Gray whales are amazing marine mammals that can grow up to 15 meters (50 feet) long and weigh up to 36 tons.
They are known for their long migrations between their breeding grounds in Mexico and their feeding grounds in the Arctic.
However, not all gray whales follow the same route.
A new study by researchers from Oregon State University has revealed that a subgroup of gray whales that feed along the Pacific Northwest coast are smaller than their counterparts who travel farther north to forage.
How did the researchers measure the size of the whales?
GUILLERMO ARIAS/AFP via Getty Images
The researchers used a combination of photo identification, fecal sampling, and drone imagery to study the size and health of gray whales in the Pacific Northwest, as per Phys.org.
They focused on a subgroup of gray whales known as the Pacific Coast Feeding Group, which consists of about 200 individuals that spend their summers feeding in coastal waters of Oregon, California, Washington, and Canada.
These whales are different from the larger group of Eastern North Pacific gray whales, which number about 16,000 and migrate to the Arctic for food.
The researchers collected data from 2015 to 2019, during which they identified individual whales based on their unique markings, determined their sex and age from their fecal samples, and measured their length, skull size, and fluke size from their drone images.
They compared these measurements with those of Eastern North Pacific gray whales from previous studies.
The results showed that Pacific Coast Feeding Group whales were significantly smaller than Eastern North Pacific whales.
The females were about three feet (one meter) shorter, and the males were about 1.5 feet (0.5 meter) shorter.
The Pacific Coast Feeding Group whales also had smaller skulls and flukes, which are important for feeding and swimming.
The researchers suggested that the smaller size of Pacific Coast Feeding Group whales could be related to their different diet and habitat.
These whales feed mainly on mysids, which are small shrimp-like crustaceans that live near the seafloor.
Mysids are less abundant and nutritious than amphipods, which are larger crustaceans that live in the Arctic and are the main food source for Eastern North Pacific whales.
The Pacific Coast Feeding Group whales also face more competition and disturbance from other marine animals and human activities in their coastal habitat.
The researchers concluded that Pacific Coast Feeding Group whales have adapted to a different ecological niche than Eastern North Pacific whales, which may have implications for their conservation and management.
They also noted that their study provides a rare example of body size variation within a single whale population.
Body size variation in whales may be influenced by several factors, such as food availability, predation pressure, thermoregulation, reproduction, and phylogeny.
Different whale species may have different optimal body sizes depending on their ecological niche and evolutionary history.
Food availability is one of the main factors that affects body size in whales, as larger whales can consume more food and store more energy than smaller whales.
However, food availability also depends on the type and distribution of prey, which may vary across regions and seasons.
For example, baleen whales that feed on krill and other plankton may have larger body sizes than toothed whales that feed on fish and squid, as plankton are more abundant and widespread than fish and squid.
However, some toothed whales, such as sperm whales, can also achieve large body sizes by feeding on deep-sea prey that are less accessible to other predators.
