Krill Questions

One of the outcomes of a 2014 ‘krill stakeholder’ workshop hosted by British Antarctic Survey (BAS), World Wildlife Fund (WWF), and the Integrating Climate and Ecosystem Dynamics (ICED) programme, was an invitation to participants to submit questions about krill and the krill fishery. These questions were then refined into a smaller set of Frequently Asked Questions (FAQs). In response to these FAQs, the Chair of the Scientific Committee, the Convener of the Working Group on Ecosystem Monitoring and Management (the expert group in CCAMLR that works on krill) and the CCAMLR Secretariat’s Science Manager developed some 'Hopefully Useful Answers'.

For each of these FAQs there are a range of potential answers. The answers that we have provided are not necessarily 'CCAMLR’s answers', nor are we responding on behalf of the Commission. We are solely providing answers that reflect our understanding of krill and the krill fishery. If you have any other questions, or you have better answers than those we have provided, please send them to ccamlr [at] ccamlr [dot] org. We will continue to revise and refine the information we have presented here as new information and knowledge becomes available.

Christoper Jones, So Kawaguchi and Keith Reid

Why are krill so important?

Krill are extremely important because they are the main diet for most of the marine predators (penguins, seals, whales, fish) in the Southern Ocean. At the same time krill themselves are the major grazer of primary production within their range. Krill plays the important role of re-packaging vast amounts of primary production into their own body by grazing micro-size phytoplankton to make them available for marine predators. Because of this role they are called the 'keystone species' in the Southern Ocean ecosystem. Antarctic krill are also regarded as one of the most abundant animal species on the planet.

Which countries fish for krill and how much do they catch?

In the last five years, eight Members of CCAMLR have fished for krill (see Table 1), the majority of the krill catch has been taken by Norway (58%), followed by the Republic of Korea (19%) and China (10%).

These data (and more) are publically available in the CCAMLR Statistical Bulletin.

Setting krill catch limits is based on mathematical models that are used to simulate a krill population and project it forward over a 30 year period. These projections are repeated thousands of times, each time varying key pieces of information, like how many krill enter the population (what scientists refer to as recruitment), how fast krill grow and how many krill survive from one year to the next. This simulates a range of possible future scenarios for the krill population and by introducing the effects of a fishery with different catch levels it is possible to determine how much krill can be taken without having an unsustainable impact on the krill population.

What level of information do we need to manage the krill fishery effectively (and do we have it)?

It might be better to think of this question as 'How do we ensure that we manage fisheries based on the information that we have or can realistically collect?' The approach to management taken by CCAMLR is one that is based on the information that we actually have and 'errs on the side of caution' when making management decisions (the so-called 'precautionary approach').

A good example of this is the current 'trigger level' (of 620 000 tonnes) for krill. The catch limit for the whole of the Scotia Sea is 5.6 million tonnes but the fishery can’t go beyond the trigger level until there is an agreed mechanism to spread the fishing effort across the whole area rather than for it to be concentrated in a few areas, where those locally high catches could potentially impact the local ecosystem. If data on the fishery and the ecosystem indicates that catches are sustainable at small scales, then the catches could increase beyond the trigger level. Importantly, if we don’t have scientifically sound information then there would not be any expansion in the fishery above the precautionary trigger level.

In 2015, the Commission agreed that we need management approaches that are not dependent upon data unlikely to be available at the spatial and temporal scales required for a particular management approach (e.g. regular estimates of total krill biomass and total predator demand for krill for the whole of the Scotia Sea). This might seem pretty obvious, but it reflects the need to design management processes that are practical and can be implemented in the real world.

What was happening before CCAMLR existed?

The Southern Ocean has a somewhat chequered history when it comes to ‘fishing’. In the late 1700’s sealing started in the subantarctic and went through a quick boom and bust cycle. Next came whaling and there was the same boom and bust. As whale populations were ‘going bust’ some nations turned their attention to the development of an Antarctic krill fishery, and there was a concern that a boom and bust pattern in a krill fishery would be a disaster for the Antarctic marine ecosystem; it was this concern, as well as concern for finfish fisheries, that led to the creation of CCAMLR.

How does CCAMLR involve scientists, fishermen and NGOs in decision making?

Each of the 25 Members of CCAMLR makes decisions about who to include on their delegation to each of the meetings depending on the issues for discussion. All CCAMLR delegations include scientists, some include fishermen (remember that many of the Members of CCAMLR are not actively engaged in fishing for krill in the Antarctic at the moment). A range of non-governmental organisations (NGOs) are also represented at the meetings of the Scientific Committee and the Commission. Because decisions are made by consensus in CCAMLR, there needs to be unanimous agreement between Members for those decisions to be made. The decisions that CCAMLR does or does not make reflects the often quite broad range of views by all of the different Members.

Is there by-catch in the krill fishery?

Because the nets used in the krill fishery are not towed along the seafloor, there is much less by-catch than in many other trawl fisheries. However, there is a relatively small level of fish by-catch and this is an area that the scientific observers* are collecting data on to determine the size of the problem and how it might be avoided.

A few years ago there were reports of fur seals being trapped in krill fishing nets and as a result of this the nets used in the krill fishery have to be fitted with an ‘exclusion device’ to avoid seals becoming trapped in the net. These devices usually consist of a ramp that lets krill through, but pushes seals to an escape hole in the roof of the net. There have been no reports of seals caught in krill nets since CCAMLR made it a requirement for nets to be fitted with exclusion devices.

*Each krill fishing boat is required to carry a scientific observer for part of the time they are fishing.

At what depth is krill fished?

