Population structure and morphology of the prawn Palaemon serratus (Pennant, 1777) in Welsh coastal waters with a consideration of two options for regulating the fishery

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Student thesis: Master's ThesisMaster of Philosophy

Original languageEnglish
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Award date2013
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Abstract

The Palaemon serratus prawn fishery contributes over half a million pounds annually to the Welsh economy. Despite its importance, the commercial exploitation of the species in Welsh waters remains unregulated. Fishermen and their Associations have long recognised that legislation is crucial if the fishery is to remain economically sustainable. Because regional variations in the morphology and structure of the population could compromise the universal applicability of legislation, sample populations from four locations around the Welsh coast were examined with a view to testing the hypothesis that there were morphologically or structurally distinct groups of P. serratus that could be regarded as separate populations of the species around the Welsh coast.
Significant differences in size were found between the sexes in all samples, confirming that because females were larger they were the main target of the fishery. Sexual dimorphism was also evident in the analysis of rostral morphology. Relative to carapace length, the length of the rostrum was found to be significantly longer in males than in females. No evidence of separate populations around the Welsh coast was found; regional variations in the morphology and structure of the sample populations were thought to reflect the depth at which samples were collected and known seasonal migratory patterns of the species. Data relating to the effect of pot mesh size on catch quantity were examined to determine what the differences in the quantities of saleable and discarded prawns were between 9mm and 14mm mesh pots. The mean number of prawns captured by the 14mm mesh pots was significantly less than the mean number captured by the 9mm mesh pots, but significantly less discard and marginally more saleable prawns were captured by the 14mm mesh pots.
Most commercial prawn fishing takes place during the winter months. The main income of pot fishermen during the summer months comes from the capture of species such as the common lobster (Homarus gammarus). Therefore, catch data for both P. serratus and H. gammarus were examined to determine if there was a period during which the prawn fishery could be closed without having an adverse effect on fishing incomes. No evidence was found in the analysis of catch data to suggest that a closed season between 1st June and 1st September would have any adverse effect on fishing incomes