Thriving grey seal population could be bad news for harbour seals

ZSL’s seal survey hopes to highlight the impact of the increasing grey seal population on the harbour seal.

Last year’s ZSL seal survey counted 451 harbour seals and 454 grey seals (pictured) in the Thames Estuary. © Dan Kitwood/Staff/Getty
Last year’s ZSL seal survey counted 451 harbour seals and 454 grey seals (pictured) in the Thames Estuary. © Dan Kitwood/Staff/Getty

The Zoological Society of London (ZSL) is undertaking its fourth annual seal survey of the Greater Thames Estuary, which may well be one of its most important to date.

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As well as providing the latest figures on seal populations in the Estuary, the survey will pay particular attention to the ratio of increasing numbers of grey seal to harbour seal, as well as looking for any emerging health issues, and will play a significant role in informing the future of seal conservation in the area.

Over the past 15 years, the population of grey seals has boomed along England’s east coast – great news for the grey seal, but not for the harbour seal.

Joanna Barker, ZSL’s European Conservation Projects Manager, believes that the increase in grey seals in the Estuary is creating a greater amount competition for food and territory among the seals.

“In addition,” she explains, “new behaviour of grey seals predating upon harbour seals has recently been observed in other European seal colonies. As the large intertidal sandbanks in the Thames are preferred harbour seal habitat, we are interested to see what impact increased competition could have for the species.”

But predation and competition for food and territory aren’t the only threats to the seal populations in the area.

Disease outbreak is also a major concern, especially given the Thames’ close proximity to mainland Europe, which – according to ZSL – means it’s likely that the area could serve as an entry point for diseases affecting seals.  

“We are particularly mindful that the last outbreak of phocine distemper virus happened 14 years ago in 2002, and if a similar pattern is observed it is predicted to return in 2016,” said Barker.

“Combine these various threats and you have what could amount to a ‘perfect storm’ for the Thames’ harbour seal population, which makes ZSL’s 2016 survey arguably the most important one yet.”

Find out more about ZSL’s Thames Seal Programme.

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