98 



Fishery Bulletin 91 ( 



1993 



In this paper we examine the feeding ecology of 

 young juvenile P. saltatrix prior to their arrival in the 

 nursery areas of the MAB. We document the predator 

 size at which teleost prey initially appear in the diet 

 and whether or not this shift to piscivory occurs coin- 

 cidentally with the habitat shift inshore. Since fish are 

 considered gape-limited predators (Hartman 1958, Ross 

 1978, Hunter 1980, Roberts et al. 1981), we examine 

 mouth width for abrupt changes that may accompany 

 an ontogenetic shift in diet. 



Methods 



Field collections 



Spring- and summer-spawned juvenile P. saltatrix were 

 sampled from transects across the MAE in 1988 and 

 1989. The area sampled extended along the eastern 

 U.S. coast from Cape May, New Jersey northeast to 

 Montauk, New York and to 125 miles offshore. Cruises 



were conducted during two time-periods: 4 April 

 1988-8 August 1988, and 4 April 1989-8 August 1989. 

 A total of 275 stations were sampled during 16 cruises. 

 Juvenile P. saltatrix were collected at 46 of these sta- 

 tions (Figs. 1,2). Offshore stations were located lOnmi 

 (18.52 km) apart, and several coastal stations were lo- 

 cated within lmi (1.85 km) of the shoreline (for com- 

 prehensive cruise track maps, see Hare & Cowen 1991, 

 Marks 1991). Cruise duration was 3-7 d with tows con- 

 ducted at regular intervals, 24 h/d. Tows consisted of a 

 10 min net deployment filtering approximately 3500 m :! 

 of seawater, at a ship speed of 3-4 kn. 



Samples were collected using a modified Methot 

 Frame Trawl (Methot 1986). The opening of the trawl 

 was 5 m 2 and the mesh was 2 mm. Total net length 

 was 13 m. Because juvenile P. saltatrix are often found 

 near the surface (Kendall & Nalpin 1981, Collins & 

 Stender 1987), trawls were conducted with the top 

 30 cm of the net above the water surface. All speci- 

 mens were preserved in 70% ethanol. 



'  • iOOn, - 



 41" N 



75" W 



7J"W 



71" W 



Figure 1 



Station locations off the coast of New Jersey where spring-spawned bluefish Pomatomus saltatrix were 

 caught during 1988 and 1989. Filled circles represent station locations (/i=9l where piscivorous bluefish 

 i»=25) were collected i.v TL=51.6mm, SD=10.60). Open circles represent station locations (;i = 13l where non- 

 piscivorous fish (n=33) were collected t.r TL=37.1 mm, SD=14.04). 



