How Detailed Mapping of the Sea Floor Is Informing Ecosystem-Based Management

A habitat map, in its most basic sense, shows where particular plants and animals are likely to live. A map that shows the location of coral reefs, for example, suggests where there will be reef-associated species. Likewise for other seafloor habitats – sandy bottom, seamounts, seagrass meadows, and so forth.

The knowledge provided by habitat maps is incredibly valuable. Fishers want to find their target species as quickly and efficiently as possible, and detailed maps can help them do that. Resource planners who want to conserve particular species and habitats, or assign specific uses to compatible areas, use habitat maps to inform these decisions.

Prior to a decade or two ago, maps of the seafloor were relatively primitive. Older navigation systems resulted in features being mapped hundreds of meters or more from their actual locations. Habitats less than a certain size failed sometimes to appear on maps at all, depending on the spatial resolution of the surveying system.

Thanks to a combination of technological advances in survey equipment and the growing demand for detailed habitat knowledge, seafloor maps are improving quickly. Some of these maps rely on expensive high-tech systems like multi-beam sonar, while others use lower-tech methods and involve resource users in the surveying. In this issue of MEAM, we examine a range of techniques being used, and how they are informing the management of marine ecosystems.

Using multibeam sonar and video recording systems to improve scallop management

In Canada's Atlantic waters, the offshore scallop industry is able to catch its quota of scallops in far less time than it took 15 years ago, and has simultaneously reduced its impacts on the seabed. A main reason is state-of-the-art habitat maps.

In 1996, scallopers noticed a set of seafloor maps the Canadian Hydrographic Service (CHS) had created using multibeam sonar surveys. Multibeam sonar works by sending a fan of sound energy toward the seafloor, then recording the reflected sound through a set of receivers aimed at different angles. The survey generates accurate data on depth as well as seafloor habitat type – sand, gravel, mud, etc. In the Canadian case, the maps the scallopers saw were much more accurate than had existed previously. The industry recognized that if such maps were produced for their entire fishing area, they could focus their fishing effort just on areas of light gravel – the preferred habitat for scallops.

The results of this realization are profiled in the August 2002 issue of MPA News, MEAM's sister newsletter. (See box "Other sources on marine habitat mapping and EBM" at the end of this article.) The six companies of Canada's Atlantic offshore scalloping industry partnered with CHS and Natural Resources Canada (another federal agency) to outfit a retired scallop vessel with a multibeam sonar system. Over the course of two years, the industry mapped three large undersea banks.

The cost to industry was more than CAD $3 million (US $2.9 million). But the mapping effectively changed their fishing process from hunting to gathering. In addition, it reduced the area of seafloor dragged in pursuit of scallops by as much as 70% – a significant advance considering the impact of scallop dredging gear on seabed habitats. And federal fishery managers were now able to monitor the scallop stock's health on an almost bed-by-bed basis.

Down the Atlantic Coast in the eastern US, the scallop industry has applied similar high quality surveys to its work. However, its maps have been based primarily on video, not sonar. Since 1999, a scallop research team at the University of Massachusetts has partnered with the scallop industry based in New Bedford, Massachusetts, to complete 26 video and scallop-tagging cruises to Georges Bank, a major scalloping ground. The cruises have produced 700 hours of video footage as well as 17,000 digital images covering 7500 km² of seafloor. The collected data provide assessments of sediment/habitat distribution, scallop abundance, and size structure in closed and open fishing areas of Georges Bank. These data now provide a basis for regional management of essential fish habitat for scallops.

When the University of Massachusetts research began, the Canadian scallop habitat mapping project – a few hundred kilometers away – had already been underway for a few years. So why did the Massachusetts team choose video for its mapping instead of multibeam sonar, which was already showing success up north? In short, they wanted to survey the scallop population as well as map its habitat.

"We wanted to count and measure the scallops within a known unit of area, plus we wanted to measure the animals associated with the scallops and the substrate they lived on," says Kevin Stokesbury of the University of Massachusetts at Dartmouth, who oversaw the study. With each video georeferenced, the researchers could work in an expandable way, with subsequent surveys gradually building a complete mosaic of seafloor habitat. "We also wanted to work cooperatively with the fishing industry using their vessels, so the sampling gear had to be mobile and compartmentalized," says Stokesbury. "And we did not want to be hampered by permits, so a non-invasive sample technique that would give us unlimited access to all areas of the bank, including closed areas, was essential." Multibeam sonar can be considered invasive, due to the potential impacts of its loud sound waves on marine life, particularly marine mammals.

