Effort Maps
UK fishermen are obliged when they land their catches to market to report the quantities of species landed, where they were caught, and what method (which gear / duration of fishing) they used to capture them. Data are linked to the first sales value of the catch by Fisheries Officers in each port throughout the UK and are then passed to the Fisheries Agencies and entered into a database.
For the purposes of this booklet effort is considered to be time spent fishing, i.e. what is sometimes defined as nominal fishing effort. Clearly the efficiency (catch per unit of effort) of boats of different sizes varies considerably and this must be borne in mind when viewing the maps. Small boats, i.e. those <10 m length which commonly operate close to shore, do not need to report their returns. The effort and overall sensitivity in these areas is thus considerably under represented by the present maps.
The reporting unit of the fisheries database is the ICES (International Council for the Exploration of the Sea) rectangle and covers 15 licence blocks. It is therefore quite coarse. In the North Sea where most rectangles are actively exploited most of the time, this coarseness matters little in mapping terms. In the maps, the effort in most rectangles is assumed to have been centrally located. One way of plotting the effort would have been to colour individual squares differently according to their effort value. But this would have resulted in areas with hard edges and clearly effort changes gradually between areas. Instead, contoured maps are presented, and a smoothing function has been used to decide, in comparison with adjacent scores, where the boundary line should be drawn. Although this is more realistic it has the consequence in some areas of reducing the area assigned to the highest effort. This illustrates that these maps, like the others in this series, are merely indicative of the real situation - discussion with local groups will be necessary to tease out detailed concerns. In some areas, e.g. west of Shetland where individual ICES rectangles have both very deep and much shallower water, allocation of the effort to the centre of the square would be inappropriate. In these squares the effort has been more accurately located, in most cases to the shallower water area. This allows the deep water effort, which is currently low, to be delineated by block from the shallow water effort. The deep water effort, however, is increasing rapidly as fishermen use bigger boats pulling heavier gears to exploit non-quota, deeper water species. Operators will wish to plan accordingly.
In the maps, UK effort is divided arbitrarily into five categories from the highest to the lowest. It is recognised that this makes little scientific sense since the distribution of effort is actually a continuum between those squares which contain little effort and those which are actively exploited. However, since the primary purpose of the maps is to inform and flag up relative sensitivities in order to encourage dialogue and resolution of potential interaction this is not thought to be an important criticism. Five maps, for demersal(excluding beam trawls), pelagic, Nephrops and shrimp, beam trawlers and static gears are presented. The value of each category is not consistent between the gears, i.e. high demersal effort does not necessarily correspond with high pelagic effort.
The potential for interaction during seismic exploration, field developments, production and decommissioning, is obvious and a knowledge of fishing effort by area will help operators in their planning processes. Some gears carry more potential threat to oilfield equipment than others. Beam trawls carry the most threat and an extra map of beam trawl effort by all countries by area is provided (it comes from Jennings et al, 1998, for reference see introduction).
Production Operations Index
