| Summary: | The whelk, Buccinum undatum, is a commercially important shellfish species found throughout the North Atlantic. Many problems face fisheries scientists attempting to assess and monitor populations of this species, due to several life history traits such as highly variable growth rates and sizes at maturity both between and within populations. One major problem has been the lack of a reliable ageing tool, limiting the ability of scientists to develop accurate population age structure estimates for stock assessments. This thesis focuses on three major areas of research: the reproductive assessment, growth and age of Buccinum undatum collected from three geographically distinct populations from the Shetlands, North Wales and the Jersey Islands. Reprodictive assessments of several B. undatum populations across the UK were undertaken by utilising several previously published maturity estimation techniques to ascertain the most accurate and reliable methods. It was found that size (total shell length) at maturity was highly variable, even over relatively small geographical distances. The timing of the reproductive cycle was assessed in a whelk population from the Menai Strait (North Wales, UK) to investigate changes in maturity assessments over an annual seasonal cycle. It was discovered that size at maturity varied throughout an annual cycle, suggesting an optimal season for maturity assessments. Spatial variations in shell morphology between populations highlighted clear differences driven by the shape of the aperture and the angle of the shell apex. The crystalline structure of B. undatum shells was also investigated for the first time; using a combination of analytical techniques a multi-layered aragonite shell structure was uncovered. The shells of B. undatum were also assessed for their potential as environmental recorders. The oxygen isotope ratio contained within B. undatum shells was found to be a reliable proxy for seawater temperature, allowing the development of a species-specific palaeotemperature equation that will greatly aid future studies of this species where seawater temperature reconstructions are required. Population growth rates were also assessed, using the isotope data, uncovering clear differences in patterns of shell growth between populations. A novel age determination technique for B. undatum was developed that utilised growth rings present in in a pair of calcium carbonate statoliths contained within the foot matrix of each whelk. An annual periodicity of the growth rings was determined by measuring growth in monthly samples of statoliths removed from laboratory reared juvenile whelks of known provenance and age. Cutting edge analytical techniques were also used to assess the structure and seasonal variations in the chemical composition of the statoliths. Following this, the use of statolith growth rings for fisheries monitoring purposes was assessed and compared to the currently used age determination method, operculum growth rings. Using data on size at age, population growth curves were constructed for a range of whelk populations across the U.K. It was confirmed that counting the annual rings in statoliths providea a more reliable assessment of the age of B. undatum, delivering a new more reliable tool for fisheries scientists to assess population age structure.
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