Geo News

The Ross Sea toothfish fishery

On January 16, 2006, a Royal New Zealand Air Force (RNZAF) P3-K Orion landed at McMurdo Sound, Antarctica for the first time. The flight to the ice was the finale to nearly two years of planning by both the RNZAF and government agen­cies, and was a trial to see whether the P3-K could operate safely in the region. Although being able to operate from the ice would be advanta­geous for some search-and-rescue operations and emergency medical evacuations, the air force’s main interest in the Antarctic region is fisheries surveillance. As Air Com­modore Dick Newlands has put it: “Future surveillance missions may operate from Antarctica on behalf of the government of New Zealand with specific emphasis on meeting the CCAMLR surveillance, deter­rence and enforcement require­ments.” The CCAMLR—the Commission for the Conservation of Antarctic Marine Living Resources—is a body established under the umbrella of the Antarctic Treaty to conserve the marine life of the Southern Ocean, which surrounds Antarctica. One of the CCAMLR’s principal concerns is fisheries. Under the commission’s auspices, the RNZAF monitors fish­eries primarily in the Ross Sea sector of the Southern Ocean. Its patrols, which are conducted in support of the CCAMLR’s System of Inspection, are intended to deter and detect illegal, unreported and unregulated (IUU) fishing, especially for tooth-fish. From Antarctica, a P3 can run considerably longer patrols in the Southern Ocean than it can from New Zealand. Toothfish are large bottom-dwell­ers found in Antarctic and sub-Ant­arctic waters at depths ranging from 300 m to 3000 m. There are two main species: the Antarctic toothfish (Dissostichus mawsoni) and the Pat­agonian toothfish (Dissostichus elegi­noides), otherwise known as Chilean sea bass. Toothfish can grow to over 2.3 m in length and can weigh more than 130 kg. Both species have a circumpolar distribution. The Patagonian toothfish is found in sub-Antarctic waters extending south to the Antarctic Convergence, where the cold Antarctic waters meet warmer, saltier waters to the north. Most of its distribution falls within the CCAMLR area, although the main fisheries lie within the Exclusive Economic Zones (EEZs) of the UK, France, Australia and South Africa, and are managed by those countries. Closer to home, Patagoni­an toothfish occur in small numbers on the Campbell Plateau and around Macquarie Island and extend south along the Macquarie Ridge into the north of the Ross Sea. The Antarctic toothfish has a more southerly distribution and is managed solely by the CCAMLR. It is caught from the Antarctic Conver­gence (at about 60°S) southwards to the Antarctic continent. Within the Ross Sea the two spe­cies are equally abundant between 60°S and 63°S, and over 90 per cent of the longlines set between these latitudes catch both fish at the same time. Fishing for Patagonian tooth-fish began in the late 1970s but didn’t become large-scale until the early 1990s following the decline in longline fisheries elsewhere. By the mid-1990s, Patagonian toothfish was a highly prized catch, branded “white gold” by industrial long-range fishing fleets. Within the CCAMLR area, most of the reported catch of Patagonian toothfish is taken around Kerguelen Island (French territory), South Georgia (British) and Heard and McDonald Islands (Austral­ian). Longlining is the preferred fishing method, although some bottom trawling for smaller fish oc­curs around Heard and McDonald Islands. Longlining for Patagonian toothfish in these areas is prohib­ited during the summer months to minimise the danger of catching the seabirds that breed on the islands at that time. The legal catch of Patagonian toothfish within the CCAMLR area was almost 15,000 t in the mid-1990s and is currently about 9500 t. In contrast, fishing for the Ant­arctic toothfish is permitted only during the summer months. The main fishery to date has been in the Ross Sea, which is covered by ice for most of the year. During January and February, areas of open water, called polynas, form, allowing access to the continental shelf and slope. New Zealand longliners initiated a small-scale fishery for Antarctic tooth-fish in 1996–97. Since then, New Zealand vessels and, more recently, vessels from other countries, includ­ing Norway, Russia, South Africa, Uruguay and the UK, have returned each summer. Longline vessels start working the northern reaches of the Ross Sea when the season opens in December, move south as the polynas form and the ice clears, and reach the southern reaches by Febru­ary, then move back north as the sea ice re-forms. The Antarctic-toothfish catch in the Ross Sea has steadily in­creased from about 40 t in 1997–98 to over 3000 t in 2005–06. Toothfish