Wildlife experts have expressed their concern after the number of seals on the east coast of Scotland plunged to a historic low.

Populations have declined dramatically in places including the Firth of Tay and Eden Estuary, where there has been a 90% drop in recent years, according to a newly published study.

It also showed the number of seals in waters around Orkney, which is classified as eastern Scotland in the survey, has fallen 75%.

The study was carried out by the Sea Mammal Research Unit (SMRU) between 2011 and 2015 and showed Scotland's total seal population had risen from 20,400 to 25,400 since the last study between 2007 and 2009.

Scottish Natural Heritage, which commissioned SMRU to undertake the study, plans to carry out a further survey in an attempt to establish the cause of the decline.

SNH principal marine adviser John Baxter said: "It's great to hear that harbour seal numbers on the west coast are doing so well but it's of real concern that numbers on the east coast remain at historical lows.

"It's still not clear what's causing the decline but we're continuing to work with colleagues at Marine Scotland and SMRU to try to get a better understanding of what is going on.

"These surveys are important to help monitor seal numbers and inform whatever management decisions are taken to help protect the harbour seals.

"This year we will be surveying Orkney, where numbers have been declining for a number of years, and the east coast of Scotland as part of a three-year programme to cover the whole of the Scottish coastline."