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Biogeographic variation in the diet of juvenile blacktip sharks across the Galapagos Archipelago

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Abstract

Juvenile blacktip sharks (Carcharhinus limbatus) are highly abundant in the mangrove-fringed bays throughout the Galapagos Archipelago, utilizing these habitats as nursery grounds. Due to spatial variation in factors including temperature and larval connectivity, fish species richness is higher in the eastern portion of the archipelago. Predator diets often reflect regional prey availability, leading us to hypothesize that juvenile blacktip sharks in the eastern Galapagos would have greater prey taxa richness than those in the west. Here, we used DNA metabarcoding of fecal matter collected via non-lethal cloacal swabs to describe and quantify juvenile blacktip shark diets. We collected samples from 107 sharks across 240 km, spanning 14 bays on four islands, and released all sharks alive. The most common prey taxa identified were Thoburn’s mullet (Mugil thoburni; 20.0%, based on percent of occurrence), followed by fishes in the genus Abudefduf (sergeant-majors; 13.4%), Galapagos ringtail damselfish (Stegastes beebei; 12.7%), scalloped hammerhead shark (Sphyrna lewini; 11.7%), and yellowtail damselfish (Stegastes arcifrons; 10.7%). Prey taxa richness was highest among sharks sampled in the bays of San Cristobal, possibly due to geographic variation in prey availability. Additionally, sharks sampled during a La Niña event in 2021 had higher prey taxa richness than those sampled during an El Niño event in 2023, which could be due to El Niño-induced declines in species richness and abundance resulting from shifts in primary productivity and upwelling. A deeper understanding of shark diets can improve our ability to predict how changes in food web dynamics and prey availability affect shark populations. This knowledge is especially vital in the face of overfishing and climate change, helping to inform more effective conservation strategies and support shark survival.

Data availability

The raw data is available at Figshare: 10.6084/m9.figshare.30359203.

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Acknowledgements

We thank Isabel Silva, Esteban Agudo, Salomé Jaramillo Gil, Mazarine Bruno, Kelly Ong, Emma Rudy Srebnik, Caroline Parker, Sydney Mantell, and Alex Reulbach for their help with the fieldwork and sampling. We also thank our boat captains, Yuri Revelo and Manuel Yépez. Animal care and use were overseen by UNC-CH’s IACUC (23-210.0). Fieldwork and data collection were performed under research permits PC-13-21, PC-18-22, PC-13-23, and MAATE-DBI-CM-2021-0174 granted by the Galapagos National Park and the Ecuadorian Ministry of Environment.

Funding

This study was funded in part by the National Science Foundation (OCE #2128592 to JFB), UNC E3P Graduate Student Research Grant (SJR), the Galapagos Conservancy (EE), and the Save Our Seas Foundation (EE).

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Authors and Affiliations

  1. Environment, Ecology, and Energy Program, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599 − 3275, USA

    Savannah J. Ryburn

  2. Scripps Institution of Oceanography, University of California San Diego, San Diego, CA, 92121, USA

    Eldridge Wisely

  3. Galapagos National Park Directorate, Puerto Ayora, Galapagos Islands, Ecuador

    Eduardo Espinoza

  4. MigraMar, Olema, CA, 94950, USA

    Eduardo Espinoza & Alex Hearn

  5. The Instituto Nacional de Biodiversidad de Ecuador, Quito, Ecuador

    Eduardo Espinoza

  6. Galapagos Science Center GSC, Universidad San Francisco de Quito and University of North Carolina at Chapel Hill, Av. Alsacio Northia, Isla San Cristóbal, Galápagos, Ecuador

    Daniel Armijos & Diana A. Pazmiño

  7. Restoration Center, Office of Habitat Conservation, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Silver Spring, MD, 20910, USA

    Haley E. Capone

  8. Colegio de Ciencias Biológicas y AmbientalesUniversidad San Francisco de Quito USFQ, Diego de Robles y Pampite, Quito, 170901, Ecuador

    Alex Hearn

  9. The Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599 − 3280, USA

    John F. Bruno

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  1. Savannah J. Ryburn
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  2. Eldridge Wisely
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Contributions

*SJR* and *EW* designed the study. *SJR* , *EW* , *EE* , *DA* , *HEC* , and *JFB* collected the samples. *DAP* and *AH* provided the permits. *SJR* and *EW* completed the DNA analysis. *SJR* analyzed the data. The manuscript was written by *SJR* with help from *JFB* . All authors revised the manuscript and gave final approval for publication.

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Savannah J. Ryburn.

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Ryburn, S.J., Wisely, E., Espinoza, E. et al. Biogeographic variation in the diet of juvenile blacktip sharks across the Galapagos Archipelago.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-37386-1

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  • DOI: https://doi.org/10.1038/s41598-026-37386-1

Keywords

  • Diet reconstruction
  • fDNA
  • Cloacal swab
  • ENSO
  • Metabarcoding
  • Carcharhinus limbatus

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