Field Analysis of the Behavioral and Ecological Factors Determining Lobster Catchability and Trap Saturation
|Jenna Wanat||UNH - Department of Biological Sciences|
|Steven Jury||Bates College|
|Jennifer Wishinski||UNH - Department of Biological Sciences|
|Dan O'Grady||UNH - Department of Biological Sciences|
|Jim Newcomb||UNH - Department of Biological Sciences|
|Dave Kooritis||UNH - Department of Biological Sciences|
|Diane Fabian||University of New Hampshire|
|Gary Smith||University of New Hampshire|
|Suzanne Schrieber||UNH - Department of Biological Sciences|
Stock assessment and management of the American lobster fishery depends on accurate estimates of abundance. At the present time, these estimates are largely based on catch per unit effort (CPUE) statistics. Unfortunately, catch data from traps provide a very poor index of abundance. One reason for this is that traps cease fishing when they become filled, or saturated, and this introduces bias in CPUE data. While the correlation between CPUE and actual density is poor, previous models and our own preliminary data suggest that the rate at which traps fill with lobsters, or the time to saturation, may be directly proportional to lobster abundance.
The primary goal of this proposal is to derive a more accurate method for using traps to determine the abundance of lobsters. In particular, we propose to investigate and then mathematically model the relationship between lobster density and the rate at which traps fill to saturation. The data collected will include:
1) Time to saturation, using traditional and vent-disabled traps
2) Lobster density, as determined by SCUBA survey in a sandy study site where very accurate counts can be obtained
3) The dynamics of lobster movements in and around a trap, obtained from time-lapse videotapes.
This empirical data will be used to modify and calibrate recent trap models and thus make them more accurate, realistic and applicable to managers charged with regulating this vital fishery.
Successful completion of this project will be facilitated by use of a system we developed that makes it possible to continuously videotape the activities of lobsters in, and around, a traditional lobster trap. We will use this lobster trap video (LTV) system, in parallel with traditional traps, to quantify lobster approaches, entries and exits from traps. These data will be obtained for lobsters of three broad size classes so that differences in catchability can be quantified. Analysis of this type of data over time, and with respect to the accumulation of lobsters in the trap, will provide insight into why traps saturate. Thus, at the end of this project we will have an improved understanding of the behavioral mechanisms that give rise to trap saturation and a technique for using time to saturation to measure lobster abundance.
1) Establish a study site with a known density and size composition of lobsters
2) Quantify all lobster approaches, entries, exits and captures of three different size classes of lobsters, using a specially designed self-contained underwater Lobster Trap Video (LTV) system
3) Determine how many lobsters approach or enter a trap multiple times during a given set
4) Measure the relationship between time-to-saturation and lobster density and catch per unit effort and lobster density for three different size classes of lobsters, using both standard and ventless traps
5) Develop a quantitative computer model of a lobster trap, based on measurements obtained during completion of objectives 1-4
Lobster density will be determined using traditional SCUBA techniques at a site where lobster density gradually increases from June to September. Both traditional and vent-disabled traps will be fished in this site to determine catch per unit effort and the time it takes for traps to saturate. In addition, a trap equipped with a video camera will be used to obtain time-lapse video of all lobsters approaching, entering and exiting the trap. Video data will be used to: 1) determine the behavioral mechanisms underlying the process of trap saturation and 2) collect data necessary to improve upon an existing computer model of how traps fish.
Stock assessment and management of the American lobster depends on accurate estimates of abundance. Currently, these estimates are largely based on catch per unit effort (CPUE) statistics, which are not very accurate. The primary goal of this proposal is to develop an improved method of assessment based on time-to-saturation.
Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant
- Jury, S., W. Howell, D. O'Grady and W. Watson, III (2001). Lobster trap video: in situ video surveillance of the behavior of "Homarus americanus" in and around traps. Marine Freshwater Research 52:1125-1132.
- O'Grady, D., S. Jury and W. Watson, III (2001). Use of a treadmill to study the relationship between walking, ventilation and heart rate in the lobster "Homarus americanus." Marine & Freshwater Research 52(8):1387-1394.
- Jury, S. and W. Watson, III (2000). Thermosensitivity of the lobster, "Homarus americanus," as determined by cardiac assay. Biological Bulletin 199:257-264.
- Little, S. and W. Watson III (2003). Size at maturity of female American lobsters from an estuarine and coastal population. Journal of Shellfish Research 22(3):857-863.
- O'Grady, D. (2001). The effect of reduced salinity on the locomotory behavior and physiology of the American lobster, "Homarus americanus." Master's Thesis, University of New Hampshire.
- Watson, W. (1999). Lobster trapability and saturation study. U.S./Canadian Lobster Summit III Lobster Stock Assessment: Towards Greater Understanding, Collaboration and Improvement, Patrice Farrey, Marjorie Mooney-Seus and Heather Tausig, eds., pp. 48-55, Rockland, Maine, March 3-4, 1999.