Sensitive skates or resilient rays? Spatial and temporal shifts in ray species composition in the central and north-western North Sea between 1930 and the present day

Historic and current survey data are compared to describe the changes occurring in abundance, species richness and length frequency of the rajid community ill the central and north-western North Sea between the periods 1929-1956 and 1981-1995. Survey data show that some species have decreased in abundance (common skate;ind thornback ray), whilst others (starry ray) have increased. The length-frequency relationship is currently truncated at 70-79 cm, whilst individuals of up to and above 100 cm used to be common. Life-history characteristics show that the sensitivity of rays and skates to enhanced mortality is species specific. The sequence of the five most common species from most to least sensitive is: Raja batis (common skate)>R clavata (thornback ray)>R Montagui (spotted ray)>R naevus (cuckoo ray)>R,radiata(starry ray). This is also the order af commercial importance. The observed changes are discussed in relation to fishing. (C) 1998 International Council for the Exploration of the Sea.