Seeing spots: developing a photo-ID catalogue

for common skates in Argyll

Steven Benjamins

Scottish Association for Marine Science (SAMS)

Dunstaffnage

Oban

© Ronnie Campbell

Why are we interested in “common” skates??

• Assessed as Critically Endangered:• Large, long-lived, low

reproductive rate

• Highly vulnerable to overfishing and bycatch

• Now absent from most of its former range; some small populations left, incl. in Argyll

• Important to know population size, movements of individual animals How do we tell individuals apart?

Photo-ID example: bottlenose dolphins

Photo-ID as a method• Non-invasive!

• Assumptions:1. Individuals can be reliably

distinguished through visible marks

2. Marks are stable over extended periods, allowing individuals to be re-identified over time

3. The proportion of identifiable individuals in a population is relatively high

4. Populations are not so large as to make recapture rates impractically low

5. Individuals can be reliably photographed without excessive effort so as to make the method impractical

By PierreSelim - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=16076350

X

By Marcobeltrametti - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=38085389

Skates are very suitable for photo-ID!

© Ronnie Campbell

Skate photo-ID

• Lots of spots!• Location, size, brightness, patterns…

• Fin nicks, scratches (nonpermanent!)

© Ronnie Campbell

Benefits of skate photo-ID

• Allows confirmation of skate identity independent of tags/scanners

• Can incorporate information from the public

• Historical photos (pre-PIT tagging) can confirm long-term presence & movements

• Photos can inform about general health, diseases etc.

Results so far…

• 486 photos from 2011-2016 (Ronnie Campbell)

• 171 photos from 2016 (SNH)

• 413 capture events over 165 days

• Mainly females

• Most pictures usable for matching

0

50

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250

2011 2012 2013 2014 2015 2016

# o

f ca

ptu

re e

ven

ts

Unknown

Male

Female

2017 data: still working on it…

Results so far…

•251 individuals in the catalogue

•34% have been recaptured at least once

•Recapture intervals vary from <1 day to 1613 days(4 years, 5 months)

0

50

100

150

200

1 2 3 4 5 6 7

# o

f in

div

idu

als

# of times recaptured

# of recaptures (2011-2016)

Please send us your pictures!

Web address: https://skates.sams.ac.uk

What makes a good picture?

•Skate flat on deck

•Photo taken from above

• In focus

•Whole body visible

•No reflections or shadows

© Ronnie Campbell

Next steps

•Enter 2017 data into database

• Independently estimate skate abundance inside MPA

• Integrate photo-ID and PIT tag databases

PHOTO ID DATA PIT TAG DATA

Other ways to monitor skates:

•Baited lander sitting on seabed, with GoPro video camera

•5x deployed in northern Firth of Lorn, for ~2 hours each time (July 2017)

•At least 7 visits by skate, incl. 4 which could be individually identified

The future?

•Continued updates of skate photo-ID catalogue

•Try to automate ID process

•Assessment of spot/mark permanence

•Annual reports to SNH

•Estimation of absolute abundance

•More lander work?

Thanks to:• Ronnie Campbell for all his help in setting up this study

• Roger Eaton for advice, and for taking us out fishing

• Jack MacGregor for advice, and providing bait for the lander study

• Danielle Sloan, Ashlie McIvor & Amie Williams, for all their hard work

• SNH for financial & logistical support

• NERC, MASTS for financial support

Any questions?

Remember: please upload any pictures at https://skates.sams.ac.uk