tial. Most estuarine and lagoonal fish species are 

 not year-round residents in North Carolina. Many, 

 like the bluetish, migrate south during the cold 

 months. Others, like adult spot and Atlantic 

 croaker, simply migrate into deeper oceanic waters 

 for the winter, although they may also undergo 

 some north-south migration. Even fishes which re- 

 main in enclosed sounds and estuaries during the 

 cold months usually move into deeper waters 

 where the temperature extremes are not so pro- 

 nounced. For instance, those spotted seatrout and 

 yearling spot and croakers which spend winters in 

 North Carolina sounds are found congregated in 

 deeper holes during cold months. These species 

 are never seen foraging out over intertidal zones 

 during winter. 



In spring, the North Carolina flats remain 

 populated by the characteristic silversides and 

 killifishes. As the waters warm in March, April, 

 and May, large schools of small postlarval and 

 adult Atlantic croaker, spot, menhaden, and 

 flounders will appear. Occasionally, the near- 

 shore waters will be dark with schools of the 

 young of these fishes. Juvenile striped mullet also 

 appear during this period, but their numbers do 

 not equal those of the juvenile spot, Atlantic 

 croaker, and menhaden at this time of the year. 

 By late spring large schools of juvenile silversides 

 are also common. Small pinfish appear during the 

 spring, but they are ordinarily restricted to grass- 

 bed habitats during this stage of their life cycle. 

 By late spring, species diversity of fishes has 

 reached a high level that is exceeded only by the 

 diversity in the fall. Species diversity of fishes in 

 North Carolina estuaries is bimodal when plotted 

 over the full year with a spring and a higher fall 

 peak coinciding with the presence of fishes on 

 their north-south migrations (F. J. Schwartz, 

 Univ. North Carolina, Chapel Hill,Pers. Comm.). 



Although fishes are common over North Caro- 

 lina's tidal flats only during the warmer months 

 of the year, most of the production of inverte- 

 brates and other prey types occurs then, too. The 

 summer is characterized by high fish abundances. 

 Species diversity of fishes is high in summer but 

 not as high as the spring level. During the summer 

 months the species described earlier are actively 

 feeding. Baitfishes, flatfishes, and rays are the 

 prominent members of the summer ichthyofauna 

 on North Carolina's tidal flats, with several addi- 

 tional species occasionally visiting the flats to 

 feed. 



In the early fall, fish species diversity reaches 

 its yearly maximum. Summer residents are still 

 present and are joined by the early fall migrants 

 to produce this high diversity. In late fall, many 

 of the warm-water residents begin to leave the 

 shallows for their migratory runs to deeper or 

 more southerly waters. Small bluefish, rare on 

 North Carolina's intertidal flats during the sum- 

 mer, invade in large schools that have come from 

 sounds farther north. These feed on baitfishes 

 over intertidal flats and in deeper waters before 

 continuing their migration southward. Striped 

 mullet begin to school up in preparation for their 

 migration south. Spotted seatrout move into shal- 

 low waters during the fall, as do kingfish [Menti- 

 cirrhus spp.). Flounders are still abundant in the 

 fall, although the adults school up and move out 

 the inlets by the end of October. The year-round 

 residents of intertidal flats, killifishes and silver- 

 sides, remain obvious on tidal flats throughout 

 the fall. 



This cyclic pattern of seasonal change in 

 abundance and diversity is a universal characteris- 

 tic of the fish fauna of east-coast estuarine sys- 

 tems. Partly responsible is the seasonal variation 

 in abundance of all fish foods from plankton to 

 marine invertebrates to smaller fishes. The physio- 

 logical temperature tolerances of the fishes and 

 breeding habits also may play a role in setting this 

 pattern of seasonality. 



In addition to seasonal patterns in fish abun- 

 dances on intertidal flats, there are strong tem- 

 poral cycles in abundance over shorter time 

 periods. The most important of these are prob- 

 ably the patterns induced by the alternation of 

 day and night. Mf)st, but not all, fishes feed more 

 actively at certain limes of day, often early 

 morning and late evening. Other behavioral pat- 

 terns are also cued into day-night cycles. In parti- 

 cular, many smaller fishes appear to forage away 

 from the cover of grass beds and other hiding 

 places only under the protection of darkness. The 

 unvegetated intertidal flats are often far more 

 heavily visited by fishes, as well as crabs, during 

 the night than in the daytime. Some of the larger 

 predators follow a day-night pattern as well. It is 

 no accident that almost all gigging for flounders 

 on the North Carolina tide flats occurs at night, 

 when flounders lie on these flats and are relatively 

 inactive. Many of the sharks that play the role 

 of top predators on the intertidal flats pay their 

 summertime visits to shallow waters at night. 



47 



