By Bill Chameides
Tagging a pilot whale that is eating shrimp. These DTags, as they are known, are used to gather data about the animal's doings far below the ocean surface. Click on image for larger view. (Danielle Waples)
Forty miles off Cape Hatteras. It's lunchtime on a sunny, calm day. You've just awoken from a mid-morning nap and you're hungry. The kids have been amusing themselves playing together. It's time to eat. You arch your back and dive down 1,000 meters to search for squid. Yum. You are, of course, a short-finned pilot whale.
Studying Pilot Whales off Cape Hatteras
We've been studying pilot whales for the past few years at a remarkable place called the Point, east and just north of Cape Hatteras on North Carolina's coast.
Pilot whales, tuna and many other creatures gather here to feast on squid that are concentrated along the edge of the continental shelf, where depths drop from a hundred to a thousand meters in less than a kilometer. The edge of the Gulf Stream meanders back and forth over the shelf break here, making it a very rich and interesting place to work.
Intrepid biologists attach a digital acoustic tag to a pilot whale. These tags help us study their goings-on so we can gain insights into these creatures that live below the depths in a seaworld unknown. (Alex Loer)
To study these fascinating creatures, we attach digital acoustic tags (DTags), developed by colleagues at the Woods Hole Oceanographic Institution, to the whales' backs with a long pole.
The tags, which stick to the whales with suction cups, record the sounds they make, such as the echolocation clicks and buzzes which they use to find their prey. (Check out these sounds here.) They also record water pressure (which we use to estimate depth) and the acceleration and direction in which the whale is heading in three dimensions.
We program each tag to jettison from the whale at a predetermined time, after which it floats to the surface. We recover the tag (by locating a signal emitted by its small radio beacon), go home, download the data and prepare the tag to be deployed again.
A pilot whale with a digital acoustic tag (or DTag) attached to its dorsal fin. We can identify individual whales using the patterns of nicks and notches on the trailing edge of the fin. (Ari Friedlaender)
The only tricky part -- OK, there are several tricky parts -- is that we are working 40 miles from Oregon Inlet in small, rigid-hull, inflatable boats. (See last photo in post.) It can be a long, bumpy, wet ride home when the weather turns nasty. Remarkably, though, we find pilot whales almost every day and, when weather conditions are good, we usually tag at least one a day.
Pilot Whales: The Knowns ...
The scientific name of these whales is Globicephala macrorhynchus. Their non-technical sobriquet, spawned by whalers of yore who hunted them for their meat and oil blubber, is "pothead" because of their enormous foreheads, which function to focus their echolocation clicks.
The pilot whale, whose scientific name is Globicephala macrorhynchus, is also known colloquially as a "pothead" because of its enormous forehead, which functions to focus its echolocation clicks. (Danielle Waples)
Pilot whales live for up to 80 years in permanent family groups centered around matriarchal females. Adult males have enormous dorsal fins that we believe serve as reproductive advertisements to females (kind of like deer antlers or a guy's Porsche). They are one of a very few mammals in which females stop reproducing well before the end of their life which, the whale's version of human menopause.
And the Unknowns
Older females continue to produce milk for many years, perhaps nursing their nieces and nephews. Scientists have speculated that the oldest females may act as important repositories of information in these social groups, much like matriarchal elephants, who know where to find water and food when ecological conditions change. We scientists just love to speculate about stuff like this.
Watching the pilot whales off Cape Hatteras leads us to think about the meso-pelagic (mid-water) ecosystem in which they feed. The stomach contents of stranded (dead) pilot whales contain a variety of small squid species.
From the tag records we've examined to date, our whales capture many prey items during each dive and occasionally bring their prey to the surface. How do they find these squid? Do they prefer particular species? We are using powerful and sophisticated echo-sounders to detect schools of small squid and even single individuals of larger species. But we would love to know what is going on down there, a kilometer down in a dark ocean.
Pilot whales at surface. (Ari Friedlaender)
Watching the whales also reminds us how little we know about the system in which they live. We know almost nothing about the biology of most of the squid they eat. Some species are known only from their beaks found in the stomachs of dead whales. And, sadly, because taxonomy is a dying profession, there are only a handful of scientists who can identify these species.
As we wait for a whale to surface from a 15-minute dive, we also wonder about the effects of the Deepwater Horizon disaster on the Gulf of Mexico's meso-pelagic ecosystem and the whales and other large marine predators that depend on it. Given how little we know about the fish and squid that live a kilometer beneath the surface, how will we ever be able to detect an effect? Can we use the whales as sentinels of the health of this poorly understood system?
Food for thought.
The intrepid field crew lounging around off Cape Hatteras. (Alex Loer)
Andrew J. Read researches the effects of human activities on populations of long-lived marine vertebrates (particularly marine mammals, seabirds and sea turtles), and attempts to find solutions to such conflicts.
Douglas P. Nowacek, a marine biologist who specializes in sound in the ocean environment, is studying the link between acoustic and motor behavior in marine mammals -- specifically, how they use sound in ecological processes.