The feeding ecology of juvenile scalloped hammerhead sharks (Sphyrna lewini) in Kane'ohe Bay, O'ahu, Hawai'i.

摘要

Diet and feeding habits were studied in juvenile scalloped hammerhead (JSH) sharks in Kāne'ohe Bay, Hawai'i, from 1995 to 1998. The most common prey items were a species of alpheid shrimp and two goby species, which were also the most abundant benthic megafauna in the bay. Sharks had small amounts of food in their stomachs (median = 0.22% of body weight). Analysis of stage of digestion data, the frequency of occurrence of empty stomachs, and the amount of food in the stomach all indicated that sharks fed more at night than during the day. Other factors that might influence the diet were also investigated, including the effects of area, sex, year, season and proximity to the patch reefs. Three major variables known to affect the rate of gastric evacuation were manipulated: meal size, prey species, and temperature. The time for 80% of the meals to be evacuated ranged from 5.4 to 22.1 hours, which is fast relative to other sharks. Daily ration estimates ranged from 2.12 to 3.54% of the body weight, which is relatively high compared to other elasmobranchs, but lower than estimates of maintenance ration for JSH. Dietary data suggest that juvenile scalloped hammerhead sharks in Kāne'ohe Bay may be surviving much of the time at consumption levels below maintenance ration.; Predictions of the basic prey model of optimal foraging were evaluated in light of our current knowledge of the biology of JSH and its prey species in Kāne'ohe Bay. Estimating encounter rates was problematic, because too little is known about the behavior of the various prey species or the foraging behavior of JSH to accurately estimate encounter rates. The highest encounter rate based on estimates of prey density and shark swimming speed was 2,359/hour, whereas the maximum encounter rates based on stomach contents was 5/hour. Although, sharks may be foraging in a manner consistent with the predictions of the basic prey model, more research needs to be conducted on JSH hammerheads interactions with its prey to allow further assessment of current models of optimal foraging theory as applied to S. lewini and its foraging behavior.