Comportamento alimentar parasita de gaivotas (Larus dominicanus) em baleias Franca-Austrais (Eubalaena australis) na Península Valdés, Argentina

Abstract

Southern Right Whales (Eubalaena australis) were close to extinction in the 20th century, however, after protective measures, their numbers began to rise, contributing to the stability of the population. Seagulls and whales have always had a commensalist association, where the former fed on cyamids that colonize the natural calluses present in these. However, in 1972 a change in the interaction between both species was observed. Seagulls (Laurus dominicanus) started to have a predatory behavior in relation to whales, pecking and injuring the loins of females and their young, which changed their behavior. Trying to mitigate the damage caused by these attacks, the government of Puerto Madryn, Chubut, Argentina, carried out a sanitary extermination of attacking gulls in 2012 and the closure of the open-air dump in 2015(EL DIARIO DE MADRYN, 2014). It was seen that the attacks did not decrease, probably because the attacking gulls were replaced by others. This created a gap regarding the outcome of this measure and the persistent occurrence of attack interactions. Thus, the objective of this work was to evaluate whether the rates of attacks by seagulls on whales increased after the extermination during the 2021 season. Data were collected from July to November 2021, using a 20- 60X. The sweeping and animal focal methodology was applied (ALTMANN, 1974) 2262 attacks were recorded, on 4735 whales, in a total of 95 hours and 37 minutes of observation. Puppies had a higher frequency of attacks (n=1699) compared to adults (n=563; p< 0.001). The attack rate was higher in July and August (84 and 70 attacks/hour, respectively) compared to September and October (22 and 15 attacks/hour). The percentage of attacks was higher than in previous years (53.3% in 2021, compared to 21.66% in 2005, 17.19% in 2006, 18.78% in 2007 and 30.03% in 2008). Between 2005 and 2008, 51.8% of attacks were on mothers with puppies and in 2021, 75.1% of them were directed at puppies. In this way, the data show that the decrease in the larus dominicanus population did not promote a reduction in their predatory behavior in relation to Southern Right whales.