NEKTON 



Ctenophores and jellyfish are a nuisance to 

 swimmers in the Bay, and can be extremely abun- 

 dant in certain areas in the summer time. Their 

 abundance is controlled by salinity, temperature, 

 and possible unidentified factors, as well as the 

 breaking up of their tissues by high wave activity in 

 the fall and winter. They are a major predator of 

 zooplankton, but arc apparently a dead end in 

 terms of trophic dynamics; they arc not known to 

 provide a major food source for any other group. 



The fish community of the Bay can be consid- 

 ered to be dominated by the Atlantic menhaden 

 which as an adult consumes phytoplankton, and 

 during the larvae stages, consumes zooplankton. In 

 fresh waters, the menhaden are replaced by other 

 clupeid fishes. In the diagram of major Bay proces- 

 ses (fig. 1), fishes are considered in two groups, At- 

 lantic menhaden and all others. This indicates the 

 importance of menhaden in grazing on the phyto- 

 plankton and in providing food resources for other 

 fishes. Menhaden also support a large commercial 

 fishery and are the main resource removed from the 

 Bay in terms of fishery yield. Removal of menhaden 

 is also removal of fish food; menhaden feed other 

 populations of commercial and recreational fishes in 

 the Bay. 



The dominance of fishes by menhaden is pre- 

 sented as a simplifying perspective on the fish com- 

 munity. Some Bay scientists disagree with this view. 



There are approximately 200 fish species in 

 Chesapeake Bay. Figure 7 shows a generalized troph- 

 ic dynamics model of this diverse fauna (Hildcbrand 

 and Schroeder 1928, Bigelow and Schroeder 1953, 

 Reintjes 1969, Markle and Grant 1970). Adult men- 

 haden and anchovies, and all fish larvae are primarily 

 plankton feeders. At various times of the year, how- 

 ever, the larvae of most of the fish species in the Bay 

 will be included among the plankton. Some fishes 

 such as bluefish (Pomatomus saltatrix), weakfishes 

 (Cynoscion spp.), and striped bass are piscivorous. 

 Bluefish arc particularly voracious predators, feed 

 ing on the juveniles and adults of all other fishes 

 found in the Bay. There is a middle group of omni- 

 vores, such as eels and Atlantic croaker (Micropo- 

 gon undulatus), whose diets may include the plank- 

 tonic crustaceans (copepods, amphipods, and my- 

 sids); benthic crustaceans such as crabs or shrimps; 

 bivalves; small forage fishes such as killifishes (Cy- 



prinodontidac); mummichog (Fundulus hetcrocli- 

 tus); silversides, anchovies, and menhaden; and 

 benthic fauna from marshes. They may also feed 

 on the epifauna and epiphytes of seagrass com- 

 munities. 



A diagram of food-web dynamics for Bay fishes 

 is very difficult to construct. To attempt accuracy- 

 only produces a diagram which is too complex to 

 be useful, with arrows from every box to every 

 other box, or with dozens of boxes. In devel- 

 oping figure 7, fishes were grouped by major food 

 habits. A different set of simplifying assumptions 

 would produce a different diagram of fish trophic 

 dynamics. Common names in the compartments in- 

 dicate adults or late juveniles. Larval fishes are all 

 plankton eaters. Production of larvae contributes 

 to Bay zooplankton, which includes icthyoplank- 

 ton. Larvae in the Bay system are indicated by 

 broken arrows; spawning may occur in the Bay or 

 outside the Bay mouth, with larvae then coming 

 into the Bay. 



As a broad overview, Chesapeake Bay supports 

 resident and migratory fishes, with planktivorous, 

 omnivorous, and piscivorous feeding habits. Men- 

 haden, striped bass, and anchovies can be found in 

 the Bay year round even though they may not nec- 

 essarily spend their entire life cycle there. Men- 

 haden arc most abundant in the spring and sum- 

 mer. Other small forage fish such as killifishes, 

 mummichog, silversides, hogchoker (Trinectes ma- 

 culatus) and gobies (Gobiidae) are found in the 

 shallow waters, among seagrasses, or feeding out of 

 the marshes throughout the year. In the spring (ap- 

 proximately March), adult fishes migrate into the 

 Bay from the Atlantic. The anadromous alosines, 

 or shad and river herring, migrate to fresh water to 

 spawn, and feed as they return to sea. White perch 

 (Morone amcricana) and striped bass, which are 

 resident in the Bay, migrate into fresher water to 

 spawn. This wave is followed by a migration of the 

 sciaenids, or croaker, drum, weakfish, and spot, 

 entering the Bay to feed after spawning in near- 

 shore shelf waters of the Atlantic. Then their larvae 

 also enter the Bay. Bluefish spawn in the ocean and 

 enter the Bay only for feeding. Bluefish are a major 

 fish predator as well as an important recreational 

 fish. They can be found up to the fresh water limits 

 in the Bay system, although they are more abun- 

 dant in waters of higher salinity. In the fall the mi- 

 gration process is reversed as many of the fishes 



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