SOUTH GEORGIA MARITIME ZONE: A SUCCESSFUL MARRIAGE OF MANAGEMENT AND SCIENCE
Katherine Ross does fisheries science for British Antarctic Survey and the South Georgia Government in this well equipped lab on King Edward Point.
By J. Brock (SARTMA)
Had South Georgia experienced a red tide such as the one in the Falklands? It's a natural question to ask, seeing that the fisheries are so close to each other. British Antarctic Survey Scientist, Katherine Ross (KR), quickly indicated that there were no problems such as those that affected the Falklands fishery.
KR: I will answer your red tide questions all together. I am not a Plankton Biologist and certainly not an expert on red tides. However, I have talked to several people and the general feeling is that plankton from the Falklands are very unlikely to survive in the cold waters around South Georgia.
At the moment, the fishery is safe. No doubt, if the wildlife were experiencing the symptoms of red tide poisoning, there would be Plankton Biologists present on South Georgia checking it out.
SARTMA: Given that Patagonian Toothfish spawn, mature and migrate, do they spend any part of their life cycle outside of the South Georgia Maritime Zone?
KR: From surveys and fishery data we know that mature, spawning toothfish are common within this management zone. Ongoing tagging and genetics work should clarify to what extent toothfish from this area mix with stocks in surrounding waters.
(The objectives of the Toothfish tagging programme are to investigate the spatial and temporal movement of the species in South Georgia and to validate the growth rate estimates.)
Interestingly we have recently caught toothfish in Cumberland East Bay, in only 200m of water. Toothfish were thought to stay in much deeper, offshore water. Their occurrence here is exciting because it means that a section of the stock may be completely protected within the 12 mile no fish zone which surrounds South Georgia.
SARTMA: Generally, what is the age of Toothfish that are caught in the Zone?
KR: We check this every year, using toothfish otoliths (ear bones) collected by fisheries observers. After grinding and polishing the otoliths we can count yearly growth rings, a bit like on a tree, and determine age range of fish caught in the fishery. I think the average size is around 90 cm or just under 10 years old. The average size and age of toothfish is very important and we keep quite a strong eye on that to check that the sizes aren't getting smaller, which can be a sign of over-exploitation.
SARTMA: Is this age range spot-on or are they too old, or too young, in your opinion?
KR: Toothfish mature at about 10 years old. But our fishery is managed in such a precautionary way, with small allowable catches, that the amount taken out, shouldn't reduce numbers of young fish entering the fishery each year. We are very confident that with all the data we've got on the abundance of fish and the age structure and the population that the amount we take out really shouldn't affect future stock levels. Ongoing monitoring also ensures that total allowable catches change annually according to the condition of the stock.
As part of CCAMLRS ecosystem approach (which means that all members of the ecosystem and not just target fish stocks are considered in fishery management) we also work on by catch species such as rat-tails and skate. Many of these species are slow growing and produce relatively few young so it is important that their accidental capture is also taken into account by fishery regulations. It makes the job very interesting for us because we get to study lots of different species.
SARTMA: Would you further explain the importance of maturity in relation to stock assessment?
Removing large amounts of immature fish can prevent a stock from sustaining itself. Careful monitoring, strict catch limits and effective enforcement of these regulations mean that this should not be a problem around South Georgia.
SARTMA: How much Krill does the wildlife indigenous to South Georgia consume?
KR: I am not sure; perhaps the biologists at Bird Island would be able to tell you. Krill don’t breed around South Georgia but are brought here from the South by ocean currents. Krill supplies can therefore fluctuate widely from year to year and much of the wildlife eats a range of krill-like plankton.
SARTMA: From what you are saying, there is enough Krill to sustain the wildlife and human consumption. Is this correct?
KR: Yes fishing only takes a tiny fraction of the Krill available in these waters and we are confident that it does not deprive other wildlife of essential food.
Unfortunately, the M/S Endeavour could not stop in at Bird Island. However, the information that was not accessible at King Edward Point is surely accessible there, perhaps to be explored in a future article about the South Georgia fishery.
The morning spent at King Edward Point was informative and my thanks goes to Pat Lurcock, Katherine Ross, Russ Jarvis and Linda Capper for their assistance in producing this two-part article.