Jan.
9, 2013 — Marine biologists are beginning to understand the varied diving
and foraging strategies of filter-feeding whales by analyzing data from
multisensor tags attached to the animals with suction cups. Such tags, in
combination with other techniques such as echolocation, are providing a wealth
of fine detail about how the world's largest creatures find and trap their
prey.
Recent
studies on the behavior of baleen whales -- which filter small fish or
invertebrate animals from seawater -- are described in the February issue of BioScience.
Jeremy A. Goldbogen of the Cascadia Research Collective in Olympia, Washington,
and his colleagues point out that tags can report not only the depth but also
the acceleration of the animal carrying them, which reveals information on its
pitch and rolling motion. Together with special software, this can allow
foraging dives to be visualized in three dimensions, along with the timing.
Studying whale behavior is logistically challenging, as it may be necessary to
coordinate the actions of several research vessels and large research teams.
Yet despite the difficulties, patterns are becoming clear.
Right
whales and bowhead whales have a very different feeding strategy from rorquals
-- the group that includes the biggest animal on earth, the blue whale. Right
and bowhead whales filter-feed by swimming relatively slowly through prey
patches, a mode called continuous ram feeding. This keeps their energy
expenditure low and makes possible dives of 10 minutes or longer, but means
they miss out on prey able to take evasive action. Rorquals, in contrast, make
high-speed lunges at prey patches that enable them to catch elusive species.
They must then pause to filter water engulfed in their large mouths, however,
and they have to surface more often to breathe than continuous ram feeders. The
new tools available mean researchers can study the efficiency of diving and foraging
in different whales and relate it to the availability of prey of different
types. Because whales are considered keystone predators that structure oceanic
food webs, such insights will shed important light on ocean ecology.
Posts
