Blue shark

For more information about this species please visit: https://www.cornwallgoodseafoodguide.org.uk/fish-guide/blue-shark.php.

Blue sharks are poorly managed across the North Atlantic due to a lack of reliable data to assess the stock status. Management requires considerable improvement to assess and protect the species from overfishing. Blue shark is a highly migratory species, found on the high seas and in numerous countries' waters. Blue shark is managed and assessed by the International Commission for the Conservation of Atlantic Tunas (ICCAT). The main management measures are a catch limit (Total Allowable Catch, TAC) and controls on fishing gear. A significant proportion of North Atlantic blue shark are caught in EU waters (around 60% of EU catches) where additional European Council regulations also guide management. Longlines account for the majority of catches of blue shark in fisheries targeting tuna and billfish. North Atlantic stocks are also directly targeted in the small Basque artisanal longline shark fishery.  Blue shark can comprise up to 70% of total longline catches and can exceed catch of target species. Recreational fisheries also catch considerable numbers of blue shark across the North Atlantic. Although discards of caught blue shark are high, both the fins and meat are valued and found in the UK and global markets. Total allowable catch (TAC) limits of 39,102 t have been in place for blue shark since 2017. Landings of 33,995 t in 2018, 27,207 t in 2019 and 20,827 have been below the TAC. However, the data used to assess stock status of blue shark in the North Atlantic are incomplete and generic reporting of shark catches has resulted in underestimation of landings. Additionally, there is a high level of uncertainty in the data and models used for stock assessment. Given the assessment uncertainty, the possibility that blue shark is overfished cannot be ruled out. The scientific committee for ICCAT recommend precautionary measures should be considered. Given that the most recent assessment for blue shark uses 2013 data and the next assessment has been pushed to 2023, there are concerns that the management of the species is not up to date or sufficiently precautionary. Additionally, options for Harvest Control Rules (HCR) have been requested by the Commission to provide catch limits, targets and threshold reference points but without a recent stock assessment these cannot be provided.Currently ICCAT cooperating parties are allowed to land shark fins separated from the fish carcass. ICCAT does have weight limits and some measures in place to avoid shark finning and carcass discards at sea. However, these are not considered suitable for recording catches to species level. Draft recommendations have been encouraged and proposed to ensure that fins are naturally attached at point of landing, but have not yet been adopted. The European Council prohibits the removal of shark fins for all EC vessels in all waters and non-EC vessels in Community waters. Management to ensure all species caught and landed are accurately identified and reported across the North Atlantic needed. Discard levels are understood to be higher than those reported. Additionally, there are concerns that bycatch and discard mortality has a significant impact on population health when combined with landings data. ICCAT requires a minimum of 5% observer coverage of fishing effort for longline fisheries to enable stock assessments and provide bycatch estimates. However, the scientific committee recommend that this is increased to 20% to provide reasonable estimates of bycatch. The lack of reliable bycatch data and management to assess and reduce bycatch of blue shark is of concern. Blue shark management is based on separated North and South Atlantic and Mediterranean stocks. However, there are some indications that the species moves and breeds across these areas. Research is starting to explore stock differentiation across the area, this information is needed for suitable management decisions to be made, especially considering that blue shark in the Mediterranean is Critically Endangered.

