Our August story, “New Stock Assessment of Pelagic Population of False Killer Whales,” regrettably included several errors and failed to note several important points. The following is intended to correct and/or clarify misstatements and omissions in our piece.
Our statement that the take reduction plan was based on an old population estimate was incorrect. The take reduction plan’s trigger for closing the Southern Exclusion Zone (SEZ) is not tied to any particular stock assessment. Rather, it was designed so that it can be adjusted to reflect current potential biological removal (PBR) and observer coverage levels.
The PBR level is based, in part, on a minimum population size estimate. In the case of pelagic Hawaiian false killer whales, the previous PBR level of 2.4 was based on a minimum population size estimate of 249 whales, which was determined using a best abundance estimate of 484 whales.
The closure of deep-set longline fishing in Hawai`i as a result of fishers killing/seriously injuring whales at a level that exceeds the PBR level would apply only to the SEZ, which includes federal waters south of the Main Hawaiian Islands and stretches past some of the Northwestern Hawaiian Islands.
Reducing fishery-related take to below PBR is the short-term (six-month) goal of the take reduction plan. The long-term goal is to reduce fishery-related take to less than 10 percent of the PBR within five years. These take reduction goals are specified in the Marine Mammal Protection Act.
The new abundance estimate for pelagic Hawaiian false killer whales — 1,503 — is approximately three times higher than the previous best estimate. A new PBR of 9.1, based on a revised minimum population estimate of 906, has been proposed in a new draft Stock Assessment Report. About one in five vessels in the deep-set longline fishery carry observers, so to arrive at an estimate of total takes (serious injury or death) of false killer whales, the number of observed takes is multiplied by five. As a result, even low levels of observed takes may still exceed the new PBR and may vastly exceed the MMPA goal of reducing take in commercial fisheries to no more than 10 percent of PBR.
While the five-year average take by the longline fleet (deep-set and shallow-set longline fisheries) between 2004 and 2008 was 7.3 FKWs/year, the latest estimate of annual take in the longline fisheries — within the Exclusive Economic Zone — is 13.8 whales (based on a five-year average from 2006-2010). The fisheries were estimated to have killed an additional 11.3 animals on the high seas over the same time period. Due to the high level of fishery take in 2009, the official five-year take average will remain high until the 2015 stock assessment report.
The estimate we gave in our August article of potential economic losses by the fishery needs clarification. A closure of the SEZ would mean a reduction of approximately 17 percent of the deep-set longline fishing area. Although the fishery generates an average of $38.9 million a year in bigeye tuna catches, it is unknown how or whether an SEZ closure would affect revenue. Any financial impacts would depend on when in the fishing year the SEZ closed and any subsequent adjustments in effort, among other things. In any case, the trigger for closing the SEZ, as previously mentioned above, is not tied to any particular stock assessment.
Volume 23, Number 3 September 2012