114
Mark S. Boyce
could be maintained at the same level until stocks were reduced to 60% of
stock size (see Fig. 8.1), whereas quotas will be reduced as stock size declines
under the RMP. This affords greater protection for exploited stocks under the
RMP.
4. Uncertainty in estimates of abundance and in MSYR is used to generate a
distribution of possible catch limits. From this distribution, an actual quota is
selected in which 41% of the calculated catch limits are less and 59% are
greater than the recommended number (Young 1993). This again yields a more
conservative quota than choosing the mean or median value, which would be
closer to 50%. As more and better data increase the confidence in estimates,
the CLA typically recommends a higher quota.
5. Before annual quotas can be set for a 5-year period, data are required on
previous harvests and sighting surveys to estimate current stocks.
6. Periodic sighting surveys must be conducted to monitor the efficacy of the
CLA for each stock. If sighting data are not collected within a prescribed
period, the RMP stipulates that the harvest quota is automatically reduced by
20% per year and set at 0 if survey data are not completed within 5 years.
7. Extensive robustness trials were performed to evaluate performance under
various assumptions. For each application of the CLA (i.e., before whaling
begins), additional “implementation trials” will be required in which computer
simulations will be performed that incorporate what is known of spatial organization of the stock.
Populations most likely to be harvested under the CLA will be Minke Whales in
the north Atlantic, the north Pacific, and possibly the Antarctic. Minke Whales are
by far the most abundant rorquals, with population estimates greater than 750,000
animals, including more than 600,000 Minke Whales in Antarctic seas (IWC
1994). Because stocks are large and proposed harvests are small, implementing
the CLA probably will not threaten the future persistence of Minke Whales.
Japan’s request to harvest 2,000 Southern Hemisphere Minke Whales annually
constitutes a kill of approximately 0.3% of current stock size. Sustainable harvests
of other animal populations have been possible given that rates of exploitation are
not excessive (Rosenberg et al. 1993).
There is evidence that rorqual stocks can recover, even after severe depletion,
and populations of several species of whales appear to be increasing (Best 1993;
Schmidt 1994). In particular, the Grey Whales (Eschrichtius robustus) in the
northeastern Pacific Ocean have staged a remarkable comeback from near extirpation at the turn of the century to approximately 21,000 animals today (Buckland
et al. 1993). This population is thought to be near or even greater than preexploitation levels (Schmidt 1994). Estimates of Bowhead Whales in the Arctic
have increased from some 1,500 whales in 1976 to at least 7,800 today, although
part of this increase is probably due to improved estimates (J. Zeh, personal
communication). Likewise, under protection, Southern Right Whales were
thought to have achieved rates of increase in excess of 7% per annum, and Sei
Whales off South Africa increased at annual rates of 9–13% (Horwood 1987);
Mark S. Boyce
could be maintained at the same level until stocks were reduced to 60% of
stock size (see Fig. 8.1), whereas quotas will be reduced as stock size declines
under the RMP. This affords greater protection for exploited stocks under the
RMP.
4. Uncertainty in estimates of abundance and in MSYR is used to generate a
distribution of possible catch limits. From this distribution, an actual quota is
selected in which 41% of the calculated catch limits are less and 59% are
greater than the recommended number (Young 1993). This again yields a more
conservative quota than choosing the mean or median value, which would be
closer to 50%. As more and better data increase the confidence in estimates,
the CLA typically recommends a higher quota.
5. Before annual quotas can be set for a 5-year period, data are required on
previous harvests and sighting surveys to estimate current stocks.
6. Periodic sighting surveys must be conducted to monitor the efficacy of the
CLA for each stock. If sighting data are not collected within a prescribed
period, the RMP stipulates that the harvest quota is automatically reduced by
20% per year and set at 0 if survey data are not completed within 5 years.
7. Extensive robustness trials were performed to evaluate performance under
various assumptions. For each application of the CLA (i.e., before whaling
begins), additional “implementation trials” will be required in which computer
simulations will be performed that incorporate what is known of spatial organization of the stock.
Populations most likely to be harvested under the CLA will be Minke Whales in
the north Atlantic, the north Pacific, and possibly the Antarctic. Minke Whales are
by far the most abundant rorquals, with population estimates greater than 750,000
animals, including more than 600,000 Minke Whales in Antarctic seas (IWC
1994). Because stocks are large and proposed harvests are small, implementing
the CLA probably will not threaten the future persistence of Minke Whales.
Japan’s request to harvest 2,000 Southern Hemisphere Minke Whales annually
constitutes a kill of approximately 0.3% of current stock size. Sustainable harvests
of other animal populations have been possible given that rates of exploitation are
not excessive (Rosenberg et al. 1993).
There is evidence that rorqual stocks can recover, even after severe depletion,
and populations of several species of whales appear to be increasing (Best 1993;
Schmidt 1994). In particular, the Grey Whales (Eschrichtius robustus) in the
northeastern Pacific Ocean have staged a remarkable comeback from near extirpation at the turn of the century to approximately 21,000 animals today (Buckland
et al. 1993). This population is thought to be near or even greater than preexploitation levels (Schmidt 1994). Estimates of Bowhead Whales in the Arctic
have increased from some 1,500 whales in 1976 to at least 7,800 today, although
part of this increase is probably due to improved estimates (J. Zeh, personal
communication). Likewise, under protection, Southern Right Whales were
thought to have achieved rates of increase in excess of 7% per annum, and Sei
Whales off South Africa increased at annual rates of 9–13% (Horwood 1987);