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.

Ocean Regime Shift is Driving Collapse of the North Atlantic Right Whale Population

“…However, it failed to protect whales effectively the following summer, likely because scientists and managers lacked a sufficient understanding of the population's behavioral responses to further changes in ocean conditions within the southern Gulf of St. Lawrence. Ironically, birth rates remained low following the shift to summer foraging in the Gulf of St. Lawrence (Figure 2d), indicating that this habitat may not have adequate prey to support successful reproduction (Gavrilchuk et al, 2021).…”

Environmental conditions and marine heatwaves influence blue whale foraging and reproductive effort

“…While these impacts of marine heatwaves have been documented across ecosystems and regions, the link to reproductive success in baleen whales has remained a gap in knowledge. Environmental fluctuations and reduced foraging are known to impact population health in multiple baleen whale species, including blue (Pirotta et al, 2019), gray (Lemos et al, 2021;Soledade Lemos et al, 2020), and right (Gavrilchuk et al, 2021;Seyboth et al, 2016) whales. While we could not investigate population vital rates with the data at-hand, the information on blue whale call function gained through this study enabled us to postulate a connection between are expected to increase in intensity and duration, including potentially annually persistent marine heatwave conditions by the end of the century under some greenhouse gas emissions scenarios (Behrens et al, 2022).…”

“…Yet a handful of recent studies have correlated decreased reproductive output with reduced foraging, by either measuring or modeling population demographic parameters. Recent diminishing prey resources appear to be insufficient to support reproduction for North Atlantic right whales, likely contributing to low calving rates (Gavrilchuk et al, 2021 ). Southern right whale reproductive success is correlated with global climate indices and the density of their prey (Seyboth et al, 2016 ).…”

Key questions in marine mammal bioenergetics

“… Fortune et al, 2013 ; Chasco et al, 2017 ; McHuron et al, 2020 ; Acevedo and Urbán, 2021 ) and predict the individual- and population-level effects of altered environments on marine mammals (e.g. Christiansen and Lusseau, 2015 ; Udevitz et al, 2017 ; Nabe-Nielsen et al, 2018 ; Farmer et al, 2018b ; Pirotta et al, 2019 ; Gallagher et al, 2020 ; Silva et al, 2020 ; Gavrilchuk et al, 2021 ). Technological and analytical advances have furthered these empirical and modelling methodologies ( Pirotta, 2022 ).…”