Sustaining a thriving lobster fishery through science and community.
Sustaining a thriving lobster fishery through science and community.
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PRELIMINARY RESULTS OF THE 1997 VOLUNTEER DATAAn initial analysis of the data was done in an attempt to assess the quality of data collected by trained volunteers and to determine the reliability of the technique developed by the biologist. The objective of this study was to test a method for generating a volunteer-gathered database to document the abundance of juvenile lobsters in the lower intertidal zone. The scientific value of any database relies on a consistent, reliable method for documention. Volunteer data (sites TLC 2-12) were compared with the biologist's data (TLC 1) in an attempt to evaluate the quality of the volunteer-collected data.
In this study, one-meter square quadrat sampling was done along fixed transects to determine the density of lobsters as the number of lobsters found per meter squared. Quadrat sampling along transects is a well-accepted ecological method and five years of sampling each month at one location (TLC 1 = is a cove on Orr's Island) has produced copious amounts of reliable data. The area of TLC 1 used as a basis for comparison is a subset of a much larger data set. TLC 1 is sampled monthly by running a series of transects along the waterline below mean low water. For comparison with the volunteer data, these TLC 1 data were taken at mean low water during the same time period when volunteer sampling took place.
The number of times each site was surveyed varied greatly. Of the ten sites covered by the current volunteer study, two were surveyed during all six months (May-Oct, 1997), three were surveyed for only five months, one was surveyed for four months, and four were surveyed only twice. The lack of data for several months at several sites makes a comparison of patterns between sites difficult. Therefore, we report densities recorded at all sites and then focus on the sites that were surveyed at least five times for more detailed analysis -- with the exception of site TLC 5 where densities were lowest. Recorded mean densities, based on sampling between 8 & 12 quadrats, ranged from 0-3.4 lobsters/m2. These densisties are similar to those reported subtidally in similar substrates (1.2-3.8 lobsters/m2). The prevalence of both inter- and intra-site variability in recorded abundance makes it difficult to identify the factors contributing to the between-site differences. There may be differences in recruitment to the sites. However, the highest densities recorded (TLC 1, 4, 7 and 8) were all based on data collected when the biologist was present, suggesting that volunteers may not detect as many lobsters. On the other hand, the lowest densities at sites TLC 1, 2, 5, 6, & 9 were also recorded with the assistance of the biologist.
Figure 1. Length-frequency histograms comparing lobsters collected by volunteers (N = 162), a biologist (N = 83) and the two combined (N = 245). Abscissas = carapace length measured in millimeters; ordinates = number of lobsters. Combining volunteer data to compare size structure of the population reveals a similar size composition for lobsters sampled by the biologist and by volunteers. Similar numbers of young-of-the-year (measuring less than 16 mm cl) were uncovered by the biologist and volunteers (figure 1). however, most of the volunteer-measured young-of-the-year were detected by one volunteer at tlc 9 (figure 2). based on these data, it is not possible to determine whether this is due to geographical variability in settlement sites or to lack of detection of recently settled individuals by volunteers. volunteers at sites tlc 6 & 12 detected larger lobsters than were found either by the biologist or by the volunteer at tlc 9, suggesting there may be a difference in the geographical distribution of size classes (figure 2).
Figure 2. Length-frequency histograms comparing lobsters collected at volunteer sites (TLC 6, 9, 12) with those collected at biologist site (TLC 1). Abscissas = carapace length measured in millimeters; ordinates = number of lobsters.
This study represents the implementation of a valuable volunteer monitoring program that is useful for documenting the presence and abundance of juvenile lobsters in the lower intertidal zone. Based on a preliminary analysis of these data, the method represents a worthwhile survey technique. A more robust data set may be gathered by sampling a larger area or by restricting sampling to the very lowest tides allowing for transects to be laid out even lower -- into the sublittoral fringe. Ultimately, though, while a comparison of volunteer versus scientist collected data unveils some differences, those discrepancies should dissipate as the volunteers gain more and more experience at locating the animals. Thus, the Intertidal Lobster Monitoring Program can be a useful tool for various towns to implement to assess the damage that local activities (town or individual) may have on lobster populations in their area. The Lobster Conservancy also acknowledges the financial support of the New England Grass Roots Environmental Fund and the State of Maine's Lobster Advisory Council's Seed Fund. Lessons Learned From Harpswell Surveys 1995-1997 What's New in our Intertidal Sampling Program -- 1998 to Present Newsletter |
