The roughly 85 species of krill, crustaceans that look somewhat like shrimp, are found living in the oceans around the globe feeding on single-celled, microscopic plants called phytoplankton. Comprising of two families, the Euphausiidae (also called Antarctic Krill), float in swarms near the ocean’s surface, and due to easier access are more commonly studied by scientists. Bentheuphausia ampblyops are the more primitive family, and they are found in waters below 30,000 feet. Numerous aquatic species from fish to penguins and whales use krill as their main source of food. It would not be incorrect to say that without krill a vast majority of the Antarctic population would become extinct.
So how is a species that is so widely hunted able to survive? According to some estimates krill constitute the greatest animal biomass on the planet. In-fact, during certain periods of the year, their masses are so immense that when they congregate in swarms, the swarms are so far-flung and concentrated that they can be seen from outer space! It has been said that the collective mass of krill on the planet is greater than that of the human population.1
A second major reason for krill sustainability is the fact that they are rather robust animals. They have amazingly long lives, up to ten years, and are skilful at avoiding predators. They sink to the freezing ocean depths thus evading hunters in daytime and float up at night to feed. It has been observed that the further down they go in the ocean, the less mobile they become. This is done to cut down on the chances of being detected by hunters and preserve energy. Furthermore, krill can survive without food for as long as 200 days. As they begin to starve their size becomes smaller, hence conserving resources.2
The female krill lays as many as 10,000 eggs in one go and at times she does this several times in a single season. This further enhances sustainability. After having been laid close to the ocean surface, the eggs begin to sink and continue sinking for nearly ten days. They hatch in the safer environment of deep ocean waters at the depth of around 3000 meters.2
As the benefits of omega-3 fatty acids and asaxanthin (nutrients which are found in abundant quantities in krill) gain acceptance among consumers, greater amounts of krill is caught and turned into supplements. To prevent overfishing of krill, the independent international organization Conservation of Antarctic Marine Living Resources (CCAMLR) regulates the amount of krill fishing. Each krill fishing boat is required to be licensed and each year limits are set on the percentage of total krill mass that can be caught.3 Not even one per cent of the assessed krill biomass is being fished for commercial use currently, which is significantly lower than that of other fish, hence scientists are not worried about the levels of krill fishing.5
While, krill fishing is not a threat to its sustainability, other human actions can negatively affect the existence of krill. Air and vehicle traffic, power stations and other uses of fossil fuels have already raised the average temperature of the Southern ocean by about 1degree over the last 50 years. Future projections predict even greater rise in ocean temperatures due to the effects of global warming. This could be detrimental not only for krill but the large variety of sea life it supports.
References:
1 http://animals.nationalgeographic.com/animals/invertebrates/krill/
2 http://www.krillfacts.org/1-krill-facts-center.html
5 http://phys.org/news/2013-08-antarctic-seas-impact-krill-habitats.html