Estimating relative abundance of whales from historical Antarctic whaling records

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Author: de la Mare, William K.
• Other Authors: Cooper, Andrew
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2014
• Subjects: Antarctic; Antarc*
• Online Access: http://dx.doi.org/10.1139/cjfas-2013-0016; http://www.nrcresearchpress.com/doi/full-xml/10.1139/cjfas-2013-0016; http://www.nrcresearchpress.com/doi/pdf/10.1139/cjfas-2013-0016

Catch per unit effort (CPUE) is often the only data available from historical fisheries for inferring distribution and abundance of exploited populations. CPUE underestimates variations in relative abundance when gross effort data are only measured in total operating days. Gross effort includes both searching time and handling time, but only searching time is useful for an index of abundance. A method is developed for estimating searching time by subtracting a maximum likelihood estimate of handling time from the gross effort. An expectation maximization (E-M) algorithm is used to combine maximum likelihood estimates of the handling time with the expected additional operating time due to handling the last catch of each day. Simulation tests show that the estimates of catch per unit of searching time (C/CSW) are much closer to proportionally related to local density than gross CPUE. Estimates of handling time are not unbiased, and some nonlinearity between local density and C/CSW may persist. The methods may be useful for other fisheries where historic gross catch and effort data involve both searching and handling.