Substrate Mapping:
Samples of recent efforts -
Great South Channel (USGS),
Stellwagen Bank (USGS),
Alaska (USGS),
Puerto Rico and US Virgin Islands (NOS)
The Canadian scallop companies are mapping the fishing grounds with a Simrad 1002 multibeam system. Focusing fishing effort on identified areas using substrate maps has significantly increased catch rates, lowered fuel consumption, and reduced the area swept by the gear. (scanned from Fishing News International, Feb 2000, ~720k) Below are images from Pittman and Roe (Clearwater Fine Foods) presentation at Scallop Plan Development Team and Advisors meeting, Warick, RI, 4/26/02
Figure 1.
Example of improved Bathymetry, eastern Georges Bank
Figure 2.
Larger scale example from Browns Bank (Todd et al, Canadian Hydrographic Service CD)
Figure
3. Color coded substrate map from backscatter, Browns Bank
Figure
4. DFO chart plotting Catch vs. Substrate type
Figure
5. DFO graphic of Economic impacts of towing identified gravel patches.
Increasing concern has been expressed about the effects of human endeavors on the ecosystems we depend on for survival. Covering the spectrum from global warming to biodiversity, these concerns have recently been focused on the effects of fishing gears on the seafloor. As a basic approach to understanding the interaction, we need to know:
1. what substrate (or bottom surface composition)
types are where,
2. which benthic communities and life stages of commercial
species are associated with these substrates,
3. what types of fishing activities
occur where and how often in these areas, and
4. what are the effects of 'natural'
disturbance, i.e. storm, current and tide, in comparison.
1.
Substrate
The first of these issues has been the subject of much speculation
and effort for many years going back to the use of tallow in the leadline for
taking hand soundings. The invention of the electric sounding machine, which came
into wide use in the fishing fleets in the 1940's, gave both fisherman and scientist
the ability to measure and record depth and, based on the reflected signal strength
and number of echoes, to get a good sense of the hardness of the bottom.
Thousands of grab samples have been retrieved and analyzed by the US Geological Survey, Woods Hole Field Center, since the 1950's. Broadscale substrate maps were published by Lawrence Poppe, et al, 1986, and are included as ArcView shapefiles on the USGS CD, A Marine GIS Library for Massachusetts Bay, Open-File Report 99-439. The current state of the technology for looking at larger areas is towed sidescan and multibeam sonars coupled with use of a grab sampling devices for 'sea truthing'. The USGS Seafloor Mapping Group webpages give an excellent overview of the the technologies and the USGS program. Another project has completed comprehensive mapping of the Stellwagen Bank National Marine Sanctuary.
Dr. Page Valentine, USGS, Woods Hole Field Center, has had his focus on fisheries related mapping projects for many years. Three areas are especially relevant to current fishery management issues:
1. Eastern end of
George's Bank, source: USGS Open File Report 91-439, Valentine and Lough.
These gravel areas are proposed as particularly important to the survival
of newly settled groundfish
species. The crux of the matter is that they are
also areas where scallop settlement is highest.
2. Stellwagen Bank National Marine Sanctuary,
NE corner (scanned portion of preliminary plot)
See also
USGS SBNMS project description and mapping.
3. Research Area in the Great South Channel, NW corner. Locus map and legend. (source-P. Valentine).
The University of New Hampshire has recently established a
Center for Coastal and Ocean Mapping.
Here's a scanned image of the
approaches to Portsmouth harbor as an example of recent projects.
See also Geozui3D link.
Shallow water multibeam studies are also being conducted by the Marine Science Research Center at State University of New York, Stonybrook. There is a call for multibeam projects, similar to the Canadian Scallop industries multibeam mapping effort, in the upcoming rfp from the NEFMC Research Steering Committee.
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Here is an image of detided current speed 1m off bottom on Stellwagen Bank produced for the Boston Harbor outfall study, having fisheries implications. How do we integrate this information with the high resolution bathymetry? Larger image (66k). image source: |
2.
Benthic communities and life history stages of commercial species
Although there are many individuals with long standing effort in the
offshore waters, in my opinion Dr. Richard Cooper and the National Undersea Research
Program, University of Connecticut, Groton, have been most instrumental in advancing
the state of our knowledge of the bottom communities along the Atlantic shelf
using manned and unmanned submersibles and ROVs, with still and video cameras.
The comprehensive NURC video archive of dives in the region contains thousands of hours of footage made during transects in a wide variety of habitats. Current efforts continue to be led by the NURC program, Ivar Babb and Peter Auster, and and the USGS program, Page Valentine and the Seafloor Mapping Group, using the SEABOSS (Seabed Observation and Sampling System).
The Northeast Fishery Science Center (NEFSC) Woods Hole, has conducted trawl and dredge surveys since the 1960's for groundfish, scallop, and surf clam. The results of these surveys are released in a annual series of Fisherman's Reports. Plotting these data by year and in aggregate has proven useful to gauge changes in resource abundance over the time. Additionally since the survey gear is lined with much smaller mesh than is allowed on commercial vessels incidental catch of the juvenile stages of commercial species serves as a good indicator of the incoming year class strength and location (presumably their preferred habitat).
3.
Fishing Activities
Fairly sophisticated pen and paper position
plotters on individual commercial fishing vessels came into widespread use
in the late 1970's in conjunction with the LoRan C chain coverages. Not only was
the signal more stable and less effected by weather and 'skip' than LoRan A, but
the automated display and plotting lessened the workload involved in signal acquisition
and tuning of notch filters, and gave both immediate feedback, a record of vessel
position and movement, and the ability to return to the same area. As can be expected
this information was most often closely held.
The US Atlantic scallop fleet has been using a Vessel Tracking System (VTS) or VMS (Vessel Monitoring System) for the last few years as a condition of utilizing the fisheries permit. Synoptic effort 'maps' of fleet activities have been produced by Mike McSherry and Paul Rago of the NMFS Northeast Fishery Science Center using this data. Although there is variation of scallop settlement from year to year clearly seen in the year by year animation of the NEFSC scallop survey data, meaning that over time the areas fished in any given years may vary, this VMS data is the most accurate in terms of gauging the spatial component or the areal extent of the fishery on a near realtime basis. Although similar VTS requirements were planned for the swordfish fleet, no other US Atlantic fishery has such detailed spatial and temporal data.
There is apparently one fishery in the Bering Sea where an independent entity is being sent catch and bycatch data from individual vessels while at sea, plotting areas of high bycatch, and then broadcasting the results back the individual vessels so that they may move to other areas, so that the fleet bycatch TAC is not reached so quickly. This use of the already available technologies would seem to be a constructive fleet response to existing regulation as it serves to increase both overall and individual catch.
4.
Natural disturbance of the bottom (incompleted as yet)
In general, severe storms seem to rearrange the bottom surface down to about 35 fathoms on a regular
basis. However, these 'high energy' environments are also seen as critical for
the early life stages of commercially important species, in particular, newly
settled cod. (see Howe et al, 2000, Mass DMF, Spring,
Fall)
All four of these issues were discussed in more detail at the CLF-MIT Conference, May 1997, and in the resulting publication Effects of Fishing Gear on the Sea Floor of New England, E. Dorsey and J. Pedersen, eds. Many individual papers are included in the December 1998 issue of Conservation Biology, Blackwell Science, Inc., Vol. 12, No. 6.