Availability, supply, and aggregation of prey (Calanusspp.) in foraging areas of the North Atlantic right whale (Eubalaena glacialis)

Abstract

The North Atlantic right whale (NARW), Eubalaena glacialis, resides primarily on western North Atlantic continental shelves where this endangered species is susceptible to vessel strike and entanglement in fishing gear. Mitigation of these threats is dependent on the ability to predict variations in NARW occurrence. North of the Mid-Atlantic Bight, the distribution of NARWs is influenced by their prey, mainly copepods of the genus Calanus. We review factors that promote suitable foraging habitat from areas where NARWs have been observed feeding. We then synthesize our findings within a conceptual framework in which availability (i.e. shallow prey depth), supply, and aggregation of prey occur together to facilitate suitable foraging habitat. By definition, the depth of prey on the shelf is constrained to ≤200 m and other mechanisms may occur locally that further enhance prey availability. Enhanced production of prey occurs in coastal currents, which transport the copepods to NARW foraging areas. Prey concentrating mechanisms are not well-characterized. Information gaps that impede rapid and dynamic prediction of suitable foraging habitat include limited data on the spatial and temporal variation of prey and environmental conditions at local scales (i.e. 0.1–1 km), motility of prey, and diving behaviour of NARWs.

Individual North Atlantic right whales identified from space

“…The environment and right whale behavior in Cape Cod Bay are generally conducive to space-based whale detection, as the bay is sheltered and the whales congregate and often skim-feed at the surface or socialize in Surface Active Groups (Kraus et al, 2007) here. However, most other parts of the whales' migratory range are less sheltered, the whales are found in lower densities, and spend less time at the surface where they can be observed (Sorochan et al, 2021). The potential for more widespread and systematic space-based right whale monitoring thus depends on the ability to detect the whales in these less optimal conditions, an ability which will likely be directly improved by an increase in available spatial resolution such that it becomes easier to differentiate whales from waves and other marine objects.…”

Highly variable basking shark (Cetorhinus maximus) diving behavior in the lower Bay of Fundy, Canada

“…Nonetheless, stage V C. finmarchicus abundance has declined in the eastern Gulf of Maine and Scotian Shelf (Sorochan et al, 2019), areas where most of the Bay of Fundy advection originates, and have resulted in declines in late season stage V C. finmarchicus in the Bay of Fundy (Record et al, 2019). It is reasonable to assume basking sharks may undergo a distributional shift as North Atlantic right whales have done, either to Cape Cod Bay where C. finmarchicus abundance remains high (Sorochan et al, 2019) or poleward to the Gulf of St. Lawrence (Sorochan et al, 2021), should the climatic changes in the western North Atlantic continue (Pershing et al, 2021). Given the intense historic climate changes that have occurred in the 100 million years since Cetorhinidae split from Lamnidae (Sorenson et al, 2014), it is perhaps reasonable to assume the species will weather coming changes.…”

“…Additionally, this variability co-occurs with variability in the stage V copepod biomass development within the bay (Sorochan et al, 2019). The strength of the phytoplankton bloom both within and outside the bay dictates the growth and survival of stage V C. finmarchicus throughout the Gulf of Maine -Scotian Shelf ecosystem (Plourde et al, 2019;Sorochan et al, 2019) while current advection determines the physical accumulation of diapausing, energy-rich copepods in the Bay of Fundy (Sorochan et al, 2021)s.…”

The distribution of North Atlantic right whales in Canadian waters from 2015-2017 revealed by passive acoustic monitoring

“…The ability of NARWs to meet their metabolic requirements is critically dependent on the presence of high-density patches of their prey (Baumgartner et al, 2007). These prey aggregations are influenced by processes that affect supply (e.g., advection, production; Sorochan et al, 2021). Climate change is altering these processes dramatically in the North Atlantic, which is affecting the spatial and temporal variation of prey abundance (Richardson, 2008;Grieve et al, 2017;Record et al, 2019;Pershing and Stamieszkin, 2020).…”