Individual species spawning maps.

There is an integrated, multinational research effort supporting the management of fish stocks in the North East Atlantic area. Research vessels from the various countries continually collect details of the distribution of eggs, larvae and young and commercially sized fish. Samples of the sea floor sediments are also routinely collected and wider areas are also surveyed using modern acoustic visualisation techniques. From these data, the spawning and nursery areas of the commercially important species of fish and shellfish have been described. They are illustrated in the following pages.

Spawning areas for most species are not rigidly fixed. In addition, fish may spawn earlier or later in the season in response to environmental change (spawning periods are summarised in a table on page 17). For sediment spawners, not all suitable sediment areas might be used in every year -use will depend on the size of the spawning stock. For these reasons, spawning distributions are under continual revision. It follows that these maps should be seen as representing the widest known distribution given current knowledge and should not be seen as rigid, unchanging descriptions of presence or absence. The table of spawning times likewise shows the generally accepted maximum duration of spawning. Normally, fish spawn earlier to the south of the British Isles than in the north, mainly due to the warmer water conditions in southern waters. This regional pattern must be remembered when interpreting the maps. Together, these facts underline the desirability of consultation with the regulatory authorities and other users of the environment prior to commencing any activity. In any given year the sensitivity of the presence of spawners in a particular area may change sufficiently to allow licence conditions to be redefined.

In relation to oil and gas exploration offshore, spawning distribution information is used to determine seismic exclusion areas (see page 33). For fish that lay their eggs on the sediment (eg herring & sandeels) or which live in intimate contact with sediments (eg sandeels and most shellfish), they are also used to advise areas where discharge controls might be needed to minimise impact.

The maps have been sized for convenience to fit sensibly on an A4 page. This has meant that the most northerly UKCS blocks (220, 221) have been excluded. Fishing effort in these areas is very low. The reporting unit of the fisheries database (see later), and the grid on the maps, is the ICES (International Council for the Exploration of the Sea) rectangle, 1/2° latitude by 1° longitude. At UK latitudes they measure approximately 30 x 30 nautical miles. One ICES rectangle covers one half of one Quadrant, i.e. 15 licence blocks.