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.
Ioannis Delis, Physiological Society (Jul 2018), £10,000
Scott Bowen, Physiological Society (Jul 2018), £10,000
Steve Clapcote, Jamie Johnston, The Dunhill Medical Trust (Jun 2018), £254,874
Adrian Goldman, MRC (Jun 2018), £98,627
Darren Tomlinson, Michelle Peckham, Megan Wright, BBSRC (Jun 2018), £150,443
Simon Walker, Royal Society (Jun 2018), £337,601
Tom Thirkell, N8 Agrifood (Jun 2018), £14,870
Stephen Muench with Glaxo SmithKline & UCB Celltech, BBSRC Industrial Partnership Award (Apr 2018), £480,225
Steve Clapcote, BBSRC (Apr 2018), £443,072
Helen Miller, Innovate UK (Apr 2018), £999,960
Elisabetta Groppelli, David Rowlands & Stanley Lemon (University of North Carolina), Medical Research Foundation Fellowship (Apr 2018), £293,494
Nikesh Patel, Medical Research Foundation fellowship (Apr 2018), £290,976
Graham Askew with colleagues in Hull and Liverpool, BBSRC (Apr 2018), £150,498
Andrew Macdonald, Neil Ranson & Richard Foster, Kidney Research UK (Apr 2018), £82,821
Jessica Kwok & Ralf Richter, Leverhulme Trust (Apr 2018), £298,273
Julie Aspden, Royal Society (Apr 2018), £20,000
Liz Duncan, Royal Society (Mar 2018), £14,602
Alex O'Neill & Ryan Seipke, BBSRC (Feb 2018), £45,489
Jim Deuchars, Royal Society (Feb 2018), £16,300
Stefan Kepinski & Netta Cohen, Leverhulme Trust (Feb 2018), £320,387
Lisa Collins, BBSRC (Feb 2018), £49,950
Alison Baker, BBSRC (Feb 2018), £30,000
Nikita Gamper, BBSRC (Feb 2018), £30,000
Lars Jeuken, BBSRC (Feb 2018), £30,000
Scott Bowen, Leducq Foundation Grant (Feb 2018), £28,470
Jessica Kwok and Ronaldo Ichiyama, International Spinal Research Trust (Feb 2018), £94,450
Alex O'Neill, Oxford Drug Design (Jan 2018), £86,098
Dave Lewis and Colleagues in South Africa, HEFCE Global Challenge Research (Jan 2018), £48,000
Sarah Calaghan, Ed White, John Colyer, Isuru Jayasinghe, BHF (Jan 2018), £128,308
Christine Foyer and Alison Baker, HEFCE GCRF Grant (Jan 2018), £71,158
Alison Baker, Yun Yung Gong and Lindsay Stringer and ICRISAT India, HEFCE GCRF Grant (Jan 2018), £27,000
Graham Askew, Simon Walker, BBSRC (Jan 2018), £699,781
Jennifer Tomlinson, Royal Society (Jan 2018), £512,801
Alison Dunn, NERC (Dec 2017), £18,000
Jennifer Tomlinson, Royal Society-Research Fellows Enhancement Award (Dec 2017), £94,681
Helen Miller, AB AGri Grant (Dec 2017), £73,600
Simon Walker, Royal Society Enhancement Award (Dec 2017), £10,000
Carrie Ferguson, Bryan Taylor, Harry Rossiter, The Physiological Society (Dec 2017), £7,392
Ralf Richter, Royal Society (Dec 2017), £6,000
Christine Foyer, British Council Newton Fund (Dec 2017), £49,840
Adrian Whitehouse and colleagues in School of Chemistry and University of Liverpool, MRC (Nov 2017), £622,319
Michelle Peckham, Neil Ransom, MRC (Nov 2017), £495,159
Dave Lewis, British Council India (Nov 2017), £22,540
Elton Zeqiraj, Royal Society (Nov 2017), £15,000
Hannah Dugdale, Royal Society (Nov 2017), £15,000
Shaunna Burke, Cancer Research UK Innovation Grant (Nov 2017), £20,000
Alex O'Neill and colleagues in Chemistry, BBSRC (Nov 2017), £431,865
Jessica Kwok, Wings for Life (Nov 2017), £87,365
Tom Bennett, BBSRC (Oct 2017), £523,679
Neil Ranson, Darren Tomlinson, BBSRC (Oct 2017), £494,318
Nikita Gamper, BBSRC (Oct 2017), £490,426
Amanda Bretman and colleagues from UEA, NERC (Oct 2017), £430,886
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Helen Miller, DSM Nutritional Products AG (Sep 2017), £69,988
Neil Ranson, Juan Fontana, Mark Harris, Michelle Peckham, Ralf Richter, Peter Stockley, Patricija Van Oosten-Hawle and colleagues in Engineering, FMH and MAPS, Wellcome Trust Equipment Call (Sep 2017), £418,000
Jamie Johnston, Physiological Society (Sep 2017), £10,000
Frank Sobott, Adrian Goldman, Mark Harris, Andrew Macdonald, Stephen Muench, Sheena Radford and colleagues in FMH and MAPS, Wellcome Trust Equipment Call (Aug 2017), £415,000