YOY bluefish. 

 Observations from the 1998 study were then analyzed 

 and compared to observations from other field surveys 

 of habitat use by YOY bluefish in the same geographic 

 region and time: inshore and other continental shelf 

 waters of southern New Jersey in 1998 (Able et al., 

 2003). 



Material and methods 



Sampling of surface waters over 

 the inner continental shelf 



Bluefish were sampled at the water surface along the 

 inner continental shelf off the southern coast of New 

 Jersey (Fig. 1). Specifically, a 4x4 station grid (total 

 area -825 km-) was sampled on ten dates between 11 

 August and 9 October 1998. Stations were grouped into 

 four transects that were aligned parallel to the coastline 

 (Fig. lA). Transects closest and farthest from the coast- 

 line were 3 km and 18 km offshore, respectively. Water 

 depths ranged between 6 and 29 m, and the shallowest 

 depths generally occurred near the shore. 



Bluefish were collected during daylight with a Methot 

 trawl deployed at the surface (Methot, 1986; Oozeki et 

 al., 2004). The frame trawl had a mouth area of 5 m^, 

 leading to an 11-m-long net (6-mm mesh) that tapered 

 to a 2-m-long plankton net (0.5-m diameter, SOO-fim 

 mesh). One tow was performed at each of the 16 sta- 

 tions per sampling date, with the exception of 11 Au- 

 gust and 9 October when only four and eight stations 

 were sampled, respectively (7; = 140 total tows). At each 

 station, the trawl was towed for four minutes in an arc 

 (tow speed -2.5-3.5 knots) to avoid the wake of the re- 

 search vessel. All tows were made at the surface (0-2 m 

 depth) with the top of the frame approximately 0.25 m 

 out of the water. Samples were immediately processed 

 after collection, and bluefish were preserved in 95% 

 ethanol for subsequent laboratory analysis. 



A General Oceanics flowmeter (General Oceanics, 

 Inc., Miami, FL) was attached to the Methot trawl 

 frame along a lower corner so that the volume of water 

 sampled could be determined (-2000 m* per tow). Sur- 

 face salinity, surface water temperature, water depth, 

 Secchi depth, and wind speed and direction were record- 

 ed at all stations. Additional wind data were available 

 as a time series (15-minute sampling interval) from a 

 meteorological platform located at the Rutgers Univer- 

 sity Marine Field Station (Tuckerton, NJ; Fig. lA; K. 

 W. Able, unpubl. data). 



