Stable isotopic analyses of carbon, nitrogen, and sulfur were performed on teeth of different ages and sexes of the longbeaked common dolphin, Delphinus capensis, from the Gulf of California. Similarities in diet are suggested between the sexes, with no significant differences in isotopic compositions being observed. Differences in the ␦ 13 C, ␦ 15 N, and ␦ 34 S signatures were found among the age groups (nursing calf, juvenile, subadult, and adult). These data suggest that this species is generally a coastal feeder, and that it changes its feeding habits with increasing age, drawing more nutrition from higher trophic level organisms later in life.
Population assessments and species monitoring for many endangered marine megafauna are limited by the challenges of identifying and tracking individuals that live underwater in remote and sometimes inaccessible areas. Manatees can acquire scars from watercraft injury and other incidences that can be used to identify individuals. Here we describe a novel method for photo-identification of Antillean manatees Trichechus manatus manatus using aerial imagery captured during flights with a small multirotor drone. Between 2016 and 2017, we conducted 103 flights to detect and observe manatees in Belize, primarily at St. George's Caye (SGC) near the Belize Barrier Reef. Review of aerial videos from these flights resulted in 279 sightings of manatees (245 adults, 34 calves). High-resolution images of individual manatees were extracted and classified according to image quality and distinctiveness of individual manatees for photoidentification. High-quality images of manatees classified as sufficiently distinctive were used to create a catalog of 17 identifiable individuals. At SGC, 21% of all sighted adult manatees (N = 214) were considered photo-identifiable over time. We suggest that the method can be used for investigating individual site fidelity, habitat use, and behavior of manatee populations. Our photoidentification protocol has the potential to improve long-term monitoring of Antillean manatees in Belize and can be applied throughout clear, shallow waters in the Caribbean and elsewhere.
We report concentrations of several classes of organochlorines (OCs) in the blubber of California sea lions (Zalophus californianus) from the Gulf of California. Summed OC levels measured in 34 wild-ranging animals were, in general, lower than those previously reported in sea lions from the eastern Pacific. The rank order of OCs was SigmaDDTs (mean=3400 ng g(-1 ) lipid weight [lw]) > SigmaPCBs (1400 ng g(-1 ) lw) > SigmaHCHs (50 ng g(-1 ) lw) >or= SigmaCHLORs (46 ng g(-1 ) lw). The most abundant OC measured was the DDT metabolite, p,p'-DDE. No significant differences in OC profiles were found between genders or rookeries. Although the mean concentrations of OCs measured in adult males and females were similar, only adult females had significantly higher (p<0.05) mean blubber concentrations of summation SigmaDDTs and summation SigmaHCHs than pups.
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