Measuring efficiency and predicting optimal set durations of pots for blue cod Parapercis colias

Abstract

Continuous video recordings of entries and exits from blue cod Parapercis colias pots in central New Zealand showed that less than 8% of approaches to pot entrances during 30 min sets led to pot entries. Thirty-four percent of the blue cod that did enter exited before the pot was hauled. Time-courses of approaches were relatively steady throughout 30 min, though the greatest number of approaches occurred during the first 10 min of sets. A more limited dataset of 60 min sets found that the number of blue cod contained in pots changed little after 30 min, indicating that maximal catch per unit effort would be derived from sets of about 30 min duration. Local topography appeared to constrain pot entries in some situations. A spreadsheet model of catch per time as a function of number of pots, set durations, haul time and catch handling time indicated that 30–40 min sets were optimal for the range of variables we considered. It is clear that efficiency of capture might be greatly improved.