Blue shark in the Atlantic are mainly landed as bycatch in longline fisheries for tuna and swordfish. While longlining is unlikely to have habitat impacts, it can have a bycatch of highly vulnerable species such as other sharks, turtles, and seabirds.Monitoring and reporting of bycatch in fisheries managed by ICCAT is poor. Most data come from scientific observers on vessels. Scientific recommendations are that 20% of a fishery should be observed for accurate data. ICCAT only requires coverage of 5%, increasing to 10% in 2022. Many fleets are not reaching this level. Details of the depth, hooks, baits and targeting strategies for blue shark are unknown making it difficult to gauge the impact on vulnerable species.There is a bycatch of loggerhead, leatherback and olive ridley turtles in longline fisheries. According to the IUCN Red List, loggerhead turtles are endangered in the north east Atlantic and leatherbacks are endangered in the north west Atlantic. Observer data for 2020 indicates 20 dead discards of turtles, 1,308 live discards and 20 discards of unknown status. Given the poor observer coverage, this is likely to be an underestimate of the total catch. Post-release mortality is 1-4%. Longliners are required to safely unhook and release alive turtles. Other scientifically recommended mitigation measures, such as using finfish bait and large circle hooks, are not mandated.Seabirds are known to be vulnerable to bycatch in longline fisheries. Bycatch of seabirds is understood to be most problematic in the southern Atlantic. However, increasing evidence indicates that northern species are also at risk in some longline fisheries. For example, up to 1% of the global population of Northern Fulmars (petrel species) is killed annually in gillnet and longline fishing in the North Atlantic. And longlines had the highest seabird bycatch in a study comparing multiple gears in the Atlantic Iberian coast. Reliable bycatch data is needed to assess whether pelagic longlines catching blue shark in the North Atlantic are a concern for seabirds. The Agreement on the Conservation of Albatrosses and Petrels (ACAP) recommends best practice measures to protect seabirds. ICCAT mitigation measures do not follow these recommendations. ICCAT requires one or more measures from a set list of options, including weighted hooks, bird scaring lines and night setting, depending on location and target species. ACAP recommends the simultaneous use of all three, or hook-shielding or underwater bait setting devices.Other sharks are both bycaught and targeted in longline fisheries in the Atlantic. Bycatch species include the critically endangered scalloped hammerhead, silky shark, and the bigeye thresher, which is endangered in Europe and the Mediterranean. Observer data for 2020 indicates 1,098 dead discards of sharks and 1,109 live discards. Given the poor observer coverage, this is likely to be an underestimate of the total catch. There are some mitigation measures, such as restrictions on finning, but no gear-specific measures. This is in spite of repeated recommendations from the scientific committee to use circle hooks, which have been shown to increase survival of shortfin mako, blue marlin and swordfish if accidentally caught. Catching silky sharks, hammerheads, oceanic whitetips, and bigeye threshers is prohibited, and catching other thresher species is discouraged. Shortfin mako, which is heavily overfished, can be caught and retained. However, measures came into force in 2022 aimed at ending overfishing of this species.There are no specific management measures to protect marine mammals, including cetaceans. ICCAT has not prioritised collecting data on mammal bycatch to date. More needs to be done to understand and reduce the impact of ICCAT fisheries on marine mammals.

ACAP, 2021. ACAP Review of mitigation measures and Best Practice Advice for Reducing the Impact of Pelagic Longline Fisheries on Seabirds. Reviewed at the Twelfth Meeting of the Advisory Committee Virtual meeting, 31 August – 2 September 2021. Available at https://www.acap.aq/resources/bycatch-mitigation/mitigation-advice/3956-acap-2021-pelagic-longlines-mitigation-review-bpa/file [Accessed on 09.12.2021].Anon., 2021. Advances on the collaborative work to assess sea turtle bycatch in pelagic longline and purse seine fleets (Atlantic and Indian oceans and Mediterranean Sea). SCRS/2021/076. Collect. Vol. Sci. Pap. ICCAT, 78(4): 155-166. Available at https://www.iccat.int/Documents/CVSP/CV078_2021/n_4/CV078040156.pdf [Accessed on 16.12.2021].Calado, J.G., Ramos, J.A., Almeida, A., Oliveira, N., Paiva, V.H., 2021. Seabird-fishery interactions and bycatch at multiple gears in the Atlantic Iberian coast, Ocean & Coastal Management, Volume 200, 105306. DOI: https://doi.org/10.1016/j.ocecoaman.2020.105306.Campana, S. E., Marks, L., Joyce, W. Kohler, N. 