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Estuarine Investigations
Contents
- Introduction
- Sampling Methods for Fish in Transitional Waters
- Visit of Mr. Steve Colclough (Environment Agency, U.K.) to Central Fisheries Board.
Introduction
Estuaries are an interface habitat – where freshwater flows from rivers mix with the tide and salinity of the open sea. As such, they provide a challenging habitat where nothing remains stable for very long. In every period of 24 hours the tidal level rises and falls twice, subjecting extensive areas to inundation and exposure. The mixing of fresh and salt waters leads to major fluctuations in salinity or salt concentration in addition to stirring up bottom sediments and creating elevated turbidity levels. It is this very changing process that gives estuaries their special qualities and makes them very fertile and productive environments for the species of plants and animals inhabiting them.
Hauling in a beach seine
Estuaries are also known as transitional water bodies, an appropriate name that identifies the transitional or changeable nature that is the true character of an estuary. Throughout history estuaries have provided a gateway to the interior for coastal explorers travelling by boat or ship. Cities and towns in Ireland have developed in the upper reaches of many such transitional waters, such as Waterford city, Limerick and Drogheda. The growth of such cities and towns has seen an associated development in industry and in facilities to handle boat traffic. In many parts of the world estuaries have come under severe ecological stress due to high density of population, industrialisation and shipping, reclamation of saltmarshes, water abstraction and discharge of waste water.
Estuaries have also been exploited by fish over a long evolutionary period. Many species avail of the highly productive nature of many estuaries for all or part of their life cycle. Other fish are migratory, travelling through estuaries from the sea to reach spawning grounds in freshwater, such as salmon and lamprey, while others, such as eel, migrate down estuaries as adults to spawn at sea.
Sorting the catch from a beach seine
Recent fish sampling in Irish estuarine waters was focussed on the anadromous lamprey and shad listed in Annex II of the Habitats Directive and on juvenile bass. In the course of these surveys, inventories of non-target species have been compiled. Such information is relevant to monitoring for the EU Water Framework Directive (WFD). This directive is an EU-wide measure designed to improve water quality in member states and includes all waters – fresh, coastal and transitional (or estuarine). The directive uses a series of quality elements, not simply water chemistry data, in assessing ‘quality’. Within the Transitional Waters or estuaries, the quality elements include phytoplankton, benthic invertebrates and fish. In the case of fish, information must be compiled on the species composition and abundance.
CFB/RFB Estuarine Sampling
In the period 2000 – 2006 the Central Fisheries Board, working with the seven Regional Fisheries Boards, initiated a national programme dedicated to the compilation of a baseline on fish species composition and abundance. This initiative has involved the Research, Angling and Conservation & Protection Units within CFB, working closely with each local RFB.
METRIC Project
In 2006, CFB undertook an additional series of fish investigations in transitional Waters in an EPA-funded study. This study, the METRIC project, was undertaken by CFB in conjunction with the Marie Institute. The study was designed to develop protocols and metrics for implementing Water Framework Directive in Irish Coastal and Transitional Waters. Colleagues from the Marine Institute undertook studies on phytoplankton and higher plants and on benthic invertebrates. CFB undertook the fish studies.
METRIC survey sites from August – November sampling, 2006
For more information contact:
Dr. Jimmy King.
Tel: +353 1 8843600
Email: jimmy.king@cfb.ie
