NURP Project Summary


	Cobble Nursery Landscapes and the Regional Abundance of the American Lobster (Year 2 of 2) Project Number: NAGL-03-01B Principle Investigators: Wahle, R. A., K. Hovel, and D. F. Belknap Region(s): Buzzards Bay, MA, Cape Cod Bay, Casco Bay, ME, Midcoast, ME, Mt. Desert Island, ME, North Shore, MA, Rhode Island Sound, York, ME

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Improving our capabilities to predict harvest trends for fishery species is crucial for proper management and the prevention of stock collapses that threaten local and regional economies. The American lobster Homarus americanus is the most economically important single-species fishery in New England. A long-term goal of the lobster scientific community is to develop a spatially explicit model that couples pelagic and benthic processes to predict lobster landings. While progress on the model is being made through the complementary efforts of several research groups, we presently lack information on how density-dependent processes operating after settlement influence linkages between larval production and adult abundance. The goal of the research proposed herein is to fill this void in our knowledge by examining factors that determine the strength of a demographic bottleneck that may limit lobster production in cobble, an essential fish habitat (EFH) for the American lobster in New England. The research plan specifically addresses three key, habitat-related factors that may influence lobster abundance: shelter limitation, the spatial configuration of cobble habitat (I.e. cobble landscape structure), and predator abundance in and around cobble habitat.

The research team consists of two benthic ecologists (R. Wahle: Bigelow Laboratory for Ocean Science; K. Hovel: San Diego State University) and a geologist (D. Belknap: University of Maine) who will use surveys and manipulative experiments to (1) determine how late-juvenile and adult lobster abundance in near-shore and offshore habitats is correlated with (i) juvenile lobster densities in nursery habitat; (ii) cobble landscape structure; and (iii) predator abundance; (2) determine if juvenile lobster are shelter-limited in cobble habitat; and (3) determine how shelter limitation, cobble landscape structure and predator abundance may influence lobster vulnerability and movement in cobble habitat. A key component of their research plan is to take advantage of large-scale variation in juvenile lobster density and predator abundance to make a regional comparison of how the three factors influence the strength of a demographic bottleneck. Moreover, they will combine region-specific data collected in this study with pre-existing, state-supported, time series of settlement and juvenile densities spanning the coastline from Rhode Island to eastern Maine to generate a better picture of how density-dependent processes influence the linkage between lobster settlement and fishery landings.

The survey component of the project will involve shore-based scuba-based surveys to assess juvenile lobster and predator densities in near-shore cobble habitat, and remotely operated vehicle (ROV) surveys in deeper offshore waters to quantify the density of large, vagile lobsters. Side-scan sonar will be used to map near-shore cobble habitats, to quantify various habitat types in near-shore-offshore transects and to site ROV surveys for lobsters and their predators in each of the eight selected regions. We are requesting from NURC-NA&GL eight days of ship time to support these side scan sonar and ROV surveys in each of two years.

The shore-based experimental component will use scuba to conduct manipulative experiments in nearshore cobble nursery areas at three sites within each of two regions (Rhode Island and mid-coast Maine) which are known to have disparate predator abundances and juvenile lobster densities. At each site the degree of size-specific shelter limitations will be assessed with shelter-supplementation experiments, lobster vulnerability to predators will assessed with tethering experiments and lobster movement throughout cobble habitat will be assessed with tagging experiments.

By focusing on processes dictating lobster abundance in and around cobble nursery habitat and on how these processes influence regional lobster production, this project directly addresses the primary goal of NURC-NA&GL to "understand the functional role of habitat in the survivorship, growth and reproduction of managed species." Results of hierarchical surveys and experiments will add to our understanding of how EFH influences H. americanus survival and abundance, especially at little-examined landscape and regional spatial scales. The research also addresses untested hypotheses that link lobster landings to pelagic and benthic processes, and the results will therefore form a crucial element in the spatially explicit model that will serve as an early warning system for lobster decline.

Project Objectives:

With the goal of evaluating regional differences in the strength of lobster mortality bottlenecks, the project is divided into a survey component and an experimental component. The survey component is supported by NURP; the experimental component is jointly supported by NURP and NSF. NURP support applied to the first two years of the three year project supported by NSF. To date we have completed the Year 1 and 2 field tasks and have analyzed and presented some of the results. The specific objectives are summarized as follows:
Survey Component

• Objective 1 - Scuba surveys at the Nursery Patch Scale: Determine the correlation between the density of lobsters at the nursery patch edge and the density of lobsters within the patch

• Objective 2 - Habitat Mapping by Sidescan Sonar and ROV surveys at the Landscape/Regional Scale: Determine how strongly the densities of nearshore and off-shore older juveniles and adults correlates with habitat or juvenile abundance.

Experimental Component

• Objective 3 - Shelter-limitation Experiment: Determine local and regional differences in size-specific shelter limitation for juvenile lobsters (i.e., identify the lobster size class most likely to be subject to a demographic bottleneck). Determine local and regional differences in the extent to which shelter supplementation augments lobster densities. Planned for 2003.

• Objective 4 - Predation Experiments: Determine local and regional differences in the size specific vulnerability to predators in open gaps in cobble habitat.

• Objective 5 – Shelter Fidelity Experiments: Determine local and regional differences in lobster shelter fidelity in cobble habitat.

Progress to Date
Survey Component:

Objective 1: All scuba surveys were completed in year 1 as planned at the 24 sites between Rhode Island and Maine. These include all diver visual transects and stationary video monitoring for fish. To date all data from the visual surveys have been entered and videos reviewed. See the full report ("NAGL-03-01B Annual Report (Wahle Hovel Belknap).doc") to view Fig. 1a and b containing examples of data generated from these surveys.

Objective 2: All told, for the two-year project we completed all our sidescan survey objectives and 49 of 64 planned ROV dives (77%). A major breakthrough during this cruise was our ability to quickly save the sidescan surveys as geo-referenced tiff files that we could then navigate from during the subsequent ROV dive. All videos from the 2003 ROV surveys have been reviewed and data have been entered; videos from 2004 are currently being analyzed. All sidescan sonar surveys conducted to date – amounting to more than 600 linear km - have been saved as geo-referenced tiff files as were the ROV track lines. Post-processing analysis of substrate cover and patchiness will be done over the course of 2005. See the full report ("NAGL-03-01B Annual Report (Wahle Hovel Belknap).doc") to view Fig. 2 containing examples of the ROV data collected to date.

Experimental Component

Objective 3: The shelter limitation experiment was successfully carried out in 2003 at all locations where it was planned (RI, Buzzards Bay, Mid-coast, and Mt Desert). See the full report ("NAGL-03-01B Annual Report (Wahle Hovel Belknap).doc") to view Fig. 3 containing an illustration of data from this experiment.

Objective 4: Tethering experiments were conducted at two sites in each of three regions (RI, Midcoast, and Mt. Desert) with two different size categories of lobsters. For each trial video surveillance was carried out for a randomly selected lobster. Three replicate trials were conducted at each site. See the full report ("NAGL-03-01B Annual Report (Wahle Hovel Belknap).doc") to view Fig. 4 containing an illustration of data from this experiment. Review of videos is presently is underway.

Objective 5: Planned for 2005 in final year of NSF project.

Web-based products:
Hatch-to-catch – On Bigelow’s website an interactive educations tool to illustrate the consequences of different larval transport and settlement pathways for lobsters - (http://www.bigelow.org/hatch_to_catch) and (http://www.bigelow.org/h2c2)