An Analysis of Trap Saturation and the Behavioral Basis of Catchability
This is a one year pilot study designed to:
1) Test the feasibility of using two new methods for estimating lobster abundance
2) Generate a number of testable hypotheses concerning the catchability of lobsters
3) Quantify saturation of lobster traps and the behaviors that cause it.
All three issues are directly related to catchability, which is the likelihood that a lobster will enter a trap and be captured. The applied value of understanding catchability can hardly be overstated. Lobster managers must have a thorough understanding of catchability to accurately assess lobster abundance and trends in the fishery. Harvesters are also interested in catchability because it has a direct influence on their catch, fishing efficiency and profits.
Given its importance to all aspects of the fishery, it is surprising that we still know very little about catchability, especially the behavioral mechanisms that influence it. If we had a better understanding of the behavioral factors that influence catchability, it would be possible to reduce the error associated with our present system of estimating lobster populations based on trap data.
1) To develop trap saturation curves, with the assistance of local lobstermen, in areas with low, medium and high density of lobsters
2) To develop finer scale, 24-hour trap saturation curves in the same low, medium and high density study areas, using our recently developed Lobster Trap Video (LTV) system
3) To calculate a time to saturation (TTS) index using the aforementioned saturation curves and determine if TTS varies as a function of lobster abundance
4) To measure lobster approaches to a trap using LTV, and determine the relationship between approaches and actual lobster density (as determined by SCUBA survey)
5) To develop one or more testable hypotheses concerning the behavioral mechanisms that give rise to trap saturation, using sea sampling data and examination of the video data obtained with LTV
Deploy standard traps in cooperation with local lobstermen in areas of three different densities at varying soak times to determine saturation curves. Deploy our lobster trap video (LTV) system on several occasions in these same areas to continuously record behaviors in and around the trap that influence saturation and catchability. Determine abundance in each area using standard traps, LTV and SCUBA surveys.
Present estimates of lobster populations, necessary for management, are highly biased due to unknown factors that influence trap selectivity. An understanding of these behavioral mechanisms affecting catchability and trap saturation is necessary to reduce this error.
Results will be useful to: fisheries managers who can more accurately assess the relationship between catch and abundance, lobster biologists interested in behavior and ecology, and the lobster industry because the results may suggest ways to optimize existing fishing gear more cost effectively.
Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant
- Watson III, W., A. Vetrovs and W. Howell (1999). Lobster movements in an estuary. Marine Biology 134:65-75.
- Howell, W., W. Watson III and S. Jury (1999). Skewed sex ratio in an estuarine lobster ("Homarus americanus") population. Journal of Shellfish Research 18(1):193-201.
- Jury, S. (1999). Behavioral and physiological responses of the lobster, "Homarus americanus," to temperature: a new synthesis. Doctoral Dissertation, University of New Hampshire.