Comparative growth and survival patterns of <i>Mytilus trossulus</i> and <i>Mytilus edulis</i> in Atlantic Canada

Abstract

Two size groups (20–30 and 45–55 mm) of Mytilus edulis and Mytilus trossulus were assessed from May to December 1992 at two locations in Nova Scotia. The two species were classified using electrophoresis based on mannose phosphate isomerase, and a discriminant function based on shell morphometry. The discriminant function misclassified less than 5% of the mussels and of these, 1% of the M. edulis were misclassified as M. trossulus, and 10% of the M. trossulus were misclassified as M. edulis. In general, both size groups of M. edulis tended to have higher shell growth rates than M. trossulus. Overall mortality was 6% and occurred primarily from mid-August to mid-September; M. edulis exhibited a slightly lower survival and for a given shell length had a higher average tissue and shell weight, as well as a greater shell height, than M. trossulus. Mytilus trossulus had a significantly lower tissue weight during the summer and was eliminated at a significantly higher rate during commercial grading trials than M. edulis. We estimated from the information on individual weight, survival, and grading losses that the economic value of M. edulis was 1.7 times higher than that of M. trossulus.