The fin whale, scientifically known as Balaenoptera physalus, is the second-largest whale species on Earth, surpassed only by the blue whale. These magnificent creatures are found throughout the world’s oceans, from the Arctic to the Antarctic, and are known for their streamlined bodies and unique feeding behaviors. This article delves into the diet and feeding habits of fin whales, exploring what they eat, how they feed, and the factors that influence their foraging strategies.
Physical Characteristics and Distribution
Fin whales have sleek, streamlined bodies with V-shaped heads, allowing them to swim at speeds up to 20 miles per hour, earning them the nickname "greyhound of the sea." They have a tall, hooked dorsal fin, about two-thirds of the way back on the body, that rises at a shallow angle from the back. Fin whales have distinctive coloration-black or dark brownish-gray on the back and sides and white on the underside. Head coloring is asymmetrical-dark on the left side of the lower jaw, white on the right-side lower jaw, and the reverse on the tongue. Many fin whales have several light-gray, V-shaped “chevrons” behind their heads; on many of them, the underside of the tail flukes is white with a gray border. Adult fin whales can reach approximately 60 to 80 feet (18 to 24 meters) in length and weigh 40 to 80 tons. Fin whales are typically found in deep, offshore waters of all major oceans, primarily in temperate to polar latitudes, but they are less common in the tropics. They occur year-round in a wide range of locations, but the density of individuals in any one area changes seasonally. Most migrate from the Arctic and Antarctic feeding areas in the summer to tropical breeding and calving areas in the winter.
Diet and Prey
Fin whales are baleen whales, which means they feed by filtering small fish and krill through their baleen plates. Their diet consists mainly of small schooling fish, squid, and krill. They are known to feed on a variety of prey, including krill, copepods, squid, and small schooling fish (including herring, capelin, and sand lance).
Krill
Fin whales consume large quantities of krill - small shrimp-like crustaceans found in cold, nutrient-rich waters. Krill is a primary food source for fin whales, especially in the Antarctic, where their prey is almost exclusively krill. In the southern hemisphere its primary food is krill. Arctic krill is also an important prey for fin whales feeding in the Gulf of St. Lawrence, representing on average 56% of the diet in 1992-2010.
Small Schooling Fish
Fin whales also feed on various species of schooling fish, such as herring, mackerel, capelin, and sand lance. In northern areas they often eat small schooling fish such as herring or anchovies. Eastern north Pacific fin whales spend the summer months feeding in the waters of Alaska, where they eat euphasiids (krill), copepods, and small schooling fish like herring and capelin.
Read also: Bowhead Whale Feeding
Other Prey
While krill and small fish constitute the bulk of their diet, fin whales are also known to consume copepods, amphipods, and squid.
Feeding Techniques
Fin whales are efficient predators, capable of engulfing large volumes of water containing their prey during each feeding lunge. They typically feed by lunging into schools of prey with their mouth open, using their 50 to 100 accordion-like throat pleats to gulp large amounts of food and water. When a fin whale takes a gulp, water rushes in to fill its ventral pouch at a rate of 20 m3/s. After just six seconds, it closes its mouth, which then contains about 70,000 litres of seawater! They then filter the food particles from the water, using the 260 to 480 baleen plates (long, flat plates made of fingernail-like material called keratin) that they have in place of teeth on each side of the mouth. Like other baleen whales, fin whales also skim the water, taking in huge volumes of water. When they close their mouths, the water is pushed out through the baleen and the prey is caught on the inside of the baleen. Each filtering allows a fin whale to engulf 10 kg of food, and a single individual can consume up to 1,800 kg a day. It is first the brain that receives information from the vibrissae located on the fin whale’s mouth, which serve to detect prey in the water.
Migration and Feeding
Fin whales undertake some of the longest migrations of any mammal, traveling up to 15,000 miles each year. Most migrate from the Arctic and Antarctic feeding areas in the summer to tropical breeding and calving areas in the winter. They typically migrate from their summer feeding grounds in polar regions to their winter breeding grounds in temperate and tropical waters. Fin whales fast in the winter while they migrate to warmer waters. For most large whales, the calves are born during the part of the annual cycle when the animals are in warmer waters, and the adults are not feeding.
