Frequent Questions—Potential Biological Removal
Information on the Potential Biological Removal level, its importance to marine conservation, and how scientists use it.
Is the Potential Biological Removal level specific to marine mammals?
No. While use of the Potential Biological Removal (PBR) framework within the Marine Mammal Protection Act (MMPA) is specific to marine mammal stocks, it has been widely used by scientists and wildlife managers to identify populations of conservation concern globally. For example, the framework has been applied to bycatch of seabirds in commercial fisheries and levels of hunting of wildlife in tropical forests. Scientists have also recommended it generally for management of exploited species.
What counts against the Potential Biological Removal level for assessing a stock’s status?
Per the MMPA, all human-caused deaths and serious injuries are compared to a stock’s PBR to determine its strategic status.
The following marine mammal incidents are not included when comparing to a stock’s PBR to determine strategic status because they do not result in individuals animals being removed from a population:
- Non-serious injuries
- Serious injuries that are resolved through human intervention (e.g., disentanglement) or if the animal manages to free itself
- Natural deaths, such as predation, illness, or starvation
How conservative is the Potential Biological Removal framework?
The value used for each element of a stock’s PBR is selected to ensure the goals of the MMPA are met with high assurance (95 percent probability), despite uncertainty. However, this does not mean that PBR is overly conservative. NOAA Fisheries’ Guidelines for Preparing Stock Assessment Reports describe how to determine the values for each element of the PBR equation. Per the MMPA, the values must be based on the best scientific information available. The guidelines provide for flexibility in determining values to ensure the goals of the MMPA are met giving varying levels of information and uncertainty.
Is the Potential Biological Removal level a limit or cap on take?
No. A stock’s PBR level is set so that there is high confidence that the goals of the MMPA will be met if human-caused mortality and serious injury remains at or below the PBR level. A stock’s PBR is not a limit or a cap, nor is it a quota with allocations to different sources of human-caused mortality and serious injury. PBR is better viewed as a biological reference point or benchmark.
When removals due to human activity exceed a stock’s PBR, it is a sign to wildlife managers that mortality and serious injury may be affecting the stock’s ability to recover or sustain a healthy population size and action may be warranted. For example, when commercial fishery-related mortality and serious injury exceeds a stock’s PBR, the MMPA directs NOAA Fisheries to convene a take reduction team, which helps us develop a take reduction plan to reduce mortality and serious injury below the stock’s PBR within 6 months.
What are the assumptions of the Potential Biological Removal framework?
The PBR framework assumes that depleted populations will grow and that some portion of that growth can be removed due to human activity without preventing recovery. This assumption likely holds true for most stocks, but not all. For example, a stock that is failing to recover for reasons unrelated to human causes, such as Cook Inlet beluga whales, does not conform to the assumptions of the PBR framework. In such cases, we still calculate and provide PBR in the stock’s assessment report. But, we recognize that even if human-caused deaths and serious injuries are less than PBR, the population size may not increase.
Is the Potential Biological Removal level applicable to subsistence harvest?
Yes. Per the MMPA, all human-caused mortality and serious injury, including those resulting from subsistence harvest, are compared to the PBR level to determine the status of a stock. However, the MMPA allows NOAA Fisheries to enter into co-management agreements with Alaska Native Organizations to promote full and equal participation by Alaska Natives in decisions affecting the subsistence management of marine mammal populations in Alaska. For stocks that are primarily subject to subsistence harvest by Alaska Natives, whether management action is warranted when human-caused deaths and serious injuries are greater than the stock’s PBR will depend on the specific situation and the results of the co-management process.
Does NOAA Fisheries divide a stock’s Potential Biological Removal level among sources of human-caused threats or countries for transboundary stocks?
In general, the PBR level for each stock is considered a single metric applicable to all sources of human-caused removals. PBR is not divided or allocated among sources of human threats or among countries for transboundary stocks.
However, in many cases, we only have information on a single or few sources of human impacts or for a portion of a stock’s range. In these cases, it can be useful to adjust the PBR level to be more comparable to the available information on human impacts, such as to help with managing U.S commercial fisheries.
For example, satellite telemetry data indicate that most blue whales off the U.S. West Coast are outside U.S. waters from November to March. So, we calculate and use a stock-wide PBR level for comparison to all sources of human-caused mortality and serious injury for assessing stock strategic status, but also calculate an adjusted PBR level for U.S. waters, as this may be more informative for managing U.S. commercial fisheries.