Diet and Prey Selectivity
Steven Newman & Dr. Samuel H. Gruber
Juvenile lemon shark stomach eversion
Abstract - The main aim of this study is to better understand the relationship between the juvenile lemon sharks and their prey, as well as the advancement of knowledge of the lemon shark, and what affects its success and survival as a juvenile. Studies have been conducted on the diet of the juvenile lemon sharks, but the effects of the seasonal changes on their diet, and most importantly the selectivity of the lemon shark and the pressures that this applies to the prey population, are not fully understood. The importance of various species to the lemon shark's diet needs to be assessed, and the presence of any switching between prey items identified. Such a quantitative description of food choice is often a necessary prerequisite to studies of predator-prey interactions (Lechowicz, 1982). Switching can be used to help explain how stability can be maintained in a small and fragile ecosystem (Bergerud, 1983), and the presence of prey switching in juvenile lemon sharks may help us to understand the dietary importance of different species to the lemon shark, and whether or not they should be protected in order to ensure the survival of the lemon shark.
Stomach content analysis
In marine communities most of the studies on predation involve sessile or sedentary species. There are very few studies on motile species, and especially little is known about lemon sharks, and whether they control their prey population biomass, or if the biomass of lemon sharks in the north sound is controlled by their prey biomass and availability. Little is known about the effects of apex predators on marine ecosystems, and information on population dynamics is required to develop a rational approach for managing this under-utilized resource (Gruber, 1981). By studying juvenile lemon sharks, it can provide a baseline for estimating rates of production, the biological basis for any resource management. Such a study is necessary because lemon shark populations may be highly vulnerable to habitat destruction, and instability. By understanding the dynamics of the predator and prey populations, lemon sharks may be managed responsibly, and their reliance on different species of prey better understood.
One of the effects of predation is that on the abundance and size distribution of the prey population. The number of top carnivores that feed on a variety of species of fish and crustaceans, could have a major impact on the trophic dynamics of the area (Holland et al., 1993). Extensive field work is required because although the controlled conditions of the laboratory or field enclosure can serve to demonstrate the nature and potential of a relationship, the importance must be assessed by extension to the spatial and temporal context of the whole system (Kitchell et al., 1994)."
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