Is Gillnet Prey Subsidizing Ontogenetic Diet Shifts and Early Weaning in Common Coastal Bottlenose Dolphins From the Southwestern Gulf of Mexico?

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ABSTRACT Artisanal gillnet fisheries can concentrate prey and provide incidental food subsidies to marine predators, but their effects on early‐life foraging behavior and demography remain poorly resolved. The Alvarado bottlenose dolphin population that lives off the coast of Veracruz, Mexico, is well known for having chronic, frequent, and recurring interactions with artisanal gillnet fisheries. Thus, we searched for ontogenetic shifts in early life stages for these dolphins using long‐term (2002–2023) mother‐calf photo‐ID sighting histories ( N = 14 females and N = 23 calves), isotopic data (δ 13 C and δ 15 N) from growth layer groups in teeth from eight dead stranded individuals (1993–2017) and fresh caught fish ( N = 123 from 25 prey species captured in 2009–2010 and 2015–2019) to understand how this population may exploit this anthropogenic foraging niche. We found short dependency periods (mean = 2.6 years), indicating an early transition from maternal provisioning to independent foraging, consistent with dentin chronologies showing lower δ 13 C and δ 15 N values in calves (0–2 years) versus juveniles (3–5 years). A Bayesian SIARMix model showed wide intervals that strongly overlapped among dolphin developmental stages, possibly due to the low number of dolphin samples; however, it suggests a directional shift from diets dominated by estuarine‐associated prey in calves, without discarding the isotopic effect of milk, towards a more mixed use of estuarine and non‐estuarine (i.e., reef, pelagic and demersal) fish in juveniles. This was also the case for the most commonly captured fish species, which showed a consistent reduction of their proportion across developmental stages, suggesting a progressive shift from fishery‐related food items to more independent exploitation of less common prey as juveniles matured. Our study shows how small‐scale fisheries may contribute to ontogenetic diet transitions and life‐history pacing in coastal cetaceans, with direct implications for conservation of heavily exploited tropical estuaries.

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