Behavioural thermoregulation linked to foraging in blue sharks

Area of Science:

• Marine Biology
• Animal Behavior
• Physiology

Background:

• Large pelagic fishes exhibit diving and surfacing behaviors, prompting questions about their function.
• Some species alternate deep-water foraging with shallow-water rewarming.
• Blue sharks possess wide-ranging vertical niches, making them ideal for studying foraging-thermoregulation links.

Purpose of the Study:

• To investigate the foraging and thermoregulation strategies of blue sharks.
• To determine if blue sharks alternate foraging and rewarming behaviors.
• To understand the mechanisms behind their expanded thermal niches.

Main Methods:

• Electronic tags, including video cameras, were used to record diving behavior, muscle temperature, and foraging events in two blue sharks.
• Muscle temperature changes were monitored during deep dives (max. 422 m).
• Swimming events were detected and analyzed across various depths.

Main Results:

• Blue shark muscle temperature changed slowly during deep dives, with sharks ascending before reaching ambient temperature.
• Muscle temperature varied within an 8°C range, narrower than the ambient 20°C range.
• Foraging events, including squid capture, and burst swimming were recorded across a wide depth range (5–293 m).

Conclusions:

• Blue sharks forage and thermoregulate continuously within the water column, rather than alternating between deep and shallow waters.
• Their heat exchange rates are not exceptional for their body size.
• Behavioral thermoregulation associated with foraging is the primary driver of their expanded thermal niches.