Density and Mortality in a Harvested Population of Quahog (Mercenaria mercenaria) in Nova Scotia, Canada

Density and Mortality in a Harvested Population of Quahog (Mercenaria mercenaria) in Nova Scotia, Canada

Kevin LeBlanc, Ghislain A. Chouinard, Marc Ouellette, and Thomas Landry

Density and Mortality in a Harvested Population of Quahog (Mercenaria mercenaria) in Nova Scotia, CanadaThis is part of Fisheries Assessment and Management in Data-Limited Situations
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Description

Innovative Fishery Products Inc. has managed a 1,682 ha quahog (Mercenaria mercenaria) lease in St. Mary’s Bay, Nova Scotia, Canada, since 1997. A management strategy based on population modeling is desired to optimize production on a long-term basis. This requires a description of life history parameters, and data on the quahog population and its commercial exploitation. The objectives of this study were to describe the data collected on the commercial fishery, estimate quahog densities, and calculate preliminary mortality rates for the population. Mean densities ranged from 48.3 to 88.4 individuals per m2 during surveys conducted in June 2001 and 2002, and May 2003. Densities were higher than those typically described for commercially harvested quahog beds. The mean age to market was 7 years. Spat recruitment was variable and age frequency graphs suggest immigration of juvenile quahogs between the ages of 3 and 6 years onto the intertidal portion of the lease area. Survival was estimated between 24 and 37% for 7-8 year old quahogs using catch curve and analysis of covariance techniques, where commercial exploitation only represented 5-10% of the loss. Causes of apparent high natural mortality are unclear, but winterkill due to ice abrasion or scouring, predation, and the movement of quahogs from the lease appear reasonable.

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