MEPS 657:223-239 (2021)  -  DOI: https://doi.org/10.3354/meps13543

ABSTRACT: Knowing the biomass of prey consumed by a marine predator is a prerequisite for assessing the potential of the predator for competition with fisheries. Here, we estimated the biomass of Fuegian sprat Sprattus fueguensis consumed annually by a small subpopulation of humpback whales Megaptera novaeangliae in the Magellan Strait feeding area. We used a velocity-dependent bioenergetic model that integrates annual energy requirements by sex, age class, and reproductive status, proportion of Fuegian sprat in the diet, and annual population size of whales. The annual energy required in kcal per individual whale was estimated to be 18.88 × 10⁷ for calves, 27.92 × 10⁷ for adults, 30.71 × 10⁷ for pregnant females, and 42.59 × 10⁷ for lactating females. These estimates result in an energy requirement of 19.32 × 10⁹ and 23.41 × 10⁹ for a seasonal abundance of 78 and 96 whales, respectively. Bayesian dietary mixing models predict that Fuegian sprat represented between 27 and 33% of the diet of the whales. This implies that humpback whales remove between 2965 and 3896 t of Fuegian sprat per year during a feeding period of 120 d. However, if estimates are extended to an abundance of 204 humpback whales during the period 2004-2017, the consumption is elevated to 8167-8383 t yr^-1. The estimates provided here are useful to apply as input data for consumption by humpback whales in the Fuegian sprat fishery management as well as for conservation plans of this small and vulnerable feeding subpopulation of humpback whales.

KEY WORDS: Bioenergetic model · Prey consumption · Humpback whale · Megaptera novaeangliae · Fuegian sprat · Sprattus fueguensis · Magellan Strait