MARINE MAMMAL COMMISSION — Annual Report for 1991 



pared by National Marine Fisheries Service scientists 

 stated: 



"If the recent level of mortality continues and 

 given the level of precision in monitoring trends 

 and abundance, it is unlikely that significant 

 changes in abundance will be detected in the 

 near future. Therefore, managing mortality 

 levels so that they do not exceed some fraction 

 of the expected net production should be consid- 

 ered as a more reasonable management strategy 

 than managing levels based on trends in relative 

 abundance. " 



Concerned that dolphin stocks had been and 

 continue to be adversely affected by the tuna fishery, 

 environmental groups petitioned to have two stocks 

 designated as depleted under the Marine Mammal 

 Protection Act and listed as threatened under the 

 Endangered Species Act in 1991. Under the Marine 

 Mammal Protection Act, any population that is below 

 its maximum net productivity level, the lower bound 

 of the optimum sustainable population range, is 

 considered to be depleted. The National Marine 

 Fisheries Service has determined that maximum net 

 productivity in small cetaceans, such as those dolphin 

 species taken incidental to the eastern tropical Pacific 

 tuna fishery, occurs at about 60 percent of carrying 

 capacity. A threatened species is one "which is likely 

 to become endangered in the foreseeable future 

 throughout all or a significant portion of its range." 



On 2 August 1991, the Committee for Humane 

 Legislation and 23 other groups petitioned the Secre- 

 tary of Conmierce to designate the eastern spinner 

 dolphin (Stenella longirostris orientalis) as a depleted 

 stock. The petition asserted that a depletion finding 

 was warranted because "[i]ncidental catches of this 

 population in the tuna purse-seine fishery have re- 

 duced it to about 20 percent of its original size over 

 the last two decades — declining from about 

 2,000,000 to 400,000." The petitioners also noted a 

 recent report published by the National Marine 

 Fisheries Service's Southwest Fisheries Science Center 

 that estimated mortality incidental to the tuna fishery 

 to have resulted in a 56 to 74 percent decline in 

 eastern spinner dolphin abundance since the 1950s. 



On 30 August 1991, the Center for Marine Conser- 

 vation, the Committee for Humane Legislation, and 



19 other groups petitioned the Secretary of Commerce 

 to list the eastern spinner dolphin as threatened. The 

 petition indicated that more than 1.5 million eastern 

 spinner dolphins had been killed incidental to the 

 eastern tropical Pacific tuna fishery since 1959, 

 reducing the population to approximately 20 percent 

 of its original size. The petitioners also noted that, 

 between 1986 and 1990, fishery-related mortality of 

 this stock averaged 13,860 animals per year. The 

 annual mortality during this period constituted about 

 2.4 percent of die population and exceeded the popu- 

 lation's estimated net productivity rate of two percent. 

 The petition also called upon the Secretary to enter 

 into bilateral or multilateral agreements to conserve 

 the species and to eliminate tuna fishing by setting 

 purse seine nets on dolphins. 



A petition seeking designation of the northern 

 offshore stock of spotted dolphins {Stenella attenuata) 

 as depleted was submitted to the Secretary of Com- 

 merce by Environmental Solutions International, 

 Greenpeace U.S.A., and seven other groups on 28 

 October 1991. Comparing the historic abundance 

 estimate for this stock adopted by the Service in its 

 1980 quota-setting rulemaking (5,030,000) with the 

 "best available" current population estimate (658,300- 

 2,205,500), the petitioners assert that the northern 

 offshore spotted dolphin is well below 60 percent of 

 carrying capacity and is therefore depleted. 



The Center for Marine Conservation petitioned the 

 Secretary of Commerce on 30 October 1991 to list the 

 northern offshore spotted dolphin under the Endan- 

 gered Species Act as threatened. Based on data 

 published by the National Marine Fisheries Service, 

 the petitioners maintained that the stock had been 

 reduced by mortality in the tuna fishery to about 30 

 percent of its original size. In addition, the petitioners 

 noted that annual incidental mortality during 1986- 

 1990 averaged 48,040 animals, for an annual mortali- 

 ty of about 3.2 percent. In the absence of evidence to 

 the contrary, mortality rates in excess of two percent 

 per year are assumed to be unsustainable by Service 

 scientists. 



The National Marine Fisheries Service published a 

 notice in the Federal Register on 5 November 1991 

 finding that the petitions presented substantial infor- 

 mation indicating that designating the eastern spinner 

 dolphin as depleted and listing the stock as threatened 



102 



