Background and purpose of survey
Fisheries science services recommenced the Irish deepwater survey program in September 2006. The purpose of the survey is to investigate the impact of fishing on the abundance and biological parameters of deepwater species. The survey is also used to collect ecological data such as hydrography, bottom sediment type and distribution of deepwater invertebrates. This will help to describe the ecosystem that the deepwater fish species inhabit.
How the deepwater survey works
During the survey, the scientists use a deepwater trawl net to fish along the continental slope at different depths. The specimen caught in the trawl are brought on board, identified, and measured. For commercial species, as well as species of specific scientific interest, other biological information such as weights, age, sex and maturity is also collected. Once a time series of the deepwater survey is established, the catch per unit effort (CPUE) will be important in stock assessment.
Preliminary results of the 2008 survey showed the unique nature of the deepwater ecosystem. The deepwater is not reached by sunlight and hydrography shows that temperature at 1500m decreased to 4ºC with little variation of temperature between the different areas. Yet although cold and dark, the ecosystem hosts a highly diverse fauna with 122 fish species and 94 species of invertebrates identified on the survey.
Some findings were alarming and did highlight the effect of fishing on this ecosystem. While many deepwater shark species were caught in large numbers, there were only very few records of the larger commercial species such as the Portuguese dogfish and the siki sharks.
For more information on this deep water survey which took place in autumn 2008 off the west and north west coast of Ireland download The Preliminary 2008 Irish Deepwater Survey Report (PDF, 1.8 MB).
Results from previous surveys are also available to download:
Areas Covered (red dots) During the Recent Deepwater Survey