[CINC] Humpback lunge feeding

[susiewilliams at sbcglobal.net]

Humpback Whales' Dining Habits And Energy Costs Of Feasting On Tiny 
Prey, Revealed

As most American families sit down to Thanksgiving dinner, a 
University of British Columbia researcher is revealing how one of 
the largest animals on earth feasts on the smallest of prey – and at 
what cost.

Some large marine mammals are known for their extraordinarily long 
dive times. Elephant seals, for example, can stay underwater for an 
hour at a time by lowering their heartbeat and storing large amounts 
of oxygen in their muscles.

"Weighing up to 40 tons, humpback whales and their close relatives 
have relatively short dive times given their large body size," says 
UBC zoology PhD candidate Jeremy Goldbogen, whose study is featured 
on the cover of the current issue of The Journal of Experimental 
Biology. "Our study suggests that this has to do with the enormous 
energy costs of its unique foraging behaviours."

Humpbacks belong to a group of whales – called rorquals – that 
includes the fin whale and the blue whale, the largest animal that 
has ever lived. Characterized by an accordion-like blubber layer 
that goes from the snout to the naval, these whales take deep dives 
in search of dense patches of tiny zooplankton, such as krill or 
copepods.

While foraging, the whales literally drop their jaws during a high-
speed dive – called a lunge – creating enormous drag akin to a race 
car driver opening a parachute. The drag forces the blubber to 
expand around a large volume of prey-laden water, which is then 
filtered out through a comb-like structure called baleen when the 
mouth closes.

Goldbogen and colleagues from the University of California, San 
Diego and Cascadia Research Collective, a non-profit organization in 
Washington, recorded the foraging behaviour of two humpback whales 
off the coast of California using a non-invasive, temporary digital 
tag that records depth, body angle and other acoustic data. After 
multiple tagging attempts, the team successfully recorded data over 
an eight-hour period; one whale performed 43 dives and 362 lunges 
while the other executed 15 dives and 89 lunges.

The team found that lunge-feeding requires a large amount of energy 
compared to other behaviours – humpback whales breathe three times 
harder after returning to the surface from a foraging dive than from 
singing. Lunge-feeding whales also spent half as much time under 
water compared to singing whales.

Not surprisingly, the team found that the longer the dive, the more 
lunges were taken – and more time and breaths were required before 
the next dive. The whales also stuck to the uppermost level of dense 
krill patches to maximize prey catch for its energy expenditure, 
according to the study.

By integrating tag data and hydrodynamic theory inspired from 
parachute inflation studies, Goldbogen now plans to compare lunge-
feeding performance among blue, fin and humpback whales to determine 
whether the energy cost of a lunge is higher for bigger rorquals.

"We believe lunge feeding is related to the overall evolutionary and 
ecological success of rorquals, but the high energy cost may impose 
a physical limit on how big, and also how small, a whale can get."

Source: University of British Columbia