Research Document - 2006/085
Relative efficiency of the Wilfred Templeman and Alfred Needler research vessels using a Campelen 1800 shrimp trawl in NAFO Subdivision 3Ps and Divisions 3LN
By Cadigan, N.G., S.J. Walsh, and W. Brodie
Abstract
In many of the multi-species trawl surveys conducted by the Newfoundland Region of Fisheries and Oceans Canada, the survey vessel "Wilfred Templeman" (WT) may be replaced by the vessel "Alfred Needler" (AN). We examined paired-trawl experiments involving these two vessels to examine for differences in catchability when both vessels fish the Campelen 1800 shrimp trawl which is the standard survey trawl used in the Newfoundland Region. The location for the comparative fishing was in NAFO Subdivision 3Ps and Divisions 3LN. The results overall suggested that there were no significant differences in the relative catchability of the two vessels. We also presented a generalized linear mixed effects model with an auto-correlated random effect that we suggest is useful for estimating relative efficiency, or the ratio of catchability, from paired-trawl survey calibration data when there is substantial local variability in stock abundance fished by each vessel. We compared these estimates with those from a more commonly used approach involving standard logistic regression. We found the mixed model approach fit the data better and produced estimates of relative efficiency that were not heavily influenced by a small number of outliers. The mixed model results indicated that differences in catchability were small and not statistically significant. However, the logistic regression approach produced some small but statistically significant estimates, and the significance seemed suspect because the effects were not apparent in graphical analyses.
Accessibility Notice
This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.
- Date modified: