Wild Side: Conservation moorings minimize impact on harbor bottom

Wild Side: Conservation moorings minimize impact on harbor bottom

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A conservation mooring system starts with a block or augur on the bottom. Above it is the elastic rode whose lower end is suspended by a "trawl" float (blue). From the rode's upper end, a line runs to a 5-foor "spar" buoy, from the top of which runs the pennant to the vessel's bow cleat. — Photo courtesy of Hazelett Marine

As bewildering phrases go, “conservation mooring” ranks right up there. The point of a boat mooring is to stay put, right? How could something immobile relate to conservation? But traditional moorings are under scrutiny for the environmental impact they can have, and an alternative way to tie up your boat is gaining credibility as a rare win-win solution for an important recreational industry.

Last Thursday at the Tisbury Senior Center, Jay Baker, Executive Director of the Massachusetts Bays Program (www.mass.gov/envir/massbays), gave a presentation on a pilot effort to evaluate the effectiveness of so-called conservation moorings, also known as elastic moorings. Sponsored jointly by Tisbury Waterways, Inc. and the Martha’s Vineyard Commission, Mr. Baker’s talk was attended by about 30 interested listeners. I got the sense that, to the extent that boaters were in the audience, Mr. Baker was preaching to the choir. But these new moorings, Mr. Baker reports, may catch on widely: they reduce wear and tear on critical aquatic vegetation — and they may do so while improving the security of boats.

At issue is the health of the region’s eelgrass, an ecologically important plant of shallow coastal waters. A true grass that happens to grow on the sea floor, eelgrass tends to occur in dense, sometimes extensive patches. The structure of an eelgrass bed provides shelter for a wide range of sea life, from young flounder to juvenile bay scallops. And eelgrass beds can absorb some of the energy of waves, reducing storm damage to nearby shorelines. It’s a humble plant, but it’s a keystone species in our nearshore ecosystem.

Conventional moorings, if they’re sited in a bed of this valuable grass, can unintentionally damage the vegetation. A heavy chain, running from a massive block or mushroom on the bottom to the bow of the boat, obliterates a round patch of eelgrass as the swinging boat drags its mooring chain across the bottom. Moreover, the scouring caused by the chain literally muddies the water, suspending sediment that reduces the amount of light that reaches the remaining eelgrass. The dragging chain can also harm other kinds of life on the bottom, such as shellfish trying to live in the mooring field.

Eelgrass is already beleaguered in Massachusetts water, its coverage reduced to a fairly small percentage of its historical area. Several factors have contributed to decades of decline. A mysterious disease hit our region’s eelgrass hard in the 1930s. And declines in water quality have compounded the damage: mainly, excess nitrogen in coastal waters has encouraged higher densities of algae, which compete with eelgrass for light.

So-called conservation moorings can’t address regional water quality problems, but they may reduce local damage to eelgrass in mooring fields. Attached either to a block on the bottom or a heavy augur-like anchor screwed into the sediment, conservation moorings (there are several kinds available) are connected directly to a mooring float with a minimal amount of scope. Tension is absorbed by an elastic component in the system, rather than a chain whose weight keeps it from coming taut. Nothing drags on the bottom, so there is no damage to eelgrass or other wildlife.

The ecological benefit to be gained by the use of conservation moorings may be modest. Less than three percent of the state’s existing eelgrass overlaps with mooring fields, according to a report co-authored by Mr. Baker, with about 1,900 moorings involved. By another measure, though, the possible gains are significant: given an average diameter of about 21 feet for a conventional mooring scar, about 77,000 square meters of eelgrass is affected. Given the dire state of this vital underwater plant, biologists agree that anything that improves the health of eelgrass is desirable.

The permitting process for replacing an old mooring with an elastic one, said Mr. Baker, is currently complicated but appears likely to be simplified in the near future. And the cost of elastic moorings, recently in the $3,000 to $4,000 range, appears poised to drop sharply as more manufacturers enter the market and economies of scale take over. But ultimately, the acceptance of conservation moorings probably depends more on how well they work as moorings than on how well they protect eelgrass.

Boat owners are understandably wary of trusting their valued property to a relatively new technology. But Tisbury Harbormaster Jay Wilbur, in the audience for Mr. Baker’s presentation, gave a strong endorsement for the new system. Estimating that about 30 conservation moorings are already in use around the Vineyard, Mr. Wilbur said that he thinks the holding power of a properly installed conservation mooring may often exceed that of a conventional mooring. Manufacturers claim that conservation moorings are cheaper to inspect and maintain than conventional moorings. And the elastic component of the new moorings reportedly eases the strain on both the mooring and the boat, absorbing some of the shock that comes when a swinging boat reaches the end of its chain in a strong blow.

Mr. Baker’s Massachusetts Bay Program is currently monitoring eelgrass re-growth and boater satisfaction with conservation moorings in Manchester and Provincetown harbors. Early results point to success on both the ecological and the boating side, suggesting in turn that conversion of conventional moorings could be the wave of the future.