Using satellite trackers, scientists humanely tagged and followed 75 Caspian seals for up to 11-and-a-half months, as part of a four-year study into their behaviour.
The species is found only in the land-locked waters of the Caspian Sea in the Middle East.
They uncovered surprising variation among individuals for when and where they migrated, how far they travelled and how they went about finding food.
As well as giving insights into the ecology of seals, this work provides vital information for conservation efforts.
Caspian seals are listed as an endangered species by the International Union for the Conservation of Nature and their population has dropped by 90 per cent in just over 100 years, from more than one million at the start of the 20th century.
This was primarily due to intensive hunting, which lasted until the early 1990s, but the main threats now come from drowning in fishing nets set by sturgeon poachers, habitat loss and other disturbance from human activities.
"The data from telemetry studies such as this can help identify key areas of seal habitat which might be incorporated into future protected areas, and planning other human activities, such as oil and gas developments so they don’t impact on seals,” said Dr Goodman.
“To date there have been limited efforts to protect Caspian seals from their many threats, but this is the kind of information needed to help prioritise areas for special protection, and how to most effectively set up and manage them.”
The study was led by researchers from the University of Leeds, together with scientists from Estonia, Kazakhstan, Russia and Northern Ireland.
Dr Goodman explained how during the summer seals could be separated into 3 behaviour groups:
However during the autumn and winter months, these differences disappeared with most animals staying in the north, where they breed on the ice which forms there each year between January and March.
The researchers suggest the differences seen in summer could be due to individual animals specialising in certain types of prey and having distinct foraging strategies.
Dr Lilia Dmitrieva, the lead author of the paper said “The question is why would some seals only travel a short distance, while others expend lots of effort to swim thousands of kilometres to find food? Why don’t they all go for the easy option?
“The evidence we have so far suggests that by expending less effort travelling to nearby foraging sites, the shallow diving seals may save energy, which could then potentially be spent on breeding activity later in the year.
"They may be choosing more productive food sources through experience, or were competitively excluding other animals.
“The long migrant, deep divers may be travelling further to avoid competing for food with other seals in the north, or the prey in deeper waters may have a higher energy density, which makes up for the extra effort involved in catching it.”
This research project was funded by North Caspian Sea Production Sharing Agreement (NCSPSA) Venture.
Ralf Richter, David Brockwell, Eric Hewitt, Jessica Kwok, Emanuele Paci and MAPS/FMH, BBSRC (Jun 2017), £600,000
Eric Blair, Adrian Whitehouse, Nicola Stonehouse, Alison Baker, Richard Bayliss, Joan Boyes, Ryan Seipke, Sally Boxall and MAPS/FMH, BBSRC (Jun 2017), £376,000
Stefan Kepinski, Yoselin Benitez-Alfonso, Tom Bennett, Michelle Peckham, BBSRC (Jun 2017), £331,000
Roman Tuma, Lars Jeuken, Paul Millner, Sheena Radford, Peter Stockley and MAPS/FMH, BBSRC (Jun 2017), £222,000
Vas Ponnambalam, Darren Tomlinson, Stephen Wheatcroft, BHF (May 2017), £107,878
Graham Askew in collaboration with Bangor University, BBSRC (Mar 2017), £477,383
Stephen Muench, BBSRC (Mar 2017), £132,945
Nic Stonehouse, MRC (Mar 2017), £906,341
Bill Kunin, Steve Sait, BBSRC (Mar 2017), £602,831
Adrian Goldman, EU (Mar 2017), £546,576
Sheena Radford, Wellcome Trust (Mar 2017), £1,836,482
Tom Bennett, Royal Society (Mar 2017), £15,000
Jamie Johnston, Royal Society (Mar 2017), £15,000
Beatrice Filippi, Royal Society (Mar 2017), £15,000
Ryan Seipke, BBSRC (Feb 2017), £52,116
Mary O'Connell, BBSRC (Feb 2017), £46,986
Hannah Dugdale, NERC (Feb 2017), £504,138
Anastasia Zhuravleva, EPSRC (Jan 2017), £100,792
Richard Bayliss, Cancer Research UK (Jan 2017), £1,600,000
John Barr, EU (Jan 2017), £339,000
Mark Harris, Royal Society (Jan 2017), £250,000
Alison Dunn, NERC (Jan 2017), £105,000
Alex Breeze, Pancreatic Cancer Research Fund (Jan 2017), £180,000
Alison Dunn, NERC (Dec 2016), £18,000
Lisa Collins, BBSRC (Dec 2016), £1,681,835
Brendan Davies, Leverhulme Trust (Dec 2016), £247,555
Alan Benson, Mark Drinkhill, Ed White, British Heart Foundaion (Dec 2016), £217,223
Adrian Goldman, Royal Society (Dec 2016), £82,999
Lisa Roberts, Alex Breeze, Brendan Davies, Timothy Devinney, Oliver Harlen, Joseph Holden, Anthea Hucklesby, Pamela Jones, Philip Mellor, RCUK (Nov 2016), £484,172
Lisa Roberts, Alex Breeze, Brendan Davies, Timothy Devinney, Oliver Harlen, Joseph Holden, Anthea Hucklesby, Pamela Jones, Philip Mellor, Wellcome Trust (Nov 2016), £119,343
Katie Field, Rank Prize Funds (Nov 2016), £20,000
Jessica Kwok, Royal Society (Nov 2016), £14,948
John Ladbury, Cancer Research UK (Oct 2016), £4,250
Miriam Wittmann, Martin Stacey, Edward Vital, Lupus UK
(Oct 2016), £34,010
Valerie Speirs, NC3Rs
(Oct 2016), £90,000
Nicola Stonehouse, Morgan Herod, David Rowlands, BBSRC
(Sep 2016), £436,424
Joseph Cockburn, Wellcome Trust
(Sep 2016), £100,000
John Barr, Public Health England
(Sep 2016), £94,471
Helen Miller, DSM Nutritional Products A/S
(Sep 2016), £54,680
Steven Clapcote, Vitaflo International Ltd
(Sep 2016), £39,285
Juan Fontana Jordan De Urries
, Royal Society
(Sep 2016), £21,793
Jing Li, Sarah Calaghan, Mark Drinkhill, British Heart Foundation
(Sep 2016), £117,585
Sheena Radford, Alison Ashcroft, BBSRC (Sep 2016), £457,216
Patricija Van Oosten-Hawle, An-Jung Chen, David Westhead, NC3Rs
(Sep 2016), £354,456
Glyn Hemsworth, BBSRC (Sep 2016), £1,024,034
David Jayne, Paul Millner, MRC (Aug 2016), £207,860
Sheena Radford, Alison Ashcroft, BBSRC (Aug 2016), £457,215
Patricija Van Oosten-Hawle, Dave Westhead, An-Jung Chen, NC3Rs (Aug 2016), £354,456
Peter Henderson, EU - European Union
EU - European Union
(Jul 2016), £123,897
Adrian Goldman, EU - European Union
(Jul 2016), £116,290
Urwin, Howard Atkinson, NERC
(Jul 2016), £105,053
Eileen Ingham and colleagues in Engineering and M&H, EPSRC (Jul 2016), £3,867,449
Michael Colman, MRC (Jul 2016), £200,956
Tim Benton, Fresca Group Ltd
(Jul 2016), £52,082