The video apparatus Stokesbury's team devised – consisting of three video cameras and a digital still camera, all mounted on a pyramid frame – was inexpensive. "To start, we didn't have much money so it had to be cheap," he says. "We kept things as simple as possible for the first few years. We tested all our gear and calibrated it in tanks on shore. The first version was very low-tech, just a couple of cables taped together and a video/TV from WalMart [a low-cost retailer]. We had to control the cable by hand. However, the images provided proof of concept and we were able to obtain some funding."

The research team discussed every development with the fishermen, who helped build some of the gear, including hydraulic systems to lower and lift the video apparatus between deck and the seafloor. (Georges Bank depths range from 20-45 meters.) Stokesbury says industry was very supportive of the research from the beginning. The bigger challenge was in convincing regional fisheries managers, who relied on a traditional dredge survey for their scallop stock data. "This took over 10 years of debate and critique, even though our work had been published in a number of scientific papers," he says. "Although the value of having two independent surveys to compare and contrast cannot be overstated, the use of a new cooperative survey design with fishermen met with a lot of resistance [from managers]." Management decisions now incorporate both the video survey and the dredge survey, the latter of which is conducted by the National Marine Fisheries Service.

The period of the video survey has corresponded with a strong rebound in the Georges Bank scallop stock and fishery. Stock estimates from the video survey supported the idea of allowing some access by scallopers to existing closures. The resulting system of rotating closures helped scallop landings increase nearly four-fold from the mid-1990s to the mid-2000s. Maps from the video survey are expected to continue to improve the fishery's management – informing decisions on the best areas to close or leave open, and addressing questions of gear impact on habitat. "The habitat data have provided a new map of the sea floor of Georges Bank that is two orders of magnitude more precise than the previous maps used," says Stokesbury. "Plus the survey design is a large Before-After-Control-Impact experiment, enabling us to track the impacts of fishing and the timing of habitat recovery."

Building a systematic understanding of the Barents Sea ecosystem

When Norway launched its Barents Sea Management Plan in 2006, it represented one of the world's first comprehensive marine spatial plans; it covered the oil and gas, fishing, and shipping industries while also safeguarding biodiversity. In crafting the plan, however, officials realized that much remained unknown about Norway's undersea environment. In fact, virtually none of the Barents Sea floor had been systematically mapped. The plan would need to be adapted over time as knowledge improved, and a concerted effort was necessary to improve that knowledge.

To address this need, Norway created the MAREANO program (the acronym stands for Marine AREA database for NOrwegian waters). Specifically, MAREANO is responsible for filling knowledge gaps related to seabed conditions, habitats, and biodiversity. The program is coordinated by the Norwegian Institute for Marine Research in collaboration with the Geological Survey of Norway and the Norwegian Hydrographic Service. Four ministries (fisheries, environment, trade, and petroleum) comprise a steering group.

In effect, MAREANO seeks to learn as much as possible about the Barents Sea benthic ecosystem, and it aims to do it relatively quickly: the entire Norwegian Barents Sea is expected to be mapped by 2020. Work is well underway. Using a range of methods including multibeam sonar, video surveys, biosampling grabs, and more, MAREANO researchers have been conducting detailed mapping of depth, sediments, bottom fauna, and pollutants in Norwegian waters.

"Since launch, MAREANO has found species that are new to science, including new amphipods and bivalves," says Börge Holte, head of MAREANO at the Institute of Marine Research. "The program has also documented new species for Norwegian waters and defined new habitat types and landscapes." One discovery for Norwegian waters was a so-called "pig-tail" soft-bottom coral (Radicipes sp.), which dominates a particular deep-sea slope area between mainland Norway and Bear Island. It has been found nowhere else in Norway and may be in space-related conflict with fishing activities, says Holte.

