This species was previously confused with Pristiurus jenseni Saemundsson, 1922, that is now considered a junior synonym of this species (Fricke et al. 2023).

The Mouse Catshark (Galeus murinus) is a small (to 63 cm total length) deepwater catshark that occurs in the Northeast Atlantic and Eastern Central Atlantic Ocean from Iceland to the Western Sahara. It is demersal on the continental slope at depths of 380–1,300 m. The species is taken as bycatch by commercial deepwater trawl fisheries operating on the Northeast Atlantic slope and possibly by deepwater fisheries off West Africa. However, this species is small and may be able to escape through the mesh of trawl nets with low and stable catches over the past few decades reported from the Northeast Atlantic. Management measures across the Northeast Atlantic have prohibited trawl fishing and gillnet fishing at depths below 800 m and 200 m, respectively, and in West Africa, fisheries operate to a depth of 800 m. Thus, the species has significant refuge at depth in both regions. There is no evidence of population decline and the species is not suspected to be close to reaching the population reduction threshold and the Mouse Catshark is assessed as Least Concern.

The Mouse Catshark occurs in the Northeast Atlantic and Eastern Central Atlantic Ocean where it is known from off the west coast of Iceland to the Faroe Islands and off Scotland, the Hebrides Islands, Ireland, France, Spain, Morocco, and the Western Sahara, including the Azores and Canary Islands (Rodríguez-Cabello et al. 2013, Barecelos et al. 2021, Ebert and Dando 2021). Since the previous assessment (Iglésias 2015), the distribution map has been refined to map this species to its known bathymetric range.

All available information on population relative abundance for this species is from the Northeast Atlantic. From 2010–2016 (no landings data were available post 2016), estimated landings fluctuated but were stable over the 6 years and averaged 3 t annually (range 1–5 t) (ICES 2022). In the Spanish groundfish surveys from 2001–2021 on the Porcupine Bank (ICES Divisions 7c and 7k) west of Ireland at depths from the surface to 1,485 m, the Mouse Catshark was not frequently encountered and only occurred in the deeper survey hauls, that is, 1,000 m with stable catches of one kg per haul over the two decades (Fernández-Zapico et al. 2022, Ruiz-Pico et al. 2023). The Scottish deepwater trawl surveys of the Rockall Trough (ICES Division 6) west of Scotland at depths of 300–2,000 m found catches of the Mouse Catshark were low and fluctuated but were stable over 15 years from 1998–2013 with peak abundances at 1,000 m depth (Neat et al. 2015). The Icelandic groundfish surveys from 2001–2021 on the Icelandic shelf and upper slope (ICES Division 5a) at depths of 20–1,500 m persistently recorded the Mouse Catshark and estimate its mean biomass as 648 t with a fluctuating but stable biomass trend over the last two decades (ICES 2022). In the Azores, the Mouse Catshark is common and appeared to be increasing in occurrence during 2010–2016 (Das and Afonso 2017). In summary, all the reported Mouse Catshark catch data and the survey data over 15–25 years indicate the population is stable in the Northeast Atlantic, as it is caught at low levels and the rate of capture has remained stable. These low and stable catch rates have also occurred in earlier years, since the 1970s (Iglésias 2015).

In the Eastern Central Atlantic, there is no species-specific population trend data available. Across West Africa, total artisanal fishing effort increased by 10-fold between 1950–2010, while the catch-per-unit-effort of artisanal and industrial vessels declined by 34% over this period (Belhabib et al. 2018). While these levels of change are not species-specific, they are informative for understanding the broader levels of decline in marine fish in the region. In southern Morocco, deepwater trawl and longline fisheries targeting hake (Merluccius senegalensis and Merluccius polli) and scabbardfish (Aphanopus spp.) have had a fluctuating but increasing trend in deepwater shark landings from 0.2 t in 2007 to 17.8 t in 2017 (Cervantes et al. 2018). These catches may include the Mouse Catshark though information on bycatch species in these fisheries is largely unknown and the Mouse Catshark would have significant refuge at depth.

Overall, the population is estimated as stable in the Northeast Atlantic. While there is no species-specific population trend data available from the Eastern Central Atlantic and the Mouse Catshark may be caught in that region, the species has significant refuge at depth and the region is a relatively minor proportion of its entire range. Thus, across both regions, there is no evidence of population decline and the species is not suspected to be close to reaching the population reduction threshold.

