FISHERY BULLETIN: VOL. 81. NO. 1 



The 1976 workshop (footnote 2) concluded that 

 the available information implies MNPL is with- 

 in the range of 50-70% of the equilibrium popula- 

 tion size, corresponding to values of Z from 1 to 

 5.1. The 1979 workshop recognized that "There 

 had been a shift of scientific opinion in recent 

 years [since 1976] towards accepting the idea that 

 relative net productivity in mammals, especially 

 large, K-selected species, is a non-linear func- 

 tion of population size," (footnote 3, p. 7) and con- 

 cluded that MNPL for these dolphin populations 

 is probably in the range of 65-80% of the equilib- 

 rium population size (Zfrom 3.5 to 11.5). I con- 

 sider the values for MNPL of 50-80% (Zfrom 1 to 

 11.5) of equilibrium population size in order to 

 explore the sensitivity of the calculations to this 

 uncertainty. 



HISTORICAL TRENDS IN 

 ABUNDANCE 



Estimates of population sizes prior to 1979 

 from Equations (2) and (3) for each population 

 are shown in Table 6. Values are given using 1) 

 two different estimates of present (1979) abun- 

 dance (from combined research vessel and fish- 

 ing vessel data, and from research vessel data 

 alone), and 2) the parameters MNPL = 65% and 

 R,„ — 0.03. For this range of parameter values, 

 the offshore spotted dolphin population in 1959 



Table 6.— Estimates of population size (in thousands) of off- 

 shore spotted, eastern spinner, and whitebelly spinner dolphins 

 from 1979 back to 1959, using Equations (2) and (3) and param- 

 eters MNPL = 65% and R,„ = 0.03. 1979 estimates are based on 

 species proportions from (FR) combined research vessel and 

 fishing vessel data and (R) research vessel data alone. 



Offshore 

 spotted 



Year 



FR 



Eastern 

 spinner 



FR = R 



Whitebelly 

 spinner 



FR 



1979 

 1978 

 1977 

 1976 

 1975 

 1974 

 1973 

 1972 

 1971 

 1970 

 1969 

 1968 

 1967 

 1966 

 1965 

 1964 

 1963 

 1962 

 1961 

 1960 

 1959 



2,775 

 2,719 

 2,668 

 2,673 

 2,675 

 2,679 

 2,754 

 2,967 

 3,064 

 3,340 

 3,264 

 3,720 

 3,844 

 4.071 

 4,335 

 4,574 

 4,695 

 4,803 

 5,169 

 5,519 

 5.590 



1,682 

 1,653 

 1,628 

 1,629 

 1,686 

 1,732 

 1,824 

 2,046 

 2,164 

 2,457 

 2,756 

 2,865 

 3,001 

 3,239 

 3,520 

 3,754 

 3,879 

 3,991 

 4,358 

 4,708 

 4,779 



293 



287 



283 



284 



320 



336 



358 



443 



488 



591 



695 



742 



799 



893 



998 



1,092 



1,141 



1,185 



1,323 



1.454 



1.481 



380 

 376 

 373 

 386 

 434 

 456 

 486 

 494 

 499 

 512 

 527 

 527 

 527 

 527 

 527 

 527 

 527 

 527 

 527 

 527 

 527 



216 

 215 

 214 

 229 

 258 

 301 

 331 

 340 

 345 

 358 

 373 

 373 

 373 

 373 

 373 

 373 

 373 

 373 

 373 

 373 

 373 



was between about 4,800,000 and 5,600,000 ani- 

 mals. The eastern spinner dolphin population in 

 1959 numbered about 1 ,500,000, while the white- 



Whitebelly 

 \Spinner 



_l I L_ 



Eastern 

 Spinner 



_L 



1960 



1965 



1970 

 YEAR 



1975 



Figure 1. — Relative population sizes of whitebelly spinner, 

 offshore spotted, and eastern spinner dolphins, 1959-79, using 

 population estimates based on species proportions from com- 

 bined research and fishing vessel data, and assuming R „, = 0.03 

 and MNPL = 65% of equilibrium abundance. Population sizes 

 are relative to estimated population sizes in 1959. 



1.0 

 0.9 

 0.8 



LU 

 N 



(/) 



Z 



o 



0.7 



0.6 



a 0.5 

 O 



a. 



iu 0.4 



> 



< 0.3 



_i 



LU 



K 0.2 



0.1 

 0.0 



Whitebelly 

 \Spinner 



\ Eastern 



N — _ Spinner 



_L_I I i_ 



1960 



1965 1970 



YEAR 



1975 



Figure 2.— Relative population sizes of whitebelly spinner, 

 offshore spotted, and eastern spinner dolphins, 1959-79, using 

 population estimates based on species proportions from re- 

 search vessel data alone, and assuming R ,„ = 0.03 and MNPL - 

 65% of equilibrium abundance. Population sizes are relative to 

 estimated sizes in 1959. 



10 



