A proposed model transformation to circumvent problems encountered with the sex-ratio approach to obtain lower confidence limits for the abundance of West Greenland minke whales

• Main Authors: Brandão, Anabela, Butterworth, Doug S
• Format: Report
• Language: English
• Published: University of Cape Town 2011
• Subjects: Greenland
• Online Access: http://hdl.handle.net/11427/19108; https://open.uct.ac.za/bitstream/11427/19108/1/Brand%c3%a3o_A_proposed_model_2011.pdf

An illustrative example is given of a transformation applied to the sex-ratio approach which operates in a way that for population sizes much greater than are realistic, the impact of catches of females on abundance is damped. This leads to finite estimates of carrying capacity K even in circumstances where the trend over time in the proportion of whales in the catch that are male is decreasing (as is the case for West Greenland minke whales). The example is shown to produce positively biased estimates of the lower 5% confidence interval for current population size. However the concern with which this should be viewed is difficult to assess since the estimator is positively biased even in circumstances where the proportion of the catches that are male does not trend downwards over time.