Freshwater pearl mussel (Margaritifera margaritifera) population declines in Northern Ireland led to an ex situ breeding programme being established on the Ballinderry River in 1998 by the Ballinderry Rivers Trust. If the causes of the initial threats or declines have been remedied it is recommended that captive- bred individuals are returned to their natural habitat to help avoid domestication by not retaining them in captivity for extended periods. Mussel silos (upwelling mussel housing system) were found to be a useful intermediate release method with a mean survival rate of 81%. Differences of survival between various size classes led to the recommendation that mussels should be maintained in the hatchery environment until they are approximately 10 mm to maximise potential survival. M. margaritifera populations in Northern Ireland are regarded as overaged and reproductively nonÂfunctional. Therefore, to delay their extinction, artificial mussel populations were assembled using translocated wild adults and captive bred juveniles which would have the potential to become selfÂrecruiting. Recovery by observers and survival varied strongly across sites with the majority of mussels moving from their initial release site during the course of the study. Broodstock for captive breeding has been maintained in the Ballinderry Fish Hatchery since 1998. Despite rotation of the broodstock in 2010 in an attempt to maintain genetic diversity in captive bred juveniles significant levels of inbreeding remain. Individuals recently discovered in the Ballinderry catchment showed distinct differences in allele frequencies from the current hatchery broodstock. It is recommended that such individuals should be used for broodstock rotation to genetic diversity in future generations. Juvenile bivalves often use pedal feeding until the ctenidia are fully developed. Serial sections of juvenile mussels suggest that mussels 4 mm long are in transition from pedal to filter feeding because, although a ventral food groove is present, the outer demibranch of the ctenidium is only beginning to form and there are no labial palps. Mussels 8 mm long have all the features found in adult mussels, including palps suggesting they are predominantly filter feeders at this stage.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:707807 |
| Date | January 2016 |
| Creators | Kyle, Rebecca Kate |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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