Browsing Irish Fisheries Investigations by Author "Lordan, C."
The distribution and abundance of cephalopod species caught during demersal trawl surveys west of Ireland and in the Celtic SeaLordan, C.; Warnes, S.; Cross, T. F.; Burnell, G. M. (Marine Institute, 2001)Distributional and abundance data on seventeen cephalopod species from three demersal trawl series are presented. Data from one the CEFAS March Celtic Sea Groundfish Survey cover the years 1994-1998 inclusive and a depth range of 57-580 m. Data from two Marine Institute surveys was for October-November 1997 only. One of these surveys was west and south west of Ireland between depths of 27-328 m, the other was conducted in deepwater (520-1174 m) to the northwest. Eleven cephalopod species were caught (14,981 individual cephalopods) during the five CEFAS surveys. Spatial and bathymetric distribution data are presented for the species caught and the interannual variability is discussed. The most numerous species in catches was Loligo forbesi (n = 6,803), however, the highest biomass caught was Illex coindetii (418.3kg). Alloteuthis subulata were common close to shore in water depth of less than 75 m. Swept area density estimates are reported for the most abundant species in catches. Ten cephalopod species were caught during the Marine Institute west coast groundfish survey (774 specimens were examined out of an estimated 8,712 caught). The results show broadly similar patterns in species composition, distribution and abundance to the CEFAS survey. Todaropsis eblanae was the second most numerous species in the survey. Only six cephalopod species (n =196) were caught in the Marine Institute deepwater trawl survey. Todarodes sagittatus was the most common species caught. Deepwater octopods including Benthoctopus piscatorum, Benthoctopus ergasticus and Opisthoteuthis massyae were also caught. This chapter provides a base line of data on cephalopod species which are caught in trawl surveys west of Ireland and in the Celtic Sea.
Using a multivariate approach to define Irish metiers in the Irish SeaDavie, S.; Lordan, C. (Marine Institute, 2009)There is an increasing need to take into account a “mixed fisheries” approach in management, assessment and sampling of fish stocks. To do this effectively it is necessary for groups of fishing trips with homogeneous fishing patterns or tactics to be defined into métiers. Presented here is the result of an Irish case study analysis in applying multivariate statistics to declared logbook landings to define Irish fleet métiers operating in the Irish Sea. Established multivariate statistical procedures, a combination of factorial and cluster analysis, were applied to five variables; landing profile, vessel length category, gear, mesh size range and month. The investigation has shown this methodology to be a suitable tool in identifying métiers without prior assumptions and enabled data to be described from a multivariate statistical perspective providing useful and informative results. In total twenty-two métiers were identified and defined from 2003 landings data, and a further 5 groups were formed to include trips which could not be assigned to a métier. Definitions were applied to 2003-2005 landings and effort data to examine their dynamics and stability. The dominant métier (in terms of effort and trips) contained high proportions of landed Nephrops taken by bottom otter trawlers using 70-89mm meshes. The effort in this métier was fairly stable over time. The greatest increases in effort and trip allocation occurred within métiers employing pots and traps for crustacean species. A small number of minor métiers (in terms of landings and effort) became obsolete over the three years examined. The effects of recent management measures are likely to have contributed to declines in the numbers of trips and effort in some métiers. For example, days-at-sea, limited mobile gears such as bottom otter trawls and beam trawls with ≥100mm mesh, have declined. Such changes within métiers over recent years have contributed to a deeper understanding of fleet dynamics in the Irish Sea. This analysis has identified and highlighted a segment of polyvalent Irish fishing vessels, which move between several métiers within a year. The definition of métiers can be used to enhance the Irish sampling programme in the Irish Sea by developing a finer scale, métier based, stratification of sampling. This in turn enables increased precision and robustness of national assessment data thus improving assessments and management advice. Defining métiers will prove advantageous in developing mixed fisheries assessments and advice.