N.H. Sea Grant Research Project Progress Report

Transcription

1 N.H. Sea Grant Research Project Progress Report Today s date: 4/23/12 Project number: R/CFR-15 Project title: Calibrating lobster ventless trap and standard trap surveys to optimize measurements of lobster abundance Project initiation date: 2/1/10 Principal investigator: Win Watson Affiliation: UNH Partner(s) and affiliation(s): Steve Jury, Lecturer, Bates College Tracy Pugh, Massachusetts Division of Marine Fisheries Bob Glenn, Massachusetts Division of Marine Fisheries Brief project overview/abstract: The overall goal of lobster management is to maintain a sustainable fishery, while at the same time maximizing the economic growth and stability of the industry. To meet this goal it is essential to have a firm understanding of the abundance of the stock so that adjustments can be made if an increase or decrease is apparent. While there are many ways to assess abundance, catch in traps is by far the easiest and yields the most data. The challenge is determining the relationship between catch and actual lobster abundance. We previously quantified some of the interactions of lobsters with traps by using a timelapse video system (LTV, lobster trap video; Jury et al. 2001). We discovered that standard commercial lobster traps are very inefficient, and thus, perhaps, not the best indicators of lobster abundance. However, one tool that has recently been implemented to improve data collection for management purposes is a ventless trap, which retains more lobsters than standard traps. However, because little is known about the dynamics of these traps and their ability to catch lobsters in a manner that is proportional to lobster abundance a major goal of this project was to analyze the interactions of lobsters with ventless traps and determine if they might provide a more accurate estimate of natural lobster populations. During this project we used a combination of techniques to compare the dynamics of ventless and standard lobster traps at two different study sights. One study is an area with naturally occurring fluctuations in lobster density. The other site is a large mesocosm that we stock with known densities of marked lobsters so that we can investigate the behavior of individual, identifiable, lobsters. At each location we conduct SCUBA surveys to determine the precise density and size frequency distribution of lobsters and we fish traps equipped with video cameras in order to quantify the interactions of lobsters with traps. In addition, at the Wallis Sands study site we also fish approximately 30 ventless and 30 standard traps and haul them at different time intervals to determine how long it takes for them to saturate with lobsters. The data from all of these investigations will be used to optimize the tools we use to monitor the abundance of lobsters and thus improve our ability to manage this important fishery. Revised 9/21/2011 1

2 Objectives: 1. Construct two 30m X 30m underwater mesocosms to use for our duplicate controlled study sites. These will contain fixed densities of uniquely identifiable lobsters. Approximately half the experiments will take place in the mesocosms, and half at a nearby field site (Wallis Sands location used in previous LTV studies). 2. Measure all lobster approaches, entries, exits, and captures in ventless and standard traps equipped with an LTV system, both inside the mesocosms and at the field site. These video and catch data will be used to calculate: a) the percentage of lobsters that approach a trap that enter (this is only possible in the mesocosm where we can mark individual lobsters); b) the percentage of lobsters that enter that are subsequently captured; c) the time to saturation (TTS); d) the number of lobsters that never approach a trap; and e) the degree to which catch composition represents the actual composition of lobsters on the bottom. All these data will be examined for all lobsters, as well as for different size classes. 3. Analyze the relationships between CPUE, TTS and lobster density and lobster size to determine which type of trap (standard or ventless) and metric (TTS, CPUE, approaches) correlates best with the abundance of lobsters on the bottom. In the mesocosms we will be able to accurately manipulate the density and at the field site the density will vary on a seasonal basis. 4. Use LTV data to calibrate the abundance estimates generated by the ventless survey traps, to account for size, sex, or life history status-based differences in capture probability. 5. Test the calibration system developed through completion of Objective 4, in the mesocosms and at the field site with different population demographics. Research findings/progress to date: We have completed most of Objectives 2-5. However, we did not succeed in completing the studies related to the mesocosms. In the first year of the project we succeeded in constructing the mesocosms and we worked out methods for labeling lobsters and stocking the enclosures. However, the lobster season ended before we were able to study a range of densities. Winter storms damaged the enclosures and we rebuilt them in When we were in the middle of those studies an Hurricane hit the NH coast and completely destroyed the mesocosms, so we terminated that part of the study to focus on the other study site. During 2010 and 2011 we hauled 247 pairs of standard and ventless traps at the Wallis Sands study site and captured 6,860 lobsters. Overall the CPUE from ventless traps was ~5 times the catch in standard traps (Fig. 1). More importantly, ventless traps gradually, over 1-3 days, filled up with lobsters, while standard traps saturated within a few hours. In fact, during the first 48 hours of a soak there is an almost linear increase in catch (Fig. 2). Therefore, we are optimistic that some metric related to the time it takes standard traps to saturate could be used to estimate the abundance of lobsters on the bottom. We also conducted 17 SCUBA surveys during which we counted 994 lobsters on the bottom. These surveys were spaced out over the summer, with each survey coupled to trap studies. While our hypothesis that time to saturation would be correlated with density was not supported by the data we did find that there was a pretty good relationship between catch and lobster density with ventless, but not standard, traps (Fig. 3). Ventless and standard traps equipped with time lapse digital video systems were fished at both study sites on a total of 25 occasions, yielding ~360 hours of video. We have been very busy analyzing these videos to determine the mechanisms that lead to trap saturation. It appears that, with ventless traps, traps saturate because they have captured most of the catchable lobsters within the area fished by the trap. There are very few escapes from ventless traps and rates of entry go down over time, even though there is plenty of bait in the trap even after three days. In summary, despite the challenges encountered with the mesocosm studies, the work has been very successful and we are looking forward to publishing and presenting the results. 2 Revised 9/21/2011

