Title: Feeding ecology of two subtropical seabird species at french frigate shoals, Hawaii
Abstract: Regurgitated food samples from black noddy. .Jnous minums. and red-footed booby. Sula sulu. were collected and anal17ed from French Frigate Shoals. Hawaii. Eighteen families of fishes. three families of cephalopods. and miscellaneous crustaceans were found in 396 black noddy samples. The most common prey were identified as fishes belonging to the families Synodontidae. Mullidae. and Microdesmidae and as the cephalopod family Ommastrephidae. Twenty-two families of fishes. primarily the Exocoetidae, Carangidae. and Mullidae. along with ommastrephid squids were found in the 456 red-footed booby samples. Our results suggest that these two species of seabirds are apex. opportunistic predators. Seasonal analyses reflect the variation of prey availability over the course of a year and lend support to the notion that this variation is a controlling factor in the timing of the species' breeding. The relationship between the trophic ecology of the seabirds and a tropical fishery is discussed. In recent years, interest involving the trophic relationships among seabirds has grown immensely. Much of the related research has been directed toward topics relevant to the management of commercial fisheries and the impact of such fisheries on seabird populations (Nettleship et al., 1984). Seabirds are generallyapex predators in marine ecosystems and, as such, are potential competitors with commercial fisheries. Overfishing (Furness, 1984; Springer et al., 1986) and natural climatic fluctuations such as an El Niiio event (Schaefer, 1970; Idyll, 1973: MacCall. 1984; Gibbs et al., 1987) have historically altered the availability, quantity, or quality of seabird food supplies and, likewise, seabird populations of many world oceans. To make management decisions or simply predict the effect of such changes, it is important to know what effects fishing practices are likely to have on seabird populations and, conversely. whether seabirds do indeed compete with commercial fisheries. Idyll ( 1 973) suggested that fishery-seabird competition is most severe when the target involves identical species in identical size classes. Basic to the examination of seabird-fisheries interactions is that we acquire an understanding of the food requirements of the involved species. In the northwestern Hawaiian Islands (NWHI), fishery development proposals prompted an investigation into the feeding ecology of the 18 breeding species of seabirds. The results of the study are described in Harrison et al. (1 983). Although the phenomenally large sample size of the study eclipsed any prior tropical or subtropical seabird trophic study, it was not without deficiencies. In an attempt to represent all seabird species from each island, sampling was still inadequate for anything other than superficial seasonal analyses. Diamond (1 983) pointed out that. because the samples were taken from such a large geographical range, the species sampled cannot be said to constitute a community. Our study was undertaken in an attempt to limit and control geographical and seasonal variables and to establish a baseline from which future sampling could be used to monitor seabird population trends and food availability.
Publication Year: 1989
Publication Date: 1989-01-01
Language: en
Type: article
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Cited By Count: 17
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