The Mouse Catshark is demersal on the continental slope at depths of 380−1,300 m (Weigmann 2016, Ebert et al. 2021). It reaches a maximum size of 63 cm total length (TL), males mature at 50−63 cm TL and females mature at 53 cm TL (Ebert et al. 2021). Reproduction is oviparous and size-at-birth is approximately 8−9 cm TL, based on egg case sizes (Iglésias et al. 2002). Little else is known of its biology.

In the Northeast Atlantic, there were previously a number of demersal trawl, longline, and gillnet fisheries targeting and incidentally catching mixed deepwater shark catch along the continental slope (Gordon 1999, ICES 2022). Since 2010, targeted deepwater shark fishing has been prohibited with subsequent prohibitions on fishing below depths of 200 m for gillnet and 800 m for trawl across most of the Mouse Catshark's Northeast Atlantic range. Despite these management measures to reduce deepwater shark fishing mortality, deepwater sharks are still captured occasionally incidentally in demersal fisheries (e.g., Moura et al. 2018). The Mouse Catshark's small size means that it could potentially escape from the mesh of trawls and its deepwater habitat likely precludes it from being taken in large numbers in Northeast Atlantic waters. The Mouse Catshark was an occasional bycatch of French deepwater trawling operating beyond 1,000 m depth off the British Isles in the 1990s–2010s. The species is apparently no longer caught by this fishery, which now limits their activities to less than 700 m (S. Iglesias unpub. data).

In the Eastern Central Atlantic, sharks and rays were already being exploited by semi-industrial fisheries in the 1950s (Walker et al. 2005). While these fisheries gradually collapsed, the demand for dried salted shark meat (for export to Ghana) and shark fins in the 1980s drove the development of artisanal targeted shark fishing across much of the region (e.g., Diop and Dossa 2011, Moore et al. 2019). Over the years, this has expanded into targeted shark and ray fisheries across many countries and is likely increasing fishing pressure on this species (Walker et al. 2005, Diop and Dossa 2011). Mixed fishery bilateral agreements between the European Union and the West African nations (Sustainable Fisheries Partnership Agreements, SFPAs) involve payments to third party countries in exchange for access to marine resources and sectorial support aimed at promoting sustainable fisheries development in the partner countries, including Morocco, Mauritania, and Guinea-Bissau (European Commission 2023). Under SFPAs, demersal trawl and longline fisheries in southern Morocco target a number of demersal fish, including black hake (Merluccius senegalensis and Merluccius polli) and scabbardfish (Aphanopus spp). Trawl fishing there occurs mostly at depths of 500–800 m and longline fishing occurs at 100–400 m (Cervantes et al. 2018). The Mouse Catshark would have significant refuge at depth in the Eastern Central Atlantic.

There is no information on the use and trade of this species.

In 2010, the European Union (EU) Fisheries Council prohibited directed fishing for deepwater sharks (including Mouse Catshark) in European Community and international waters, and in 2012, no allowances for bycatch were implemented (ICES 2022). From 2017–2020, a restrictive bycatch allowance (10 t) was trialled, permitting limited landings of unavoidable catches of deepwater sharks in directed artisanal demersal longline fisheries for Black Scabbardfish (Aphanopus spp). This was discontinued after 2020 with a return to prohibition on directed fishing for deepwater sharks in those fisheries (ICES 2022). Since 2005, trawls and gillnets in waters >200 m are prohibited in the Azores, Madeira, and Canary Islands (ICES 2022). Since 2006, gillnets are prohibited at depths below 200 m in the NEAFC Regulatory Area (all international waters of the ICES Area) (ICES 2022), with comparable measures also in place for EU and United Kingdom waters, albeit with a provision for maximum bycatch limits of 5% deepwater shark for those fisheries targeting European Hake (Merluccius merluccius) and monkfish (Lophius spp.) at depths of 200–600 m. In European waters, since 2016, demersal trawl fishing is prohibited at depths below 800 m (ICES 2022). In the Azores, further management actions since 2009 for demersal deepwater fisheries include area restrictions by vessel size and gear, gear restrictions (hook size, maximum number of hooks on longline gear), a network of closed areas in Azorean waters, and closure of the Condor seamount to deepwater fishing in 2010 (ICES 2022). Further research is needed on population size and trends, and life history, and catch rates should be monitored.