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North Carolina Department of Environment Quality

NC Department of Environment and Natural Resources
Marine Fisheries - Hard Clam

Marine Fisheries

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HARD CLAM, Mercenaria mercenaria

8-point rule

Hard clam

Life History

Hard clams (Mercenaria mercenaria) are mostly estuarine-dependent, filter-feeding shellfish found in sandy and vegetated bottoms from Prince Edward Island, Canada to the Yucatan Peninsula, Mexico. Spawning occurs from May through November when water temperatures are between 68 degrees and 86 degrees Fahrenheit. The larvae go through several stages before settling onto a suitable bottom. During the juvenile stages, hard clams tend to be dominantly male and then become either male or female as they mature into adults. Sexual maturity is reached in hard clams when individuals reach a certain size, and the timing is therefore dependent on the rate of growth. Growth rates are highly variable because of temperature, food availability, and genetic disposition. Legal size (one inch thick) is typically reached at age 3 in North Carolina, with the oldest individual known living to 46 years.

Fisheries

Hard clam landings have fluctuated historically, often in response to changes in market demand, improved harvesting methods and increases in polluted shellfish area closures. It is assumed that trends in the overall hard clam landings from both private (leases) and public (wild) bottom can be attributed to changes in landings trends from only public bottom. Public bottom landings have made up about 88 percent of the overall hard clam landings since 1994. Freshwater runoff after storm events often increases shellfish harvest area closures, resulting in a short term reduction in effort that can impact annual landings. Hard clams are a live product that must go to market quickly after harvest because of a short shelf life. Competition with hard clams grown in private culture from other states is also a known contributor to reduced market demand for wild hard clams since a more consistent product can be provided from private grow out facilities.

The annual average North Carolina hard clam landings from 2007 to 2016 was 19.1 million clams (Figure 1). Annual landings in 2011 were the lowest on record since 1975. There has been a slight uptick in hard clam landings since the low in 2011, but they still are at one-fourth of their peak in the 1980s.

Figure 1

The recreational harvest of hard clams in North Carolina does not require a fishing license, and due to this the total amount of recreational landings cannot be estimated and remains unknown. However, a mailout survey has been used since 2010 to estimate harvest from Coastal Recreational Fishing License holders. This population of recreational harvesters makes up an unknown proportion of total recreational harvest, but still provides insight into catch rates, harvest trends, and scale of harvest. In 2010 surveys were only mailed out November and December, so harvest estimates are very low (Figure 2). Harvest and catch rates have seen minimal fluctuations, except for 2016, which was well below average for both. This is most likely due to large rainfall events in July and August which caused widespread shellfish closures.

Figure 2

Management

A state Fishery Management Plan was approved in 2001 by the North Carolina Marine Fisheries Commission and Amendment 1 was approved in 2008. for all hard clams occurring within North Carolina coastal waters. Amendment 1 recommended that the state continue to harvest at current daily harvest limits, eliminate the mechanical clam harvest rotation in Pamlico Sound, institute a resting period in the northern Core Sound mechanical clam harvest area, and develop sampling programs to collect information necessary for the completion of a stock assessment. Amendment 2, adopted by the North Carolina. Marine Fisheries Commission in February 2017 recommended status quo on recreational harvest limits, eliminated mechanical harvest in Pamlico Sound by rule, instituted shading requirements for harvesters from April 1 to Sept. 30, made modifications to shellfish lease provisions, and added theft on shellfish leases and franchises to the types of violations that could result in license suspension or revocation.

Stock Status Overview

The status of the hard clam stock in North Carolina is considered unknown because population size could not be determined and the rate that hard clams are removed from the population could not be estimated. While landings records reflect population abundance to some extent, not enough information on hard clams is available to determine trends in effort, landings, age distribution and recruitment (survival to harvestable size).

A hard clam monitoring program in Core Sound provides some baseline data on abundance and collects environmental information. This sampling is limited to one small area in the state and would need to be expanded to evaluate the entire North Carolina population. Thirty stations are sampled each year using small patent tongs. Three samples are taken at each station, and very few hard clams are caught due to the nature of the gear and sampling design. The catch per unit effort, or number of clams per station, has ranged annually from 0.39 to 1.27 clams per station from 2007 to 2016 (Figure 2). No overall trend is apparent from this sampling; however, 10 years of data is considered a short time series relative to the life span of hard clams.

Figure 3

Research Needs

Research needs for hard clams include improving catch estimates and conducting socioeconomic surveys of recreational harvesters; developing juvenile and adult abundance estimates and the determining the effect of mechanical harvest, water qualityand shoreline development on them; surveying commercial shellfish license holders without a record of landings to estimate hard clam harvest from this group; and supporting collaborative research to more efficiently track bacterial sources for land-based protection and restoration efforts.

Links

Management Agencies

North Carolina Division of Marine Fisheries

Fishery Management Plans Amendments, Revisions and Supplements

North Carolina Fishery Management Plan

Contacts

For more information,
contact Jeff Dobbs at Jeffrey.Dobbs@ncdenr.gov
or 252-808-8193
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N.C. Division of Marine Fisheries • 3441 Arendell Street • Morehead City, NC 28557 • 252-726-7021 or 800-682-2632

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