Historic foraging ecology of the endangered Lahille's bottlenose dolphin (Tursiops truncatus gephyreus) inferred by stable isotopes

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The study of resource partitioning within a community is central to understanding the processes that enable interspecific competition and coexistence. This study aimed to understand the resource partitioning and habitat preferences among odontocetes in Uruguay. We analyzed stable carbon and nitrogen isotopes data from the bone tissue of common dolphins (Delphinus delphis), Fraser's dolphins (Lagenodelphis hosei), false killer whales (Pseudorca crassidens), Lahille's bottlenose dolphins (Tursiops truncatus gephyreus), Burmeister's porpoises (Phocoena spinipinnis), and franciscana dolphins (Pontoporia blainvillei). Based on the isotopic values, false killer whale individuals were divided into two different ecological groups (ecotype 1 and 2). Isotopic values also suggest that franciscana dolphins, Burmeister's porpoises, Lahille's bottlenose dolphins, and false killer whales ecotype 1 feed on the continental shelf and/or high trophic level preys. At the other end of the gradient, values suggest Fraser's dolphins and false killer whales ecotype 2 use resources from the oceanic environment and/or lower trophic preys. Isotopic niche overlap was found between the common dolphin and Lahille's bottlenose dolphin and between Lahille's bottlenose dolphin and false killer whale ecotype 1. This work provides novel basic information about the trophic habit and feeding habitat of the odontocetes inhabiting one of the most important estuaries of South America.

Section: Discussionmentioning

confidence: 99%

Resource partitioning in a cetacean community from Uruguayan waters

Valdivia,

Valenzuela,

Berriel

et al. 2023

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“…The stocks of M. furnieri were heavily exploited during the 1980s and 1990s, leading to a significant decline in biomass (Vasconcellos & Haimovici, 2006). This decline has also been reflected in the diet of other predators in coastal waters of southern Brazil, such as Pontoporia blainvillei and Tursiops truncatus gephyreus, which have increased predation on other fish species of low or no commercial value (Botta et al, 2022;Campos-Rangel et al, 2021;Machado et al, 2018;Secchi et al, 2003Secchi et al, , 2017. Therefore, it is likely that the overfishing of M. furnieri also contributed to its decreased occurrence in the SAFS diet.…”

Section: Marine Debrismentioning

confidence: 99%

Feeding habits of South American and sub‐Antarctic fur seals during their nonbreeding season in the southwestern Atlantic Ocean

Lima

Albernaz

Secchi

et al. 2023

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Stomach contents of South American (Arctocephalus australis) (n = 219) (SAFS) and sub‐Antarctic (A. tropicalis) (n = 37) (SFS) fur seals were opportunistically sampled from 1980 to 2021 to examine their feeding habits and resource partitioning in southern Brazil while in their nonreproductive periods. SAFSs mainly consumed abundant coastal pelagic species, such as Anchoa marinii and Doryteuthis sanpaulensis, resulting in high sexual trophic niche overlap. The frequency of occurrence (%FO) of fish prey, especially the overexploited Micropogonias furnieri, decreased between 1980–1992 and 2007–2021, while squid increased. For SFSs, offshore squids such as Ommastrephes bartramii and Illex argentinus were the most important prey considering both sexes in the long‐term. The interspecific trophic niche overlap was low, but it is likely underestimated since it increased with the inclusion of scat samples from SFSs. This sample‐size effect was also observed in Shannon's diversity index, which was lower for underrepresented SFSs. Marine debris ingestion was detected in both species (SAFS %FO = 2.7; SFS %FO = 8.3), with only flexible plastic material found. This study brings novel information on feeding habits of fur seal species in the extreme south of Brazil, as well as unprecedented information about their ecology during the nonreproductive period.

A practical guide on stable isotope analysis for cetacean research

Teixeira

Troina

Daura‐Jorge

et al. 2022

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Trophic ecology information about cetaceans is essential to understand their role in ecosystem dynamics. Stable isotope analysis is a valuable complementary approach to conventional methods usually applied to the study of the foraging behavior of cetaceans because it provides dietary information over different time scales and can potentially use tissues archived in scientific collections. However, the considerable increase in stable isotope analysis by a growing number of cetacean research groups demands the use of proper protocols to ensure that accurate isotopic data are obtained. We provide a theoretical background of stable isotope analysis and its application to assess cetaceans‘ trophic ecology. We review the factors that can influence isotopic measurements and propose a practical guideline with suitable techniques for sample preparation of biological tissues to be employed by researchers to yield reliability in the interpretation of isotopic data. We summarized the main assumptions and inherent limitations that can lead to confounding interpretations of isotopic data, such as species‐ and tissue‐specific discrimination factors, temporal or spatial variation in prey, and baseline isotopic values in the context of cetacean ecology. Our detailed review offers important guidance for researchers who want to use stable isotope analysis to address different ecological questions with cetacean species.