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Marine Ecology Progress Series

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MEPS 669:227-240 (2021)  -  DOI:

Dietary plasticity of two coastal dolphin species in the Benguela upwelling ecosystem

Michelle Caputo1,2,*, Simon Elwen3, Tess Gridley3, Sophie A. Kohler4, Jean-Paul Roux5, Pierre William Froneman2, Jeremy J. Kiszka1

1Institute of Environment, Department of Biological Sciences, Florida International University, 3000 NE 151 St., North Miami, FL 33181, USA
2Department of Zoology and Entomology, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
3Department of Botany and Zoology, University of Stellenbosch Cape Town, South Africa, c/o Sea Search Research and Conservation NPC, 4 Bath Road, Muizenberg, Cape Town 7945, South Africa
4Animal Demography Unit, Department of Biological Sciences, Private Bag X3, University of Cape Town, Rondebosch 7701, South Africa
5SEACODE and Namibia Nature Foundation, PO Box 583, Lüderitz 9000, Namibia
*Corresponding author:

ABSTRACT: Defining the trophic relationships of marine predators and their dietary preferences is essential in understanding their role and importance in ecosystems. Here we used stable isotope analysis of skin samples (δ15N values reflecting trophic level and δ13C values reflecting foraging habitat) to investigate resource partitioning and spatial differences of the feeding ecology of dusky dolphins Lagenorhynchus obscurus and Heaviside’s dolphins Cephalorhynchus heavisidii from 2 coastal study sites separated by 400 km along the coast of central (Walvis Bay) and southern (Lüderitz) Namibia in the Benguela upwelling ecosystem. Overall, isotopic niches of both predators were significantly different, indicating partitioning of resources and foraging habitats. Despite their smaller body size, Heaviside’s dolphins fed at a significantly higher trophic level than dusky dolphins. Stable isotope mixing models revealed that both species fed on high trophic level prey (i.e. large Merluccius spp., large Sufflogobius bibarbatus, and Trachurus t. capensis) at Walvis Bay. The diet of both dolphin species included smaller pelagic fish and squid at Lüderitz. Spatial differences highlight that Heaviside’s and dusky dolphins may exhibit dietary plasticity driven by prey availability, and that they likely form distinct population segments. Important prey for both dolphin species, specifically Merluccius spp. and T. t. capensis, are the main target of trawl fisheries in the Benguela upwelling ecosystem, highlighting potential resource overlap between dolphins and fisheries.

KEY WORDS: Cetaceans · Foraging · Stable isotopes · Trophic ecology · Mixing models · Dusky dolphin · Lagenorhynchus obscurus · Heaviside’s dolphin · Cephalorhynchus heavisidii

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Cite this article as: Caputo M, Elwen S, Gridley T, Kohler SA, Roux JP, Froneman PW, Kiszka JJ (2021) Dietary plasticity of two coastal dolphin species in the Benguela upwelling ecosystem. Mar Ecol Prog Ser 669:227-240.

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