NOTE McBride: Spawning, growth, and overwinter size of Prionotus carotinus and P evolans 



645 



depth and latitude explained a significant (r->0.30; P< 

 0.01) amount of the variability of the mean size of age- 

 P. coroliniis during winter (Fig. 5). Each variable also 

 contributed significantly (P<0.02) to a multiple regression; 

 nearly half (r^=0.47) of the variance of the mean age-0 

 P. carolinus size between individual trawl tows was ex- 

 plained by the linear, least-squares equation 



mean SL = -158 + 0.37 x i.depth[m]) + 5.7 x Uatitudei'N]). 



36 



24 

 12 





 36- 

 24- 

 12; 



0- 

 36- 

 24- 

 12- 



0- 



Prionotus carolinus, age-0 (n=1 12) 



in.n,n,n,n,n,nr,n,n,n,n,n,n 



p. carolinus, age-1 (n=30) 



-^ 



^A^DA^ 



,n,n,n,nn, 



p. evolans, age-0 (n=28) 



— r- 

 30 



40 



I 

 60 



I 

 70 



T^ I I I I I 



50 60 70 80 90 

 Standard length (mm) 



100 110 120 



Figure 4 



Size frequency of Prionotus carolinus (open bars) and P. 

 evolans (filled bars) based on collections from continen- 

 tal shelf habitats in February-March 1993 (see Figure 

 IB). The upper boundary (120 mm SL) represents the 

 size cutoff used during field collecting and does not nec- 

 essarily define the maximum size attained for any age 

 class, n = number offish in sample. 



A Y = 47.9-t-0.499*(X)r2 = 0.40 B Y = -296-^9.85(X) r'=0.3Q 



120 

 100 

 80 

 60 

 40 

 20 

 





50 



I  



100 



—I 



150 



o<f. 



^ 



0% 



34 



I ' 

 35 



— 1 — 

 36 



—I — ' 

 37 



— 1 — ' 

 38 



Station deptti (m) 



Degree latitude (Nortti) 



Figure 5 



Linear relationships between mean size (standard length [mm]) of age-0 

 Prionotus carolinus and depth (A) or latitude (Bl of sampling location. All 

 fish were collected during February-March 1993 with bottom trawls in 

 continental shelf waters (see Fig. IB). See text for further details of multi- 

 variate analysis and results. 



Similar analyses for P. evolans suggested that depth, but 

 not latitude, was correlated with age-0 size variations. 

 However, samples sizes of P. evolans were smaller than 

 those for P. carolinus and age-0 P. evolans grow larger than 

 the maximum size saved in field collections; therefore it is 

 possible that age-0 P. evolans have a similar response to 

 depth and latitude as age-0 P. carolinus. 



Life history consequences 



Late-summer spawning by Prionotus is not unique among 

 fishes in waters offshore of the middle Atlantic states: 

 Scophthalmus aquosus spawn late in the summer (Morse 

 and Able, 1995) and three hake species {Urophycis bilin- 

 earis, U. chuss, and U. regia) have peaks in spawning 

 during July-September (Wilk et al., 1990). Late spawn- 

 ing is not even evident for all Prionotus throughout their 

 range. McBride et al. (2002) noted that the reproductive 

 season for Prionotus varies with respect to latitude and 

 coastal depth, and their observation that late spawning 

 was common only offshore of the southern middle Atlantic 

 states is consistent with the data presented in the present 

 study for larger (i.e. presumably older) P. carolinus found 

 during winter at higher latitudes. Sherman et al. (1984) 

 noted a close association between Prionotus spawning 

 cycles and zooplankton abundance cycles in continen- 

 tal shelf waters, and they suggested that the Prionotus 

 spawning season is adapted for larvae to experience 

 optimal prey encounter rates. However advantageous 

 this match between larvae and their prey may seem, late- 

 spawned Prionotus have an apparent size disadvantage 

 during winter compared to many other species because of 

 a shorter growing season. 



Generally, coastal fishes of temperate waters appear to 

 spawn in a manner that maximizes growth rates and size 

 of their progeny, particularly in response to size-selective 

 mortality (Conover, 1992; Sogard, 1997). Overwintering 

 sizes of age-0 P. carolinus, however, do not suggest that 

 such a scenario is occurring. Age-0 P. caroli- 

 nus are smaller than or about the same size 

 as typical age-0 prey species on the conti- 

 nental shelf, such as Menidia menidia and 

 Anchoa mitchilli (Conover and Murawski, 

 1982; Vouglitois et al, 1987 ). Despite their 

 small size, reports of age-0 Prionotus in gut 

 contents of predatory fishes are rare (Mar- 

 shall, 1946; Richards et al, 1979; Maurer 

 and Bowman'). Size-selective mortality, a 

 process that would select for early spawning 

 and fast growth rates, may not be important 

 because Prionotus are capable of burying 

 themselves in the substrate (Bardach and 

 Case, 1965)— an antipredator tactic. If size- 

 selective mortality is not important, then 



I ' 

 39 



— 1 

 40 



1 Maurer, R. O., Jr, and R. E. Bowman. 1975. 

 Food habits of marine fishes of the northwest 

 Atlantic-data report. Laboratory Reference 75- 

 3, 90 p. Northeast Fisheries Science Center 

 Woods Hole, MA 02543. 



