McBnde et a\ Larval and settlement periods of Pnonotus carolinus and P cvolans 



67 



versus hS days after hatching) \V\g. 4). Both species set- 

 tled as early as 18-19 days after hatching, but this was 

 more characteristic of P. cvolans: most P. canilinus did not 

 settle until 24-25 days old. 



Both species grew relatively slowly, and approximately 

 linearly, during the larval and early juvenile period (i.e. 

 <0.3 mm/d; Fig. 4, and next subsection). These slow growth 

 rates, combined with the late peak in spawning (i.e. around 

 August), resulted in small body sizes by the onset of win- 

 ter. These smaller body sizes were particularly true for P. 

 carolinus, for which the most pronounced size mode was 

 10-15 mm SL in autumn 1991 and 1992 (Fig. 5). At this 

 time (i.e. September-December), individuals <50 mm SL 

 constituted 85% of P. carolinus and 52% of P. evolans from 

 all beam trawl tows combined; during autumn a majority 

 of Prionotus spp. were <25 mm SL. 



At beam trawl stations, densities of P. carolinus were 

 consistently higher than those for P. evolans in both 1991 

 and 1992 (Fig. 6). Geometric mean densities of age-0 P. 

 carolinus during the peak period of settlement (Septem- 

 ber-October) were much higher in 1991 (8.98 fish 100/m-) 

 than in 1992 (1.56 fish 100/m-'). Geometric mean densities 

 of age-0 P. evolans during September-October were also 

 higher in 1991 (0.32 fish 100/m2) than in 1992 (0.09 fish 

 100/m-'). These interannual differences were consistent 

 with higher larval densities of both species in 1991 versus 

 1992 (Fig. 2). Maximum densities of age-0 searobins 

 at a single station reached 28.9 P. carolinus 100/m- 

 and 3.2 P. evolans lOO/m^, both in September 1991. 

 Searobins larger than 150 mm SL were collected infre- 

 quently from June to October; occasionally they were 

 found together with age-0 conspecifics in the same 

 beam trawl tows. Age-0 searobins of both species were 

 collected primarily in continental shelf versus estua- 

 rine habitats during July-December (Fig. 7). 



Settlement of Prionotus carolinus 



The seasonality of settlement by P. carolinus, although 

 lasting from at least July to October, 1991, was punc- 

 tuated by a 2-3 week period in September when the 

 vast majority of larvae appeared to settle near Beach 

 Haven Ridge (Fig. 8). Densities of age-0 P. carolinus 

 near Beach Haven Ridge were very low during both July 

 and August (geometric means ranging from 0.0 to 1.1 

 fish 100/m-). During September, densities increased dra- 

 matically (range: 0.8-7.3 and 0.8-28.9 fish lOO/m^ on 

 September 12 and 23-24, respectively). Individuals were 

 collected at all stations along a depth transect, from 6 to 

 16 m, in late September Settled, age-0 P. carolinus were 

 still widespread and abundant in late October (0.0-13.3 

 fish lOO/m^), but they were not collected on 2 December 

 1991, and on 28 January and 10 March 1992. 



Collections for 23 September 1991 demonstrate a 

 wide range of P. carolinus developmental stages and 

 ages present at Beach Haven Ridge (Fig. 9A). All flex- 

 ion stages were present (6.5% preflexion, 26.0% flex- 

 ion, and 67.4% postflexion; /? = 169). Planktonic larvae 

 subsampled randomly from a Tucker trawl tow (;!=34; 

 Table 2) had hatched during a two-week period from 



5 10 15 20 25 30 35 40 45 

 Age (days after tiatctiing) 



Figure 4 



Relationship between daily age and length for Pnon- 

 otus carolinus (open symbols) and P. evolans (filled 

 symbols) for preflexion and flexion stages collected 

 with a Tucker trawl (circles), postflexion stages col- 

 lected with a Tucker trawl (triangles), and settled 

 juveniles collected with a beam trawl (squares). The 

 upper dashed line indicates the approximate size at 

 settlement, and the lower dashed line indicates size 

 at completion of flexion for both species. 



10 



Pnonotus carolinus 



Summer. 1991 

 r7=63 



.rprm 



Pnonotus evolans 



20 



10 



69.7 



Autumn, 1991 

 n=267 



Summer, 1991 

 n=^ 



Autumn, 1991 

 n=39 



Q- 10 



Summer, 1992 

 n=52 



T1 , ,n r|ff][|l1lr]lln}i 



85.7 



10 



Autumn, 1992 

 n=42 



50 100 150 200 50 



Standard length (mm) 



Figure 5 



Size frequency of Prionotus carolinus and P. evolans for beam 

 trawl collections near Beach Haven Ridge (daylight tows at the 

 landward and seaward stations (Fig. 11). Data were pooled by 

 season: summer (May-August) and autumn (September-Decem- 

 ber), n = total number of fish collected. No data for January- 

 April 1992 are shown because only a single fish (P. carolinus; 

 4.5 mm SL) was collected at these stations during this period. 