2005. Catch, by-catch, and indices of population status of blue shark (Prionace glauca) in the Canadian Atlantic. ICCAT Collective Volume of Scientific Papers, 58(3): 891–934. Available at: https://www.flyingsharks.eu/literature/iccat/CV058030891.pdf [Accessed 21.12.21].Campana, S.E., Joyce, W., Manning, M.J., 2009. Bycatch and discard mortality in commercially caught blue sharks Prionace glauca assessed using archival satellite pop-up tag. Marine Ecology Progress Series 387:241-253. DOI: 10.3354/meps08109Clarke, S., Sato, M., Small, C., Sullivan, B., Inoue, Y. & Ochi, D. 2014. Bycatch in longline fisheries for tuna and tuna-like species: a global review of status and mitigation measures. FAO Fisheries and Aquaculture Technical Paper No. 588. Rome, FAO. 199 pp. Available at https://www.fao.org/3/i4017e/i4017e.pdf.Colston-Nepali, L., Provencher, J.F., Mallory, M.L. Franckowiak, R.P., Sun, Z., Robertson, G.J., Friesen, V.L. 2020. Using genomic tools to inform management of the Atlantic northern fulmar. Conserv. Genet. 21, 1037–1050. DOI: https://doi.org/10.1007/s10592-020-01309-yHobbs CAD, Potts RWA, Bjerregaard Walsh M, Usher J, Griffiths AM., 2019. Using DNA Barcoding to Investigate Patterns of Species Utilisation in UK Shark Products Reveals Threatened Species on Sale. Sci Reports 9(1):1–10. Available from: https://www.nature.com/articles/s41598-018-38270-3ICES, 2021. Working Group on Elasmobranch Fishes (WGEF), Publication Reports - 01 WGEF Report 2021.pdf. Available from: https://www.ices.dk/sites/pub/Publication%20Reports/Forms/DispForm.aspx?ID=38116. [Accessed 12.11.21].ICCAT, 2015. Report of the 2015 ICCAT blue shark stock assessment 2015 session, 27 – 31 July, 2015, Available at: https://www.iccat.int/Documents/SCRS/DetRep/BSH_SA_ENG.PDF [Accessed on 16.12.21].ICCAT, 2018. Position Statement International Commission for the Conservation of Atlantic Tunas 21st Special Meeting, PLE-135/2018. November 2018 Dubrovnik, Croatia, Available at: https://www.iccat.int/com2018/tri/PLE_135_Shark_Groups_Opening_Statement.pdf  [Accessed on 21.12.2021].ICCAT, 2019. Recommendation by ICCAT amending the recommendation 16-12 on management measures for the conservation of the North Atlantic blue shark caught in association with ICCAT fisheries. Available at: https://www.iccat.int/Documents/Recs/compendiopdf-e/2019-07-e.pdf [Accessed on 21.12.21]ICCAT, 2020. The development of the seabird component of the ICCAT ecosystem report card. SCRS/2020/045. Collect. Vol. Sci. Pap. ICCAT, 77(4): 144-156. Available at https://www.iccat.int/Documents/CVSP/CV077_2020/n_4/CV077040144.pdf [Accessed on 16.12.2021].ICCAT, 2021a. Report of the Standing Committee on Research and Statistics (SCRS), 27 September - 2 October 2021, Available at https://www.iccat.int/Documents/Meetings/Docs/2021/REPORTS/2021_SCRS_ENG.pdf [Accessed on 14.12.2021].ICCAT, 2021b. Secretariat Report on Research and Statistics. PLE-105 presented to the 27th Regular Meeting of the Commission. 15-23 November 2021, Online. Available at https://www.iccat.int/com2021/ENG/PLE_105_ENG.pdf [Accessed on 15.12.2021].ICCAT, 2021c. Panel 4, Swordfish Billfishes Sharks Small tunas, SCRS Report 2021. Available at: https://www.iccat.int/com2021/presentations/SCRS_Chair_2021_PA4_Presentation.pdf [Accessed on 16.12.21].ICCAT, 2021d. Compendium management recommendations and resolutions adopted by ICCAT for the conservation of Atlantic tunas and tuna-like species Available at: https://www.iccat.int/Documents/Recs/COMPENDIUM_ACTIVE_ENG.pdf [Accessed on 21.12.21].ICCAT, 2021e. PA4_807, Draft recommendation by ICCAT concerning the conservation of sharks caught in association with fisheries managed by ICCAT. Available from: https://www.iccat.int/com2021/ENG/PA4_807_ENG_SPONS_1.pdf [Accessed on 21.12.21]Official Nominal Catches 2006-2019. Version 15-10-2021. ICES, Copenhagen. Available from:http://ices.dk/data/dataset-collections/Pages/Fish-catch-and-stock-assessment.aspx [Accessed on 20.12.21]Rigby, C.L., Barreto, R., Carlson, J., Fernando, D., Fordham, S., Francis, M.P., Herman, K., Jabado, R.W., Liu, K.M., Marshall, A., Pacoureau, N., Romanov, E., Sherley, R.B. & Winker, H. 2019. Prionace glauca. The IUCN Red List of Threatened Species 2019: e.T39381A2915850. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T39381A2915850.en. [Accessed on 16.12.21].SharkTrust, 2020. Blue shark (Prionace glauca) ID Guide. Available from: https://www.sharktrust.org/FAQs/blue-shark-id-guide [Accessed 21.12.21]Okamoto, K., Ochi, D., and Oshima, K., 2017. Review of sea turtle by-catch data in the ICCAT convention area obtained through Japanese scientific observer program. SCRS/2017/155. Collect. Vol. Sci. Pap. ICCAT, 74(7): 3698-3713 (2018). Available at https://www.bmis-bycatch.org/system/files/zotero_attachments/library_1/BYJUU4PR%20-%20CV074073698.pdf [Accessed on 16.12.2021].