Publication Abstract

Underwater TV surveys are increasingly being used for the assessment of Nephrops stocks due to the uncertainties surrounding catch data and the difficulties in age determination. Video footage of the seabed is reviewed by a number of personnel, and the number of burrow complexes recorded over a 10 minute period. The number of entrances per burrow complex is variableand Nephrops are often not the only burrowing animals living within the areas surveyed. Burrow complex identification is therefore a subjective process and the criterion used by each counter is likely to differ. An experiment was designed to look at the effects of counter experience, relative burrow density and whether counters worked alone or concurrently. As expected, the variance of total burrow counts per tow generally decreased with the level of counting experience, however even experienced counters had significantly different mean counts. Some counters experienced “day effects” where all counts were simultaneously higher or lower than average. Analysis of within-tow counts indicated that whilst total count variance can be low, the consistency of burrow identification can be relatively poor. Concurrent counting had a significant effect on individual counts, all counters became significantly more conservative than when counting alone. These results highlight the need for a standardised counting protocol and more extensive training and calibration exercises both within and between countries.