Title : Spatial refuge and reproductive potential of the vulnerable the picked dogfish (Squalus acanthias) in the Georgian black sea: Evidence from experimental trawl survey
Abstract:
The Picked Dogfish (Squalus acanthias), a slow-growing and late-maturing elasmobranch, has undergone substantial population declines throughout its range due to historical overfishing and insufficient spatial protection (Ebert et al., 2021). In the Black Sea, the species is listed as Vulnerable on the IUCN Red List (IUCN, 2023), yet region-specific ecological and distributional data remain scarce, particularly in the eastern basin.
To address this gap, an experimental bottom trawl survey was conducted in the Georgian sector of the Black Sea (GSA 29) in winter 2025. The study was carried out following the International Bottom Trawl Survey in the Black Sea (iBOTS) protocol, a standardized scientific methodology being developed by the General Fisheries Commission for the Mediterranean (GFCM) as the Black Sea counterpart to the MEDITS protocol applied in the Mediterranean.
Sampling across four depth strata (10–100 m) revealed a restricted distribution pattern: S. acanthias was recorded in only 25% of hauls (n = 60 individuals), with 85% of specimens concentrated within fishing-restricted zones. This spatial clustering underscores the ecological significance of low-impact areas as essential habitats for vulnerable demersal species (Grüss et al., 2011). According to Dimarchopoulou et al. (2018), fishing-prohibited areas consistently support higher densities and larger sizes of demersal fish, illustrating the resilience potential when anthropogenic pressure is minimized.
Furthermore, refuge habitats have been shown to serve as critical “safe havens” for maintaining biodiversity and functional ecosystem processes, especially for species with life-history traits such as delayed maturity and low fecundity (ScienceDirect Topics, 2024).
Depth-specific analysis showed a bathymetric preference for 50–90 m, with mature females dominating in deeper strata. The estimated length-at-maturity parameters (L?? = 590 mm, L?? = 810 mm; CVs < 0.004) indicate the presence of reproductive individuals, while overall biomass (253.5 kg/km²) and abundance (169.9 ind/km²) exhibited high variability (CV > 1.1), suggesting fragmented distribution and low density.
Consistent with growth models for Squalus acanthias (Jones & Geen, 1989), this patchiness likely reflects habitat selection linked to reproductive behavior and environmental stability.
These findings demonstrate the critical role of spatial refugia in sustaining remnant populations of Squalus acanthias and highlight the urgent need for area-based conservation strategies. Our study provides rare empirical evidence from the eastern Black Sea supporting the expansion of habitat protection measures tailored for elasmobranch conservation, contributing to a broader understanding of how spatial management mitigates vulnerability in marine predator populations.
Keywords: Picked Dogfish, vulnerable, sampling, refuge, depth-specific
