Diet shift and site-fidelity of oceanic whitetip sharks Carcharhinus longimanus along the Great Bahama Bank

Abstract

Identifying the driving forces behind oceanic pelagic shark movements is key to a better understanding of their life history. Some oceanic pelagic shark species have been shown to aggregate in specific regions to mate and/or exploit abundant food resources. The oceanic whitetip shark Carcharhinus longimanus, a subtropical, ectothermic, oceanic pelagic shark that has experienced severe population declines, aggregates seasonally around Cat Island (CI) in The Bahamas. Large pelagic teleosts (e.g. billfish, tunas, and dolphinfish) are abundant in this region and oceanic whitetips are anecdotally reported to feed heavily on recreationally caught teleosts. However, it was unknown whether feeding habits at CI substantially differ from longer-term feeding habits. We used tag-recapture to assess site-fidelity of adult oceanic whitetips to CI and stable isotope analysis (SIA) of 2 different tissues (blood plasma and white muscle) to compare short-and long-term feeding patterns. The relatively high recapture rate (20.3%) confirmed that individual whitetips exhibit site-fidelity to CI. The aggregation consisted of adult individuals; females were more common, more than half were gravid, and no physical or behavioral evidence of mating or parturition was observed at CI. SIA-based Bayesian mixing model estimates of short-term (near CI) diets showed more large pelagic teleosts (72%) than in long-term diets (47%), showing a spatiotemporal difference in oceanic whitetip feeding habits. This suggests that availability of large teleost prey is a possible mechanism underpinning site-fidelity and aggregation of whitetips at CI. These results provide insight into the function of one of the last known aggregations of this once-abundant top predator.

Effects of lipid and urea extraction on stable isotope values (δ13C and δ15N) of two batoids: A call for more species‐specific investigations

“…Pure protein has an expected C:N ratio of ~ 3 and it is accepted in the literature that lipids need not be removed in tissues with C:N ratios < 3.5 (Post et al ). Following this rule, numerous studies evaluating elasmobranch resource use with stable isotopes have chosen not to extract lipids due to C:N ratios similar or often lower than those of pure protein (e.g., Abrantes and Barnett ; Vaudo and Heithaus ; Madigan et al ). The increase in C:N ratio following urea‐extraction in the present study, as in other studies (Kim and Koch ; Li et al ; Carlisle et al ), suggests that C:N ratios are not a good proxy for lipid content in tissues containing urea, and that the influence of urea on C:N ratios can mask lipid content, and may lead to incorrect decisions to not extract lipids (Carlisle et al ).…”

Philopatry and Regional Connectivity of the Great Hammerhead Shark, Sphyrna mokarran in the U.S. and Bahamas

“…Furthermore, philopatric behaviors were in some cases limited to different life stages; small juvenile sandbar sharks (Carcharhinus plumbeus) demonstrated seasonal climatic migrations of more than 200 km from their natal estuary during their first winter, returning to the natal estuary in subsequent summers for at least 3 years (Grubbs et al, 2007;Grubbs, 2010). More recently, a study on oceanic whitetips (Carcharhinus longimanus) at Cat Island, Bahamas, revealed the first evidence of philopatry and seasonal site fidelity in a highly mobile pelagic species (Howey-Jordan et al, 2013;Madigan et al, 2015). For lemon sharks (Negaprion brevirostris), this behavioral trait has even been extended to natal homing to specific nursery sites (Feldheim et al, 2014).…”

Into the deep: the functionality of mesopelagic excursions by an oceanic apex predator

“…Analysis of muscle tissue sample collected from oceanic whitetip sharks at the Cat Island aggregation, where sharks were tagged for the present study, estimated that pelagic squid constituted 44% of oceanic whitetip sharks' long‐term (>1 year) diet while short‐term (70–200 day) diet consisted of 23% squid (Madigan et al. ). Although the species of squid could not be identified in the analysis, many species of squid inhabit Atlantic waters below the thermocline (Voss and Brakoniecki ).…”

“…; Madigan et al. ). Consequently, we do not consider interactive behaviors to be a viable hypothesis.…”