NatureScot Fisheries Management Advice – Supporting information for basking shark in relation to interaction with static nets (tangle in particular)

https://www.nature.scot/doc/naturescot-fisheries-management-advice-supporting-information-basking-shark-relation-interaction

Please note - The advice below was produced (March 2024) to assist the development of proposed management measures for fishing activity for MPAs and PMFs (11 most sensitive to bottom contact gear) outwith MPAs. Further considerations were made by Marine Directorate and the final proposed management measures being consulted upon in 2026 are available via Scottish Government’s website.

March 2024

Purpose

This note has been produced to provide an overview of the rationale for static gear fisheries (particularly tangle nets) advice proved in NatureScot’s Conservation and Management advice documents for MPAs for basking sharks, such as the Sea of Hebrides NCMPA.

Background

There is quite a lot of evidence of accidental catches of basking sharks in gillnets from outside of Scotland. However, there is no specific evidence for tangle nets. Although given how gear can be grouped, tangle nets may have been incorporated within the ‘gillnet’ gear type depending on the data that has fed into the various reports and papers listed. We have not been able to ascertain whether this is the case though. Given basking shark use of the water column and seabed (see below) without further evidence we think we would need to assume a similar potential risk of bycatch for tangle nets as gillnets.

Previous advice

  • Fisheries guidance note for basking shark (June 2019) – produced for the public consultation on the Sea of the Hebrides MPA designation and outlines the interactions as we understood them between basking sharks and fishing gear and the evidence for this.
  • The published NatureScot report ‘Identifying zones where basking sharks occur more frequently within a possible MPA to aid management discussions’ describes in more detail the areas where basking sharks occur more frequently within the MPA and it discusses bycatch/entanglement in section 2.8 with some useful maps showing the overlap between the zones for basking shark and fisheries VMS data for creels,  Nephrops trawling and scallop dredging, but there is no mapping for set nets as there were no data layers available for those. These areas could be overlaid with information on tangle nets if this is obtained from fishers in the area.

Other supporting information

Water column use

Basking sharks do use the entire water column, including areas very close to the seabed, over a variety of substrates including sand and rocky/boulder, as individuals but also in groups (for video footage from previous survey work see our basking shark webpage).

Scottish Entanglement Alliance (SEA)

Report on marine animal entanglement in the Scottish creel fishery;

  • A questionnaire was completed by 159 Scottish commercial creel fishers in 67 different harbours around Scotland, to find out about their experiences of marine animal entanglement over a 10-year period between 2008-2018.
  • Almost half of fishers had experienced at least one entanglement in the last ten years.
  • Entanglements are a rare event at an individual fisher level and for most this was a single event.
  • 146 marine animal entanglements involving at least 12 different species were reported during the interviews. The main species reported were minke whale (Balaenoptera acutorostrata) and basking shark (Cetorhinus maximus).
  • Over 70% of recorded entanglements were found dead in the gear.
  • Minke whales and basking sharks were more often found entangled in groundlines. Average fishing depth and gear hauling frequency were associated with experiencing a marine animal entanglement.
  • It was recommended that the project should be extended to include other fishing sectors such as trawls, purse-seines and static nets, which would allow us to further investigate marine animal entanglement in Scottish waters.

FeAST sensitivity assessment

Assessment for basking sharks for the pressure ‘Removal of non-target species (including lethal)’. Assessment completed in 2019.

Sensitivity score: High

Evidence base: The basking shark was reported to be a victim of entanglement in fishing gear (e.g. trawls, longlines, prawn and cod traps) in the Pacific Canadian waters (DFO, 2009; McFarlane et al., 2009). In the Northeast Atlantic, there are anecdotal reports of the basking shark being incidentally caught in gillnet and trawl fishing gear (ICES, 2016). In 1993, 28 records of basking sharks entangled in fishing gear were reported in the Irish Sea (Berrow, 1994; Berrow & Heardman, 1994) and at least 22 % of the sharks died as a result of the entanglement. Furthermore, the Marine Conservation Society (MCS) reported 63 sharks suffering from ship strike or entanglement in fishing gear between 1992 and 2013 (Solandt & Chassin, 2013). Entanglement in ropes and nets was reported from Scotland and southwest England (Bloomfield & Solandt, 2006). Basking sharks are also accidentally caught by towed gear (Francis & Duffy, 2002). Small numbers (130 individuals over 21 years) of incidentally caught basking sharks continue to be reported in the UK (Witt et al., 2012). As a result of the zero total allowable catch (TAC) and the requirement of EU fishing industry to discard all incidentally caught basking sharks, there is little recorded information about these incidents. It is also difficult to quantify the impacts (ICES, 2016). Although the impact of accidental removal by fisheries and entanglement on populations is not quantified, fishing gear poses a threat to individuals of this species and the population as whole. Based on the observed mortality of basking sharks due to fishing gear in the Irish waters alone tolerance is assessed as ‘None’, recovery as ‘None’, and sensitivity is assessed as ‘High’.

International Council for the Exploration of the Sea (ICES) 

2024 Report of the Working Group on Elasmobranch Fishes (WGEF).

See section 7.3.2 Discards (page 201), this section covers information on bycatch, citing similar references to the sensitivity assessment from FeAST above and there are Norwegian and French data indicating gillnet and other bycatches up to 2014 – see tables 7.3 and 7.4.

References

Berrow S.D. 1994. Incidental capture of elasmobranchs in the bottom set gill-net fishery off the south coast of Ireland. Journal of Marine Biological Association UK, 74, 837-847. 

  • Noted that 77-120 sharks were caught annually in gillnet fishery in the Isle of Man. Bycatch in the herring fishery and the pot fishery (entanglement in ropes) was estimated at 14-20 sharks annually.

Berrow S.D. & Heardman C. 1994. The Basking Shark Cetorhinus maximus (Gunnerus) in Irish Waters: Patterns of Distribution and Abundance. Biology and Environment: Proceedings of the Royal Irish Academy, 94B(2), 101-107. 

  • 28 of 142 records of basking shark in Irish waters were of basking sharks entangled in fishing nets, usually surface gillnets.