Feeding ecology, gull harassment and reproductive success of female Southern right whales

Many factors can affect reproductive success in animals. In marine mammals, both nutritional and environmental stresses have been shown to influence maternal fertility and offspring survival. The southern right whales (Eubalaena australis) that calve off Península Valdés, Argentina, have experienced increased rates of calf death since 2003, but the cause(s) of this elevated mortality remain unknown. My research addresses the possible effects of diet and Kelp Gull harassment on the reproductive success of the whales. This study also provides novel insights into the diet composition, patterns of fattening, behavior, and reproductive life histories of right whales. I first asked whether dead calves show a reduced proportion of fatty acids that are essential for calf growth, but I found no evidence to support this hypothesis. Then, I asked whether mothers of dead calves feed in different feeding grounds than mothers of living calves, but I found no significant differences among the two groups. Third, I investigated the diet composition of whales, and found that some mothers rely more than others on certain copepod species. Next, I asked whether the body fat condition of calves worsens in years with high calf mortality, or in calves with more gull-inflicted lesions. I found no evidence to suggest a decline in the body fat condition of calves. Then, I evaluated how blubber thickness changes with calf growth and found that calves acquire a more streamlined body shape as they age. I asked whether the incidence of gull-inflicted lesions in mothers and calves has increased in the 2000s (coincidentally with calf deaths). The numbers and areas of lesions in calves have increased greatly compared to mothers, suggesting that the health of nursing calves could be compromised if wounding continues to increase. Finally, I investigated the occurrence of abnormal calving intervals and found that they increase significantly in years of high calf mortality compared to years of low mortality. I modeled the potential effects of a sustained increase in calf deaths and found that if elevated rates of calf mortality continue for some years, the population’s growth could be slowed substantially.