Individual Specialization and Dietary Niche
Dietary niche varies among species largely as a result of evolutionary processes. However, optimal foraging theory and the niche concept predict feeding strategies to be continuously affected by resource availability or quality. The adaptive capacity of a population to changing resources depends on the degree of individual specialization within the population, with specialist feeders typically expected to be less adaptivethan in generalist feeders. A variety of factors likely influence the degree of individual specialization within a population, including intra- and interspecific competition, and food web complexity. Individual specialization may also arise from an ecological “opportunity” created for instance, by the increase of a novel and valuable resource or conversely, by an increase in competition for a shared resource. In the face of the major changes currently observed in the trophic structure of northern ecosystems with the “Atlantification” of Arctic ecosystems, a widening of the trophic niche of the population through diet specialization of individuals on different prey might represent an efficient strategy to cope with these changes.
A study examined skin biopsies from 99 fin whales sampled in the St. Lawrence Estuary (Canada) over a nine year period (1998-2006) during which environmental change was documented. An abrupt change in fin whale dietary niche coincided with a decrease in biomass of their predominant prey, Arctic krill (Thysanoessa spp.). This dietary niche widening toward generalist diets occurred in nearly 60% of sampled individuals. The fin whale population, typically composed of specialists of either krill or lipid-rich pelagic fishes, shifted toward one composed either of krill specialists or true generalists feeding on various zooplankton and fish prey. This change likely reduced intraspecific competition.
Read also: Minke Whale Feeding
Factors Affecting Diet
The fin whale's diet can be influenced by several factors, including:
- Prey Availability: Changes in prey distribution could lead to changes in foraging behavior, nutritional stress, and diminished reproduction for fin whales. The availability of different prey species in a particular region can influence what fin whales eat.
- Oceanographic Conditions: Altered oceanographic conditions, as well as the timing and distribution of sea ice coverage, can impact the distribution and abundance of prey species.
- Climate Change: The impacts of climate change on baleen whales may result from altered oceanographic conditions, as well as the timing and distribution of sea ice coverage.
- Competition: Fin whales may compete with other marine predators for food resources, influencing their dietary choices.
Threats to Fin Whales
Currently, the major threat to this species comes from vessel strikes. Fin whales are probably the most vulnerable species to ship strikes after North Atlantic Right Whales. The projected increase in ship traffic arising from the opening of trans-polar shipping routes (as arctic sea ice continues to decline) will increase the risk of vessel strike and also increase ambient noise and pollution.
Fin whales can become entangled in fishing gear, either swimming off with the gear attached or becoming anchored. They can become entangled in many different gear types, including traps, pots, or gillnets. Once entangled, whales may drag and swim with attached gear for long distances, ultimately resulting in fatigue, compromised feeding ability, or severe injury, which may lead to reduced reproductive success or death.
Underwater noise negatively affects whale populations, interrupting their normal behavior and driving them away from areas important to their survival. Increasing evidence suggests that exposure to intense underwater sound in some settings may cause some whales to strand and ultimately die.
Conservation Efforts
NOAA Fisheries is committed to the protection and recovery of fin whales. Under the ESA, NOAA Fisheries is required to develop and implement recovery plans for the conservation and survival of listed species.
Read also: Ecological Impact of Gray Whale Feeding
The recovery plan for the fin whale was published in July 2010. Its goal is to recover the species, with an interim goal of down-listing its status from endangered to threatened.
The major actions recommended in the plan are:
- Reduce or eliminate injury or death caused by ship collision
- Reduce or eliminate injury or death caused by fisheries and fishing gear
- Protect habitats essential to the survival and recovery of the species
- Minimize effects of vessel disturbance
- Continue the international ban on hunting and other directed take
- Monitor the population size and trends in abundance of the species
- Maximize efforts to free entangled or stranded fin whales and get scientific information from dead specimens