FOOD AND FEEDING HABITS 



In the context of the total ecosystem, fish species may best be considered as 

 a group occupying a specific feeding niche (Langton and Bowman 1978) . These 

 niches are determined by the fishes' feeding habits (food items and habitats 

 used) and may change with size or life stage. The majority of fishes are 

 secondary or higher level consumers in their respective aquatic systems. A 

 single species may utilize several different feeding habits during its various 

 life stages. Different species may share the same food resources in a given 

 area or at a given time. This information is necessary to develop an accurate 

 understanding of energy transfer and trophic organization in aquatic systems. 



Fishes are classified as planktonic, nektonic, or demersal/semidemersal 

 feeders (figure 11-3). Planktonic feeders, such as the herrings, Atlantic 

 menhaden, and American sand lance feed high in the water column. Planktonic 

 food organisms for these fish are largely pelagic crustaceans (amphipods, 

 copepods , euphausiids, and mysids), schooling fishes, fish eggs, and larvae. 

 Fishes that feed on the nekton feed throughout the water column, on pelagic 

 crustaceans and fishes. The majority of the characterization area's migratory 

 fishes are nektonic feeders. The demersal/semidemersal feeders utilize 

 typical bottom food items, such as crustaceans, molluscs, echinoderms, fish, 

 polychaete worms, insects, algae, and detritus. The majority of the area's 

 resident marine, estuarine and freshwater fishes are demersal/semidemersal 

 feeders. The feeding habits and major food items of the fishes of coastal 

 Maine are listed in table 11-5. Data are organized by habitat, feeding habit 

 and principal foods. Fishes that share a given resource and may be impacted 

 by the availability or quality of food items may be perceived as a group. 



Detailed published work on food habits of Maine marine and estuarine fishes 

 are Tyler (1971 and 1972), Langton and Bowman (1978), and Maurer and Bowman 

 (1977). The latter two sources are the products of a comprehensive ongoing 

 effort by the National Marine Fisheries Service to compile food habit data on 

 80 major species of Northwest Atlantic marine fishes. 



Tyler (1972) looked at the food resources of the demersal marine fish of 

 Passamaquoddy Bay and compared the diets of the residents and seasonal 

 migrants for overlap and seasonal specialization. He found that the seasonal 

 migrants did not feed on a unique set of prey species but shared some food 

 resources with the resident species. Among the factors determining which 

 species a predator took were prey size, prey habitat (whether the prey were 

 nektonic, epifaunal, or infaunal), and whether or not the prey had a hard 

 shell (Tyler 1972). Within the species, diet varied with the size of the 

 individual . 



Langton and Bowman's (1978) investigations also indicate that when the diets 

 of taxonomically related pairs of species are analyzed, important differences 

 are apparent (figure 11-4). The similarity in diet is a relative measure of 

 overlap in food habits, i.e., use of the same resource by more than one 

 predator regardless of food abundance. Competition for food exists only if 

 the demand for prey exceeds the immediate supply. The index of diet overlap 

 shows where there is a potential for food resource competition given a certain 

 set of circumstances, e.g., significant decreases in prey populations and/or 

 increases in predator populations, or reduced feeding areas. 



11-23 



10-80 