3 b b a a Figure 1. A comparison of CPUE after 24 and 48 hour soak times in standard and ventless traps. At this time of year, when the density ws 0.04 lobsters/m 2, standard trap CPUE was significantly less than ventless trap CPUE (P value < , unpaired t-test). e e e CPU E a b c d d Soak Time (hr) Figure 2. A comparison of CPUE over time in ventless and standard traps. Note that standard traps will catch as many lobsters at all time intervals, while catch in ventless traps increases at a consistent rate until 48 hours. Letters indicate significant differences in CPUE between time periods. Thus, because catch is the same at 24, 48 and 72 hours, the traps have saturated. Revised 9/21/2011 3

4 CP UE Soak Time (hr) Figure 3. The influence of lobster densities on catch. Note that when lobster density is higher, CPUE is also greater at most time points. Impacts to date: So far, because we have not published our data, there are no significant impacts that are easily measured. However, the data are solid and have been communicated to those who manage the lobster fishery in several New England states, so it will likely influence how we monitor and manage those fisheries. Accomplishments: 1. We have presented our results at several different forums, including the International Lobster Conference. 2. Due to our success to date, we have been asked by the Maine Division of Marine Fisheries to conduct a complementary study in Maine waters this coming summer. 3. One graduate student, Abigail Clark, is basing her entire MS Thesis on this project and she is due to graduate at the end of the summer of Economic benefits realized to date: None. Tools, technologies or information services resulting from this project that are being used to improve ecosystem-based management: We continue to be on the cutting edge of technology for underwater video. During this project we developed a new underwater timelapse video system that others will likely use in the future for related projects. The saturation study we developed was also very successful and we anticipate several state agencies might try it as a tool for determining lobster abundance. Patents: None 4 Revised 9/21/2011

5 Technology transfer (Has a private company utilized this research successfully?): No. But, we have been discussing developing a system that uses sounds to attract lobsters to traps. Related grants and contracts (Other grants and contracts that funded this research or that were obtained as a result of this research.): None at the current time. However, as mentioned above, we are beginning to develop a collaboration with Maine Division of Fisheries that will involve repeating aspects of this study in Maine coastal waters. Problems encountered: The only major problems we encountered were related to the storm events mentioned above. These destroyed our mesocosms and thus prevented us from accomplishing the associated goals. Publications to date: One is submitted and several are in preparation. The one submitted is: Watson, WH III and S.H. Jury. The relationship between American lobster catch, entry rate into traps and density. Marine Biology Research, submitted. Presentations to date, with published abstract citation if applicable: In the fall of 2010 I was the Keynote Speaker at the College of Charleston Graduate Student Research Colloquium. I included data from this project in one of my two talks. I gave a presentation that included some of this work at the International Lobster Conference in Norway in June of The abstract is below. Abigail Clark, my graduate student, gave a presentation at the 2012 Benthic Ecology Meeting on this topic. The abstract of this presentation is also pasted below. Does the behavior of lobsters in, and around, ventless and standard lobster traps influence catch? Winsor H. Watson III, Steven Jury, Abigail Clark, Tracy Pugh, Tom Langley and Jason Goldstein. Effective management of the American lobster (Homarus americanus) fishery is dependent on accurate estimates of lobster abundance. While several methods are used to obtain these estimates, catch from lobster traps remains a very useful and cost effective approach. Furthermore, vent disabled or ventless traps have become increasingly important in some monitoring programs. The first goal of this project was to understand the relationship between catch in traps and the size structure and density of lobsters on the bottom. We fished traps with and without video cameras mounted on them, while simultaneously conducting SCUBA surveys to quantify lobster density in the same study area. At this study site we found that catch in traditional commercial lobster traps correlated to the density, as long as the abundance was low. This was due, in part, to the fact that traps saturated in 24 hrs, or less. Our second goal was to compare the dynamics of ventless traps, identical to those used for surveys by many New England State agencies, with standard commercial traps. In general, ventless traps captured far more lobsters, took longer to saturate, and the mean size of lobsters captured was smaller. Data will also be presented, based on analysis of videos obtained from both types of traps, that illustrate the differences in how each type of trap fishes and how this can be applied to the use of ventless traps as a management tool. Revised 9/21/2011 5

