Document ID: chunk:federal_register_of_legislation:F2015L01633:body:0:p33
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krill abundance may have decreased in the Southern Ocean due to the decrease in predator abundance from whaling. This apparent paradoxical relationship may exist because baleen whales release iron stores in krill through their faeces and thereby increase ocean productivity109. This means that recovery of blue whale and other baleen whale stocks may cause a positive feedback loop by increasing krill stocks and consequently further increasing whale stocks. The re-assertion of iron nutrient cycling will also be beneficial for the whole ocean ecosystem.

5.2 Threat Prioritisation
The threats to blue whales identified in the previous section were assessed using a risk matrix which evaluates the likelihood of a threat causing an impact and the consequences of it at the population level. The resulting risk assessments in turn determines the priority for conservation and/or management action. Threat ratings were undertaken for Australian pygmy and Antarctic blue whales separately to account for potential differences in exposure to threats and resulting impacts. Threats may act differently on Antarctic blue and pygmy blue whales and different populations at different times of year, but the precautionary principle dictates that the threat category is determined by the group at highest risk.
Population-wide threats are generally considered to present the highest risk. Where mitigation/management measures for a threat exist, the threat is assessed assuming that these measures are being applied appropriately. For example, the seismic guidelines contain practical measures that minimise the likelihood of physical impacts to whales from seismic surveys. However, measures specific for behavioural impacts are not included in the seismic guidelines.
After consideration of ongoing mitigation, the threat is then classified within the risk matrix, including consideration of
     1. Knowledge of the effectiveness of the mitigation/management measure;
     2. The coverage of the mitigation/management measure; and
     3. The scope of the mitigation/management measure.
The risk matrix and ranking of threats is based on information in the peer reviewed literature and expert opinion. Definitions used for the risk assessment are:
       * Likelihood:
                + Almost certain: expected to occur every year
                + Likely: expected to occur at least once every five years
                + Possible: might occur at some time
                + Unlikely: such events are known to have occurred on a worldwide basis but only a few times
                + Rare or Unknown: may occur only in exceptional circumstances; OR it is currently unknown how often the incidence will occur

       * Consequences:
                + Not significant: no long-term effects on individual or populations
                + Minor: individuals are affected but no affect at population level
                + Moderate: population recovery stalls or reduces
                + Major: population declines
                + Catastrophic: population extinction
The level of risk and the associated priority for action are shown in Table 3 using the following criteria:

       * Very