Transitional waters (estuaries & lagoons) are an interface habitat, where freshwater, flowing from rivers gradually becomes more saline as it mixes with seawater close to the mouth. Transitional waters provide a challenging habitat to survey because their tidal nature means that nothing remains stable for very long. In every 24 hour period, the tide rises and falls twice, subjecting large areas to flooding and exposure.
Monitoring Ireland’s transitional waters
Transitional water surveys are carried out by Inland Fisheries Ireland each year and are repeated on an on-going basis. This helps us to determine the overall health of fish stocks within a waterbody and designate ecological status, a requirement of the EU Water Framework Directive.
In general, the ecological status of a waterbody will be good if there are lots of fish species present, their numbers are healthy and they span a range of ages from young to old.
Unlike in rivers and lakes where the number of fish species is relatively low, transitional waters have lots of different species, occupying a broad range of habitat niches. Some fish swim out in open water, some remain close to the shore and others stay close to the bottom. Therefore, to survey transitional waters effectively, we need a few different netting approaches, including beach seine netting, beam-trawl netting and fyke netting.