LO and SMITH: INCIDENTIAL MORTALITY OF DOLPHINS 



for both large and small vessels for all years, and 

 4) the kill rate itself for sets with backdown did not 

 change over the years. 



Although each of the unaccounted for factors could 

 have an effect on the estimated numbers of dolphins 

 killed, the magnitude of such effects is probably 

 smaller than the magnitude of the effects of vessel 

 size, set success, and use of backdown described in 

 this study. For example, although the kill rate data 

 available are few, there are some additional data 

 which are not available to us, but which are reported- 

 ly similar (Smith and Lo 1983). The last three 

 assumptions noted above deal with the dolphin kill 

 rates with and without backdown, and would tend 

 to both increase and decrease the estimates, if they 

 could be taken into account. 



Our estimates of the total number of dolphins 

 killed (Table 4) are slightly lower than previous esti- 

 mates made using the same method (Smith 1979 6 , 

 1983). The previously estimated total number of 

 dolphins killed from 1959 to 1972 was 5.1 million 

 (total of Smith's [1983] table 4, divided by 0.96 for 

 other species and by 1.048 for injured animals). The 

 difference between the two estimates resulted from 

 the revision of the estimated number of sets that cap- 

 ture tuna associated with dolphins (Punsly 1983) and 

 of the numbers of dolphins killed per set (Smith and 

 Lo 1983). 



There are alternate approaches to estimating the 

 numbers of dolphin killed. For example, estimates 

 could be made from data on the numbers of fishing 

 trips made (kill-per-trip), or the number of tons of 

 tuna caught (kill-per-ton). These approaches make 

 different assumptions about the fishing process (Lo 

 et al. 1982; Hammond and Tsai 1983), and require 

 data which are not as precise as are data on the total 

 numbers of sets. For example, fishing trips are dif- 

 ficult to count consistently because they may not be 

 completed within the calendar year and may be ex- 



6 Smith, T. D. (editor). 1979. Report of the Status of Porpoise 

 Stocks Workshop, August 27-31, 1979, Southwest Fisheries Center, 

 La Jolla, California Southwest Fish. Cent., Admin. Rep. LJ-79-41, 

 120 p. 



tended by partial unloading of the catch. There are 

 fewer such problems with the data for kill-per-set 

 estimators on the number of dolphins killed, and the 

 problems that exist have already been resolved 

 (Punsley 1983). 



LITERATURE CITED 



Anonymous. 



1962. How tuna seining paid off for the U.S. fleet in 1961. 

 Fish Boat, Feb., p. 19-30. 

 Barham, E. G., W. K. Taguchi, and S. B. Reilly. 



1977. Porpoise rescue methods in the yellowfin purse seine 

 fishery and the importance of Medina panel mesh size Mar. 

 Fish. Rev. 39(5): 1-10. 

 Green, R. E., W. F. Perrin, and B. P. Petrich. 



1971. The American tuna purse seine fishery. In Hilmar 

 Kristjonsson (editor), Modern Fishing Gear of the World, Vol. 

 3, p. 182-194. Fish. News (Books) Ltd., Lond. 

 Hammond, P. S., and K. T. Tsai. 



1983. Dolphin mortality incidental to purse-seining for tunas 

 in the eastern Pacific Ocean, 1979-81. Rep. Int. Whaling 

 Comm. 33:589-597. 

 Lo, N. C. H., J. Powers, and B. E. Wahlen. 



1982. Estimating and monitoring incidental dolphin mortality 

 in the eastern tropical Pacific tuna purse seine fishery. Fish. 

 Bull, U.S. 80:396-401. 

 Perrin, W. F. 



1969. Using porpoise to catch tuna. World Fishing 18(6): 



42-45. 

 1969. The problem of porpoise mortality in the U.S. tropical 

 tuna fishery. Proceedings of the 6th Annual Conference on 

 Biology, Sonar, and Diving Mammals, p. 45-48. Stanford 

 Research Institute 

 Perrin, W. F, T. D Smith, and G. T. Sakagawa. 



1982. Status of populations of spotted dolphin, Stenella at- 

 tenuate/,, and spinner dolphin, S. longirostris, in the eastern 

 tropical Pacific In FAO, Mammals in the seas, Vol. IV. Small 

 cetaceans, seals, sirenians, and otters, p. 67-83. 



Punsly, R. G. 



1983. Estimation of the number of purse-seiner sets on tuna 

 associated with dolphins in the eastern Pacific Ocean dur- 

 ing 1959-1980. Inter-Am. Trop. Tuna Comm. Bull. 18:229- 

 299. 



Smith, T D. 



1983. Changes in size of three dolphin (Stenella spp.) popula- 

 tions in the eastern tropical Pacific Fish. Bull., U.S. 81:1-14. 

 Smith, T. D, and N. C. H. Lo. 



1983. Some data on dolphin mortality in the eastern tropical 

 Pacific tuna purse seine fishery prior to 1970. U.S. Dep. 

 Commer., NOAA Tech. Memo. SWFC-TM-NMFS-34, 26 p. 



33 



