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Juvenile Lobster Monitoring Program, 2002:

Preliminary Report

by Sara L. Ellis and Diane F. Cowan

April 2003

Juvenile Lobster Monitoring Program, 2002
Preliminary Report

The Juvenile Lobster Monitoring Program (JLMP) is a unique scientific research program that investigates lobster population dynamics at intertidal nursery grounds in the Gulf of Maine (Ellis and Cowan 2001). Harboring “baby” lobsters (some only the length of a fingernail), these nursery grounds are accessible once a month at the lowest low tides. Their accessibility makes them extremely valuable as indicators of lobster fishery health: the baby lobsters counted today will be keepers when caught in lobstermen’s traps six or seven years from now. The indicator nursery sites TLC is identifying may tell us if the Gulf of Maine lobster population is increasing, decreasing, or remaining stable. Fisheries managers and lobstering communities can use this information to manage the resource sustainably.

Determining patterns of juvenile lobster abundance within the Gulf of Maine requires long-term sampling over a wide geographical range. SCUBA-based subtidal sampling methods are labor and resource intensive, making it difficult to sample many sites in a given year. The relative ease of sampling in the intertidal zone makes it possible to sample frequently throughout the year (Cowan 1999; Cowan et al. 2003), and the simplicity of the JLMP methodology is amenable to widespread use by trained volunteers.

Volunteers have been participating in the JLMP since 1996 under the supervision of the TLC scientists. The work-force provided by citizen volunteers allows cost-effective coverage of a wide geographical area, which because of logistical and financial constraints, could not easily be covered by conventional methods. The data collected by volunteers in the JLMP are forming the basis of a time series of abundance and distribution of juvenile lobsters around the Gulf of Maine, which will be used to estimate and detect changes in the abundance of juvenile lobsters both temporally and spatially. These data will ultimately be used to test the hypothesis that trends in juvenile abundance can be used to predict recruitment to the fishery.

Here we report on preliminary results from 2002, the 7th year of long-term monitoring by volunteers.

In May 2002, volunteers began monitoring juvenile lobsters at 20 established sites from Isle au Haut, Maine, to Marblehead, Massachusetts. During the field season we trained 8 new volunteers at 4 new sites: Nahant, Massachusetts; Lowells Cove, Maine; Round Pond, Maine; and Winter Harbor, Maine. By the end of the monitoring season in October 2002, there were 22 lobster monitoring sites in the volunteer-based JLMP (Figure 1).

In addition to our volunteer-based sampling, data were collected monthly on a year-round basis by TLC staff and volunteers at 2 additional monitoring sites: Lowell’s Cove in Casco Bay, Maine (10th year) and Friendship Long Island in Muscongus Bay, Maine (4th year). The long-term mark and recapture program at these sites is yielding important information about lobster growth, survival, and movements in the wild (Cowan 1999; Solow et al. 2000; Cowan et al. 2001).

Figure 1. In 2002, 65 volunteers were involved in TLC’s Juvenile Lobster Monitoring Program. Volunteers and TLC scientists surveyed lobsters at 24 lobster nursery sites in coastal Maine, New Hampshire and Massachusetts.

Preliminary Results

In 2002, 65 volunteers and 5 TLC scientists participated in the JLMP, monitoring 24 sites (19 sites in Maine, 2 in New Hampshire, and 3 in Massachusetts). Here we report on only 22 sites (Table 1), since the year-round data collected at Friendship Long Island and Lowells Cove are currently being analyzed separately. Methods used to sample for lobsters in the intertidal zone are described elsewhere (Cowan et al. 2003; Ellis and Cowan 2001).

Volunteers gathered data on 1,169 lobsters (Table 1). Carapace length ranged from 4 mm CL to 85 mm CL. Mean carapace length was 33.3 mm CL. All lobsters but one were below minimum legal size (83 mm CL).

Recently-settled lobsters (i.e., <10 mm CL) were detected at 16 out of 22 sites (Table 1). First-years lobsters (<17 mm CL) were detected at 19 of 22 sites, i.e., all but Lanes Island, Drift Inn Beach, and Odiorne Point.


Table 1. Summary of lobsters found at 22 sites in the JLMP 2002.

Volunteers began sampling at Winter Harbor in Downeast Maine and Lowells Cove DK/TP in Casco Bay in 2002, however sampling began too late in the season at these two sites for them to be compared with other sites where sampling occurred from May through October. Thus only 20 sites are represented in all remaining analyses in this report. The mean density of lobsters at each site ranged from 0.09 to 1.14 lobsters/m2 (Fig 2a). Density of first year lobsters ranged from 0.0 to 0.39 lobsters/m2.

Figure 2a. Mean density of all lobsters at 20 sites sampled from May through October, 2002.

Figure 2b. Mean density of first year lobsters (< 17 mm CL) at 20 sites sampled from May through October, 2002.

By Region
The wide geographical range covered by volunteers allows us to look for patterns on a regional scale. Five regions represented in 2002 were Penobscot Bay (PBME), Midcoast Maine (MBME including Muscongus Bay and Southport), Casco Bay (CBME), New Hampshire (NH), and Massachusetts Bay (MA).