Krill are caught with midwater trawls. These are trawls that do not come into contact with the seabed and fishing typically takes place at depths up to 200 m, although it can occur at depths down to 600 m. The depth of fishing tends to follow a fairly regular pattern of being deeper during the day and shallower at night in response to the vertical migration of krill towards the surface at night. Similarly, there is a tendency for fishing to be deeper during winter than in the summer, and this may reflect some seasonal changes in the depth distribution of krill. The changes in the depth that krill are fished show a similar pattern to the changes in the diving behaviour for krill predators such as penguins and seals, and so can actually provide some very useful insights into ecosystem dynamics throughout the year.

Which is the less environmentally harmful fishing practice: continuous or traditional trawling?

This question assumes that both methods of fishing are 'environmentally harmful', which is something of a value-judgement rather than one based on scientific data. The environmental impact of any fishing activity cannot really be judged solely on the length of time a net is in the water, which is the main difference between these two fishing techniques. The way in which krill are caught is only one part of the overall process of the krill fishery, and the choice of what nets to use, what depth to fish, what sort of krill to catch, how the krill are processed on board the vessel and what products to make from a particular catch can be different for each vessel.

Is there any scientific evidence that links declines in some penguin species to the operation of the krill fishery?

In short, no. There is no scientific evidence at the moment that changes in the populations of any penguin species can be attributed to the operation of the krill fishery. That does not mean that CCAMLR is not concerned about those documented declines in penguin populations, as they are clearly indicating that some major changes are taking place. Determining whether these changes are due to climate change, the long-term effects of historical (pre-CCAMLR) harvesting or current fishing activities remains a very active area of scientific debate.

How much krill is there in the Southern Ocean?

This is a very difficult question to answer because krill abundance is highly variable between and within years. On average, the biomass has been suggested to fall within the range of 60 to 420 million tonnes, with current best estimate of 389 million tonnes. However, this estimate is largely based on our past understanding of krill habitat range. Historically, the main krill habitat was thought to be within the top 200 m of the water column, but there is increasing evidence of krill occurring regularly near the seafloor at abyssal depths. Technological developments are now allowing us to reveal evidence of a vast amount of krill biomass in places scientists never suspected. We have yet to understand the dynamics and extent of those deep krill and its relation to the surface population.

How do you estimate krill abundance?

Krill abundance is actually estimated as a measure of biomass rather than as a count of the number of indivuals in the population. The way we measure the biomass of krill is by using hydroacoustic surveys. Ships will travel along a series of transects using echosounders and record the echo signals reflected from krill in the water. Targeted trawls will also be conducted along the way to verify the composition of echo signals so that we know how much of the signals should be attributed to krill. Based on this information and a set of equations, the echo signals will be converted to krill abundance. CCAMLR has a set of stringent standard protocols for acoustic methods to increase the accuracy and minimise uncertainties in the biomass estimation.

What Antarctic species eat krill?

Krill are eaten by many Antarctic species, including:

• Penguins (chinstrap, Adélie, emperor, gentoo, macaroni, king, rockhopper)
• Seals (fur, crabeater, Weddell, elephant, leopard)
• Baleen whales
• Most species of finfish
• Squid
• Albatrosses and most other species of flying seabirds.

How much krill do predators such as penguins, seals and whales eat?

Just like the question on how much krill is in the Southern Ocean, this is a really difficult question to answer. Scientists have been grappling with this question for quite some time and putting together the pieces to what is a very complicated jigsaw. Even something as apparently simple as counting how many penguins there are and how much krill they eat is actually very complex; the ability to use satellites to count penguins from space is an exciting leap forward. However, an analysis in 2007 by Simeon Hill and colleagues suggested that fish actually consumed much more krill than penguins and whales put together. Coming up with a total consumption estimate requires a lot of individual estimates, each of which has some uncertainty associated with it. When you add up all the individual estimates you also add up the uncertainties (which may mean that the eventual total is very hard to use in management). Rather than trying to come up with an absolute estimate of the total krill consumption we use indicators such as diet composition, foraging behaviour and breeding success to detect changes in the relative consumption of krill.

What does ‘recruitment’ mean and what influences the level of recruitment? Do we know where krill nursery areas are?

In population models we use the term recruitment to describe the process of young individuals joining the adult population. In the case of krill, recruitment occurs when a krill larva develops and survives through the winter to join the adult population in the following spring. The level of recruitment is usually expressed as proportional recruitment which is the proportion of one-year-olds to the two-year-olds and older. Krill use the habitat created beneath sea-ice to survive their first winter as the underside of the ice supports algal growth on which krill can feed and so it provides a nursery ground for larval krill. Ice algae production in early spring also boosts growth of adult krill after the winter period when food is scarce. As the sea-ice retreats, a phytoplankton bloom promotes krill growth and ovarian maturation for the summer reproduction period. The sequence and the timing of these processes occurring within the seasonal ice zone are the key determinants for successful krill recruitment and subsequent abundance.

How is climate change/ocean acidification predicted to impact krill abundance and distribution?

Because krill life history is strongly related to sea-ice, reduction of sea-ice in the future may reduce krill habitat and abundance. Further, warming is expected to cause a pole-ward reduction in areas of the habitat that can support growth of krill because under rising seawater temperatures krill may need more energy to live, which will negatively affect their ability to grow. Krill eggs are sensitive to ocean acidification. Based on projections of future CO² distribution in the Southern Ocean it is suggested that some of the important krill habitats could become unsuitable for krill recruitment in the next century. These environmental changes are thought to act in concert to modify the abundance, distribution and lifecycle of krill.