Relative abundance of dolphins associated with tuna in the eastern Pacific Ocean: Analysis of 1991 data
Anganuzzi, A.A.; Buckland, S.T.; Cattanach, K.L.
Report of the International Whaling Commission 1993(43): 459-465
Methods for estimating relative abundance of seven dolphin stocks in the eastern Pacific Ocean, using sightings data collected on commercial tuna vessels by trained observers, were developed by Buckland and Anganuzzi (1988) and Anganuzzi and Buckland (1989). Buckland et al. (1992) developed a method for estimating the underlying trends in abundance and assessing their significance. using a smoothing procedure and bootstrap resampling. The 1991 tuna vessel data are analysed here. and the estimated trends in relative abundance are updated. The results indicate that for most dolphin stocks, there is no evidence of trends in population size in recent years. The exception is the northern stock of common dolphin, which shows a significant decrease over the last ten years. Possible reasons for the apparent decline are discussed. Potential biases introduced by the inclusion of data from cruises with no dolphin-associated fishing ('dolphin safe' cruises) are assessed.