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Upper Penobscot Bay Shellfish Survey 1966-1967

From: Conference in the Matter of Pollution of the Navigable Waters of the Penobscot River & Upper Penobscot Bay in the State of Maine, April 20, 1967, Belfast, Maine.

Since soft-shell clams were discovered as a food source, the type of equipment used in Maine to harvest them has varied little. The area available for harvesting this resource has also remained the same. The mud flats, or intertidal zone, provides the entire area of harvest. Soft-shell clams, however, do inhabit some of the bottom below the extreme low water mark, but because of equipment restrictions, imposed by law, they are unavailable to the commercial market. Resource assays within this study area are, therefore, confined to tidal areas available to both the commercial and sports digger and were conducted using a similar type of "hoe" or clam rake.

Although all sizes of clams were collected, only those above 1-1/4 inches were considered in calculating results. The survey was conducted during the period July 17 through August 11, 1966. Estimates of this soft-shell clam resource were acquired by sampling 2,035 stations in 1,000 acres.

Results of the resource survey are reported on a town-by-town basis and contain an estimate of the standing crop of soft-shell clams found within the boundaries of each town. In addition, calculations were made on the potential harvest of this 1966 crop, if the presently restricted areas were opened to commercial digging.

Yield during a second year of harvest (1967) was calculated from an estimated growth rate of 1/2 inch in the size range of 1-1/4 inch to 1-3/4 inch size group. Accordingly, there would be no recruitment into the 1-3/4 inch group from the previous season 1 inch class. Sizes within the 2 inch and 3 inch group were assumed to grow a minimum of 1/4 inches during a growing season which is somewhat less than usual. Projected estimates of recruitment from these sizes, consequently, are low or minimum estimates.

The reduction in the second year's standing crop in some cases is half or less than the previous year. This should not, as it appears, give a false impression that a stock is approaching a state of depletion -- the decrease would be caused by the potential cropping off of about 70 percent of the marketable soft-clams accompanied by an estimated 50 percent mortality of the remaining clams, which would result from digging and natural causes. The individual flats should then, with normal digging pressure, reach an equilibrium between recruitment and natural mortality.

Percentages of natural and digging mortality were applied from reports from Glube (2) and Dow, Wallace, and Taxiarchis (3) and, when combined, averaged 50 percent per harvest season. Using these factors of recruitment and mortality, estimates were made on the second season's standing crop and the potential value to the fishermen and the community.

Mr. D. E. Wallace of the Maine Department of Sea and Shore Fisheries had determined that a bushel of softshell clams has a value of $7.77 to the fisherman, and has calculated that the community value is worth 2.5 times this amount or $19.43. Mr. Wallace (4) explained how these figures were determined:

"It is difficult to get a precise accounting of the production of clams in the area because of the many ways in which they are sold locally and the numerous outlets. They are sold to intrastate dealers who operate small shucking houses, to direct customers from roadside 'clam stands', peddled house to house as well as to the one local interstate shellfish dealer. Because of these local markets in an active tourist area and family income from processing, the 'value added' to the incomes of the producers is considerable.

"For example, a bushel of clams dug and shucked locally and sold to a restaurant or fried clam stand, and then sold to the consumer, has a consumer value of approximately $50.

"In 1965 there were 32 full-time diggers in the two towns (Stockton Springs - Searsport), digging year-round, and producing 19,200 bushels of clams with an average value of $7.77 per bushel, or a total income to the diggers of $149,184.

"From our data, it appears that it is reasonable to consider that the resource value to the community is worth 2 and one-half times the amounts paid to the diggers or $327,960, plus the value of clams taken in the sport fishery."

Economic studies by the Merrimack River Project on the resource value of clams, in addition to considering factors that Wallace used, also included the effect of shipping the clams in interstate commerce. The data show that the overall market factor can be as high as seven times the value paid to the digger. The potential value of the clam resources, considering the overall market, would thus be $54 per bushel. The 2.5 to 7 market factors would represent the low and high range used for calculating the value of the clams.

The results of the soft-shell clam resources study are summarized on a town basis. Included are descriptions of the area sampled, estimates of standing crop and value of this resource to the community.