The Greenland halibut situation in Disko Bay has long been in the making

Greenland Institute of Natural Resources’ response to letter to the editor in Sermitsiaq no. 44

14.11.17

By Helle Siegstad and Emma Kristensen, Greenland Institute of Natural Resources

In a letter to the editor in Sermitsiaq no. 44, Henrik Lund-Andersen questions the scientific basis, which the Greenland Institute of Natural Resources provides for the biological advice on Greenland halibut in Disko Bay. Moreover, Henrik Lund-Andersen suggests that the advice is nonfactual and that the scientists of the Institute use terms such as ”collapse” and ”in danger of extinction”.

With the present letter, the Greenland Institute of Natural Resources wishes to correct the misunderstandings in the letter to the editor and, at the same time, clarify which scientific basis supports the advice. Furthermore, it is emphasised why the Institute has not used terms such as ”collapse” and ”in danger of extinction” in the debate about the Greenland halibut in Disko Bay.

The scientific basis and quality assurance

Each year, the biologists evaluate the state of the stock, including whether the stock increases or decreases, and which years are included in the stock. The data is extensive and comes from a variety of sources, both from fisheries (log books, catch numbers and biological samples) and from biological studies with med trawl and yarn (biomass, combination of males and females, size groups, weight, and much more).

The assessment of the stock provides the basis for the scientific advice, and this is submitted via the international advisory body NAFO (North Atlantic Fisheries Organisation). NAFO is the body that completes the advice, and all data and calculations are critically evaluated by international experts. This process ensures the quality assurance of the work of the Greenland Institute of Natural Resources and with it also the scientific objectivity and credibility.

15 years of downward trends

Over the last 15 years, all available data from biological studies and fisheries have shown that the stock of Greenland halibut in Disko Bay has decreased. Nowadays, the fishermen in Disko Bay catch less than previously (see box). According to NAFO’s assessment, the primary cause for this is the fishery, not sudden changes in the halibut’s environment (temperature or other) (see box). The natural increase of new fish and fish growth can simply not follow the heavy pressure from fisheries. Fishing on smaller and smaller fish results in fewer years. This increases the risk of large fluctuations in catches from year to year, due to natural fluctuations in recruitment.

Continued fishery in the same extent is therefore not sustainable. Consequently, biologists use the term ”overfishing” in relation to the stock’s productivity. Thus, since 2012, the advice has recommended a reduction of the catches.

However, it has not been mentioned that the Greenland halibut is in danger of extinction, neither do the biologists use the term “collapse” in the stock. Fortunately, each year new halibuts arrive to Disko Bay from the offshore spawning areas. The decline in stock can therefore be reversed through fisheries management, where the stock’s growth potential is utilised optimally and sustainably with the greatest possible continued catch. 

 

Halibut are very robust

The halibut can be characterised as a robust deep-sea fish that lives around the entire Arctic Ocean. The Greenland halibut that we fish in West Greenland has a distribution area from New Foundland (Flemish Cap) in south all the way up to Qaanaaq in the north. The Greenland halibut is found both in the fjords and in the offshore area between Greenland and Canada.

The large area of distribution, along with many biological studies in the North Atlantic, shows that the halibut can live under many different conditions and is robust in relation to changing environmental conditions.

Sea temperatures are often mentioned as a reason for declining halibut catches, but studies in Disko Bay show no significant changes in the seabed temperature. Here the temperature has been measured to be between 2 and 3 degrees since 1997.  

Therefore, the Greenland Institute of Natural Resources cannot point to any changed environmental conditions being the reason for the lower catch numbers of halibut in Disko Bugt in 2017.

The caught halibut has become considerably smaller

Specifically, the average size of the caught halibut has decreased by 10 cm over the last 15 years, and today large halibuts are only rarely seen compared to earlier. The continued change toward smaller fish indicates that the fishing pressure is too intense.

If allowed catches are decreased, the halibut will have a better chance to grow, and the growth potential of the stock could be utilised better.

The fact that the halibut has become 10 cm smaller in average means that the fishermen in Disko Bay today must catch twice as many halibut in numbers to achieve the same catch in kilo, compared to the beginning of 2000.

 

 

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Photo: Else Olsvig