MAREANO has found new coral reef areas, three of which are among the largest known cold-water reefs in the world, and vast sponge-dominated areas off northern Norway. In the case of the latter, program researchers anticipate studying how the significant sponge biomass influences benthic ecology in the Barents Sea, as well as production on nearby fishing grounds. "MAREANO is laying a platform for new questions that need to be answered to fulfill the Government's demand for ecosystem-based management of Norwegian marine resources," says Holte.

The Barents Sea Management Plan underwent its first official revision this year (2011). MAREANO findings contributed to the revision, particularly with regard to offshore areas already defined in the plan as valuable or vulnerable. The program provided new and detailed information about the biological and physical composition of the sea bottom in these areas. MAREANO also contributed insights on defining indicator species for particular habitats, as well as establishing a climate change monitoring program.

The work has only just begun, however. Holte describes the area of the Barents Sea mapped so far by MAREANO as very small. "The high-diversity shelf areas containing coral communities, the shelf slope areas, and the fish-rich bank areas still must be mapped," he says. "And knowledge of the most remote Norwegian offshore deep sea areas is almost nonexistent." Among the few deep sea discoveries made so far: seafloor seep areas that could be valuable for mining, and newly documented vent areas that could potentially support bioprospecting.

Mapping reefs by crowd-sourcing the work

Seafloor mapping does not always involve highly trained scientists. In South Africa, a program to map the country's reefs (coral, rocky, wrecks, and other types) harnessed a free workforce to do it: recreational divers with cameras.

The Reef Atlas Project, completed in December 2011 and managed by the South African National Biodiversity Institute (SANBI), created the first national map of the country's reef systems. "We undertook this project with the goal of including different reef habitats in South Africa's 2011 National Biodiversity Assessment," says Kerry Sink, SANBI marine program manager. (SANBI reports to the South African environment minister on the status of the country's biodiversity.) The atlas is based on underwater photographs and corresponding GPS coordinates submitted by reef users, primarily divers.

The project was inspired by a photograph that Sink saw on the cover of the African Journal of Marine Science. The photo was of a South African offshore reef complex (Riy Banks). "At the time there was very little information for reefs available, especially distant offshore reefs in our more temperate region," says Sink. "The photograph provided a glimpse of the biodiversity found on the reef, and thus the idea to use underwater images from the public was born." The project went on to take lessons from terrestrial atlas projects that were based on crowd-sourced information, such as the South African Butterfly Conservation Assessment and the South African Bird Atlas Project.

The crowd-sourced aspect was also born of necessity. SANBI had only a small project team to map the country's reefs – two people with many other commitments – and it was clear the project would require extra hands. "We needed to engage divers," says Prideel Majiedt, marine project manager for SANBI. It was not a straightforward process, however. The competitive nature of the dive industry in South Africa meant that many dive business operators were reluctant to publicize their preferred dive locations in any way, particularly with photos and GPS coordinates in the atlas database. By doing so, they could lose competitive advantage, or even alert fishers to healthy reef areas the fishers did not previously know.

"It was quite sensitive information," says Sink. "A commitment was made to keep dive business reef data confidential, and this effectively built trust and assisted with data sharing. The operators then helped us engage their clients. The resolution of maps based on the data and used in reports so far has been at a national scale, so the public can't use it to find new dive or fishing spots. In mid-2012, we will generate a map showing areas of high reef density, but we plan to have it as a broad polygon so you cannot read off individual points, thereby protecting the secret spots."

Ultimately the project gathered thousands of photos, mapped 340 reef systems, and determined threat status and protection levels for 19 different reef habitat types. "The project has helped identify priority reef types for improved management action," says Majiedt. "This includes those that should be included in new marine protected areas and those that need improved protection within existing MPAs." Atlas data on deep reefs and hard grounds were used in recent analyses to identify focus areas for offshore biodiversity protection, and to inform comments on mining prospecting reports. In the future, says Majiedt, the atlas data will be used to support further spatial planning.

For more information:

Kevin Stokesbury, University of Massachusetts, Dartmouth, Massachusetts, US. E-mail: kstokesbury@umassd.edu

Börge Holte, IMR, Bergen, Norway. E-mail: boerge.holte@imr.no

Kerry Sink, SANBI, Claremont, South Africa. E-mail: K.Sink@sanbi.org.za

---