Abstract
At least 626 southern right whale (Eubalaena australis) calves died at the Península Valdés calving ground, Argentina, between 2003 and 2014. Intense gull harassment may have contributed to these deaths. In the 1970s, Kelp Gulls (Larus dominicanus) began feeding on skin and blubber pecked from the backs of living right whales at Valdés. The frequency of gull attacks has increased dramatically over the last three decades and mother-calf pairs are the primary targets. Pairs attacked by gulls spend less time nursing, resting and playing than pairs not under attack. In successive attacks, gulls open new lesions on the whales’ backs or enlarge preexisting ones. Increased wounding could potentially lead to dehydration, impaired thermoregulation, and energy loss to wound healing. The presence, number and total area of gull-inflicted lesions were assessed using aerial survey photographs of living mother-calf pairs in 1974–2011 (n = 2680) and stranding photographs of dead calves (n = 192) in 2003–2011. The percentage of living mothers and calves with gull lesions increased from an average of 2% in the 1970s to 99% in the 2000s. In the 1980s and 1990s, mothers and calves had roughly equal numbers of lesions (one to five), but by the 2000s, calves had more lesions (nine or more) covering a greater area of their backs compared to their mothers. Living mother-calf pairs and dead calves in Golfo Nuevo had more lesions than those in Golfo San José in the 2000s. The number and area of lesions increased with calf age during the calving season. Intensified Kelp Gull harassment at Península Valdés could be compromising calf health and thereby contributing to the high average rate of calf mortality observed in recent years, but it cannot explain the large year-to-year variance in calf deaths since 2000.
Highlights
An individual's health and reproductive success may be strongly affected by many environmental stressors
Most calving events usually occur in August for the southern right whale population that calves off Península Valdés, Argentina, [11] and mother-calf pairs usually stay on this calving ground for approximately three months before migrating to their feeding grounds [12]
Almost all known observations of gull harassing right whales have have ocurred at Península Valdés
Summary
An individual's health and reproductive success may be strongly affected by many environmental stressors. Southern right whales (Eubalaena australis) usually migrate from their high-latitude feeding grounds in the summer to their low-latitude calving grounds in the winter where females give birth to their calves after a year of gestation [10]. Most calving events usually occur in August for the southern right whale population that calves off Península Valdés, Argentina, [11] and mother-calf pairs usually stay on this calving ground for approximately three months before migrating to their feeding grounds [12]. Unusual high calf mortality events have occurred in this population. From 2003 to 2014, at least 626 calves died at Península Valdés with an average of more than 50 deaths per year [15,16,17] Fig 1. Despite considerable research effort since 2003, the cause(s) of the recent high-mortality events remain undetermined [15,18]
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