Sustainability of shellfish stocks in the Irish Sea - Essay Example

A critical from the seminar on sustainability of Shellfish Stocks in the Irish Sea Abstract from the seminar on sustainability of Shellfish Stocks in the Irish SeaShellfish are commercially harvested marine invertebrates such as decapods crustaceans and Bivalve molluscs. They are of great economic importance and are a source of seafood up to 50% by value. They are also a source of food for wildlife and important in stabilising the seabed. However the marine invertebrates are facing extinction due to pollution and climate change that causes acidification and rise in sea temperatures respectively, parasites and diseases, overfishing, unexplained mass die offs, unexplained and unpredictable migrations (Galway, 2009)1.

The seminar presentation seeks to find ways that could help sustain the population of fish stocks in the Irish Sea. In order to achieve this, the organisms must be organized into different breeding groups, migration patterns; productivity, genetics and habitats must be first explored and understood. The shellfish were organized into a population structure whereby a population is a group of organisms of one species which can freely interbreed and live in the same place at a time (Atkinson, 2000)2.

Populations can be further divided into sub-populations where interbreeding is restricted and the organisms accumulate genetic differences and may locally adapt to the environment. Another way of organizing the shellfish is by the use of the stock concept. This involves division into stocks for easier management. However, this may not accurately reflect genetic sub-division because in subdivision and productivity concept, each sub-population contributes absolute productivity to the total population which may vary depending on environmental conditions.

While extirpation of subpopulations decreases, total productivity may increase vulnerability to environmental change and decrease genetic diversity. In considering subdivision and gene flow, the reduction in size or density of subpopulations may reduce migration between subpopulations and increases genetic drift or may increase migration into some subpopulations. Migration of locally harvested stock contribute to breeding populations over a much wider geographical area, for example, salmon and trout harvested in the ocean contain migrants from many different freshwater streams which are genetically isolated subpopulations and locally adapted to breeding streams (Nielsen, 1994)3.

The methodologies used include the migration of larvae or adults between subpopulations, DNA extraction of haemolymph or muscle, DNA analysis through gene sequencing and screen for microsatellite markers used to measure genetic diversity. Another methodology is the use of particle tracking models that explore the use of simulations which is based on known oceanographic processes such as currents and fronts. It also explores the use of larvae released from various locations where the model predicts their travel pattern.

And finally the use of limitations in which the behaviour of larvae is unknown and several alternative scenarios must be modelled like passive transport, tidal migration and diel migration. The results obtained for example with cockles, show that the genetic structure exists but are not primarily geographic and the gene flow supports the predictions of the particle tracking model (Thorpe, 1995)4. Another example of the results obtained is with the Flamborough Head population, monitored using microsatellite markers in which the historical data obtained from otolith samples, show that between 1954 and 1970, genetic diversity declined due to harvesting while between 1970-1998 genetic diversity increased despite continued intensive harvesting and due to immigration which has as a result caused the loss of original genetic characteristics.

Conclusion from case study is that shell disease syndrome of crabs and lobsters may be associated with the sediment type, heavy metal pollution and insecticide pollution. It is also noted that genetics can help in identifying parasites and other agents of disease trough phylogenetics, describe population structure and identify source population of introduced shellfish and parasites (Dublin, 2009)5. It is thus recommended that current harvest be reduced to increases long-term sustainability, reverse historical declines though this will cause hardship for dependent communities like the coastal fishermen.

Another decision is that, measures to reduce long-term genetic harm are more likely to be accepted but only if they produce short-term benefits such as maintaining large, old individuals. BibliographyAtkinson, P. W. (2000). The effects of changes in shellfish stocks and winter weather on shorebird populations: results of a 30-year study on the Wash, England. Thetford: British Trust for Ornithology. Dublin, I. (2009). Shellfish stocks and fisheries: review 2009. Galway: Marine Institute. Galway, I. (2009). Shellfish stocks and fisheries review 2009: an overview of shellfisheries legislation, management and economic value in Ireland and assessement of selected stocks.

Galway: Marine Institute. Nielsen, R. (1994). Fish and shellfish: shared Nordic marine stocks. Cph.: Nordic Council of Ministers. Thorpe, J. E. (1995). Conservation of fish and shellfish resources managing diversity, London: Academic Press.