Following Scotland’s Sharks: The common skate and the spurdog
James Thorburn Thank you’s
This project could not have happened if it were not for the support and help of many people:
Knox Marine services, Ronnie Campbell, Roger Eaton, Inverlussa staff, Ian Burrett, Derek Bailey, David Isaacs, Gordon Shearer, Lismore Seafoods, Jake Crossley, David Morris and Rob Main, Colin Currie, Simon Exley, Lea-Anne Henry, Calmac, Scottish Sea Farms, the anglers and fishermen who have returned tags and receivers to us What’s it all about!?
“Conserving and managing Scottish elasmobranch’s effectively”
How!? Fisheries – management options
• Total Allowable catch
• Prohibition
• Real time closure Species specific legislation
• Wildlife and Countryside Act 1981 • Basking Shark
• CITES ( Convention on International Trade in Endangered Species ) • Appendices 1 & 2 Marine Protected Areas
• A designated spatial area with some form of management
• Only really of use in areas with strong philopatric behaviour • Residential • Return
• Generally only protect one age/sex class at a time
• Thought to be most suitable for critical life stages • Protection of nursery areas highly prioritised Elasmobranch nursery grounds • Protected areas
• Coastal • Estuaries • Shallow bays
• Reefs inc. deep water Home range
Size/Age of Shark Elasmobranch nursery grounds • Protection of nursery grounds prioritised, taken from teleost (bony fish) management such as cod. • The increase in home range as a shark grows often means the move out of the protected areas as they get bigger • Late maturity (up to 15 years of age) means that the sharks may spend a large proportion of their life unprotected. Late maturity means sharks may be fished before they reproduce – no nursery anymore Adult MPAs
Some behaviours promote the suitability of MPAs for adult sharks: • Site fidelity; repeated use of same area • Residency; remaining within an area for large amounts of time. Need to understand movement Movement can be split into 3 broad categories:
1. over 24 h (usually associated with feeding and resting) 2. seasonally (including movement in relation to the breeding cycle) 3. Ontogenetic shifts (changes in habitat type in relation to body size and dietary preferences) Movement
How do we track elasmobranchs? • Real time • Observational • Monitoring
• Post processing • Collect and store data Acoustic Tagging
• Tags actively transmit a unique signal.
• Receiver units continually listen for the signal and record the date and time when they receive one (approximately 500m radius).
• The tagged fish needs to swim close to a receiver unit!
Archival tags
• Record certain variables • Depth • Temperature • Light • Acceleration • Magnetic field
• Shark must be recaptured This Project - combination
• Archival tags (depth & temperature 2 min resolution) • Star Oddi milli tags
• Acoustic tags with a static array • Vemco V13 • Thelma biotel ADT 13 (some with pressure) • 60-90 second
• 14 month deployment of receivers • 39 VR2W and VR2 AR • Firth of Lorn • Loch Etive Flapper skate (Dipturus intermedia) (Common skate - Dipturus batis )
Long life history (‘K’) • 15 yr maturity • 30-60 eggs per annum • Large birth size • Long lived • Localised extinction Acoustic array
16% coverage Tagging • 65 fish tagged with archival tags (25 returns total!) • 43 double tagged (27 F, 16 M) Tagging sites Detections plots ---Female Tag date Detection Tag removal Detections plots ---Male Tag date Detection Tag removal Proportion of tagged skate detected Days detected Temperature Recapture event caused increase in temperature Skate 1522 – F, 145cm long (stunted tail) ~20200 detections
Skate 1509 – F, 135cm long, ~20900 detections
Skate 1548 – M 196cm long, ~1500 detections
Skate 1518 – M 198cm long – ~75 detections 4 days March 2016 Residency within array One DST returned from Mallaig
Skate make use of shallow water depths over winter Fine scale habitat use within the MPA - an opportunity with high residency? Skate summary
• Females have higher occupancy in the MPA • Males appear to move out the area, noticeably over summer • Deep water to the south appears preferable habitat • Good chance to study • fine-scale habitat use • Social networks Spurdog ( Squalus acanthias ) • Once a very common species – 95% reduction in NE Atlantic biomass • Critically endangered in the NE Atlantic by the IUCN*. • Late to mature • Traditionally viewed as a highly migratory species but recent research is showing more local movements *IUCN - International Union for the Conservation Of Nature Loch Etive
30 km2 0 20 40 60 80 100 140 Temperature (deg C)
Image adapted from: Aleynik et al, 2012, Oxygen dynamics in basins with restricted exchange: A case study of a Scottish fjord (Loch Etive, NW Scotland)
59 spurdog were tagged with acoustic tags • 8 in the Firth of Lorn (8 male) • 42 in Loch Etive (20 female and 22 male) • 9 in Falls of Lora (9 female)
Detections plots ---Female Detections in Loch Etive Detections in the FOL Detections in Loch Etive Detections plots ---Male Detections in the FOL Proportion of tagged animals detected Days detected Spurdog Summary
• High residency in the Loch (95% 250 days+) • High number of tags detected • Seasonal fidelity in the Firth of Lorn • Opportunity to look at sex/size segregation • Individual responses to temperature Summary
• Combination of data along with high residency presents opportunities to study many aspects of skate behaviour and ecology on an individual and population level
• Useful to informing management
• Essential to incorporate different data types to fully understand movement Thanks!