Science Response 2009/020

Size at sexual maturity and catch characteristics of the yellowtail and winter flounder fishery in the Magdalen Islands

Context

Because of the decline in the herring and mackerel catches, coastal flounder species (especially yellowtail flounder, Limanda ferruginea, and winter flounder, Pseudopleuronectes americanus) make up a significant portion of the bait supply for Magdalen Islands fishers. Yellowtail and winter flounder make high-quality bait and are an important resource for lobster fishers. These fish are harvested in the spring, once the ice has melted, by vessels equipped with trawls, seines or gillnets. Since 2001, a certain number of lobster fishers have been authorized to engage in non-commercial fishing to obtain bait. Although the catch for each species appears to have decreased since 2006, the proportion of catches made by vessels engaging in non-commercial fishing increased in 2007 and 2008 (Table 1). Non-commercial fishing is done by small vessels with small trawls and 130‑mm cod-end mesh. Commercial fishing is done by larger vessels with trawls, seines or gillnets with mesh measuring 140 mm or more. Landings of these two species in the Islands have amounted to between 200 and 400 tonnes annually since 2001 (Table 1).

In 2006, the DFO managers of the Magdalen Islands Area office expressed interest in acquiring more biological knowledge of these species, especially the length at which yellowtail and winter flounder reach sexual maturity. That information was not available from the research surveys conducted each year in the fall or summer (Morin and Forest-Gallant 1996). Sampling programs to monitor the biological characteristics of these species in the fishery were carried out from 2006 to 2008. The goal of the monitoring was to characterize, in the Magdalen Islands area, the relationship between sexual maturity and length, as well as the size composition and sex ratio for each species in the catches from the various types of fishing gear. The information obtained on the biology of these species will help with defining and/or modifying the management protocol aimed at protecting juvenile fish.

A request for scientific advice was submitted by DFO’s Fisheries and Aquaculture Management sector for an evaluation of the results of the data gathered during the three years of monitoring of the fishery. The evaluation was reviewed on October 16, 2009, and this document presents the results and conclusions relating to the questions raised. Size at sexual maturity, estimated using this study, is not considered representative of the population around the Islands. However, the size frequency distributions demonstrate that a large proportion of the yellowtail flounder catches are currently below the minimum size of 25 cm.

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