Maturation patterns and genetic diversity of the spinytail skate Bathyraja spinicauda

Abstract

With the expansion of fisheries into deeper waters and climate change, it is increasingly important to determine the status of the species affected by these changes. One of these species is the spinytail skate Bathyraja spinicauda, an understudied skate species with vulnerable life history traits such as slow maturation and a low number of offspring. To address the lack of basic knowledge about the species, this thesis utilized individuals collected during multiple surveys in Norwegian and other waters over the past 15 years, and focused on morphometric and genetic analyses as well as reviewing the existing literature on the target species and its genus. The morphometric analyses were performed to identify patterns in sexual dimorphism, maturation, and spatial distribution. The genetic analysis was carried out using the mitochondrial NADH2 marker for samples from the Barents Sea, the North Norwegian Sea, the South Norwegian Sea, the Faroes, and Greenland. Significant morphometric differences were found between the sexes and throughout growth. No direct correlation was found between depth and total length; however, there was a link in distribution wherein larger individuals were found on the Barents Shelf compared to the Norwegian Sea. Notably, there were no mature females in the collected samples. The estimated size at maturity (L50) for males was determined to be 131 cm. This suggests that maturity is reached at approximately 72% of the maximum total length for the species, which is within the range 41.9-90.9% for comparable sized Bathyraja species. There was no clear genetic population structure found between the study regions, indicating either high genetic connectivity or limitations of the chosen markers, or potentially both. This study identified the knowledge gaps that should be further investigated for the species, such as the total population size and the scarcity of mature females. Additionally, the study emphasizes the necessity of employing more fine-scale genetic methods to better assess the population structure.