FEATURE ARTICLE
Measuring Success in Conservation
Assessing efforts to restore populations of marine mammals is partly a matter of epistemology: How do you know when enough is enough?
Leah Gerber, Douglas DeMaster, Simona Roberts
Success?
All populations of large whales currently listed as endangered under the ESA were severely depleted, or threatened with severe depletion, as a result of commercial whaling. Commercial whaling of these species ended sometime between the 1930s and the 1980s. The first and simplest test regarding the successful conservation of endangered populations of large whales is whether all of these populations have fully recovered; that is, whether they are no longer in danger of extinction. The answer is "no." Only the eastern North Pacific population of gray whales seems to have fully recovered.
Although a majority of populations for which we have data are reported to be increasing, there are several notable failures, including all populations of the northern right whale, eastern Arctic and Okhotsk Sea populations of bowhead whales, the western North Pacific population of gray whales and several populations of blue whales. For some of these populations, illegal commercial whaling in the late 1960s and early 1970s is certainly a key factor in preventing recovery. On the other hand, the western North Atlantic population of right whales has not been illegally harvested, yet it still fails to recover.
Fishery interactions and ship-strikes may contribute to the persistent failure of populations to expand, but there may be a more important factor. It may be that when large whale populations become "too small" (yet to be defined), they will not recover. It is crucial in the future that this lesson not be ignored. The good news for these populations is that none has become extirpated in the last 25 years, although their current status is perilous at best.
Even if many populations have failed the full test of successful conservation, are they at least on their way toward recovery? Clearly, any evaluation of recovery using quantitative criteria is hampered by our limited knowledge of population structure within a species, as well as our lack of information on abundance and trends in abundance. Nevertheless, significant recovery has been reported for several populations of humpback whale in the North Atlantic and Southern Hemisphere, right whales in the Southern Hemisphere, blue whales off the West Coast of the U.S., and the western-Arctic population of bowhead whales. In addition, several other populations seem to have reached relatively high abundances, but trends in abundance and population structure are unknown. These include populations of North Atlantic fin whale, North Pacific fin whale and North and South Pacific sperm whale. Thus it looks like a majority of populations for which we have adequate information to evaluate recovery are indeed recovering.
The lesson here seems to be that at least some large whale populations can recover from overexploitation, but only if their numbers are not reduced to some level, beyond which the "extinction vortex" reaches out and starts pulling them inexorably towards extinction. To ensure that such low population levels do not occur, we recommend that human-related mortalities be limited to something under 2 percent of a conservative estimate of abundance per year. This level of mortality is considered sustainable based on our understanding of basic large-whale biology and the potential for recovery from stochastic events.
Another lesson from this approach is that moratoria on harvest alone are insufficient to guarantee adequate conservation. Without adequate monitoring, it is not clear to what extent management objectives have been or will be achieved. Adequate monitoring programs, such as that for the eastern North Pacific gray whale, will not be inexpensive and will not be brief.
A related question is why some populations are recovering while others are not. Two lessons may be derived from our case studies regarding this question. First, despite the over 60-year moratorium on the harvest of right whales worldwide, there are several recovering populations in the Southern Hemisphere, whereas Northern Hemisphere populations continue to be in danger of extinction. Second, despite the continued harvest of bowhead whales in the western Arctic, this population is recovering, whereas the other four unharvested populations are not. The western Arctic and Southern Hemisphere may be distinguished by a comparatively low amount of human activity on the margins of the oceans as compared with the rest of the world's oceans. We therefore speculate that the lack of recovery in some populations may be slowed by non-harvest impacts such as fishery-gear entanglement or ship collisions. Furthermore, in some ocean basins significant oceanographic changes may have taken place. However, without long-term monitoring studies on habitat use, trends in abundance and feeding ecology, it will not be possible to ascertain why certain populations of large whales are recovering, while others are not. As the 20th century comes to a close, the threat of large-whale depletion at the hands of commercial whalers is no longer imminent. Today indirect effects from human activities such as shipping, fishing, pollution, habitat degradation and mineral exploration are the primary threats facing large whales. Although it is still important to consider any lingering effects of direct over-exploitation, it is also time to focus on what dangers—whether human or environmentally driven—these animals are currently facing and how these dangers may influence their continued survival.
For several populations of large whales, the current status under the ESA needs to be reconsidered. In developing ESA classification schemes for populations, such as the North Atlantic humpback whale and the western Arctic bowhead whale, decision makers will be hard pressed to develop and use an objective set of criteria for all populations of large whales. Yet such objective criteria are exactly what are needed when agencies are faced with an emotionally charged public, a lack of biological data and a clear need to set priorities for allocating limited resources.
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