Report of the International Whaling Commission (1996)


Our estimates of total harbour porpoise bycatch in the Gulf of Maine sink gillnet fishery for 1990 to 1993, with 95% confidence intervals in brackets, are 2,900 [1,500-5 ,500], 2,000 [1,000-3,800], 1,200 [800-1,700] and 1,400 [1,000-2,000] respectively, rounded to the nearest 100. These estimates are based on total landings and on sampling data from onboard observers in the fishery. Because the method estimates and allows for the statistically significant undercounting in some of the observer data, the estimates are higher than previously published estimates, which did not make such an adjustment. Variance and confidence intervals are obtained by bootstrapping and possible sources of bias are discussed.