Almost Angels? The Critically Endangered Angelshark (Squatina squatina) in its Last Refuge, the Canary Islands

Once so abundant as to be called the ‘common’ angelshark, Squatina squatina has been extirpated from nearly the entirety of its historical range, from the eastern North Atlantic, to the Mediterranean (IUCN Red List Critically Endangered). The angelshark now seems to occur in any abundance only in the waters surrounding the Canary Islands. We present the first genetic assessment of the angelshark’s population dynamics and diversity. Tissue samples were collected between 2007-2016 from three islands within the archipelago: Gran Canaria, Tenerife, and Lanzarote. To investigate the genetic population dynamics, a three part approach was adopted: (i) DNA sequencing four mitochondrial regions commonly used in vertebrate population analysis [control region, COI, ND4, and ND2] of 300 angelsharks, (ii) Whole mitochondrial genome sequencing of nine individuals to identify and examine the comparative sequence variability in other gene regions, and (iii) assessment of nuclear diversity with 40 species-specific microsatellites. Results reveal exceptionally low genetic diversity across all individual mitochondrial regions sequenced, with single haplotypes in each region found across nearly all individuals. Mitogenome analysis follows this trend with only 11 single nucleotide polymorphisms seen across all Canary Island individuals in a genome of 16,689 bp. Furthermore, screening of 40 microsatellite markers across 32 individuals has shown all but two loci to be monomorphic. Such low levels of genetic diversity may have implications for the evolutionary persistence of this species and ultimately underscore the angelsharks’ highly vulnerable state.