Some like it cold: Temperature-dependent habitat selection by narwhals.

Area of Science:

• Marine Biology
• Arctic Ecology
• Animal Behavior

Background:

• Narwhals (Monodon monoceros) are high-Arctic marine predators.
• Arctic ecosystems face rapid environmental changes, including rising sea temperatures and reduced sea ice.
• These changes impact apex predators like narwhals.

Purpose of the Study:

• To investigate the habitat use and thermal niche of narwhals in East Greenland.
• To understand how narwhals select foraging grounds based on temperature and depth.
• To assess the sensitivity of narwhals to changing thermal conditions.

Main Methods:

• Satellite-linked transmitters (Fastloc-GPS) tracked whale movements.
• Time-depth recorders and Acousonde™ recorders collected diving and temperature data.
• Hydrographic profiles provided detailed environmental data.

Main Results:

• Narwhals foraged in specific depth ranges (300-850 m) with preferred temperatures between 0.6-1.5°C.
• Buzzing activity, indicative of foraging, was concentrated at colder temperatures (around 0.7°C) and depths >300 m.
• Whales actively selected cold coastal waters and avoided warmer offshore Atlantic water, especially in winter.

Conclusions:

• Narwhals exhibit a narrow thermal niche for foraging, preferring cold waters.
• This preference suggests potential vulnerability to rising sea temperatures due to climate change.
• Strong site fidelity combined with specific thermal requirements emphasizes the sensitivity of narwhals to habitat alterations.