The three types of killer whales. From R. Pitman, P. Ensor, J. Cetacean Res Manage 5(2):2003.

Ross Sea killer whales appear in the McMurdo Sound area and the southern Ross Sea, in early December and ply various fast ice edges (ice attached to the land), which as the season progresses recede further and further south toward the continent. They also apparently forage under or along the edge of the Ross Ice Shelf by Cape Crozier on the other side of Ross Island. These whales feed on fish that live under the fast ice and as the ice recedes the whales are able to exploit more and more feeding territory. Sightings of these whales, from land, helicopters and ships have been carried out through the years, most recently from the Cape Crozier and Cape Royds penguin colonies on Ross Island, where it has been noticed that the presence of whales (including minke whales) follows a shift in the diet of the penguins.

Killer whales foraging in a sea ice crack.

In 2005 the ratio of C to B killer whales was 50-1, but over the next few years it steadily dropped to 16-1 by 2008. As the observed numbers of B whales (seal eaters) did not change during this time, the altered ratio was due to the decrease in Ross Sea killer whales. During the years of these observations another important series of events was taking place.

Although commercial fishing of the Antarctic toothfish (sold as “Chilean sea bass”) in the Ross Sea began in 1996, it was expanded in 2004 from 9 to 22 fishing vessels; not surprisingly that same year the catch reached its allowed limit of 3500 tones. These boats target the largest adult toothfish, which is the same size those taken by the whales. Toothfish are a slow growing species which do not reach maturity until 16 years old. Many of these fish taken in the fishery were over 25 years old, some older.

Antarctic toothfish.

Since 2004, the commercial catch has remained steady year by year. Catch and release efforts of toothfish by scientists in McMurdo Sound remained steady from the years 1974 to 2000, but dropped 50% in 2001 a few years after the commercial fishing began and then to 4% in 2007, only 3 years after the peak commercial catches began. It would appear that the drop in Ross Sea killer whale numbers is related to the increase in the commercial fishing of the toothfish.

Are there any other animals that would be affected by the reduction in toothfish numbers?

Weddell seals also take toothfish as a primary food source and their numbers have not decreased in McMurdo Sound, though trends elsewhere along Victoria Land are unknown. Seals are able to dive deeper and stay under longer than the whales and therefore able to catch the fish which are safe from the whales. Seals therefore not only forage where the whales forage, but also in areas the whales can not reach, places covered with extensive fast ice where small cracks provide breathing holes. Seals also eat silverfish. It is thought that whales also eat silverfish but there are no confirmed sightings for this. The whales therefore may be more sensitive to changes in toothfish availability. If the toothfish industry continues to extract the current yearly numbers, it is predicted these creatures will decline more rapidly.

For more information about the Ross Sea, the toothfish industry and how it is affecting penguins, whales and seals go to The Last Ocean.

For some time it was thought that Weddell seals did not eat the toothfish and therefore would not be affected by the reduction of these fish in the ocean. The fishing industry has pushed to increase catch limits based on this assumption. We’re learning, though, that this is not true by indirect means.

One way researchers determine what an animal eats is by sorting through their scats (body waste). Indigestible parts pass through the body of seals and whales and can be identified. In the case of fish, the ear bones, or otoliths, are used to determine not only what species of fish are eaten, but how old and large they are. Toothfish otoliths have not been found in seal waste. But recently we’ve learned why.

Antarctic Toothfish ear bone (otolith).

As is the case with many discoveries chance plays a large part. While out on a diving expedition one researcher discovered the heads of many toothfish near a crack in the ice. The only predators in the area are seals, so these heads must be the remains of their meal. No wonder there are no otoliths in the seal waste, they don’t eat the heads! By observing seals in holes drilled through the ice for scuba access, it has been observed that seals remove the heads so this information was already known. But many people still doubt the implications of this or contend that it is a ‘local’ phenomenon. Finding these heads, in the company of seal holes, was another clear indication that this belief is wrong. Retrieving these heads would also mean that scientists could remove the ear bones (otoliths) and determine the age of the fish as well as where the fish grew up (one of the many mysteries about toothfish that remains unsolved).

The crack, where seals come to find toothfish hiding under the ice.

The helicopter landed us in this remote place on the McMurdo ice shelf.

