How Do Narwhals Eat? Feeding Behaviors of Unicorn of The Sea
Narwhals are medium-sized toothed whales that inhabit the frigid waters of the Arctic. They are uniquely adapted to survive and feed in this extreme environment. Narwhals have a very specialized diet, feeding behaviors, and adaptations that allow them to thrive.
Here’s How Narwhals Eat:
Narwhals feed by swimming towards prey and sucking it up by creating a vacuum in their mouths. Their diet consists mainly of Arctic cod, halibut, squid, and shrimp. Narwhals stun small fish with their tusks before eating. They can dive over a mile deep to find food under sea ice.
Diet and Prey
Narwhals have a relatively restricted diet compared to other whales. The most common prey items are Greenland halibut, polar and Arctic cod, shrimp, cuttlefish, and armhook squid. Additional prey found in narwhal stomachs have included wolffish, capelin, skate eggs, and sometimes rocks, accidentally ingested when whales feed near the bottom.
Narwhals change their diet seasonally based on prey availability and distribution. In winter, they feed intensively on bottom-dwelling prey like Greenland halibut and gonatus squid under dense pack ice. During the summer months, narwhals consume more pelagic fish like Arctic cod and capelin. The summer feeding period is less intense overall compared to winter.
The size of prey consumed by narwhals can be up to 2 feet long. However, their relatively small throats and mouths limit the maximum size of prey a narwhal can swallow.
Feeding Methods
Due to having vestigial teeth, narwhals are believed to feed by swimming towards prey until it is within close range. They then suck up their food by creating a vacuum in their mouths. This is similar to how beaked whales feed.
Underwater footage has shown narwhals stunning small fish with their tusks before eating them. The tusk likely helps immobilize prey, making it easier to swallow. However, the exact role of the tusk in feeding remains uncertain.
Narwhals have flexible necks which allow them to scan large areas of the seafloor for potential prey. Their flexible rib cages also enable deep dives in search of food. Once prey is detected, narwhals use echolocation clicks and buzzing sounds to continuously visualize it until moments before striking.
Diving and Foraging Behavior
Narwhals make some of the deepest dives of any cetacean, plunging over a mile deep to find food. Their flexible rib cages and ability to withstand tremendous water pressure allow narwhals to feed at extreme depths.
During winter months, narwhals dive and feed under dense, coastal pack ice. They create breathing holes in the ice to access the air. In summer, they migrate to offshore open waters to forage.
Narwhals can spend entire months underneath packed sea ice with less than 3% open water access. Their blubber insulation allows them to withstand frigid water temperatures. Some adaptations like countercurrent heat exchange in their flippers help retain body heat.
When foraging, narwhals emit frequent echolocation clicks to detect prey. Just before striking, they produce a buzzing vocalization. Listening devices have recorded these sounds during presumed feeding dives.
Competition and Predation
Narwhals occupy a narrow ecological niche in the Arctic marine ecosystem. Their highly specific diets and distributions likely help avoid competition with other whales like belugas. Belugas tend to be more generalized feeders.
Polar bears and orcas are the main natural predators of narwhals. Their tusks may function as sensory organs to detect changes in water chemistry that could indicate the presence of predators. Avoiding predators in the water may be why narwhals spend so much time sheltered under ice.
In some regions, narwhals are still hunted by indigenous Arctic peoples for subsistence. However, hunting levels are not believed to threaten current population numbers. Climate change and receding sea ice pose greater long-term risks.
Adaptations for Arctic Living and Feeding
To thrive in brutally cold Arctic waters, narwhals have evolved a number of specialized adaptations:
Blubber and Insulation
- Narwhals have a thick blubber layer, comprising up to 50% of their body mass.
- The blubber insulates vital organs and helps retain body heat.
- Countercurrent heat exchange in their flippers also prevents heat loss.
Diving Physiology
- Flexible rib cages allow their bodies to be highly compressed at depth.
- Physiological adaptations help them cope with extreme water pressure.
- Efficient oxygen use allows dives over 25 minutes long.
Sensory Organs
- Their tusks have millions of nerve endings to detect prey and changes in water chemistry.
- Narwhals echolocate with clicks and buzzing to find food and navigate.
- Flexible necks give them a wide visual field to spot prey.
Diet and Feeding
- Specialized diet of a few Arctic fish and invertebrate species.
- Vestigial teeth and vacuum suction allow them to swallow prey whole.
- Minimal feeding in summer, relying more on fat stores.
Behavior
- Spend months underneath dense, coastal sea ice each winter.
- Migrate along ice edges to access open water for summer feeding.
- Tusks may help stun prey, making it easier to consume.
Habitat
- Occupying deep Arctic waters year-round.
- Following seasonal advance and retreat of pack ice.
- Rely on sea ice for shelter, breathing holes, and access to prey.
How Do Narwhal Calves Feed and Develop?
Narwhal calves are born in coastal summering grounds after 14-16 months of gestation. They emerge already equipped with a thick blubber layer to endure frigid waters.
Newborn calves are nearly 5 feet long and weigh around 150 pounds. They suckle milk from their mothers for about 20 months until being weaned.
Young narwhals likely begin eating solid foods like shrimp, Arctic cod, and squid after several months. Their milk teeth help grip slippery prey until permanent tusks develop. Weaning coincides with the eruption of adult tusks used for stunning larger prey.
Calves continue growing rapidly on a diet of fat-rich Arctic fish and invertebrates. Adult size is attained between 5-8 years old for females and 8-12 years for males. Lifelong accumulation of blubber reserves helps prepare narwhals for the extreme feeding conditions they will endure.
How Does Climate Change Affect Narwhals and Their Prey?
Narwhals rely heavily on sea ice for survival. But climate change is causing rapid melting and loss of Arctic sea ice due to rising temperatures.
Less sea ice allows more ship traffic and chances for sound pollution that may disrupt feeding. Receding ice also opens up new areas to predators like orcas.
A warmer, less icy Arctic Ocean could force narwhals to alter their migrations and distributions. The impacts on their specialized diets are still unknown. But prey like Greenland halibut and polar cod may decline without cold, ice-covered habitat.
If key prey species shift locations or decrease in abundance, narwhals cannot easily switch to new food sources. Their highly specific diets give them little flexibility. Starvation and lower calving rates could occur.
To help track and understand the effects of climate change on narwhals, scientists satellite-tag individuals to follow their movements and feeding patterns. This research will provide insight into how well narwhals can adapt as their frigid realm warms.
Conclusion
Narwhals possess unique adaptations enabling them to dive over a mile deep and feed year-round in ice-covered Arctic waters. Their specialized diets, insulated blubber layers, flexible rib cages, heat-retaining physiology, and sensory tusks allow narwhals to exploit a narrow niche.
Climate change threatens the sea ice habitat narwhals rely on for shelter and access to prey. Continued research into their ecology and behavior will help predict the impacts of a warming Arctic on these elusive unicorns of the sea. Tracking narwhal responses also provides a key indicator for the health of the broader polar ecosystem.
References
- Understanding narwhal diving behaviour using Hidden Markov Models with dependent state distributions and long range dependence. Search NCBI databases. Retrieved February 6, 2024, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6417660
- Narwhal. NOAA Fisheries. Retrieved February 6, 2024, from https://www.fisheries.noaa.gov/species/narwhal
