1999 

 OUR LIVING OCEANS 



Spinner dolphins. 



thci 



inablc 



were Delow their optiniiim Mistainanlc popula- 

 tions. 



Although the greatest mortaliry oeeurred in 

 the 1960'sancl 1970s, incidental mortaliry of ETP 

 dolphins was still lairK- high as recently as 1986 

 when 133,1 74 dolphins were estimated killed, and, 

 out ot eight stocks for which a PBR level can now 

 be calculated, seven had incidental mortaliries that 

 exceeded their PBR's. In 1991, mortality in the 

 three stocks ot greatest concern (northeastern spot- 



ted, eastern spinner, central common) still ex- 

 ceeded their PBR's. These comparisons are illus- 

 trative only, as the MMPA specifically manages 

 ETP dolphins by quotas, not calculated PBRs. In- 

 cidental mortaliry ot northeastern spotted dolphins 

 increased in 1986 to 7% ot their abundance esti- 

 mate, a level that is not likely to be sustainable, 

 and this apparently led to another significant de- 

 cline in the stock between 1983 and 1994. The 

 data also indicate that the central stock ot com- 

 mon dolphins is still significantlv below its 1975 

 level. 



N4t)rtality ot EIP dolphins has been declin- 

 ing since 1986 and has decreased dramatically since 

 1991 Clable 23-2). A 1992 international agree- 

 ment to manage the incidental mortaliry ot ETP 

 dolphins, which included individual vessel quo- 

 tas, has led to a decrease in the total mortalitv 

 (2,914 dolphins of all species) in 1997. Since 1992, 

 the incidental mortality has been less than the es- 

 timated PBR tor all stocks, and the annual inci- 

 dental mortality of each stock is now less than 

 0.2% ot their estimated abundance. Such low 

 mortaliry rates should be sustainable and should, 

 if continued, allow the northeastern spotted dol- 

 phin and the eastern spinner dolphin populations 

 to increase and eventuallv recover. 



Table 23-2 



Mortality of dolphins in the 

 eastern tropical Pacific due 

 to the tuna fishery. 



' Comparison ot recent incidental mortality to potential biological removal levels (PBRs) calculated for slocks of eastern tropical Pacific dolphins It sfiould 

 be noted thai ETP dolphins are explicitly excluded from management under the PBR section of the Marine Mammal Protection Act Nonetheless, the 

 calculated PBRs still provide a useful guide for mtepreting the significance of dolphin mortality Abundance estimates are from Wade and Gerrodette 

 (1992) PBRs were calculated using an assumed maximum net productivity rate of 04 and a recovery factor of 5 m each case 



^Hall and Lennert, 1997 



■lennert and Hall. In press 



■* Listed as depleted under the Marine Mammal Protection Act 



244 