So off we go. First a helicopter ride to the place where the fish heads were first found, and then a 10 km walk over and around the rough terrain along the crack in search of other evidence. All in all the remains of 30 fish were found, and 20 heads were brought back to the lab to extract the otoliths.

Antarctic toothfish heads, the remains of a Weddell seal feast.

Searching for Antarctic Toothfish heads on the McMurdo Ice Shelf crack.

Bagging Antarctic Toothfish heads.

As it turned out, most of the heads had become mummified, i.e. freeze-dried, and acidic action in the flesh during the process of decomposition in many cases dissolved the otoliths. There were just little ‘puffs’ of white stuff where the otoliths should have been. Skuas had eaten the otoliths in other of the heads. But, we did find otoliths in 6 heads, and these will be tested and analyzed in a lab in the US. Providing evidence to fishery biologists that toothfish are an important food source for seals will help the argument to limit the commercial catch.

Learn more about Antarctica toothfish and conserving the Ross Sea for all marine organisms by visiting The Last Ocean.

The morning of July 11th was the culmination of the conference: I finally presented my Antarctic toothfish work. Presenting at a conference is not about being the star of the show; it’s about our responsibility as scientists to communicate our work to our colleagues, the public, and in my case, to resource managers.

Presenting my Antarctic toothfish work at SCAR.

I came upon Antarctic toothfish four years ago when I started graduate school. I had been interested in fisheries management for years and was looking for a way I could contribute to this global problem. Antarctic toothfish erupted onto the fishery scene in the last ten years because of declines in its cousin fish, Patagonian toothfish. Both species are more commonly known on the market as the popular and expensive Chilean Sea Bass.

Prior to my work, I didn’t know much about Antarctic fisheries. Like most people, I couldn’t imagine why fishermen would travel so far for fish. But world fishery trends hold the answer. Recent Food and Agricultural Organization statistics state that 97 percent of our world fisheries are fully exploited, overfished or collapsed, leaving a mere 3 percent unexplored, pushing fishermen into remote places like Antarctica.

A Russian fishing vessel.

You can imagine how hard it is to manage fisheries in a place like Antarctica, but in 1982 an international group came together to do just this. They formed the Convention for the Conservation of Antarctic Marine Living Resources and have been managing Antarctic wildlife every since. My study met a request by CCAMLR for more life history information about Antarctic toothfish, with the hopes of sustainable management for the growing fishery.

Holding an Antarctic toothfish.

I stood before my colleagues at SCAR and presented what I had learned about Antarctic toothfish, including how they grow slowly and live a long time — close to 40 years. Many fish that share these characteristics have been overharvested quickly because they can’t grow and reproduce fast enough to keep up with demands of the fishery. I discussed past trends and future concerns.

To my delight, some of the folks from CCAMLR were there in the audience. After the talk, we continued to discuss toothfish management. Is it even possible to have a sustainable toothfish fishery? And if so, what would it take? The first step is to apply the research to management. With their help, this toothfish work is now being presented at the yearly CCAMLR management meeting in Hobart, Australia, and all my years of toiling will not go to waste.

Presenting my Antarctic toothfish work at SCAR.

The conference ended on a high note. I had an amazing experience partaking in this international collaboration of scientists, all of us working together to find solutions to global problems and dedicated to learning more about our poles. Thanks for joining me and keep up with Ice Stories as we collectively share our work with you in the second half of International Polar Year.

Cassandra and an Antarctic toothfish on 2006 AMLR fish cruise off the Antarctic Peninsula.

Yet over evolutionary time scales, spanning thousands to millions of years, Antarctic fish species have adapted to changes in their environment with success. During the second day of the SCAR conference, Karel Janko from the Czech Academy of Sciences and others demonstrated this fact during their talk entitled “Does the life history affect the ability of Antarctic fish to cope with climatic changes?” The team used population genetics to see the effect of past major climate shifts on fish populations and tried to predict what may happen in the future as we are in the midst of another major shift.

Over the past millennia, the ice sheets of Antarctica have advanced and retreated multiple times, each time drastically changing the available habitat for fish. Massive ice sheets originally form on the continent of Antarctica and grow outward toward and into the ocean. In times when the ice is expanding, it grows out over the continental shelf and due to its massive weight, it becomes grounded into the shelf. When this happens, all the benthic organisms that live on the continental shelf get pushed out and cease to thrive.

