Mussels secrete byssal threads regularly to the substratum, and the strength of these threads can fluctuate with time. The present study examined weekly variations in the attachment strength of 2 yr old cultured mussels Mytilus edulis on submerged longlines in a semi-enclosed lagoon from late May to mid-October. Some possible factors influencing attachment strength were investigated: environmental factors (temperature, food availability, wind velocity and hydrodynamic conditions such as current velocity, turbulence and wave height) and reproductive condition were measured concurrently. Attachment strength was measured directly on cultured mussels using a dynamometer. Attachment strength varied 2-fold from summer to fall, a difference related not only to the number of byssal threads but also to their individual strengths. The hierarchical influence of each factor on attachment strength is discussed. Our results suggest that spawning seemed to be correlated with an important decrease (-32%) in attachment strength, and that water temperature (negative relationship) and turbulence (positive relationship) were the most important factors explaining the variation in mussel attachment strength. In contrast to previous studies carried out in intertidal zones, no trade-offs were observed between reproduction and attachment strength.

No abstract

-Mussel culture relies on the mussel self-attachment capacity through byssus production. By doing so, no cages or containment devices are needed. It has been previously suggested that thread production requires a nonnegligible part of the energy expenditure in blue mussels Mytilus edulis. Therefore our work investigates the relationships between byssal thread production, mussels energetic reserves and phospholipids profiles in the foot. The relationship between thread production and heterozygosity was also examined. The study was realized in a small lagoon of the Îles-de-la-Madeleine, southern Gulf of St. Lawrence, Canada, on four sampling dates between June and September encompassing the pre-to post-spawning periods. Our results show a significant relationship between the thread numbers and attachment strength. However, no correlations were found between energy reserves, phospholipids composition of the foot or heterozygosity level and byssal production. Our results suggest that mussels in suspension culture in this lagoon were not energy-limited so that the energy reserves did not influence the byssal thread production.

Laboratory experiments were conducted to assess shelter use and behaviour of juvenile Spotted Wolffish, Anarhichas minor, using time-lapse video. Information about the behaviour of Spotted Wolffish and its habitat utilization is sparse due to the great depth at which this species lives. Four experiments were conducted using one or two fish per tank, with and without a shelter. The positions and movements of fish in the tanks and interactions between fish were monitored over 24-h periods. In experiments in which no shelter was available, Spotted Wolffish spent very little time exploring the water column. They did not show fidelity to a particular area on the bottom of the tank and exhibited few signs of aggressiveness to each other. When a shelter was made available, fish spent most of their time in the shelter or close to the shelter. The presence of a single shelter did not enhance aggressive behaviours in fish kept in pairs. When day and night observations were compared, no clear diel pattern emerged. The Canadian recovery plan for Spotted Wolffish calls for research aimed at describing their use of demersal habitats. The present study suggests that shelter availability might be an important feature of the habitat requirements of juvenile Spotted Wolffish.