Trawl Impact Research Presentation by Visiting Scientist
Dr. Roland Pitcher with the Australian Commonwealth Scientific and Industrial Research Organization (CSIRO) presented a seminar titled "An integrated approach to assessment of seabed habitat and biodiversity in support of trawl management on the continental shelf of the Great Barrier Reef" on 6 April at the AFSC in Seattle, Washington.
His talk summarized a series of related research projects over the last 15 years in the Great Barrier Reef that assessed the impact rates of bottom trawling for prawns on megabenthos; monitored subsequent recovery rates and measured natural dynamics of sessile megafauna; mapped the distribution of seabed habitats and megabenthos species; and integrated these results with fishery effort data in a dynamic modeling framework. This framework was then used to evaluate alternative strategies for sustainable management of these species.
The methods he described included direct sampling with benthic sleds and bottom trawls, underwater video, and statistical modeling to predict the distribution of species from biophysical relationships with broad-scale datasets such as bathymetry, sediments, remote sensing, and oceanographic model output. The modeling framework simulated trawl impact and recovery for the predicted species distributions, based on measured estimates of rates and existing data on trawl effort distribution and intensity, in order to estimate the regional scale implications of past trawling.
An evaluation of management actions over the last 10 years showed that effort reductions lead to positive responses in benthic invertebrate populations, while spatial closures of low effort areas had negligible responses. AFSC staff had an opportunity to meet informally with Dr. Pitcher to discuss their personal research problems and the applicability of his analytical methods in Alaska. This work is particularly relevant to the research plan that is currently being developed for the Northern Bering Sea Research Area.
By Bob McConnaughey
Planning Ahead for the Northern Bering Sea Research Area (NBSRA)
Figure 4. Northern Bering Sea Research Area (NBSRA).
Receding sea ice in the northern Bering Sea (NBS) appears to be shifting the ecosystem in favor of some groundfish species. As recent AFSC bottom trawl surveys indicate, the distributions of some commercial fish and crab populations are extending northward into the subarctic bounds of the NBS. This trend is expected to attract a corresponding movement of the Bering Sea nonpelagic bottom trawl fleet, which targets mainly flatfishes such as yellowfin sole, rock sole, flathead sole, turbot, and arrowtooth flounder.
Historically, commercial bottom trawling effort has been negligible in the remote and often ice-locked NBS. Fishery and ecology research also has been limited there. However, many marine mammal and seabird species have long thrived in this rich, benthic-based ecosystem, feeding on the abundant clams, crustaceans, and other invertebrates on the seabed. Some of these benthic predators are currently listed under the Endangered Species Act, such as the spectacled and Steller’s eiders, or are under consideration for listing, such as the walrus.
At the top of the food web are native Alaskan peoples, who have subsisted for generations in coastal communities through fishing and hunting. Climate change and commercial bottom trawling can potentially cause adverse effects on the environment and the subsistence coastal communities.
Warming of the boreal seas and the loss of sea ice already are changing energy flow through the ecosystem. There has been a significant decrease in benthic productivity and biomass over the past decade. The complex effects of this shift are still little understood but are certain to propagate to upper trophic levels.
The additional stress that bottom trawling might impose on the benthic habitats of the NBS and its radiating effects on animals and people are cause for concern. Presently, there is a lack of up-to-date baseline information on the benthic habitats and ecology of the NBS for assessing the effects of bottom trawling.
Amendment 89 to the fishery management plan for groundfish of the Bering Sea and Aleutian Islands management area establishes the Northern Bering Sea Research Area (NBSRA) for studying the impacts of bottom trawling on benthic habitats (Fig. 4 above). Pursuant to the Amendment, bottom trawling is prohibited in the NBSRA. The North Pacific Fishery Management Council (Council) has requested that the AFSC formulate a scientific research plan to study the benthic habitats of the NBSRA and the potential effects of bottom trawling so as to inform management actions.
The RACE Division is spearheading a joint effort within the Center and the NMFS Alaska Regional Office to develop a research plan for the NBSRA. A preliminary outline of the plan was presented to the Council's Scientific and Statistical Committee (SSC) for review at the June 2009 Council meeting. The plan features trawl impact studies as the principal research element. The proposed studies are modeled after trawl impact experiments (TRAWLEX) conducted in Bristol Bay by the RACE Habitat Research Group (www.afsc.noaa.gov/RACE/groundfish/hrt/impact.htm). In the plan, previously untrawled sites representative of the major benthic habitat types in the NBSRA are chosen for the studies. The impacts of bottom trawling are measured in the biological and physical changes in the benthic habitats before and after trawling.
Other proposed research elements are bottom trawl surveys and habitat studies. These studies will provide baseline data on fish population dynamics and the benthic environment. Also suggested in the plan is the granting of exempted fishing permits (EFP) to some commercial trawling vessels for limited fishing in the NBSRA. This will provide more realistic information on catch and effort, fishing patterns, and interactions with nontargeted species and subsistence fisheries.
After reviewing the outline and considering the testimonies of the fishing industry, environment advocates, and Alaskan communities, the Council advised that an extended period should initially be invested in compiling baseline habitat information. The Council believes that a sound research plan requires more substantial knowledge of the environment, species, and people. Further analysis of the plan should follow baseline data compilation and review.
AFSC is focusing on gathering available data, building databases, and producing resource and habitat maps in support of NBSRA research planning. This involves mining information from past studies, canvassing researchers presently active in the NBS, and consulting with government agencies, the fishing industry, and Alaskan communities.
Meetings with these different groups are tentatively scheduled for early 2010 to solicit input and forge partnerships in the planning process. The tentative date for completing the final plan is late 2011. Interested parties are kept informed of the developments through the Council website at www.fakr.noaa.gov/npfmc/current_issues/ecosystem/NBSRA.htm.
