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

Abstract

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.

Keywords:

• Lobster
• Homarus americanus
• video
• catch
• catchability
• traps
• crustaceans

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

We thank the University of New Hampshire Ocean Projects students who developed and tested the initial LTV prototype and Bob Champlain who constructed many underwater housings and specialty fittings throughout the development phase of the system. In addition, we acknowledge the help of Noel Carlson, Liz Kintzing, Dan O'Grady, Jen Wishinski, David Kooritis, Walt Golet, Darren Scopel, Sue Krull and others for diving assistance. Dave Koortis, Sue Krull, Gary Smith, Suzanne Watson, Briana Calore, Jen Wishinski, Adrienne O'Connor and many others contributed a great deal of time to the analysis of videotapes, and for that we are very grateful. Comments from two anonymous reviewers also improved the paper. This study was funded by the New Hampshire Sea Grant Program (NOAA).

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark