McBiide et al Ldivdl dnd settlement peiiods of Pnonotus catolinus and P cvolans 



65 



500 \\n\ were removed and mounted whole on glass slides 

 in immersion oil. Otoliths longer than about 500 pm were 

 mounted in nail polish on a glass slide, sanded with 1500 

 grit sandpaper along the sagittal plane, and polished with 

 0.3-pm grinding powder. Immersion oil was used liberally 

 to enhance the clarity of all otoliths, and polarized light 

 aided the viewing of microincrement structure. Micro- 

 increment counts were made with a compound microscope, 

 typically at 400x. Slides were coded and microincrements 

 were counted by one reader on three separate occasions. A 

 constant of 4 days, representing the period between hatch- 

 ing and deposition of the first ring, was added to the mean 

 microincrement count to estimate age since hatching (Mc- 

 Bride2). Preserved (95% ETOH) P. carolinus and P. evo- 

 lans were selected in a stratified i0.5-mm intervals), ran- 

 dom manner to compare ages and lengths. Microincrement 

 counts from this comparative material ranged, based on 

 all individuals, between 07i and 32% of the mean micro- 

 increment count for each otolith (mean=12.0'~f ; 11=41). 



Pnonotus carolinus were collected in far greater num- 

 bers than P. evolans and they were examined in greater 

 detail. Size and age distributions were initially defined 

 from collections made during the period of peak seasonal 

 abundance (i.e. late September 1991), when a random 

 sample of 34 larvae was selected from a Tucker trawl sam- 

 ple for 23 September. Another sample of juvenile P. caro- 

 linus was selected from a 2-m beam trawl tow on 23 Sep- 

 tember 1991 at a station near the above plankton tow 

 (Table 2). Four final samples were selected from 2-m beam 

 trawl tows set one month later (21-22 October) at four sta- 

 tions along a transect of varying depths. Otoliths from all 

 juveniles collected at these stations were analyzed (i.e. on- 

 ly fish that were mutilated or that had cracked otoliths or 

 otoliths sectioned beyond the core were e.xcluded). Gener- 

 al methods of measuring and staging individual fish, and 

 preparing otoliths, followed that described above. Sagittal 

 microincrements were counted on two (for lai-vae) or three 

 (for juveniles) separate dates by one reader. The range of 

 these microincrement counts, for all individuals, was from 

 0.0% to 25.0% (mean=9.6%; n = 127) of each mean count. 



Results 



Interspecific comparisons 



Prionotus carolinus were more numerous and occurred 

 more frequently than P. evolans in nearly all collections, 

 typically by an order of magnitude (Table 1). Spawning 

 by both species occurred from at least July to October off- 

 shore of southern New Jersey (Fig. 2). Modal size of larvae 

 generally increased with time, but there were exceptions 

 that indicated a pattern of multiple spawning events. For 

 example in August 1991, modal size for Prionotus spp. and 

 P. carolinus was notably smaller (3-4 mm) than the pre- 

 vious month (5-6 mm) (Fig. 3). Peak larval abundances 

 varied somewhat between years but were highest from 

 July to September. 



Prionotus carolinus was the smaller but older congener 

 at each developmental stage. Size and stage were com- 



