This skate was previously thought to be conspecific with Dipturus batis. Data deficient. All Northern Ireland records should now recognised be as D. intermedius (formerly all being recorded as D. batis before species split). Largest skate in the world, reaching up to 2.85 m and over 100 kg. Updates are required to legislation (e.g. Wildlife (NI) Order) to reflect this taxonomic update.

In brief

• Largest skate in the world, with a lifespan of up to 100 years.
• Previous confusion over taxonomic status - previously thought to be conspecific with D. batis.
• All Northern Ireland records should be considered to be D. intermedius.
• Critically endangered, and in the past subject to severe overfishing, as this species was specifically targeted. Still caught as accidental bycatch.

Species description: This large skate reaches a maximum size of 2.85 m wing tip to wing tip, and can weigh up to 113 kg. It has a long, pointed snout and a long tail. When young they are an olive-green to dark brown colour with some lighter spots, maturing to a solid grey-brown in adult skates. The underside is light grey to white in colour when mature, with younger skate being darker underneath.

Life cycle: These skate can live up to 100 years, and females don't reach sexual maturity until they are around 11 years old. They lay large (10-14 cm wide x 13-24 cm long) egg cases. These are generally laid in spring/summer and a single female can only produce up to 40 egg cases every 2 years. It is believed that embryos take over a year to develop, before emerging as a miniature version of the adult.

Similar species: Could be confused with Dipturus batis, although all Northern Irish records should be considered to be D. intermedius.

How to see this species: Prefer coastal waters with soft sandy sediment or gravel. Can occasionally be found in relatively shallow water (around 20 m) but much more commonly at 600 m, sometimes being recorded from depths down to 2000 m, on the continental shelf. Scattered records from all around Britain and Ireland. D. intermedius is generally found in northern areas when compared to D. batis.

Current status: Critically endangered/population is depleted. Data deficient. It has become locally extinct in some areas where it was once common.

Why is this species a priority in Northern Ireland?

• Criterion 1: Internationally listed species.
• Criterion 2: Decline based on available data and expert judgement.
• Criterion 4: NI stronghold or endemic – both stronghold range/population and designation as ‘endemic’ subject to expert judgement.

Threats: Fishing - historically it was deliberately targeted in areas where it was once common, resulting in this species suffering severe decline and now being critically endangered. Although it is now prohibited to land D. intermedius (and D. batis) it is still caught accidentally as bycatch during bottom trawling and set net fishing. The impact of recreational fishing still needs to be evaluated, as impacts from catch and release fishing are poorly understood.

Action: Records of new sites for this species, with details of habitat and population are always valuable. Observations with a photograph can be recorded using iNaturalist, find the MBDP-NI iNaturalist project here.

Alternatively, records can be sent to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down, BT18 0EU. Tel 028 9039 5257, e-mail cedar.records@nationalmuseumsni.org, or via the online portal.

Objectives:

• Monitor and maintain current population levels.
• Assess impacts of currently permitted fishing for this species and revise if necessary. If results are unclear or data are deficient a precautionary approach should be applied.
• Introduce measures to reduce or eliminate accidental bycatch.
• Revise wording of relevant legislation to reflect new taxonomic information surrounding the D. batis species complex.

Conservation:

• Listed as critically endangered on Irish, European and Global Red List.
• On OSPAR list of Threatened and/or Declining species and habitats.

Distribution Map from NBN: Dipturus intermedius at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Dipturus intermedius at iNaturalist World Species Observations database.

WoRMS: Dipturus intermedius at World Register of Marine Species. Accepted name: Dipturus intermedius (Parnell, 1837). AphiaID: 711846.

Classification: Biota; Animalia; Chordata; Vertebrata; Gnathostomata; Chondrichthyes; Elasmobranchii; Neoselachii; Batoidea; Rajiformes; Rajidae; Dipturus