Sexual segregation in the diet of the dimorphic Imperial Cormorant breeding in northern Argentine Patagonia

IBARRA, C.; SUÁREZ, N.; CORTÉS, J.; NAVOA, X.; SILVA, C.; YORIO, P.

Conferencia; 3rd World Seabird Conference; 2021

Knowledge of sexual differences in dietcomposition is key to properly understand aspects of seabird life history,their role in marine food webs, and how human activities such as fisheries maydifferentially affect individuals of each sex. We assessed differences in dietcomposition between male and female Imperial Cormorants (Leucocarbo atriceps)breeding at Islas Blancas (44°46´S, 65°39´W), Argentina. Imperial cormorantsshow sexual size dimorphism, with males being 18% heavier than females. Weobtained stomach samples through induced regurgitation from 60 adultindividuals, 10 of each sex during three stages of the breeding cycle (incubation,small chicks and large chicks) in 2019. At least 11 and 28 prey taxa wererecorded in stomach samples of males and females, respectively. Femalesconsumed a greater diversity of prey species and a significantly higher numberof prey items per stomach content. A two-way crossed analysis of similaritiesshowed significant sex differences in diet composition in terms of numericalfrequency along the breeding cycle. Males mainly consumed demersal species,with Argentine Red Shrimp Pleoticus muelleri (43.6%) and Argentine Hake Merlucciushubbsi (35.9%) being the main prey during incubation, and hake (>77%)the dominant prey during both chick rearing stages. Females preyed upon benthicspecies mostly inhabiting rocky reefs. Prey with higher representation in thediet in the three stages analyzed were the fishes Patagonotothen spp. (30.84%,36.43% and 19.37%). Results show a clear sexual segregation in the diet ofImperial Cormorants, in agreement with studies in other dimorphic seabirds, andalso suggest that sex differences reflect the spatial segregation in feedingbehavior of male and female individuals. Males and females may be playingdifferent roles in coastal food webs and may be differentially affected bycoastal trawl fisheries as hake and shrimp are their main target species.