Optimizing cultured mussel yields: second-set dynamics and avoidance strategies

• Main Author: Macneill, Patrick Sean
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2005
• Subjects: Canada; Newfoundland
• Online Access: https://research.library.mun.ca/10955/; https://research.library.mun.ca/10955/1/Macneill_PatrickSean.pdf

A major production constraint for some mussel farms in Canada and elsewhere is related to 'second-set'- an accumulation of unwanted mussel seed on mussel socks. Accumulated seed may originate from primary settlement (annual settlement of mussel larvae) or secondary settlement (post-settled spat that drift) and may be severe enough to decrease growth of production mussels, reduce harvest yields, and increase production costs (extra flotation, transportation and processing costs). The objectives of the present study were to identify the biotic and abiotic factors involved in second-set dynamics through environmental and biological monitoring, as well as current husbandry observations. A multifactorial field experiment was undertaken to examine the temporal (monthly) and spatial patterns (2 sites; 3m, 6 m, 9 m depth) of larval and post-larval mussel settlement at two commercial mussel farms in Newfoundland in an attempt to understand second-set dynamics. Laboratory trials investigated mussel seed crawling behaviour under varying environmental conditions (food, temperature) with two seed sizes (5-10 mm and 15-20 mm) to explore a possible relationship with second-set accumulation. Finally, the influence of initial socking density (approximately 100, 200, 250, and 300+ mussels per 30 cm), sock deployment depth ( 4 m and 9 m), time of deployment (spring and autumn) and husbandry practices on the timing and intensity of second-set was examined. -- Results indicated that environmental conditions influenced mussel spawning times, with seed collection heaviest during August. The seasonal thermocline may have led to heavy seed collection at a depth of 9 m, however, growth of seed was less than at 3 m or 6 m. There was evidence of secondary settlement of post-settled spat (byssal drifting) which may be a source of second-set accumulation. Crawling behaviour of seed mussels was influenced by temperature and seed size, with implications for optimal socking strategies. Second-set accumulation was significantly reduced with ...