6 A comparison of ventless and standard American lobster trap dynamics Clark, Abigail S. 1 ; Watson, Winsor, Watson H. III; Howell, Hunt; Jury, Steven H. 2 1 Department of Biological Sciences, University of New Hampshire, Durham, New Hampshire 03824, USA 2 Steve s affiliation The American lobster (Homarus americanus) is the most valuable marine resource in New England and, as with any fishery, effective management depends on accurate measurements of abundance, and adjustments of fishing effort to control fishing mortality. The purpose of this study was to examine the efficacy of standard and ventless traps in order to determine which trap type provides the best index of the actual lobster population on the bottom. We fished both types of traps in a study area along the NH coast, while simultaneously conducting SCUBA surveys. Ventless trap catch data best reflected actual size of the population and size frequency distribution, confirming that ventless traps provide a better index of lobster density than standard traps. Understanding the relationship between catch and the population means also understanding trap saturation, the point at which there is no increase in catch. Fishing ventless and standard traps for different lengths of time confirmed that ventless traps saturate between 24 and 48 hours. Comparing lobster trap video (LTV) footage to catch and dive data suggests that ventless traps capture and retain most lobsters within the trapping area, thus, resulting in low entry and escape rates. Through implementation of LTV technology, American lobster behavior surrounding traps is now better understood for conservation and ecological purposes. Students Supported (see next page) 6 Revised 9/21/2011

7 Students Supported Student Name Institution/ Department Duration of support Jason Goldstein DBS, UNH Summer 2010, 2011 Tom Langley DBS, UNH Summer 2010, 2011 Type of support (stipend, travel, supplies, etc.) Type of degree: Undergrad Master s PhD Year degree awarded Tracy Pugh DBS, UNH Summer 2010, 2011 Supplies PhD Only in Second Year of PhD Ben Marcek DBS, UNH Summer 2010 Kate Masury Biology Dept, Summer Holy Cross 2010 Audra Chaput DBS, UNH Summer 2010 Title of thesis if supported by N.H. Sea Grant Salary PhD 2012 The impact of seasonal temperatures on the movement, egg development, and larval release in ovigerous American lobsters (Homarus americanus) Salary MS 2012 The influence of seasonal changes in water temperature on the movements of sexually mature and immature lobsters in the Great Bay estuary The reproductive success of American lobster: evaluating the influence of males and the subsequent impacts to lobster fishery management Where is he/she now? NEERS Fellowship Salary BS 2010 N/A Graduate School Salary BS Still in N/A Still in School school Salary BS 2010 N/A Graduate School Revised 9/21/2011 7

8 Student Name Institution/ Department Duration of support Abigail Clark DBS, UNH Summer 2011 Elizabeth Dubofsky DBS, UNH Summer 2011 Alysia Campbell DBS, UNH Summer 2011 Kyle Jenks DBS,UNH Summer 2011 Type of support (stipend, travel, supplies, etc.) Salary, Travel, Supplies Type of degree: Undergrad Master s PhD Year degree awarded Title of thesis if supported by N.H. Sea Grant MS 2012 A comparison of ventless and standard trap dynamics. Where is he/she now? Getting PhD at Florida State starting Fall 2012 Salary MS 2012 The biological rhythms expressed by juvenile horseshoe crabs Salary BS 2011 Five-year Education Degree at UNH Salary BS 2011 Research Technician at Dartmouth 8 Revised 9/21/2011