No information is currently available on population size or structure, however this species is thought to exhibit patchy distribution. There is probably little or no exchange between subpopulations separated by depth or occurring in different water bodies, which are considered to form distinct regional subpopulations (Compagno and Cook 2005). The overall trend in European waters for this species seems to be of a general decrease.

Northeast Atlantic

This subpopulation size or structure is unknown in the Northeast Atlantic, however, for the purposes of stock assessment and management, the Azores/Mid-Atlantic Ridge subpopulation is considered to be separate from the Northeast Atlantic Slope subpopulation (ICES 2006, 2013). However, the species seems to be more abundant in the south area of the Mid-Atlantic Ridge International Council for the Exploration of the Sea (ICES; Area X), and is less frequently recorded elsewhere in the Northeast Atlantic.

Beginning in the early 1970s this species was targeted by handline and gillnet fisheries in the Azores, and landings increased rapidly to over 947 tonnes (t) in 1981. From 1981 to 1991 landings fluctuated considerably, following market fluctuations, and peaked at 937 t in 1984 and 896 t in 1991 (ICES 2006, 2013). After 1991, reported landings declined linearly until the fishery was closed at the end of the 1990s due to stock collapse. The stock has remained collapsed in the Azores region with landings ranging from zero to two tonnes between 2010 and 2012 (ICES 2006, 2013). Stock assessments of the targeted Azores fishery for this species were made during the 1980s (da Silva 1987). The stock was considered intensively exploited with the average observed total catches (809 t) close to the estimated maximum sustainable yield (MSY=933 t). During the Development of Elasmobranch Assessments (DELASS) project, the stock was considered depleted based on the probability of the biomass in 2001 being less than the biomass that could sustain maximum sustainable yield (BMSY; Heessen 2003). Preliminary assessment results suggest that the stock may be depleted to about 50% of virgin biomass. However, further analysis is required, particularly analysing the effect of liver oil prices on the fishery.

Although targeted fisheries have ceased, this species is still bycatch in various deepwater fisheries, with total bycatch landings of around 47 t reported across the Northeast Atlantic ICES area in 2005 (ICES 2006). In mainland Portugal, bycatch landings have been recorded since 1988, with 282 t in 2000 and 119 t in 2003 (ICES 2006, 2013). These landings reached zero tonnes in 2010 and have not increased since. In the Azores, landings of < 15 t were reported from 2004–2005 (Pinho 2006). For the Northeast Atlantic slope subpopulation, a comparison between recent Scottish trawl surveys and United Kingdom Ministry of Agriculture, Fisheries and Food (MAFF) surveys in the 1970s showed a 94% observed decline in catch rate. However, this value must be treated with caution as it is likely that other species were mistakenly identified as this species in the initial 1970s survey (Jones et al. 2005). Furthermore, the Scottish trawl surveys took place at the limit of this species’ geographical range, which may explain the observed low catch rates.

Considering a 50% decline for the 1972-2001 period based on the above DELASS data, and if an exponential decline is assumed, the annual proportional change would be 0.9764. Therefore, the reduction for the time period 1972-2059 (87 years, three generations) is 87%. When projecting this decline into the future (2015-2102, three generations), a 64% decline is estimated.

Mediterranean

In the Mediterranean, the range of this species appears to be confined to the western and central basins and biomass seems to be very low (Baino et al. 2001). The “Gruppo Nazionale Dermersali” (GRUND) experimental trawl surveys carried out on the continental and upper slopes of the central Mediterranean Sea suggest a positive trend in catches of this species between 1985 and 1998 although the dataset was small; only 1.9 specimens were obtained on average per hour over 12 years of surveys (Relini et al. 2000). This species was present in < 2% of bottom trawls across the Mediterranean Sea (Relini et al. 2000). A bottom trawl fishery for Red Shrimp (Aristeus antennatus) operating in the Gulf of Valencia collected data between 1988 and 1989 on the frequency of catches for this species. It was found to be present in 28.6% of trawls carried out at 450–675 m depth, with a mean abundance of 0.06 specimens per hour of trawling (Guallart 1990). During exploratory surveys to collect data of the exploited and virgin stocks of deep-sea Red Shrimp (DESEAS project), this shark species was caught in all three areas of the study (the Balearic area, the western Ionian and the eastern Ionian). Abundance decreased with depth in the Balearic area and the species was found to be more abundant between 1,000 and 1,499 m in the western Ionian and was present at shallower depths in the eastern Ionian (Sion et al. 2004).

In the Mediterranean, considering a 15% decline for the 1972-2004 GRUND data, and if an exponential decline is assumed, the annual proportional change would be 0.9949. Therefore, the reduction for the time period 1972-2059 (87 years, three generations) is 36%. When projecting this decline into the future (2015, 2102, three generation), a decline of 36% is also estimated.

Assuming that the proportion of the population present in the Mediterranean and in the Northeast Atlantic is roughly equal, an overall reduction of 62% is calculated for European waters for the 1972-2059 period (87 years, three generations). A reduction of 52% is projected for the 2015-2102 period (87 years, three generations) into the future.