By region, mean carapace length ranged from 28.5 ± 0.64 mm CL (n = 459) in Casco Bay to 44.3 ± 1.41 mm CL (n = 80) in Penobscot Bay (Table 2; Fig. 3). Regions differed significantly in size-frequency distribution of lobsters (Kruskal-Wallis test, P < 0.001). Casco Bay ranked lowest, indicating that a higher proportion of more small lobsters were detected in this region than elsewhere (Fig. 3).


Table 2. Carapace length (CL) of lobsters at 20 intertidal sites in the Gulf of Maine by region, in 2002. (Regional abbreviations: PBME = Penobscot Bay, ME, MCME = Mid-Coast Maine; CBME = Casco Bay ME; NH = New Hampshire; MA = Massachusetts)

Figure 3. Size distribution of lobsters at 20 intertidal sites in the Gulf of Maine, 2002 (n = 1,126) by region. In these box plots the 25th, 50th, and 75th percentiles are shown by lines at the left, middle, and right of each box, respectively. The largest and smallest values that are not outliers are shown as thin horizontal lines; open circles show outliers (regional abbreviations as per Table 2).

To compare patterns of settlement among regions in 2002, we examined density of first year lobsters (< 17 mm CL). Except for Penobscot Bay, where no first-year lobsters were detected, abundance of first-year lobsters followed a strong seasonal pattern, and was generally highest in August and September (Figure 3). Densities of first year lobsters were highest in Casco Bay and Midcoast Maine (Figure 3).

Figure 4. Inter-regional comparison of mean density of first year lobsters (< 17 mm CL) at 20 intertidal sites in the Gulf of Maine, 2002 (regional abbreviations as per Table 2).

By Year
Long-term monitoring allows us to look for interannual patterns over time. The JLMP began in 1996 in Casco Bay, and expanded to other regions starting in 1998. It wasn’t until 2000 that all five regions were included in the study. Given that there are regional differences in carapace length and abundance (as noted above; also Ellis and Cowan 2001), we can only make interannual comparisons of CL for 2000-2002. Mean carapace length was significantly lower in 2002 than in the two previous years (Table 3), indicating that a greater proportion of small lobsters were found in 2002, which is corroborated by size frequency histograms (Figure 4). The higher proportion of small lobsters is suggests that 2002 was a strong year for settlement.


Table 3. Mean carapace length by year, in the JLMP 2000-2002 (n = 20 sites)


Figure 5. Annual size frequency distribution of lobsters at 20 intertidal study sites in the Gulf of Maine, 2000-2002.


Figure 6. Mean density of first year lobsters at 20 sites in the JLMP, 2000-2002.

Looked at as a whole, lobster settlement appears to have increased over the past 3 years, as indicated by increasing mean density of first year lobsters (Figure 6) in 201 and 2002 respectively.

However, on closer inspection, this pattern of increasing settlement was not true for all regions (Figure 7). Based on our sampling, it would appear that in Maine, settlement has trended downward in Penobscot Bay, but trended upward in Midcoast Maine and Casco Bay. In New Hampshire, settlement has trended upward, while in Massachusetts settlement has declined slightly between 2001 and 2002 (Figure 7).


Figure 7. Mean density of recently-settled lobsters (grey bars) and first year lobsters (white bars) by year and by region, as determined by JLMP sampling between 1997 and 2002 (regional abbreviations as per Table 2).


The data collected by volunteers in the JLMP is valuable as it allows us to determine trends in the abundance of juvenile lobsters temporally and spatially. Preliminary results indicate that settlement was strong in 2002 in Midcoast Maine and Casco Bay, while settlement appears to be decreasing in the more northern and southern reaches of our studies, i.e. Penobscot Bay Maine, and Massachusetts Bay. The factors leading to the patterns have yet to be explored.


Special thanks are extended to the many volunteers who have participated in the Juvenile Lobster Monitoring Program, without whom this research would not be feasible. We are grateful for support from Bruce J. Anderson Foundation, the Community Fisheries Project of the Collaboration of Community Foundations for the Gulf of Maine, Darden Environmental Trust, Davis Conservation Foundation, Greater Piscataqua Community Foundation, Island Institute, Maine Community Foundation, Maine Department of Marine Resources, Maine Lobster Advisory Council, Maine Sea Grant, National Fish and Wildlife Foundation, Massachusetts Division f Marine Fisheries, New England Grassroots Environment Fund, New Hampshire Fish and Game, UpEast Foundation, and individual donors. Chris Brehme of the Island Institute prepared the map in Figure 1.

Literature cited

Cowan, D.F. 1999. Method for assessing relative abundance, size-distribution, and growth of recently settled and early juvenile lobster (Homarus americanus) in the lower intertidal zone. Journal of Crustacean Biology 19(4):738-751.

Cowan, D.F., S.L. Ellis, and J.R. Roundy. 2003. Field Handbook: Juvenile Lobster Monitoring Program. Published by The Lobster Conservancy, Friendship, ME. 65 pp.

Cowan, D.F., A.R. Solow, and A. Beet. 2001. Patterns in abundance and growth of juvenile lobster, Homarus americanus. Marine and Freshwater Research 52: 1095-1102.

Ellis, S.L. and D.F. Cowan. 2001. Volunteer-based monitoring of juvenile American lobster, Homarus americanus. Marine and Freshwater Research 52:1103-1112.

Solow, A.R., Beet, A., and Cowan, D.F. 2000. Optimal seasonal sampling for estimating an interannual trend. Israeli Journal of Zoology 46: 351–54.

©2003 The Lobster Conservancy.
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