is an excellent eating species, with strong markets in the US and Japan, and is therefore very valuable. The fact that it provides the most valuable fishery in the Southern Ocean, an area difficult to police be­cause of its remoteness, has encour­aged extensive IUU fishing. With the annual value of the illegal catch in the hundreds of millions of US dol­lars, there has been a major incen­tive to harvest toothfish illegally. IUU fishing was first detected in the mid-1990s, around South Georgia. Over successive years an IUU fleet of up to 50 vessels moved steadily eastwards through the Southern Ocean, decimating toothfish stocks and killing tens of thousands of sea-birds as it went. As a result, Patagonian toothfish stocks plummeted to less than 10 per cent of their initial levels around Prince Edward Island (South African ter­ritory) and Crozet (French). Stocks around South Georgia, Kerguelen Island, and Heard and McDonald Islands have also been hit hard. Over the past few years the number of IUU vessels appears to have diminished, but vessels have also moved into the high seas and further south towards the Antarctic continent, where they are harder to detect. The IUU catch is esti­mated to have peaked at 54,000 t in 1996–97—exceeding the legal take by a factor of four—but is currently believed to have dropped to less than 5000 t. In an effort to combat IUU fish­ing, the CCAMLR has developed a raft of management measures. These include a catch-documenta­tion scheme with associated trade restrictions, mandatory coverage by satellite-based vessel-monitoring systems, schemes involving trade sanctions and requiring non-party vessels to adhere to CCAMLR regula­tions, and vessel-identification and -marking requirements. It is believed that these measures, combined with increased surveillance by aircraft and patrol vessels within EEZs, as well as some well-publicised chases on the high seas, have led to a decline in IUU activity. Another important reason for the careful management of toothfish is the incidental mortality of sea­birds, including several species of endangered albatross, through their being caught on longlines. This was a major problem in the Patagonian toothfish fishery and resulted in the CCAMLR imposing a range of mitigation measures, including night setting and the use of tori lines (bird-scaring streamers). Recent observer reports have shown that these meas­ures, when fully implemented, have reduced seabird by-catch by legal fishers to very low numbers. Thanks to good management and a proactive approach by the fish­ing industry, seabird by-catch hasn’t been an issue in the Ross Sea, where fisheries observers have recorded only one seabird death since fishing for toothfish began there. Although illegal fishers are unlikely to employ measures to avoid catching seabirds, it is also true that illegal fishing hasn’t been as big a problem in the Ross Sea as in other parts of the Southern Ocean. As an alternative approach to combating IUU activity, Greenpeace has pushed to have toothfish listed on Appendix II of the Convention on International Trade in Endangered Species (CITES). It claims that IUU fishing is a larger problem than the CCAMLR believes, and estimates that up to 100,000 Southern Ocean seabirds, including endangered spe­cies of albatross, have been drowned by pirate fishers each year. Appendix II lists species not yet threatened with immediate extinction but which may be if exploitation continues. Commercial trade in these species is allowed on condition that speci­mens are legally obtained and the trade isn’t detrimental to remaining populations. Australia and New Zea­land have supported CITES listing of Patagonian toothfish, although other CCAMLR members have resisted, arguing that the commission can manage the fishery through other means. Although considerable research has been carried out on Patagonian toothfish, little was known about the biology of Antarctic toothfish prior to 1999. With the help of US scien­tists, the National Institute of Water and Atmospheric Research (NIWA) has recently developed a validated method for ageing Antarctic tooth­fish—a first for any toothfish species. For over 20 years, US scientists at McMurdo Sound, in the Ross Sea, have both tagged Antarctic toothfish and injected them with oxytetracy­cline. This chemical is deposited in the hard parts of the fish and acts as a date marker, a record of when the fish was released. Recent recapture and analysis of six fish (including one that had been at liberty for seven years) has confirmed that rings in the otoliths (or ear bones) form annually. Antarctic toothfish grow at a rate similar to that of some New Zea­land temperate-water middle-depth species, such as hoki, hake and ling. They reach a length of