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Interactions between rock crab Cancer irroratus populations and mussel aquaculture productivity in PEI



Historically, the by catch of rock crab during the lobster fishery has been relatively low. However, due to an emerging demand for the rock crab, a directed fishery has evolved over the past twenty years. In 2003, landings from the rock crab directed fishery in the Gulf totalled 3,715 mt . The fishing effort is mainly concentrated in the Northumberland Strait and north-eastern New Brunswick.

Concurrently, the mussel aquaculture industry has expanded considerably in many areas overlapping the rock crab fishing grounds. In the southern Gulf of St. Lawrence, the mussel production has grown to approximately 18,700 mt with a landing value of $25.8 M for 2003. Both of these activities are viewed as important in sustaining the economic viability of coastal communities.

One of the important husbandry methods employed by growers to reduce epifauna on mussel socks is to sink their longlines to the bottom. This periodic lowering of longlines enables the rock crab to climb onto the socks and feed on the epifauna and the second set of mussel spat, which is considered a nuisance.. Although the direct effectiveness of the rock crab in cleaning the socks has not been tested scientifically, the method is widely used among the growers. Due to the fact that this species has been considered beneficial by the industry, there have been concerns raised by mussel growers regarding the possible impacts the rock crab fishery could have on cultivated mussel sites. Another risk factor for the rock crab abundance is the introduction of the green crab in several areas of PEI, as the green crab could compete with the rock crab for habitat and food. Furthermore, the green crab may not have the same effects on mussel socks.

The project objectives are:

  • to determine whether rock crabs are effectively attracted to mussel socks on a longline;
  • to examine whether there is a decline in the abundance of rock crab on and under mussel lines during and following the directed fishery;
  • to verify the widespread assertion that rock crabs are beneficial to mussel longline productivity;
  • to evaluate the impact of the green crab on mussel line productivity.

The results from this study could set a working base to improve the rock crab fishery management measures and thus ensuring that both industries can realize their full potential. The scientific investigation will also contribute in applying strategies for coastal integrated management of human activities.

Program Name

Aquaculture Collaborative Research and Development Program (ACRDP)


2004 - 2008


Atlantic: Gulf of St. Lawrence, St. Lawrence Estuary

Principal Investigator(s)

Marc Ouellette

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