Habitat and Biology
Depth zone: Shelf (50 m - 200 m). Vertical distribution: Demersal/Benthic.
Jurisdictional distribution: Shared between nations
Considered a single stock: Yes
Factors affecting the fisheries and the stockThe effects of regulations
In 1999 the EC introduced a TAC for skates and rays. This TAC was gradually decreased. Based on the level of recent landings it is obvious that the current TAC has become restrictive for some countries, which may increase discarding. Discard survivorship, however, is not known. There are no management measures in place for the demersal sharks (Scyliorhinus, Mustelus, Squatina
) in this ecoregion.
MethodologyScientific basisData and methods
Survey data are the basis for the advice of skates, rays, and demersal sharks in the North Sea (examples in Figure 22.214.171.124).
In most countries skates and rays are landed together, most often sorted in particular size categories, rather than by species. They are usually gutted, and sometimes only wings are landed. For assessment purposes, species-specific catch data are essential. Only some countries report (part of) the landings by species, e.g. Sweden and . As a result of market sampling programmes the species composition of the landings can now be estimated for some of the countries landing skates and rays. This should improve from 2008 onwards because the EC now requires species-specific landings data.Uncertainties in assessment and forecast
The analysis of survey data is hampered by uncertainties about the proper identification of some species of skate, and starry ray
may have been misidentified as thornback ray
on some occasions. This leads to problems in the interpretation of some survey data.Comparison with previous assessment and advice
In 1997 ICES gave an overview of the relative status of the main skate species in the North Sea. In 2005 ICES produced advice for these species for the first time. ICES previously recommended that the catches for skates and rays be set to zero if, and only if skates and rays were landed as a generic group. Since it is now required to report by species, ICES is now providing advice for the main species. The basis for the advice is the same as in 2006.
|Figure 126.96.36.199. Rays and skates in the North Sea, Skagerrak, and eastern English Channel. Landings (in t) of all species combined. Data for 2007 are incomplete. |
|Figure 188.8.131.52. Demersal elasmobranchs in the North Sea. Time-series of catch rates (number per hour) for thornback ray, spotted ray, starry ray, cuckoo ray, lesser spotted dogfish, and smooth hounds (smooth hound in black, starry smooth hound in white, and none determined data in grey). Data from the IBTS quarter 1 survey, roundfish sampling areas 1–7. |
Overall Assessment Results
Scientific AdviceSingle-stock exploitation boundariesNo fisheries
Species where indicators show extirpation
No target fisheries
|Angel shark ||This species is (nearly) extirpated in the North Sea and eastern English Channel and should receive the highest possible protection. |
Species where indicators show depletion
Status quo catch
|Target fisheries for these species should not be permitted and measures should be taken to minimize bycatch. |
Species where indicators show stability or increase
Thornback ray in
|Fishing mortality should not increase and the fishery should be closely monitored. Measures to deter fisheries that target spawning concentrations of thornback ray in Division IVc should be considered because this is the most vital part of the thornback ray spawning in the southwestern North Sea. |
Smooth hound &
Starry smooth hound
|These species have a relatively higher productivity than similar elasmobranchs and can probably sustain fisheries. Management measures should prevent overexploitation. Fisheries should only expand when accompanying measures lead to improved data collection and biological studies to ensure its sustainable harvest. |
|Lesser spotted dogfish ||The stock shows a general increase in abundance and they have a high discard survival. The current exploitation rates on this species appear to be sustainable. As there are no apparent detrimental impacts on the stock from current commercial fisheries, no management actions are required for this species at this time. |
Species where indicators are unknown
Conclusion on exploitation boundaries
Thornback ray in
|Because these species have a tendency to form aggregations, they may be prone to localized depletion. |
Subject to the individual recording of landed species, combined catches for demersal skates and rays should be set on the basis of the recent average landings (2002–2006). Targeted fisheries of the most threatened species (common skate and undulate ray) should not be permitted, and measures should be taken to minimize bycatch.
Angel shark should not be landed and, as inshore species, are likely to have a reasonable discard survival (depending on capture method).
|ICES Advice ||Single-stock exploitation boundaries ||Predicted catch corresponding to advice ||Predicted catch corresponding to single-stock exploitation boundaries || |
|ICES landings |
|1992 || |
| || || || ||5.8 |
|1993 || |
| || || || ||5.8 |
|1994 || |
| || || || ||6.4 |
|1995 || |
| || || || ||6.3 |
|1996 || |
| || || || ||6.4 |
|1997 || |
| || || || ||4.6 |
|1998 || |
| || || || ||4.6 |
|1999 || |
| || || ||6.1 ||3.4 |
|2000 || |
| || || ||6.1 ||4.0 |
|2001 || |
| || || ||4.8 ||4.0 |
|2002 ||Reduce exploitation || || || ||4.8 ||3.6 |
|2003 || |
| || || ||4.1 ||3.8 |
|2004 || |
| || || ||3.5 ||2.5 |
|2005 || |
| || || ||3.2 ||3.0 |
|2006 ||Zero catch ||F=0 || ||0 ||2.7 ||2.8 |
|2007 ||Zero catch ||F=0 || ||0 ||2.2 ||(1.1) (2) |
|2008 ||Zero catch ||F=0 || ||0 ||1.6 || |
|2009 ||Combined catches of recent average landings (2002–2006) ||NA ||3.1 (3) ||NA || || |
|2010 ||Same advice as 2009 ||NA ||3.1 (3) || || || |
Weights in ‘000 t.
