(Published in the Quoddy Tides, October, 2000)
When you hear talk in Cobscook Bay about 'wrinkling', most local residents know that it means harvesting periwinkles along the shoreline. There are three types of periwinkle that live along the bay's shores, but the common periwinkle is the most abundant and the only one that is commercially harvested.
Found in intertidal and subtidal areas of the bay, the common periwinkle is actually one of the more recent settlers of the region. It is believed that the species was introduced to Nova Scotia from Europe in the mid 19th century, and then rapidly spread westward along the Northeast coast. In many areas of Maine's coast, it pushed native populations of the smooth and rough periwinkles to the edges of their preferred habitat. Now a dominant grazer of the rocky intertidal areas in Cobscook Bay, it has a significant influence on what some of these shoreline communities look like.
The common periwinkle prefers to feed on certain types of seaweed, using a tongue like organ called a radula to scrape the surface of the algae. Although it will feed on young shoots of the larger seaweeds, its favorite foods are the fleshy green sea lettuce and the Enteromorpha algae, which is often referred to as 'green slime'. The common periwinkle is considered a habitat "generalist," as it can adapt to a variety of living conditions from subtidal to higher intertidal areas, but prefers hard surfaces. Where it is abundant, it influences the amount and types of seaweed that grow in a particular area, and indirectly impacts the other marine animals that also depend on seaweed or other affected vegetation for food or habitat.
The spawning period for common periwinkles varies along the Maine coast, but typically occurs during late winter and early spring. The females shed fertilized eggs at night and only during high tide to ensure that the egg capsules will be dispersed and will not be exposed to air. After about six days, the eggs hatch into a larval stage called a "veliger" that floats around in the water column. Within several weeks, the veligers transform into tiny periwinkles that settle in subtidal areas and move into the intertidal area as they grow larger. Females grow faster than males, and it generally takes about two and a half years to reach one inch in size.
Interestingly, the other two species of periwinkle have developed different strategies for reproduction. The rough periwinkle, which is found high in the intertidal zone, produces live juvenile snails that crawl away from the parent. Smooth periwinkles deposit eggs on the fronds of certain species of seaweed, which then hatch directly as juvenile snails.
Patterns of marine life are often different in Cobscook Bay than in other areas, and the common periwinkle offers no exception. Through 15 years of studying marine life in the bay, marine ecologist Robin Hadlock Seeley has observed unusual patterns in the location of common periwinkles. "I've been confused about common periwinkles in the Cobscook Bay area for a long time," says Seeley. "In some places, like Carrying Place Cove at West Quoddy Head, they are everywhere. But in other areas where I would expect to find them, like in the sea lettuce beds at Reversing Falls, there are virtually none."
The green crab is one of the major predators of periwinkles, yet in Cobscook Bay the green crab does not seem to have had a significant impact on common periwinkle populations.
According to the Department of Marine Resources, periwinkles have always been a relatively small fishery except for a brief period in the late 1980's, when new markets were established in Europe and Asia. Most harvesting occurs in Washington County due to the larger size of common periwinkles along that area of the coast. Most of the periwinkles harvested here go directly to the Boston market and are distributed from there to markets across the United States and in Europe and Asia.
No scientific estimates of the size of the periwinkle population or sustainable harvest levels of the resource are currently available. Through two public meetings held in Machias in 1997 and 1998, DMR received feedback from harvesters and others interested in the fishery to determine the status of the periwinkle industry. They are considering suggestions from these meetings, but feel no sense of urgency to propose regulations. Currently, periwinkle harvesting is unregulated in Maine, other than requiring a commercial fishing license.
Periwinkles are typically harvested by hand or with lightweight drags. Russell Wright, a marine patrol officer for the Cobscook Bay area, has seen an increase in the number of pickers out on the beaches, and comments, "Typically you might have one or two pickers on a beach, and now there's six to ten on a beach. The periwinkles don't come in fast enough to keep up with demand."
He adds, "During a good tide, 40, 50, 60 pounds is the best they can do. Usually, they can do 100-200 pounds in a day on the big tides."
Across the border in New Brunswick, common periwinkles are also harvested, but there appears to be little concern about overharvesting this species. Biologist Glyn Sharp, of the Department of Fisheries and Oceans office in New Brunswick, comments, "Only a very small part of their range is being harvested, and the populations in harvested areas recover through immigration of periwinkles moving up from subtidal areas." The Canadian harvests also go directly to the Boston market.
As an introduced species, the common periwinkle has found a place for itself in the intertidal communities of Cobscook Bay. Yet, the role it plays in the ecology of the bay is not fully understood. For example, it has been suggested by some people that because periwinkles feed on green algae, there is a linkage between the removal of large numbers of common periwinkles and the increased appearance of green algae growth on the intertidal flats. The answer to this question, and others like it, awaits further research.
This column was prepared by Cheryl Daigle and Jim Dow. Cobscook Soundings was a monthly column produced by the Maine Chapter of The Nature Conservancy. Its purpose was to share what is known about the workings of the Cobscook Bay marine environment, so that all who make decisions about the use or care of the bay have the best available information.
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