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

Abstract

Historic and current survey data are compared to describe the changes occurring in abundance, species richness and length-frequency of the rajid community in 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 and 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 of commercial importance. The observed changes are discussed in relation to fishing.