preference may reduce the effects of 

 intra- and interspecific competitive 

 interactions in food-limited habitats. 

 Second, there are probably age- or size- 

 related changes in the energy requirements 

 of fish. Possibly the metabolic demands 

 of species change with age, necessitating 

 shifts in dietary preference. Many near- 

 shore individuals are juveniles that, as 

 they grow, tend to move into deeper waters 

 (Haedrich and Hall 1976). 011a et al. 

 (1974) described differences in habitat 

 preference in the tautog. Large tautog 

 foraged at greater distances from resting 

 sites than small individuals. Also, older 

 fish migrated offshore during colder 

 months while younger fish remained near- 

 shore and became torpid. Finally, broad 

 dietary preference may reflect the unpre- 

 dictable nature of food supplies in marine 

 temperate environments. Pronounced sea- 

 sonal and local variations in primary and 

 secondary productivity may favor general- 

 ized feeding habits. 



4.3 GEOGRAPHIC DISTRIBUTION PATTERNS 



Fish communities north and south of 

 Cape Cod show distinctive differences in 

 species composition, apparently related to 

 seasonal differences in water temperature 

 (see Chapter 1). Fish communities north 

 of Cape Cod tend to be dominated by 

 boreal, non-migratory forms while those to 

 the south primarily consist of warm-water, 

 migratory species (Colton 1972; Colton 

 et al. 1979). Species composition on a 

 large scale, therefore, is determined by 

 temperature. 



Temperature effects on a more local 

 scale have also been observed in northern 

 Atlantic coast fish communities. Tyler 

 (1971a), working in a deep, nearshore site 

 in Passamaquoddy Bay, New Brunswick, and 

 Maine, classified four broad types of 

 demersal fish according to their residence 

 patterns: year-round residents, winter 

 residents, summer residents, and occa- 

 sional species. The fish community 

 reflected patterns of temperature fluctua- 

 tion throughout New England. Areas exhib- 

 iting greater annual temperature fluctua- 

 tion (e.g., south of Cape Cod) had more 

 temporary residents and fewer year-round 

 species (Figure 10). 



bO 



I- 

 2 

 UJ 



o 



U 



a 



iO 



20 



SEASONAL5 



A 



V 



"t^<^ 



v^ 



9 



r 



> 



<0' 



nJ 



.o-^ 



o 



,^" 





^' 



Figure 10. Percentages of 



poral components in fish 



the northeast Atlantic coastline (modified 



from Tyler 1971). 



different tem- 

 species along 



Recksiek and McCleave (1973), working 

 in the Sheepscot River-Back River estuary 

 at Wiscasset, Maine, found pelagic fish 

 assemblages corresponding to Tyler's com- 

 munity structure groups. The relatively 

 warm Back River estuary had a summer 

 pelagic component consisting mostly of 

 alewives, blueback herring, and Atlantic 

 menhaden, while the relatively cooler and 

 oceanic Sheepscot River estuary had a sum- 

 mer migrant pelagic component of Atlantic 

 herring, Atlantic mackerel, and spiny dog- 

 fish. Rainbow smelt was the only year- 

 round resident and Atlantic herring was 

 the only winter resident species. It ap- 

 pears, therefore, that although pelagic 

 and demersal fish assemblages can be 

 divided into similar residency patterns, 

 species composition varies with tempera- 

 ture regime both within and between lati- 

 tudes along the New England coastline. 



37 



