A further occurrence of Atherina boyeri Risso 1810 in North-Eastern Atlantic waters

Synopsis A further occurrence of Atherina boyeri in British waters is recorded. This species has a distribution which can be broadly defined as Mediterranean but has been occasionally recorded in waters which are beyond the northerly limits of its normal range. These records have usually been associated with localised thermal pollution but, at Oldbury-upon-Severn, England, this is probably not so. Morphometric and meristic data are presented which show clearly that this is a genuine record of A. boyeri. The existence of this species in waters with minimal, if any, thermal enrichment raises interesting questions regarding its distribution.This example and the other abnormal records of A. boyeri are, therefore, considered in relation to a number of environmental parameters. The parameters discussed, namely increased water temperature, decreased salinity and lagoon conditions have all been implicated in previous records.The conclusion tentatively reached is that A. boyeri is capable of surviving under a cooler temperature régime than that with which it is normally associated. Normally its range is restricted by inter-specific competition. In conditions of calmer water, however, in which there is also reduced salinity it is able to compete and maintain itself successfully.