As Janko described, during glacial times when the ice shelf advances, benthic ecosystems, including fishes, are depleted whereas pelagic fishes, that don’t depend on the benthos, flourish. In contrast, during interglacial times, when there is little ice, the continental shelf is exposed and benthic ecosystems flourish, with little affect on the pelagic species. Since in the present, the ice has been retreating, we are currently in a time of benthic species expansion.

An Antarctic toothfish (Dissostichus mawsoni)

Of course, this is all on an evolutionary time scale, meaning that Antarctic fish will not likely disappear altogether. They will instead continue to evolve and adapt with some species flourishing and others dying out completely. Based on the work of Janko and others, we can guess that benthic species will have more available habitat as the ice continues to retreat, but we still don’t know the physiological effect of warming on their bodies which are adapted specifically for cold environments. Other IPY studies are looking at this and will reveal more information with regards to the future of Antarctic fish. For more information, visit http://www.ipy.org/ and click on OCEANS.

Cassandra Brooks is a marine scientist and science writer based in California. She’s studied Antarctic marine resources since 2004 at Moss Landing Marine Laboratories (MLML) and with the Antarctic Marine Living Resources (AMLR) Program.

Cassandra Brooks first began studying Antarctic toothfish in 2004 as part of her master’s thesis at Moss Landing Marine Laboratories. Antarctic toothfish are large, deep-sea predatory fish found only in the ice-laden waters surrounding Antarctica. Biologists who were fascinated with their ability to live in these freezing waters were the first to study these fish. It turns out that Antarctic toothfish have special proteins in their bodies that act like anti-freeze to keep their blood from freezing, thus enabling the fish to live in the icy waters off Antarctica.

Commercial fishermen took notice of the Antarctic toothfish only in the last ten years when populations of its sister species, the Patagonian toothfish, became depleted. Patagonian toothfish are found in the northern waters of the Southern Ocean, off the tip of South America and around sub-Antarctic islands. Both species of toothfish are more commonly known by their market name “Chilean Sea Bass,” though they bear no relation to sea bass. The depletions of Patagonian toothfish were likely caused by the large illegal pirate fishery, which has been estimated at up to 70 percent of the total harvest of this species.

As the subantarctic waters where the Patagonian toothfish lives were overharvested, vessels moved further south, into the remote and pristine waters of the Ross Sea, Antarctica, in search of the Antarctic toothfish. The commercial catch of Antarctic toothfish has increased steadily over the last ten years, even though very little is known about the basic biology of this fish. Cassandra’s work focuses on life history and population structure of this species. Her goal is to provide information on their age, growth, and spatial distribution to the toothfish’s managing body (CCAMLR) in order to facilitate sustainable management of this large Antarctic species.

Antifreeze Fish

Some of the coldest ocean waters on earth, where temperatures fall below the freezing point of fresh water, are found in the Southern Ocean surrounding Antarctica. Nearly every fish on the planet would freeze to death if it tried to brave such harsh conditions. The Antarctic toothfish, however, thrives in this icy environment. How does it do it?

Antarctic toothfish have evolved remarkable traits that allow them to survive in sub-freezing waters. One of these traits is a slow heartbeat—a beat only once every six seconds. The main secret of these unique fish, though—who have a natural lifespan of 40 years and can weigh in at over 200 pounds when full-grown—lies in a special protein that acts like antifreeze. By making this unique antifreeze glycoprotein, the Antarctic toothfish are able to keep their blood from freezing. It’s a remarkable evolutionary solution to surviving in the frigid waters of the Antarctic.

One of the most amazing things about these Antarctic antifreeze fish is their corollary in the Arctic, where waters reach similar subfreezing temperatures. There, fish carry a similar but different antifreeze protein—evolutionarily distinct from that of the Antarctic toothfish. What this means is that fish at both ends of the planet evolved similar antifreeze survival strategies through completely different methods.
For more on this awesome evolutionary achievement, please visit our Origins site here.

Background on AMLR

The United States is one of 25 nations that are bound by the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR). CCAMLR is an international treaty, the aim of which is to conserve marine life in the Southern Ocean and to ensure the harvesting of marine resources is done in a sustainable manner without disrupting the Antarctic ecosystem. The United States Antarctic Marine Living Resources (AMLR) program is responsible for collecting scientific information that will be used to develop and support US policy regarding the conservation and management of the marine resources in the waters surrounding Antarctica. For over 20 years, scientists with the AMLR program have investigated the effects of krill, crab and finfish fisheries on the ecosystem, including the effects on seal and seabird populations. The Antarctic Ecosystem Research Division (AERD), located at the Southwest Fisheries Science Center branch of NOAA Fisheries, manages the AMLR Program.