(1) EU only.
(2) Preliminary data.
(3) Subject to the individual recording of landed species, no targeted fisheries and minimal bycatch of common skate and undulate ray, and no landings of angel shark.
Management unit: No
Management objectives have not been adopted. An EC Action Plan on elasmobranchs is under development in 2008.
Management AdviceManagement considerations
North Sea demersal elasmobranchs are landed as a bycatch in demersal fisheries. A few inshore vessels target skates and rays. They have usually been landed and reported in mixed categories such as “skates and rays” and “sharks”. For assessment purposes species-specific landings data are essential. Since 2008 countries are obliged to report landings for the major skate species separately. On the basis of a longer track record on a species basis (at least five years) it will be possible in future to advise on species-specific catches.
From 2005 to 2008 the TAC for North Sea skates and rays has been reduced by approximately 50%, and is now significantly lower than average recent landings. TACs only regulate the landings, and a low TAC on a low-value bycatch species could induce more discards. Because the elasmobranch species are caught as a bycatch in demersal fisheries, they would benefit from a reduction in the overall demersal fishing effort.
Elasmobranchs are typically slow growing, have a high age-at-maturity and a low reproductive capacity. Measures to afford protection to the largest individuals should be considered. A Maximum Landing Length (MLL) of 100 cm for all skates and rays would be beneficial for common skate while not influencing most other species.
Landings of demersal sharks are not effectively restricted in the North Sea. Although lesser spotted dogfish are generally discarded, markets have developed for smoothhounds. Appropriate species-specific landings (for Scyliorhinus
spp.) and genus-specific landings (for Mustelus
spp.) are required before the level of a status quo
catch could be advised on.
Biological State and Trend
In the absence of defined reference points, the status of the stocks of demersal skates and rays (members of the family Rajidae) and demersal sharks (of the genera Scyliorhinus, Mustelus
, and Squatina
) cannot be evaluated. The following provides a qualitative summary of the general status of the major species based on surveys and landings:
Skates and rays (Rajidae)Common skate –
|Species ||Scientific name ||Area ||State of stock |
|Common skate ||Dipturus batis ||IVa (likely merging with VIa & IIa) ||Depleted |
|Thornback ray ||Raja clavata ||IVc, VIId ||Stable/increasing |
| || ||IVa,b ||Uncertain |
|Spotted ray ||Raja montagui ||IVb,c ||Stable/increasing |
|Starry ray ||Amblyraja radiata ||IVa,b, IIa ||Stable |
|Cuckoo ray ||Leucoraja naevus ||IVa,b ||Stable |
|Blonde ray ||Raja brachyura ||IVc, VIId (patchy occurrence) ||Uncertain |
|Undulate ray ||Raja undulata ||VIId, merges with VIIe ||Uncertain, reasons for concern |
|Lesser-spotted dogfish ||Scyliorhinus canicula ||IVa,b,c, VIId ||Increasing |
|Smooth hound & Starry smooth hound ||Mustelus mustelus & Mustelus asterias ||IVa,b,c, VIId ||Increasing |
|Angel shark ||Squatina squatina ||IVa,b,c, VIId ||Extirpated |
is depleted. It was formerly widely distributed over much of the North Sea but is now found only rarely, and only in the northern North Sea. The distribution extends into the west of Scotland and the Norwegian Sea.Thornback ray –
distribution area and abundance have decreased over the past century, with the stock concentrated in the southwestern North Sea where it is the main commercial skate species. Its distribution extends into the eastern Channel. Survey catch trends in Division IVc have been stable/increasing in recent years. The status of R. clavata
in Divisions IVa,b is uncertain.Spotted ray –
stable/increasing. The area occupied and abundance has fluctuated without trend.Starry ray –
stable. Survey catch rates
increased from the early 1970s to the early 1990s and have decreased slightly since then.Cuckoo ray –
uncertain. Since 1990 the area occupied has fluctuated without trend. Abundance has decreased since the early 1990s, but has been stable in recent years.Blonde ray
– uncertain. This species has a patchy occurrence in the North Sea. It is at the edge of its distributional range in this area.Undulate ray
– uncertain, reason for concern. Mainly limited to Division VIId where it merges with Division VIIe. Occasional vagrants in Division IVc. The biology of the species and recent disappearance from surveys give rise to concern. It has a patchy and localized distribution, possibly forming discrete stocks, which make the undulate ray sensitive to local depletion. Additionally, the species has disappeared from the English beam trawl survey in Division VIId in the last two years.Demersal sharksLesser spotted dogfish –
abundance and area occupied are increasing.Smooth hound and starry smooth hound –
abundance appears to have been increasing in recent years both in survey catches and in commercial and recreational fisheries, but the stock status is uncertain. Identification by species is considered unreliable in the surveys.Angel shark –
is now extirpated in the North Sea. It may still occur in Division VIId.
Source of information
ICES. 2008. Report of the ICES Advisory Committee, 2008. ICES Advice, 2008.