Behavioral and Foraging Pattern of Sharks across Oxygen Minimum Zones in The North Atlantic Ocean: Using Blue (Prionace glauca) and Shortfin Mako (Isurus oxyrinchus) Sharks as Model Species

Abstract

Climate change is thought to increase the vertical and horizontal expansion of oxygen minimum zones, either compressing the vertical habitat of pelagic fish or causing a shift in their distribution. However, it is unclear how these affect their foraging behaviour and prey-predator interactions. This study provides high-quality information on the movement, behaviour, and habitat preferences of blue sharks (Prionace glauca) and shortfin mako sharks (Isurus oxyrinchus) to oxygen minimum zones using satellite tags (PSATs) and environmental models, as well as in situ data in the central north and eastern tropical Atlantic. The comparison between oxygen modelled and in situ data showed no significant difference (p=0.07) in the ETA-OMZ. In contrast, the oxygen concentrations of both datasets in the North and South Atlantic showed significant differences (p=0.04). The combination of various factors, which include ocean warming and ocean deoxygenation associated with climate change, has contributed to the vertical habitat compression of blue and mako sharks’ habitats and increased their vulnerability to fishing. Results showed how the maximum diving depth of sharks responds specifically to different dissolved oxygen gradients. Spatiotemporal occupancy of blue and mako sharks was associated with oceanographic fronts, foraging and prey-predator interactions along Cape Verde’s EEZ and Western Sahara. Additionally, the Mako shark’s occupancy of Western Sahara has been attributed to a high concentration of chlorophyll-a that overlaps with high pelagic longline fishery activities. As the global status of these model species continues to decline, conservation and management measures offshore need to be implemented.