Krill-based fish feed, as well as krill derivatives used in a number of dietary and medical products are behind the rapid rise in the harvest of the crustacean
over recent years. The growth in annual harvest is rapid with the Chinese the latest to join in. The Marine Stewardship Council (MSC) has certified the krill fishery
as sustainable, a controversial decision given that the dominant purpose of the fishery is for fishfeed and krill lie at the start of the foodchain, core to the
existence of many large sea animals.
They feed on the dissolved nutrients (mainly nitrates and phosphates) that come to the surface with the upwelling of the cold Antarctic waters at the Antarctic
convergence, where during the long summer days primary production of planktons etc is prolific. But because krill are large compared to the other phytoplankton
eaters that makes them the food source of large animals such as seals, penguins, whales and a myriad of birds.
Because the fall in Antarctic sea ice over recent years, the population of krill has fallen dramatically – up to 80% over the last 30 years. The algae clinging
to the bottom of the sea ice is a ‘nursery’, feeding the krill larvae during winter. The rising krill catch, in the context of the sea ice-induced reduction, portends
Another species, the catches of which have long been controversial, is that of the Antarctic toothfish. Again that is one the MSC is considering certifiable
as sustainable, and with the main line of objection to that being the lack of knowledge of the impact upon the stock, given the age to reproductive maturity (up
to 10 years) of this species. Secondly there have been significant instances of unregistered ships harvesting here (and arrests) that makes competent management
of the fishery quite uncertain. The Convention for the Conservation of Antarctic Marine Living Resources, covers management of finfish in Antarctic waters and permits
fishing down the stock of toothfish to 50% of its original biomass. Currently it’s estimated to be 85% of that original stock.
But the removal or substantial reduction of a species from an ecosystem has a system-wide effect from reducing food for its predators (sperm whales, type-C killer
whales and Weddell seals) and spurring the population of its prey (silverfish, cods and squid). At issue is whether the effect of fishing down a population like
the toothfish, significantly changes the local food web and wider ecosystem and if so, how? The reduction in the food supply of toothfish prey due to their burgeoning
numbers is of relevance in terms of the sustainability of the fishery. Research on these ecosystem-wide effects continues, the reality being that so far too little
is known to be confident that a reduction of the population by 50% is sustainable. Taken together with the extent of illegal (unauthorised, unregistered) fishing
for the species, and the impact on seabirds (especially albatross) from the fishing techniques has led the Australians to ban longlining in their Antarctic and