When Cassandra goes to sea with AMLR, she primarily studies zooplankton under Dr. Valerie Loeb, a marine biologist at Moss Landing Marine Laboratories (MLML) and a contact scientist for AMLR. Valerie studies the abundance, demography, and distribution patterns of krill, and is head of the krill and zooplankton component of the AMLR program. Valerie and the AMLR crew study krill because these small (approximately 2–2.5 inches, or 5-6 cm) shrimp-like crustaceans are the most abundant and important food source in Antarctica. The whales, seals, fish, and seabirds in the Southern Ocean all depend on krill for their survival.

Me with an Antarctic toothfish.
Photo by Darci Lombard

In the late 1960s fisherman began trawling around the sub-Antarctica islands, mostly for Notothenia rossi (the marbled rock cod) and some species of Icefish. Catches rose steadily, and by 1990, the marbled rock cod population was reduced to 5% of its pre-exploitation level. As shallow water species became depleted, fishermen began targeting the large deep-water Patagonian toothfish, finding a temporary goldmine. But legal commercial fishermen weren’t the only ones interested; pirate fishermen also wanted their share. Within ten years local population declines and stock closures ensued. Consequently, fishing boats pushed into the southernmost reaches of the Antarctic waters in pursuit of the Patagonian toothfish’s cousin species, the Antarctic toothfish. Toothfish are more commonly known by their snazzy market name “Chilean Seabass.” And they are an incredibly expensive and gourmet fish – prices are well over $20 per pound – which is the main reason why the fishery plunders on, despite stock depletions and the potential vulnerability of these fish.

Why would people go all the way to Antarctica to fish? Indeed, it makes little sense to use so much gas, time and energy traveling to the most remote corner of the globe in pursuit of fish. But our fisheries closest to home have been highly exploited and can no longer meet the needs of a growing world population. Current Food and Agricultural Organization (FAO) statistics regarding world fisheries show that 38% are fully exploited, 28% are overfished, and 29% are collapsed. That leaves only 3% of our world fisheries unexplored, including some stocks of Antarctic toothfish. Fishermen are forced to voyage into deeper and more remote waters to keep up with world demands and continue fishing, with or without a license to do so.

Close-up of a toothfish.
Photo by Darci Lombard

The problem with deep-sea fisheries

Last year I attended a symposium on deep-sea fisheries at the AAAS meeting in San Francisco. I listened in earnest, scribbling down notes as all the fishery biologists on the panel – including world renowned fishery experts like Daniel Pauly – stood up and talked about the vulnerability of deep-sea fisheries. Deepwater fish tend to grow slowly, live a long time, mature later in life and have low fecundity (reproductive capability.) The symposium led to a clear conclusion: deep-sea fisheries are not resilient to heavy commercial exploitation. In the past we realized this too late, after the deepwater fishes had been over-harvested.

While Antarctic toothfish can live to be over 200 pounds, they are usually caught at quite a young age.
Photo by Sunhild Wilhelm

Toothfish fall into the category of relatively slow-growing and long-lived fish — 50 years for the Patagonian species and about 40 for the Antarctic species. They don’t mature until about 10 years of age and are caught well before that time, one of the reasons we have yet to understand their reproduction and fecundity. While the Patagonian toothfish has already been overexploited in some areas, the fishery for Antarctic toothfish is still relatively new, though it is growing and will continue to do so. Given the trends of Antarctic and deep-sea fisheries, the chances that toothfish could withstand heavy fishing pressure seem slight. Toothfish are the largest fish in the southern ocean, and decimating their population could be damaging to the whole Antarctic ecosystem.

Will we learn from the past quickly enough to keep the Antarctic toothfish from becoming another over-fished FAO statistic? My job as a fisheries biologist is to provide life history information on the species. The managers’ job is to use that information to implement sustainable management. And your job as a consumer is to make the best choices about where the fish you eat come from. Being out here in the Southern Ocean, the question I can’t shake from my mind is: Do we really have any business commercially harvesting fish that come all the way from Antarctica?

For more on Antarctic fish, check out the BBC’s recent article on the Antarctic toothfish by clicking here.