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US coast guard icebreaker POLAR STAR, opens a channel for ships to
re-supply McMurdo Station in the Ross Sea.
Every year these killer whales follow the ice breaker into
McMurdo allowing access to new areas of feeding in the Ross Sea.
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Photo : Bob Pitman
- May not be re-produced without permission form the author. |
April 16, 2004
Unraveling the Mystery of Killer Whale Ecology in Antarctica
Real Audio -
28k
Log Transcript
This is Genevieve Johnson speaking to you from the Odyssey. Bob Pitman, a marine biologist from Southwest Fisheries Science Center in La Jolla, California, recently joined us for our last research leg in the Maldives. Spending up to eight months a year at sea studying sea birds, sea turtles, flying fish and marine mammals, Bob prides himself on having done a little bit of everything throughout a career spanning thirty years. Recently, his interests have moved toward researching killer whales in Antarctica.
Bob Pitman - Marine Biologist - Southwest Fisheries Science Center:
"After I got involved working with marine mammals, it doesn't take long to get attached to certain groups. Some people like large whales a lot; I spent a lot of time working with dolphins so I have a certain affinity for dolphins. Over the years, killer whales were always in the background. I've worked in the tropics a lot and you don't see a whole lot of killer whales there. About 10-12 years ago, I started working in Antarctica, there is a lot more killer whales down there and I've had a growing appreciation for killer whales - what they do, the influence they have on other marine mammals through their predatory habits, and just an appreciation for their social structure and the intelligence of these animals. It's an animal that I wasn't immediately attracted to, but over the years they have become more and more important and to me, they are by far the most interesting marine mammal out there."
Genevieve Johnson:
Prior to the 1970's, little was known of the biology of killer whales. Most observations were of stranded animals, animals taken in whaling operations and occasional observations at sea. In general, killer whales were thought to be a single species of opportunistic feeders that occurred throughout the world's oceans. However, a more accurate picture is slowly beginning to develop.
Bob Pitman:
"[In recent years], there has been a lot of interesting work on killer whales, mainly in the Pacific Northwest. What they [scientists] have shown is that there are sub-populations of killer whales that co-occur in different areas. Some specialize on marine mammals, some specialize on fish, and there are also areas of the world where killer whales eat primarily sharks and rays. These animals look slightly different, they have different vocalizations and they don't interbreed. So killer whales as it turns out are a lot more interesting and a little more complicated than we had ever guessed. Right now we are in the process of re-evaluating killer whales ecologically and taxonomically worldwide to see what is there."
Genevieve Johnson:
In recent years, Bob's growing interest in killer whales led him to study these animals in Antarctic waters. For a long time, scientists believed a single species of killer whale migrated to the higher Antarctic latitudes in the summer months to feed, moving away again as winter approached. Some time ago, Russian whalers proposed the existence of two separate species, but their results were inconclusive. This inspired Bob to investigate Antarctic killer whales in greater detail.
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To find their way from one breathing hole to the next,
Killer whales living in Antarctic pack-ice must 'spyhop' - lifting their head above the surface to get a better view
before picking their way through the shifting channels of ice.
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Photo : Bob Pitman
- May not be re-produced without permission form the author. |
His research suggests there are three forms of killer whale (Orcinus orca) that occur in Antarctic waters. Type A is the form we are all familiar with. It has a medium sized eye patch,
lives offshore in ice-free waters and preys primarily on Antarctic minke whales (Balaenoptera bonaerensis). Type B has an eye patch almost twice as large as the Type A
killer whale. It regularly occurs in pack ice and seals appear to be its most important prey item. Type C has the smallest eye patch and also occurs in the pack ice.
However, this type is predominantly a fish eater and appears to be referable to the type described by the Russians Berzin and Vladimirov in 1983 - Orcinus glacialis.
It seems these three types of killer whale warrant separate species status. However, for this to occur, Bob must show this
interpretation is consistent with genetic results taken from biopsy samples, in addition to further morphological studies.
