FISHERY BULLETIN: VOL. 83, NO. 4 



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NUMBER OF DOLPHINS KILLED 



Figure 5.— Relative frequency distributions of number of dolphins killed incidentally during sets 

 made after March 1981 through 1982, by observer type 



Table 5.— Numbers of dolphin sets (n) made from 1979 through March 1981. Sets are classified by observer type (NMFS, lATTC), by area 

 of set (North Inside, North Outside, South), by date of set relative to period (1 = Jan.-Mar., 2 = Apr.-Dec), and by numbers of dolphins 

 killed (0, >0). Percents of column totals (%), expected frequencies (e), and the statistic Z are also tabulated. Values of Z > 1.64 are signifi- 

 cant, as indicated by an asterisk. 



'Computation of overall test statistic not possible because of one-sided alternative, and because of lack of data In one stratum (Period 1, North Outside). 



DISCUSSION AND CONCLUSIONS 



We established the existence of an observer effect 

 on the number of dolphins killed incidentally in the 

 ETP yellowfin tuna fishery by following two lines 

 of argument. First, we demonstrated a decrease in 



the percent of sets with no dolphins killed on NMFS- 

 observed trips after March 1981, when monitoring 

 compliance with dolphin-release regulations was 

 removed as a data collection purpose (Ikble 3). We 

 further showed that this difference was not due to 

 a temporal trend in fishing conditions by examin- 



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