Validation of Standard Weights and Raising Coefficients for Discard Estimation: Report of a Survey Aboard MFV Roisin Bairbre

Abstract

This survey was carried out to verify the Marine Institute's discard sampling protocol and the standard weights and conversion factors used when calculating discard rates. The MFV Roisin Bairbre was chartered to fish as normal on the Aran Prawn Grounds using twin rig prawn gear. The entire bulk catch was weighed, as well as the entire retained catch, thereby getting an accurate rate of discarding for this trip, as well as accurate individual basket weights. Retained catch was also weighed by species prior to and after gutting, to check the raising factors used when changing gutted landings back to round. This survey showed that the rate of discarding for this trip was 62% of the total bulk catch. There was no significant difference between the measured bulk catch weighed and the estimated bulk catch derived from using the standard weights. This validates the standard weights used. There was no significant differences between the observed conversion factors (from gutted to whole weight) and those currently used routinely in weight conversions. A standard weight for big baskets of bulk catch on a fish directed trip of 34.5 kg, and 28kg for a Nephrops directed trip were achieved.