Tag attachment innovation on spurdog (Squalus acanthias) reveals year-round coastal association of pregnant females in northeastern Atlantic waters.

The spurdog (Squalus acanthias Linnaeus, 1758) is a globally distributed squaliform shark that has historically been overfished but is now recovering in the northeast Atlantic. Data series on spurdog movement and habitat use have been somewhat limited to research surveys due to challenges associated with electronic tagging. Here, we offer a revised attachment method for externally attached pop-up satellite archival tags that was successful in long-term deployments on pregnant females.

Seasonal habitat use and diel vertical migration in female spurdog in Nordic waters.

Background: Studying habitat use and vertical movement patterns of individual fish over continuous time and space is innately challenging and has therefore largely remained elusive for a wide range of species. Amongst sharks, this applies particularly to smaller-bodied and less wide-ranging species such as the spurdog (Squalus acanthias Linnaeus, 1758), which, despite its importance for fisheries, has received limited attention in biologging and biotelemetry studies, particularly in the North-East Atlantic.

Methods: To investigate seasonal variations in fine-scale niche use and vertical movement patterns in female spurdog, we used archival data from 19 pregnant individuals that were satellite-tagged for up to 365 days in Norwegian fjords.

Of three sharks and one chimaera: varied habitat preferences across a latitudinal range revealed by coastal and offshore surveys.

Using national and international research survey data and applying a combination of models and mapping tools, this study revealed temperature and depth as the crucial environmental drivers of both the distribution and the abundance of four benthopelagic chondrichthyans inhabiting Norwegian and Icelandic waters: rabbitfish (Chimaera monstrosa), velvet-belly lanternshark (Etmopterus spinax), blackmouth catshark (Galeus melastomus) and spurdog (Squalus acanthias). C. monstrosa and E.

Introgressive hybridisation between two widespread sharks in the east Pacific region.

With just a handful of documented cases of hybridisation in cartilaginous fishes, shark hybridisation remains poorly investigated. Small amounts of admixture have been detected between Galapagos (Carcharhinus galapagensis) and dusky (Carcharhinus obscurus) sharks previously, generating a hypothesis of ongoing hybridisation. We sampled a large number of individuals from areas where the species co-occur (contact zones) across the Pacific Ocean and used both mitochondrial and nuclear-encoded SNPs to examine genetic admixture and introgression between the two species.