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Editorial: Steller sea lions
Blueprint for Recovery
What should be done to promote the recovery of Steller sea lions, and, when should the species be taken off the list of endangered species?
These two fundamental questions are addressed in the revised recovery plan for Steller sea lions, which is now available for public comment. Once finalized later this year, the plan will represent the ‘blueprint’ for actions considered necessary for the conservation and recovery of the species. Other than the relatively small number of folks involved with endangered species on a regular basis, most of us have a limited understanding of the recovery planning process under the Endangered Species Act (ESA) in general, or specifically for Steller sea lions. Below are a few of the key issues involved in the complex, and often contentious, world of sea lion recovery.
The largest sea lion in the world (males can reach over 1000 kilograms), Steller sea lions have a geographic range that extends across the rim of the North Pacific Ocean from northern Japan, through Russia, Alaska, British Columbia, and south to California. There were probably about 250,000 Steller sea lions in the 1950s, with the center of that worldwide population abundance in the Aleutian Islands and Gulf of Alaska. By 1990, the U.S. portion of the population had declined by about 80 percent, and was listed as threatened under the ESA. In 1997, two distinct populations were recognized, and the western population was listed as endangered while the eastern population was listed as threatened; Cape Suckling, east of the Copper River Delta, is the dividing point between the two populations. This spring, a 17 member recovery team representing marine mammal scientists, the commercial fishing industry, Alaska Natives, and environmental organizations drafted a revised recovery plan for both populations. The recovery plan indicates that the number of sea lions in the threatened eastern population has increased slowly for a sufficient period of time such that it should now be considered for removal from the ESA, i.e., delisted. The information below pertains to the strategy promoted for the endangered western population to reach a level sufficient for delisting.
The strategy within the recovery plan for the western population of Steller sea lions is based on a review of the management actions implemented over the last 15 years and the results of an extensive research program. A critical component of the review was an assessment of the factors that influence the population dynamics of sea lions, recognizing that multiple factors affect these animals and those factors likely vary across time and space. The recovery strategy comprises three primary actions:
1. Maintain current fishery management measures; i.e., restrictions on when and where fishing can occur
2. Design and implement an adaptive management program to evaluate fishery management measures
3. Continue population monitoring and research on the key threats potentially impeding sea lion recovery
The rationale for maintaining the fishery management measures is two-fold: Commercial fisheries affect the amount and quality of prey available to sea lions, and when management measures were implemented, the rate at which sea lion numbers declined slowed. Is this definitive evidence that commercial fisheries are impeding the recovery of sea lions? No. For this reason, combined with relatively minimal evidence indicating sea lions are not obtaining sufficient prey, and an apparent increase in the number of sea lions since 2000, an argument can be made to remove or relax the fishery management measures. However, we currently have limited knowledge of how fisheries impact sea lion prey or foraging sea lions. Similarly, we do not understand the potential long-term affects of commercial fisheries on top level predators like the sea lion or their marine ecosystem. In addition, a precautionary approach is required for ESA listed species, and thus fishery management measures should be maintained until substantive evidence demonstrates they can be reduced without impeding sea lion recovery.
How can that “substantive evidence” be obtained? Design and implement an adaptive management program to evaluate fishery management measures, which is the second component of the recovery strategy for the western population of sea lions. Essentially, a genuine adaptive management program can be considered a structured two-stage process of “learning by doing.” The first step is to make predictions, based on existing knowledge, about the results of alternative management approaches. The second step is to design and implement those approaches as experiments, and what we learn from those experiments then guides us toward new management strategies and policies. This adaptive approach needs to be applied to determine how fishery management measures affect fish populations (i.e., sea lion prey) at the spatial and temporal scales of foraging sea lions, and ultimately, the sea lion population. Some efforts are currently underway in this regard, yet they need to be expanded and continued for several years. Without such an approach, distinguishing between the impacts of fisheries and other factors, in particular natural oceanographic variability (e.g., “regime shifts”), will be quite difficult. This is because fisheries and oceanographic variability may both result in reductions in sea lion prey, and their effects on sea lions will be similar, representing a fundamental challenge to identify which threat is impeding recovery and which mitigation measures would be most effective. The feasibility of an adaptive management program must be thoroughly examined and subsequently developed by experts in sea lion ecology, fisheries management, experimental design, and oceanography.
The third component of the recovery strategy for the western population of Steller sea lions is to continue monitoring the population and also conduct research on the key threats potentially impeding recovery. This will require aerial surveys to periodically count the number of sea lions among numerous rookeries and haulouts, assess their health on a regular basis, and determine the essential ecological characteristics of their habitat. That information can then be combined with studies designed to determine how factors such as predation by killer whales and toxic substances impact the number of sea lions. For example, only recently have biologists conducted surveys to estimate the number of killer whales throughout the range of sea lions, and information on how often killer whales kill sea lions remains limited. Without such new information, substantial uncertainty will result in minimal confidence in our estimates of the impact of predation by killer whales on sea lions. Additional studies, including modeling, should be pursued to combine with existing data to determine how various factors interact and cumulatively impact sea lions. These studies must integrate our knowledge of marine ecosystem dynamics and attempt to distinguish between changes from natural versus anthropogenic (i.e., human-caused) factors to determine the feasibility and effectiveness of management strategies.
Certainly, we have learned a great deal about sea lions and their environment over the last 10-15 years. Yet, our knowledge of how marine mammal populations are influenced by the complexity of marine ecosystem dynamics and anthropogenic effects remains quite limited; seriously, rocket scientists have it easier! I believe implementing the recovery strategy for the western population of Steller sea lions will provide the information needed to most effectively achieve their recovery.
Bob Small is the Marine Mammals Coordinator for ADF&G and Chair of the Steller Sea Lion Recovery Team.
The draft revised Steller sea lion Recovery Plan can be found at: http://www.fakr.noaa.gov/protectedresources/stellers/recovery/sslrpdraft0506.pdf
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