Calibrating Lobster Ventless Trap and Standard Trap Surveys to Optimize Measurements of Lobster Abundance

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Project Type: 
Research
Project Number: 
R/CFR-15
Inception Date: 
2010
Completion Date: 
2011

Participants:

Tracy Pugh UNH - Department of Biological Sciences Collaborator
Winsor Watson UNH - Department of Biological Sciences Principal Investigator
Steven Jury Bates College Collaborator
Robert Glenn Massachusetts Division of Marine Fisheries Collaborator

Students Involved:

Tracy Pugh UNH - Department of Biological Sciences
Abigail Clark UNH - Department of Biological Sciences
Elizabeth Dubofsky UNH - Department of Biological Sciences
Alysia Campbell UNH - Department of Biological Sciences
Kyle Jenks UNH - Department of Biological Sciences
Jason Goldstein UNH - Department of Biological Sciences
Tom Langley UNH - Department of Biological Sciences
Ben Marcek UNH - Department of Biological Sciences
Kate Masury College of the Holy Cross
Audra Chaput UNH - Department of Biological Sciences
Liz Morrissey UNH - Department of Biological Sciences
Chris Chambers UNH - Department of Biological Sciences
Elsa Lindgren UNH - Department of Biological Sciences
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 time-lapse 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.

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.

Methodology: 
Previously we developed a system to obtain time-lapse video recordings of the activity of lobsters in, and around, standard lobster traps. In this project we will use that system to quantify the trapping dynamics of the ventless and standard traps used by some agencies for their lobster assessments. A key part of this study will be deploying these traps in mesocosms, in which we can identify the lobsters and control the density.
Rationale: 
Appropriate and effective management of the American lobster fishery depends on having a firm understanding of the abundance of the stock. Ventless trap surveys contribute in a significant way to this process, yet we know little about the relationship between catch in ventless traps and the abundance and size composition of lobsters on the bottom. The data we obtain will allow managers to calibrate their catch in standard and ventless traps and thus base their decisions on a better understanding of the stock.
Accomplishments: 

2014

Underwater video footage from N.H. Sea Grant research incorporated into new lobster exhibit
NHSG-funded research focused on calibrating two types of lobster traps to more accurately determine lobster abundance based on catch. These traps were fitted with underwater video cameras to assist in the data collection process. The video footage taken during this research was incorporated into a new lobster fishery exhibit at the Maine Maritime Museum in 2014. The exhibit educates professionals in the fisheries field about the latest lobster research in New England and helps scientists who conduct ventless trap surveys to assess the accuracy of their data.

2013

Lobster bait deterioration reduces catch after one day in N.H. study
Previous research has shown that ventless lobster traps provide a more accurate estimate of natural lobster populations than standard traps. However, trap saturation may impact these catch values. In 2013, N.H. Sea Grant-funded researchers conducted studies to determine if ventless lobster traps saturate because they capture all the lobsters in the area fished by the trap, the bait in the trap loses its attractiveness, or once a certain number of lobsters are in the trap aggressive interactions lead to an increased rate of escape. Their findings indicate traps do not capture all the lobsters in the area. Rather, a combination of bait deterioration and increased escapes after 24 hours were primarily responsible for reduced catch after the first day the trap is on the bottom. These data indicate that ventless traps may be a useful tool for estimating the abundance of natural lobster populations, especially if steps are taken to adjust for the factors that lead to trap saturation.

Video documenting N.H. lobster research is finalist in Ocean 180 competition
With funding provided by N.H. Sea Grant, researchers conducted studies to determine if the new ventless lobster traps provide a more accurate estimate of natural lobster populations than standard traps. In 2013, the researchers recorded, edited and produced a short video about this research called: What do lobster traps tell us about the lobsters on the bottom? They entered the video into the Ocean 180 Video Challenge, a competition designed to inspire scientists to communicate the meaning and significance of their scientific research to non-scientists. Their video was a finalist in the competition. In addition to gaining national exposure for this topic, the video provides an outreach component to help the layperson understand the importance of natural resource research.

Connection between N.H. Sea Grant research and natural resource organization encourages coordinated lobster management
N.H. Sea Grant-funded researchers conducted studies to determine if new ventless lobster traps provide a more accurate estimate of natural lobster populations than the standard commercial traps. This research is valuable to resource managers who rely on accurate data to help conserve the lobster populations while ensuring a healthy commercial fishery. One of the students who worked on this project was also in charge of the ventless trap surveys conducted by the Massachusetts Division of Marine Fisheries in 2013. This connection provides a direct line of communication between researchers and resource managers, allowing up-to-date research results to be incorporated into lobster management decisions as soon as they are available.

American lobster research in N.H. leads to natural resources employment opportunity
N.H. Sea Grant-funded research focused on the calibration of new ventless lobster traps and standard trap surveys to optimize measurements of lobster abundance. The research supported a number of graduate and undergraduate students, including one Veteran. The experience this student gained from working on this project led to an employment opportunity conducting similar surveys beginning in 2013, with the environmental consulting group Normandeau Associates based in Portsmouth, N.H. This research has directly led to a well-trained professional entering the local workforce and thus contributing to the advancement of lobster and resource management in New England.

2010

Sea Grant Research Helps Refine Lobster Management Tools
The American lobster fishery, valued at close to $400 million annually in New England, is managed based on abundance estimates from standard lobster traps. N.H. Sea Grant has funded research to determine if the new ventless traps that retain more lobsters also provide more accurate estimates of natural lobster populations than the standard traps. Using underwater video cameras, researchers captured footage to determine trap catch per unit effort, time to saturation, lobster density and size for both types of traps deployed in New Hampshire and southern Maine. Researchers determined that ventless traps provide a more accurate estimate of natural lobster populations than standard traps. Abundance estimates may also be influenced by potential sperm limitation in the lobster fishery, so researchers examined the reproductive potential of lobsters in New England. Data indicate that either immature female lobsters occasionally mate, or the size at maturity has shifted towards smaller size classes. Results from these studies will influence the estimates of lobster reproductive biomass in New England waters and potentially the way the fishery is managed.

Publications

Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant

Journal Article

  • Jury, S. and W. Watson (2013). Seasonal and sexual differences in the thermal preferences and movements of American lobsters. Canadian Journal of Fisheries and Aquatic Sciences 70(11):1650-1657, November 2013.
  • Clark, A., S. Jury, J. Goldstein, T. Langley and W. Watson (2015). A comparison of American lobster size structure and abundance using standard and ventless traps. Fisheries Research 167:243-251, July 2015.
  • Watson, W. and S. Jury (2013). The relationship between American lobster catch, entry rate into traps and density. Marine Biology Research 9(1):59-68, 2013.

Thesis/Dissertation

  • Clark, A. (2012). A comparison of standard and ventless American lobster trap dynamics. Master's Thesis, University of New Hampshire.
  • Dubofsky, E. (2012). Activity rhythms expressed by juvenile American horseshoe crabs, "Limulus polyphemus." Master's thesis, University of New Hampshire.
  • Pugh, T. (2014). The potential for sperm limitation in American lobsters ("Homarus americanus") as indicated by female mating activity and male reproductive capacity. Doctoral dissertation, University of New Hampshire.
  • Goldstein, J. (2012). The impact of seasonal movements by ovigerous American lobsters ("Homarus americanus") on egg development and larval release. Doctoral Dissertation, University of New Hampshire.

CD/Video

  • What do lobster traps tell us about the lobsters on the bottom? (http://vimeo.com/80803280) (2013) (video)