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, I ;11 : ,I 402 Recovery of Long-lived Species Jacobs and Swink 1982). High conductivity and turbidity of the Green River reduce elec- trofishing efficiency. I therefore used an arbi- trary range of 4 %-20% to obtain maximum and minimum estimates of 155/0.04 = 3875, and 155/0.2 = 775 adult squawfish; average = 2325 fish. Method 3 Despite the above estimations, electrofishing efficiency for capture of squawfish in the Green River is unknown. However, an effi- ciency can be calculated from the population estimate for razorback suckers of 948 fish from 171 km. I used a catch of 0.2 fish hr-1 from Tyus (1987) rather than the 0.49 given by Lanigan and Tyus (1989), because the lat- ter was estimated for effort concentrated in a reach of greatest razorback sucker abun- dance. A capture rate of 0.2 razorbacks hr -., assuming travel time of 4 km hr - 1 and two shorelines, gives a catch per kilometer of 0.1 fish. Calculation of catch for the upper Green River would thus be (171) (0.1) = 17 fish. Electrofishing efficiency would then be calcu- lated by 17/948 fish in the population, or 0.018. If one assumes that Colorado squaw- fish and razorback suckers are equally vulner- able in spring, the population size of squaw- fish would be approximated by: 155 fish (method 2 calculation)/0.018 = 861 I adult individuals. Method 4 The total number of Colorado squawfish tagged in the Green River by the USFWS from 1979 through 1987 was 625; 7 of 77 fish captured in 1988 were recaptures. A crude ap- proximation of number of fish at large, disre- garding constraints of geographic and demo- graphic closure, would be 7166 = 6251x, or 5893 fish. In addition to other problems, this approximation does not consider tag loss. (Wydoski and Emery 1983), an important fac: tor in active, migrating fishes. Tag loss may be: as high as 42% (Dunning et al. 1987) for some external tags. If limits of 25% and 50% tag loss are assumed, the value of 5893 would be converted to 7369 and 8840 adults, aver- age = 8105. Methods 5 and 6 I employed a modified Delphi technique (Crance 1988), using six biologists experi- enced in e1ectrofishing for squawfish in the Green River. Their experience averaged about four and a half years. Each was asked two questions: (I) what was the ratio of squawfish to razorback suckers; and (2) what was the maximum number of squawfish per mile of river, based on their best estimate of number of adult fish e1ectrofished and relative e1ec- trofishing efficiency. The responses consisted of a range of numbers per individual. Group averages were then provided to all partici- pants, who were asked to supply best average numbers. Their estimates varied from 2 to 50 squawfish per razorback; group averages varied from 4.5:1 to 12.8:1, with a grand mean of 10.3:1. Estimated Colorado squaw- fish population sizes were (4.5) (948) = 4266, (12.8) (948) = 12,134, and (10.3) (948) = 9764, respectively (948 is the razorback popu- lation size estimated by Lanigan and Tyus [1989]). The number of squawfish estimated per mile varied from 2 to 500, the range-of aver- ages was 5.6-80 fish km -., and the grand av- erage was 20.2 fish km -1. An estimate of squawfish abundance using the above range of averages is (5.6) (552 Ian) = 309 I, and (80) (552) = 44,160 fish, respectively. The grand average was calculated as (20.2) (552) = II,I50 adult squawfish.