Host choice and behavioural responses to flow change in the freshwater pearl mussel, Margaritifera Margaritifera, in Scotland

• Main Author: Clements, Elizabeth Anne
• Format: Thesis
• Language: English
• Published: 2015
• Subjects: GB Physical geography; QH Natural history; QL Zoology; Salmo salar
• Online Access: http://theses.gla.ac.uk/6516/; http://theses.gla.ac.uk/6516/1/2015clementsmsc%28r%29.pdf; https://eleanor.lib.gla.ac.uk/record=b3114006

Margaritifera margaritifera are one of the longest-lived invertebrates in the world. They are threatened across their range but Scotland remains a stronghold for this species. Even so, in Scotland the population is showing evidence of decline. This study comprised of two parts: The intricate life cycle of M. margaritifera includes a parasitic stage as glochidia attached to the gills of salmonids. The preferred salmonid host in Scotland is thought to be Salmo salar and Salmo trutta in the absence of S. salar. This has not been empirically tested in the field. Eight rivers in the North West of Scotland were surveyed using standard electro fishing techniques. Glochidia encysted on the gills of fish were counted immediately prior to drop off. Results of the study suggest that S. trutta is used as the primary host fish for glochidia attachment in the rivers surveyed. The second part of the study looked at behavioural responses, horizontal and vertical movement, to changes in flow regime. Mussels were found to bury significantly deeper in conditions of gradually increasing water velocity compared with fast increases in water velocity or where water velocity was kept constant throughout the experiment. Sixty-eight per cent of individual mussels washed out when the water velocity was rapidly increased. No differences in horizontal distance travelled were observed. In conclusion the velocity conditions within which mussels beds are maintained are varied and complex, as is the relationship of M. margaritifera glochidia and host fish species. There remains a need for standard habitat description for each discreet population of M. margaritifera before management actions can be sufficiently targeted to prevent the continued decline of this species.