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RESEARCH ARTICLE
Contents Vol 57(7)

Do large rock lobsters inhibit smaller ones from entering traps? A field experiment

Thomas F. Ihde A C , Stewart D. Frusher B and John M. Hoenig A
+ Author Affiliations
- Author Affiliations

A Virginia Institute of Marine Science, College of William and Mary, PO Box 1346, Gloucester Point, Virginia 23062, USA.

B Tasmanian Aquaculture and Fisheries Institute, University of Tasmania, GPO Box 252-49, Hobart, Tasmania, Australia 7001.

C Corresponding author. Email: tihde@vims.edu

Marine and Freshwater Research 57(7) 665-674 https://doi.org/10.1071/MF05238
Submitted: 5 December 2005  Accepted: 19 July 2006   Published: 31 August 2006

Abstract

Indices of recruitment are often derived from trap surveys. If legal-sized lobsters inhibit smaller ones from entering traps, the overall catch-rate may depend on population composition and not just on overall abundance, and recruitment strength can be overestimated as average length decreases in a population. A controlled field experiment was used to examine whether trapping inhibition of Jasus edwardsii occurred during spring (November) or summer (February) in south-eastern Tasmania. Four treatments were applied. Baited traps were seeded with either: one large female, one large male or two sublegal-sized female lobsters. Baited traps with no seed were used as a control. Seeded traps always caught fewer sublegal-sized lobsters than control traps. When catches in both seasons were examined by sex of entrants, seeded traps caught fewer small lobsters than control traps in 11 of 12 comparisons. However, a strong inhibitory effect was observed only for female-seeded traps during summer. The data obtained in the present study suggest that sublegal-sized indices of recruitment are likely to be influenced in summer by the number of large females present. Spring trials suggest that corrections to a sublegal-catch index may be unnecessary during this season, but more work is required in order to better understand the complex, sex-specific and seasonal patterns of interactions of this species.

Extra keywords: catchability, selectivity, southern rock lobster, trapability, trapping behaviour.


Acknowledgements

This work was supported by a National Marine Fisheries Service-Sea Grant Joint Graduate Fellowship in Population Dynamics, the Tasmanian Aquaculture and Fisheries Institute (TAFI), and the Virginia Institute of Marine Science (VIMS). We especially thank TAFI staff, including Caleb Gardner and the Crustacean Section for their support in the field, the Aquaculture Section for their support in maintaining the lobsters used as seeds, and Captain Matt Francis and the crew of the FRV ‘Challenger’ for the collection of many of the lobsters used in this study. We also thank Larry Jacobson, Jack Musick, Mike Prager, Jeff Shields, and two anonymous reviewers, whose thoughtful suggestions have improved this study and manuscript. This is VIMS contribution number 2762.


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