Lunge Feeding - What a Drag

Baleen whales (or Mysticeti) are among the largest vertebrates ever to have evolved on our planet. That they did so from a deer-sized terrestrial ancestor over the last 50 million years is even more remarkable. Today’s baleen whales are highly streamlined marine mammals that use their powerful tail flukes for highspeed swimming and long distance migrations.


Unlike their sister taxon, the toothed whales (or Odontoceti), baleen whales lack teeth and instead use a rack of thin keratinized baleen plates that hang from the rostrum to form a comb-like structure for filtering tiny organisms from the water. To do so, requires unique foraging styles. Gray whales (Eschrichtius robustus) forage on the bottom by straining food from benthic sediments. Right whales and bowhead whales swim through swarms of prey with their mouths open using continuous ram feeding. In contrast, the largest and fastest mysticete whales, the rorquals (Balaenopteridae), use lunge feeding.


Lunge feeding allows these whales to engulf massive quantities of water and prey. As the whale approaches a shoal of prey it accelerates (or lunges), opens its mouth, and uses the dynamic water pressure to inflate the mouth cavity. As the whales passes through the cloud of prey it closes it’s mouth engulfing a huge volume of prey and water; the water is expelled through the baleen plates and out the sides of the mouth, while the prey are captured on the sieve-like fringes of baleen inside the mouth.





Figure 1. A series of images from underwater video of a minke whale feeding. Note the gape angle and the expansion of the throat region. (from Arnold et al., 2005)


Lunge-feeding whales have evolved a suite of adaptations to facilitate capturing large volumes of tiny prey. In addition, to baleen plates, these whales have:1) long rostrums that increase the gape of the mouth opening,2) rows of longitudinal furrows on the throat and belly that act like an accordian to expand the throat and anterior abdomen into a massive pouch, and3) a frontomandibular stay apparatus, or a strong fibrous tendon that prevents the lower jaw from being hyperextended beyond a 90 degree angle.





Figure 2. A diagram of the physical forces of a lunge feeding fin whale. The red line represents the gape angle, the blue line is the mouth area, speed is the black line , and volume of the mouth is the green line. (from Goldbogen et al. 2007)


Unfortunately, lunge feeding is energetically expensive. Swimming with an open mouth, especially one as large as those in rorquals, creates a great deal of drag. An adult fin whale engulfs roughly 71 cubic meters of water per lunge, a volume larger than that of the whale’s entire body.


In a series of recent papers, Goldbogen and colleagues (2006, 2007) tagged fin whales (Balaenoptera physalus) with a hydrophone, a depth gauge and a dual-axis accelerometer, to gather data on the kinematics of lunge feeding. Their data reveal that fin whales routinely dive to over 200 meters where they execute several feeding lunges per dive. Importantly, they showed that each lunge results in a rapiddeceleration of the body despite continued swimming (fluking). In fact, maximum drag occurred at the point of maximum gape as the mouth cavity was filling with prey-laden water, and slows the whale nearly to a standstill. The whale must expend considerable energy to re-accelerate after each lunge as it continues to hold its breath. Their data support the hypothesis that lunge feeding is energetically expensive (due to high drag forces associated with an open mouth) and may constrain foraging time (dive duration) and subsequent recovery time.


Using these data, Goldbogen and colleagues estimated that a fin whale engulfs an average of 11 kilograms of prey per lunge. This means that a fin whale requires an average of 83 lunges per day, or roughly 21 dives, to meet its daily energy requirements. On average a fin whale can meet these requirements in 3.1 hours of foraging at average prey densities.


Despite the high energetic cost of lunge feeding, this foraging strategy appears to be quite efficient overall as it is found in all members of the Balaenopteridae. These studies support the hypothesis proposed by Lambertsen and colleagues (1995) that lunge feeding was a key evolutionary innovation that promoted the evolution of large body size and long distance migration in baleen whales.





References

Arnold, P.W., Birtles, R.A., Sobtzick, S., Matthews, M., and A. Dunstan. 2005. Gulping behavior in rorqual whales: underwater observations and fnctional interpretations. Memoirs of the Queensland Museum, 51:309-332.

Goldbogen, J.A., Calambokidis, J., Shadwick, R.E., Oleson, E.M., McDonald, M.A., and J.A. Hildebrand. 2006. Kinematics of foraging dives and lunge-feeding in fin whales.
The Journal of Experimental Biology 209, 1231-1244. doi:10.1242/jeb.02135

Goldbogen, J.A., Pyenson, N.D., and R. E. Shadwick. 2007. Big gulps require high drag for fin whale lunge feeding. Marine Ecology Progress Series, 349:289-301.

Lambertsen, R., Ulrich, N. and J. Straley.
1995. Frontomandibular stay of balaenopteridae – a mechanism for momentum recapture during feeding. Journal of Mammalogy, 76, 877-899.