Interannual variation in the stable isotope differences between mothers and their calves in southern right whales (Eubalaena australis)

• Main Authors: Valenzuela, L.O., Sironi, M., Rowntree, V.J.
• Format: Journal/Newspaper
• Language: unknown
• Subjects: Eubalaena australis; Fractionation; Mother-calf pairs; Nutrition; Southern ocean; Southern right whales; Stable isotopes; annual variation; carbon isotope; food availability; hypothesis testing; isotopic fractionation; isotopic ratio; juvenile; lactation; nitrogen isotope; nutrient availability; parent-offspring interaction; stable isotope; whale; Cetacea; Mammalia; Southern Ocean; Southern Right Whale
• Online Access: https://hdl.handle.net/20.500.12110/paper_01675427_v36_n2_p138_Valenzuela

Lactation is the most energetically expensive aspect of mammalian reproduction. As capital breeders, lactating southern right whales (Eubalaena australis) are completely dependent on their stored nutrients. The relative proportion of different endogenous nutrient pools used during lactation could be assessed using stable isotopes. We determined the stable carbon and nitrogen isotope difference between skin samples of 42 southern right whale mothers and their calves. The mean δ15N value of calves was 0.51‰ higher than that of their mothers, but their δ13C values were identical. However, when analyzed by year, the mother-calf pairs showed no isotope differences in 2004, but calves had higher δ15N (0.85‰) and δ13C (0.63‰) in 2003 and 2005. We hypothesize that the inter-annual variability was a consequence of different levels of nutritional stress. A decline in food abundance prior to the nursing seasons could result in mothers with relatively poorer physical condition that would not be able to meet the high energetic demands of their offspring. Thus, the calves would be forced to utilize proteins as well as lipids to meet this demand, increasing their nitrogen and carbon isotope ratios. This hypothesis is supported by an independent assessment of the proportion of stranded whales over the same time period.