The relationship between American lobster catch, entry rate into traps and density

Management of the American lobster (Homarus americanus) fishery depends on accurate estimates of lobster abundance. Catch from traps remains a widespread indicator, as it is widely accepted that catch per unit effort (CPUE) is correlated with density. However, surprisingly few studies have rigorously tested this relationship. We fished traps, and conducted concurrent SCUBA surveys to determine lobster densities, in the same study area along the New Hampshire coast, USA. We found that catch in standard commercial lobster traps loosely correlated with density (r(2) = 0.471), particularly for pre-recruit lobsters at lower densities. Video observations revealed that small lobsters entered early in the soak and larger individuals entered later, which likely influenced trap saturation. When traps were pre-stocked with a single adult lobster there was a reduced rate of entry by pre-recruit lobsters, but overall CPUE was unchanged relative to normal traps. These data indicate that, while standard commercial traps are a reasonable indicator of pre-recruit lobster abundance under some conditions, due to the behavioural characteristics of lobsters, the relationship between catch and density is limited, particularly at higher densities and for legal-sized lobsters. A better understanding of the behavioural mechanisms that influence catch could improve the use of catch data to predict abundance.