Feeding habits of the tiger shark, Galeocerdo cuvier, in the northwest Atlantic Ocean and Gulf of Mexico

Abstract

Sharks are apex predators that structure marine communities through predation. Studies of diet and feeding patterns contribute to developing ecosystem models and it is critical that whenever possible, diet information specific to the area of concern is applied when developing an ecosystem model. Despite a number of studies conducted on tiger shark feeding, most comprehensive studies have been from the Pacific Ocean. There is little knowledge of the diet of tiger sharks in the Atlantic Ocean and Gulf of Mexico, with most studies in that area being localized and anecdotal. This study examines diet by life stage and tests for the presence of ontogenetic shifts, as well as how the diet of these sharks might be changing under certain environmental conditions and geographic variations. This study reviews the information collected on tiger shark feeding to date. It summarizes the results from previous studies on tiger shark diet: what prey items were found in studies of Pacific tiger sharks, and results from the anecdotal studies in the Atlantic, most of which took place in the early to mid 1900s, included small sample sizes, and were conducted in localized regions. For this study 169 sharks were caught as part of the U.S. shark bottom longline fishery and by the National Marine Fisheries Service Apex Predators scientific survey. Sharks were caught from North Carolina to Southern Florida and throughout the Gulf of Mexico and were divided, based on fork length, amongst three life-stage groups: young-of-the-year (YOY), juvenile, and adult. To quantify diet, index of relative importance was computed. Prey items were classified to the lowest taxon possible and sorted into 15 categories: aves, cephalopods, cnidarians, arthropods, elasmobranchs, bryozoan, mammals, molluscs, plants, reptiles, teleosts, porifera, other (rocks, trash), unknown, and free-living nematodes that were not tiger shark parasites. Overall, teleosts were the most significant prey category, followed by molluscs and birds. For YOY sharks, molluscs were the dominant category, followed by teleosts and birds. Juveniles primarily fed on teleosts, followed by molluscs and birds. Adults primarily consumed teleosts followed by reptiles and cephalopods. Cumulative prey curves were created for overall tiger sharks and each life stage to examine if sample size was large enough to describe the diet. Cumulative prey curves showed that the number of overall stomachs examined was enough to define the diet in the northwest Atlantic and Gulf of Mexico. However, although individual life stage curves approached asymptote, they did not fully reach one, indicating sample size was not necessarily sufficient for each individual life stage. Diet by life stage and region was also looked at using the Simplified Morisita-Horn Coefficient, as well as prey diversity using Simpson's Index. Dietary overlap was significant between all life stages except for YOY and adult. Prey diversity increased as sharks transitioned from one life stage to another. Effects of environmental factors (se...

A matter of taste: Spatial and ontogenetic variations on the trophic ecology of the tiger shark at the Galapagos Marine Reserve

“…Comparison of the diet between large and small tiger sharks within the GMR revealed an ontogenetic shift, with small tiger sharks generally feeding on lower trophic groups. Pelagic fish and squid were the main prey items, similarly to other trophic studies in sub-adult individuals along the coast of Ecuador [22], Western Australia [17] and the north-western Atlantic [21]. Ontogenetic dietary shifts, in which the number and size of prey items increase as tiger sharks increase in size, have also been reported around Hawaii [13], New Caledonia [11], and South Africa [20].…”

“…In the northwestern Hawaiian Islands, seabirds are the most important prey items [18]; while tiger sharks around the main Hawaiian islands display a broader diet composition [13,19]. A limited number of studies are available from other geographical areas, such as the Indian [20], Atlantic [21] or Eastern Pacific [22] ocean basins. In the Tropical Eastern Pacific, diet studies for this species have been limited to the analysis of stomach contents from just six individuals from the coast of mainland Ecuador [22].…”

Movement patterns and habitat use of tiger sharks (Galeocerdo cuvier) across ontogeny in the Gulf of Mexico

“…A more likely explanation for lower transmission rates at smaller sizes is behavioral, namely that smaller animals simply spend less time at the surface than larger individuals. Younger individuals in the GoM are reported to forage disproportionately on benthic gastropods [83], whereas adults, which are known to spend the majority of their time at depths <5 m [48,84], more commonly consume sea turtles and fishes [83]. Additionally, smaller individual tiger sharks are likely more susceptible to predation from larger sharks and as such may avoid these areas at younger life stages to improve survival.…”

Pinpointing Drivers of Extirpation in Sea Snakes: A Synthesis of Evidence From Ashmore Reef

“…Several species of sharks prey on sea snakes (Heatwole et al, 1974;Tuma, 1976;Lyle, 1987;Cliff and Dudley, 1991;Simpfendorfer, 1992;Lowe et al, 1996;Fergusson et al, 2000;Heithaus, 2001;Kerford, 2005). Notably, tiger sharks are important in this respect (Dicken et al, 2017;Ferreira et al, 2017;Aines et al, 2018; Figure 6). In coastal waters of Queensland, Australia, Heatwole (1974) found that 31% of the 637 tiger sharks that contained food had at least one sea snake in their stomachs.…”