Foraging habitat of North Atlantic right whales has declined in the Gulf of St. Lawrence, Canada, and may be insufficient for successful reproduction

Abstract

Climate-induced changes in calanoid copepod (Calanus spp.) availability in traditional feeding areas might explain why a large proportion of the North Atlantic right whale Eubalaena glacialis population has fed in the Gulf of St. Lawrence (Canada) in recent years. However, little is known about the distribution of copepods in the gulf, and whether their abundance is sufficient to energetically sustain right whales. We used a mechanistic modelling approach to predict areas within the gulf that have foraging potential for adult female right whales, based on the annual energetic needs of resting, pregnant and lactating females, and their theoretical prey density requirements. We identified suitable foraging areas for right whales by coupling a foraging bioenergetics model with a 12 yr data set (2006-2017) describing the abundance and 3-dimensional distribution of late-stage Calanus spp. in the gulf. Prey densities in the southern gulf (from Shediac Valley to the Magdalen Islands) supported all 3 reproductive states in most (≥6) years. However, foraging habitat became progressively sparse in the southern gulf over time, with noticeably less suitable habitat available after 2014. Few other potentially suitable foraging areas were identified elsewhere in the gulf. Overall, the availability of foraging habitat in the gulf varied considerably between years, and was higher for resting females than for pregnant and lactating females. Our findings are consistent with the recent low calving rates, and indicate that prey biomass in the Gulf of St. Lawrence may be insufficient in most years to support successful reproduction of North Atlantic right whales.