about 60 cm in five years, about 100 cm in 10 years, and about 150 cm in 20 years. The maximum age recorded is almost 50 years. The spawning cycle of the Ant­arctic toothfish is poorly understood because the Ross Sea is covered with ice for six months of the year. Some spawning fish have been found to the north in May, so it is likely that spawning continues from then through to early spring. Larvae and juvenile fish live in the upper layers of the ocean until about 15 cm long, after which they start to spend more time near the seabed. Juveniles are typically found in the shallow waters of the continental shelf, and move deeper down the continental slope as they get older. However, the largest and oldest fish are found on the seamounts, banks, and ridges to the north of the Ross Sea. Stomach content analyses by NIWA indicate that adult Antarc­tic toothfish feed mostly on other fish, especially rattails and icefish, but also take squid and crusta­ceans. Some of the more unusual food items identified include three penguins, numerous skate egg cases and a large quantity of rocks. Adult Antarctic toothfish are in turn preyed upon by a variety of marine mam­mals including sperm whales, killer whales and Weddell seals. Once the biology of the Antarctic toothfish was understood, scientists turned their attention to monitoring its abundance. Because toothfish live so deep and have no swim bladder, traditional methods of determining abundance, such as trawl surveys and acoustic surveys, are unlikely to succeed. An alternative approach is tagging, and in 2000–01 New Zea­land initiated a tagging programme. This was very successful thanks to industry co-operation, programme design and international co-ordina­tion by the Ministry of Fisheries, and technical support from NIWA. Following the success of this pro­gramme, in 2002–03 the CCAMLR adopted tagging as the main method of monitoring Antarctic toothfish stocks and made it compulsory. Now every vessel must tag and return one toothfish out of every tonne caught (about one animal in 25). The Antarctic toothfish fishery is managed by the CCAMLR as an “ex­ploratory” fishery, i.e. one in which there is a strong emphasis on data collection and research. In order to set appropriate quotas, fisheries managers need scientifically robust estimates of stocks and the levels of harvest they are able to sustain. Scientists from NIWA have recently completed the first stock assess­ment for Antarctic toothfish, and the first for any exploratory Antarctic fishery. The assessment incorporates standard fisheries data, such as age frequencies and catch against effort, as well as tag–release-and-recapture data. It is estimated that the initial Ross Sea Antarctic toothfish spawning stock stood at 69,000 t, and that the current stock stands at 61,000 t—the equivalent of about 2.3 million mature fish. Based on NIWA’s yield estimate, the CCAMLR has set the quota for the 2005–06 season at just under 3000 t. This equates to about 100,000 fish, with a total wholesale value of NZ$50 million. NIWA’s model has introduced the CCAMLR to a new methodol­ogy of assessing fish stocks. Within 18 months, this has become widely accepted and is now being applied by overseas scientists to a range of other toothfish fisheries, including Patagonian toothfish around South Georgia. In addition, the New Zealand government has just released its Ross Sea strategy. According to this, New Zealand will seek to balance the harvesting of fish with such protec­tion of the marine environment as will ensure the long-term viability of ecosystems, maintain biological diversity and conserve areas poten­tially vulnerable to human impact. The government is currently build­ing a scientific case for a protected area in international waters around the Balleny Islands archipelago, on the edge of the Ross Sea. Other key components of the strategy are measures to combat illegal fishing in the Ross Sea and Southern Ocean, to increase marine research and to im­prove fisheries management within the area covered by the CCAMLR. So far, IUU fishing has not been a major problem in New Zealand’s sector of the Southern Ocean, and the CCAMLR and RNZAF hope to keep it that way. Perhaps the greatest challenge in the Ross Sea fishery is to understand the potential impacts of fishing on marine ecosystems. NIWA and the Ministry of Fisheries have already started pulling information together on the various aspects of the Ross Sea ecosystem as a whole and working with other scientists, from both New Zealand and overseas, to understand it better. Only when this work has been completed will we be able to answer truly the question of whether fishing the icy waters of the Ross Sea is sustainable.

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