Dipturus

Abstract: Are extinctions of marine vertebrates as rare and unlikely as current data indicate? Long-term research surveys on the continental shelf between the Grand Banks of Newfoundland and southern New England reveal that one of the largest skates in the northwest Atlantic, the barndoor skate (Raja laevis), is close to extinction. Forty-five years ago, research surveys on St. Pierre Bank (off southern Newfoundland) recorded barndoor skates in 10% of their tows; in the last 20 years, none has been caught, and this pattern of decline is similar throughout the range of the species.

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.

Abstract: Skates (Rajiformes: Rajoidei) are a highly diverse fish group, comprising more valid species than any other group of cartilaginous fishes. The high degree of endemism exhibited by the skates is somewhat enigmatic given their relatively conserved body morphology and apparent restrictive habitat, e.g. soft bottom substrates. Skates are primarily marine benthic dwellers found from the intertidal down to depths in excess of 3,000 m. They are most diverse at higher latitudes and in deepwater, but are replaced in shallower, warm temperate to tropical waters by stingrays (Myliobatodei). The number of valid skate species has increased exponentially, with more species having been described since 1950 (n = 126) than had been described in the previous 200 years (n = 119). Much of the renaissance in skate systematics has largely been through the efforts of a few individuals who through author–coauthor collaboration have accounted for 78 of the 131 species described since 1948 and for nine of 13 genera named since 1950. Furthermore, detailed regional surveys and accounts of skate biodiversity have also contributed to a better understanding of the diversity of the skates. A checklist of the living valid skate species is presented.

Abstract: Recent molecular evidence has called into question the identity of skates collected in the waters off the Falkland Islands previously identified as Zearaja chilensis. NADH2 sequence data indicate that these specimens are not conspecific with those currently referred to as Z. chilensis from Chile and, in fact, represent a novel cryptic species. This study aimed to investigate this hypothesis based on morphological comparisons of specimens from the coasts of both western and eastern South America. In total, 50 specimens from Chile and 41 specimens from the Falkland Islands were collected and examined; morphometric data were generated for a subset of specimens from both areas. NADH2 sequence data were generated for a total of 19 specimens from both areas, as well as specimens of Z. nasuta from New Zealand, D. pullopunctatus from South Africa, D. oxyrinchus from the Azores, Okamejei hollandi, and O. cairae from Borneo, and O. kenojei from Japan. Based on morphological and molecular analyses, Zearaja is synonymized with Dipturus and species assigned to the former genus are transferred to the latter genus. A neotype is designated for D. chilensis and this species is redescribed. Dipturus lamillai sp. nov. is described based on specimens from the Falkland Islands. Comparison of our NADH2 data with data for mitochondrial genomes generated from tissue samples taken from two specimens originally identified as Z. chilensis, indicate that, while the sample from Chile came from a specimen of D. chilensis, that from the skate steak obtained from a restaurant in Korea actually came from a specimen of D. lamillai sp. nov. This emphasizes the importance of confirming both the provenance and identity of specimens from which sequence data are generated and submitted to GenBank if misidentifications are to be avoided.