CCAMLR: Record Antarctic Haul Not a Sure Sign of Replenished Stocks
03 Jan 2007 - Interviews, Flora & Fauna, Antarctic
Marbled Notothenia (Notothenia rossii), the main target of the fishery activities near Elephant Island in the eighties.
© IPF / AWI / G. Chapelle
The first part of the expedition ANTXXIII/8 on Polarstern focuses on biological investigations on fish stocks as a contribution to the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR), following a dozen similar surveys since 1976. Researchers monitor previously fished areas located in the western part of the Antarctic Peninsula to determine the state of stock recovery.Gauthier Chapelle, our media officer onboard the vessel, has interviewed Dr Karl-Hermann Kock from the Federal Research Centre for Fisheries in Hamburg (BFAFI), leader of the CCAMLR working group.
Dr Kock, as one of the most experienced Antarctic fisheries specialists, can you explain how the Antarctic fish stocks are managed differently by CCAMLR, in the context of today's near collapse of most of commercial fish populations worldwide ?
The CCAMLR which came into force in 1982 was the first convention which embodied an ecosystem approach to management of marine resources. As such, it was an attempt to allow exploitation without affecting negatively predators which depend on the same species as food resources.When estimating total allowable catches for krill, for example, the model encapsulates a 75% escapement rule for krill, which means that only 25% of the stock is available for fisheries, whereas the untouched 75% can escape in order to satisfy the needs of krill predators.
Models to harvest fish stocks, such as Patagonian and Antarctic toothfish (Dissostichus ssp)., incorporate rules which aim to minimise the likelihood of exploited fish stocks falling below a certain level. So far, this approach has worked successfully.
However, one should always bear in mind the problems posed by illegal, uncontrolled and unregulated (IUU) fishing. As it is virtually impossible to monitor each fishing vessel on this huge ocean, this illegal fishing has the potential to undermine all positive management efforts in a very short period of time.
Germany has been conducing demersal fish surveys for 30 years around Elephant Island, with some of them occurring before, during and after commercial fishing operations: how did stocks change over this period?
Most commercial fishing around Elephant Island and the South Shetland Islands occurred over a comparatively short period of 4-5 years from the late 1970's to the early 1980's. The target species were Marbled Notothenia (Notothenia rossii) and Mackerel Icefish (Champsocephalus gunnari). For Marbled Notothenia, we know that the commercial fishery took almost as much as we had estimated to be the stock size two seasons earlier. This led us to the conclusion that the commercial fishery took most of the stock and stock size was depleted to low levels.
Mackerel Icefish is a slightly different story. The commercial fishery took most of the icefish before they were sexually mature and could contribute to the spawning stock. Thus, the commercial fishery missed the opportunity to increase spawning stock size which could have led to larger and more stable catches a few seasons thereafter.
Both examples illustrate how dangerous it might be when fishing occurs on species and stocks without a thorough knowledge of their biology and population dynamics.
What impacts did commercial fisheries have on non-targeted species?
Usually, the effect commercial fisheries have on non-target species (so called 'by-catch' species) should be less than on targeted fish species. The situation has been a little more complicated in parts of the Southern Ocean, such as South Georgia, where by-catch species, such as Yellow Notothenia (Gobionotothen gibberifrons), Scotia Sea Icefish (Chaenocephaliusaceratus) and the South Georgia Icefish (Pseudochaenichthys georgianus) suddenly became target species in the fishery when the stock size of the initial target species Mackerel Icefish became depleted. This led to substantial declines in the stocks of former by-catch species. After CCAMLR had prohibited any targeted fishing on these species their stock size increased again to previously known levels.
On the other hand, near Elephant Island, by-catch species never represented more than a few percent of the catch, thus their populations remained unaffected by commercial fishery activities (fishing in the area has been prohibited since 1989/90).
The biggest Antarctic fish catch for Polarstern: more than 5 tons of Marbled Notothenia
© IPF / AWI / G. Chapelle
Some days ago, Polarstern's biggest Antarctic haul in history brought 5 tons of fish on the deck. However, you were quick to warn that this should not be taken as a signal to get commercial fisheries back in this area. Can you explain why one shouldn't draw early optimistic conclusions ?
The species, we caught was Marbled Notothenia. The species is highly gregarious and tends to concentrate in comparatively small areas while vast areas are only very thinly populated. Stock size estimates have to take this behaviour into account. If they do not, you expect a much higher fish biomass than is actually present. If the 5 tonnes have come out of the middle of a fish concentration the number will tell you at most that there has been a concentration of fish but does not tell you how many fish are in a particular area and could potentially be exploited. Only the analysis of the complete data set at the end of the survey will tell us how many fish are there and in which proportions. It is only then, that we can tell if and to what extent fish stocks have recovered and if it is advisable to re-open the area for commercial exploitation. However, so far, none of the surveys has demonstrated that certain stocks have increased to a size which might allow a viable fishery.
By: Richard de Ferranti
