Rangewide Population Structure of the Clearnose Skate

Skates (family Rajidae) are benthic elasmobranchs that are highly vulnerable to incidental fishery bycatch, are discarded at sea, and are poorly accounted for in catch records. Many aspects of skate life history, such as population structure, are not well understood. Without this knowledge, indiscriminate removal may have deleterious effects on scientific, conservation, and management efforts. The Clearnose Skate Rostroraja eglanteria is seasonally migratory and widely distributed in the coastal waters of the eastern United States and in the northeastern Gulf of Mexico. This study used molecular techniques to assess the population structure of Clearnose Skate for use as a biological reference point for further research and management. Specimens were collected from 2014 to 2019 by fisheries-independent surveys. High-throughput genotyping-by-sequencing was used to identify single nucleotide polymorphisms, resulting in two data sets: one consisting of 8,914 loci (outlier and neutral) and the other comprised of 30 outlier loci. Results from all analyses and using both data sets indicated a high level of genetic differentiation between specimens from the Gulf of Mexico and specimens from the U.S East Coast. Using the outlier data set, a low but significant level of genetic differentiation was also found among specimens from the U.S. East Coast, with a subtle break near the North Carolina and South Carolina border. Genetic differences along the U.S. East Coast were spatially autocorrelated, indicating a latitudinal genetic gradient. The level of observed genetic differentiation between the Gulf of Mexico and the U.S. East Coast is likely due to physical barriers such as Florida and the Gulf Stream current, while the subtle structure along the U.S. East Coast is likely attributable to isolation caused by dispersal limitations and local temperature preferences. The results from this investigation of Clearnose Skate population structure can be used to better monitor and manage this vulnerable elasmobranch.