Bob Pitman:
"The Russians - while they were whaling in Antarctica, described two additional species of killer whales. The descriptions weren't very good, for instance you can't tell if they are trying to describe the same new species or two different new species, but it was pretty convincing evidence that there was a smaller species of killer whale in Antarctica - probably one that lives in the ice.
I was doing a series of cruises down there [Antarctica] and thought this would be an interesting thing to look at. So, during those cruises we kept records of all the killer whales we saw, took photographs and we started collecting tissue samples to, to see if we could tell them apart genetically. It became apparent fairly quickly that there are in fact three forms of killer whales in Antarctica. There is the regular killer whale that most people around the world are familiar with - it migrates to Antarctica every year and feeds mainly on minke whales - possibly entirely on minke whales. These killer whales stay in the open water beyond the pack ice, but there are two other forms of killer whales that live in the pack ice. They are quite easy to tell apart, in fact now that I have written a paper describing these forms; it's really surprising to me that no one ever noticed how different these are in the past. The two forms live in the pack ice, one feeds primarily on seals, and the other form feeds primarily on fish. So we are finding out that there are three forms of killer whale in Antarctica and that they have prey specialization.
This is very similar to what we (scientists) are seeing in the Pacific Northwest where we have what are called resident killer whales that feed on fish, mainly salmon. Then there are transient killer whales. These are marine mammals specialists feeding primarily on harbor seals, but also taking porpoises or sometimes Grey whale calves, but always mammals. Then there is a third form called 'offshores'. They (scientists) know less about these, they may be fish eaters, or they may be prey generalists - we are not sure yet. They are a little out of reach of most studies that are currently going on."
Genevieve Johnson:
Bob Pitman's intention is to add to the accumulating base of knowledge about Antarctic killer whales and to find out what is going on with them worldwide. For instance how many species are there and how do new species form - a process called 'speciation'.
Bob Pitman:
"We know a lot about birds and fishes, but we really don't know a lot about how marine mammals speciate. For terrestrial animals, there are a lot of different kinds of habitats for them to evolve in and it's easy to see how birds that live on one side of a mountain range can't interbreed with birds on the other side for instance. But in the ocean, these animals have unlimited opportunity to interact with each other and it's much more difficult to understand how cetaceans [whales and dolphins] can and do manage to speciate. I think killer whales are going to give us some opportunities to see how those processes occur."
Genevieve Johnson:
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A Type C mother and calf pair 'spyhop' through the ice.
This fish-eating type is three to five feet shorter than Type A, with markings that are yellowish in color
instead of white. This coloration is characteristic of both pack-ice types, but not of Orcinus Orca.
It is believed to be caused by microscopic phytoplankton that occur in polar waters under the ice.
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Photo : Bob Pitman
- May not be re-produced without permission form the author. |
Biodiversity in the oceans is under threat and killer whales are no exception. Fortunately killer whales face few direct threats from humans - whalers no longer hunt them. However, indirect threats are increasing. Pollutants such as Polychlorinated Byphenols (PCB's) are strongly suspected to be causing some declines in the Pacific Northwest where the population isn't replacing the males.
Meanwhile, fisheries management plans may fail to take into account the needs of all species of killer whales before scientist fully understand their role in the ecosystem.
Bob Pitman:
"In Antarctica for instance, the one form of killer whale that feeds on fish down there, happens to feed on a fish that can weigh up to 200 kilograms - the Antarctic toothfish. There is a fishery starting to take off down there now on this toothfish. I am working in Antarctica currently, trying to collect tissue samples for doing genetic analysis and looking for additional morphological evidence to substantiate that these ice forms are a separate species. Because when they do management plans for places like Antarctica, they still consider killer whales as one species that feeds on whatever comes along. If it turns out that there is a different species that feeds mainly on this fish for instance, if those fish populations are knocked way down, it could very much adversely affect these killer whale populations. They may not have something else to fall back on if those populations are depleted so it's that I think we need to look at and is what I am interested in."
Links:
Log written by Genevieve Johnson.
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