McBride and McKown: Consequences of dispersal to temperate estuaries for Caranx hippos 



535 



o 



5 10 15 20 25 30 35 

 Salinity 



Figure 6 



Scattergram of temperature and salinity 

 measured at stations where young-of- 

 the-year Caranx hippos were collected in 

 Haverstraw (open circles) and Jamaica 

 (filled circles) bays. Data were collected 

 with 61-m seine nets and pooled for all 

 vears, 1986-1993. 



from temperate estuaries to reproduce. Traits such as early 

 spawning season (i.e. winter or spring), fast growth rate, 

 large YOY body size, generalized habitat requirements, 

 and fast swimming speeds are favorable traits for any spe- 

 cies attempting to complete a life-history circuit within 

 one year between subtropical and temperate waters of the 

 western North Atlantic. These traits are found in several 

 finfish species in the Carangidae, Scombridae, and Mugi- 

 lidae. Grouping species by spawning, larval, and juvenile 

 characteristics and comparing their fate in these large 

 oceanographic systems will help define the appropriate 

 spatial scale for sampling these populations in the western 

 North Atlantic, as well as in other systems such as the Sea 

 of Japan (Nishimura, 1965), the Agulhas Current (Beck- 

 ley, 1985), and the East Australian Current (Miskiewicz, 

 1981) where similar dispersal patterns of subtropically 

 spawned species to temperate waters have been described. 

 An initial screening for such characters allows research- 

 ers to begin to evaluate whether a specific "subtropical" 

 species can or cannot survive once dispersed to temperate 

 habitats. 



Some of these subtropically spawned species are dis- 

 persed to temperate waters during less favorable condi- 

 tions (e.g. winter) and, presumably, others do not grow to 

 a sufficient size or have the behavior characteristics to 

 migrate in autumn. A nonadaptive outcome of dispersal 

 for many species on an ecological timescale is not, however, 

 necessarily surprising. An examination of the paleontologi- 

 cal record, which is most complete for invertebrates, shows 

 that biogeographic assemblages lag notably behind envi- 

 ronmental changes at an evolutionary timescale (Briggs, 

 1974; Pielou, 1979). A modeling and theoretical method, 

 such as that used by Hare and Cowen (1993), could help 

 explain why the larvae of so many species are dispersed 

 into large oceanographic systems even when expatriation 



N 



42N 



40'= 



38= 



78° 



76° 



74° 



72° 



36° 



34° 



^-.t^ Cape Hatteras 

 Cape Fear 



■34° 



78° 



76° 



74° 



72° W 



B 



30 

 >, 25 

 § 20 



cr 



r IS- 



c 



(D 



y 10- 



0) 

 Q. 



Il^oftti (n = 177) DSoutti (0=459) 



^! t,ivH-f )--! I 



5 10 15 20 25 30 

 Fork length (cm) 



Figure 7 



(A) Distribution of tows containing Caranx hippos based 

 on sampling of the continental shelf between Cape Fear 

 and southern New England. iB) Size frequency of C. hippos 

 collected north (filled bars) and south (open bars) of 36°N. 

 Samples are from bottom trawl collections for the years 

 1972-1996. There were no records of C. hippos farther 

 north or east of Long Island (but see Bigelow and Schro- 

 eder, 19.53). n = number offish measured. 



is likely, but more natural history data are necessary 

 before such a method can be widely applied. A more com- 

 plete record of which species are and are not expatriated 

 within large-scale systems will contribute to understand- 

 ing the processes underlying these biogeographic patterns, 

 provide opportunities to examine further the evolution of 



