Sexual mismatch between vessel-associated foraging and discard consumption in a marine top predator [SIA dataset]

Paper:Giménez et al. (2021) Sexual mismatch between vessel-associated foraging and discard consumption in a marine top predator. Frontiers in Marine Science.

Dataset:Stable Isotope data from northern gannets breeding in Great Saltee Island, Co. Wexford, Ireland (52.10933o N, 6.62213o W). Years 2010, 2011, 2017, 2018, 2019.

Abstract:
Sex-based differences in diet and foraging strategy are common in sexually dimorphic species, often driven by differences in cost of locomotion or ability to exploit different ecological niches. However, sex-specific foraging strategies also occur in monomorphic or slightly dimorphic species where the drivers are poorly understood. Here, we study sex-based differences in foraging strategy of Northern gannets (Morus bassanus), where females are only slightly larger than males. Using concurrently tracked gannets and fishing vessels across five years, we quantify individual-based vessel-associated putative foraging, and relate this to consumption of fishery discards. We found a significant positive relationship between time spent in vessel-associated foraging and discards consumption for both sexes. However, while females showed greater proportions of vessel-associated foraging than males, discarded fish contributed less to the diet of females in all years. These results contrast with previous suggestions that female gannets interact with vessels less than males, and results are consistent with competitive exclusion of females from trawler-associated discards. Our findings give insight into sexual differences in foraging behaviour in the absence of dimorphism that are necessary to predict their response to environmental and anthropogenic changes.