Orwell dolphins are 'at high risk of stranding'

The discovery of a pod of dolphins frolicking in a river has delighted both those who saw them and readers of their story.

According to onlookers from Woolverstone Marina and Lodge Park the six dolphins played for about an hour around their boat on the River Orwell, in Suffolk.

So how common is it to see dolphins in rivers and what does it signify?

The conservation group the Cetecean Research and Rescue Unit (CRRU) said the mammals swimming in the River Orwell were common dolphins known as Delphinus delphis.

"These are a pelagic, offshore and highly gregarious species. It is rare to see such dolphins so close to shore, which suggests all may not be well," a spokesman said.

And according to Dr Kevin Robinson, executive director of the CRRU, the pod's move inland was concerning.

"[They are] typically found in water depths of [more than] 200m, so this small group is inevitably out of their natural habitat and therefore are at a high risk of stranding."

Dr Robinson added: "One of the most significant risks to these animals is climate change, as it poses threats to their health through various interconnected mechanisms.

"For example, rising ocean temperatures and altered currents can lead to a decline in prey species, compelling cetaceans to expend more energy in foraging, or resulting in changes in their natural distribution as they are forced to seek food elsewhere.

"Shifts in ocean temperatures and currents can also alter the distribution of pathogens and parasites, increasing disease risks for these marine mammals."

Dr Robinson added that the reproductive health of the mammals was intricately linked to environmental stability.

He said further exploration of how stranded cetaceans could be used to improve current understanding of cetacean health remained a priority.

He also emphasised that boat users should be respectful and avoid approaching them.

Rescue organisations were presently on standby should the animals live-strand, said the CRRU.

In January, a dolphin had to be rescued when it became stranded in a Cornish river after swimming about six miles (9.6km) inland, believing it was following food sources.

The successful rescue was carried out by the British Divers Marine Life Rescue (BDMLR) which said it had never before seen one in Lostwithiel on the River Fowey.

Two years ago, two dolphins died after they swam 445 miles (72km) up the River Great Ouse in Cambridgeshire before becoming trapped in reeds.

But it's not all negative.

Dr Ben Garrod, professor of evolutionary biology at the University of East Anglia, said: "About half the whales, dolphins and porpoises around the whole of the British coastline are found off the Norfolk and Suffolk coast and that's great news.

"So to see a pod of dolphins like this is becoming increasingly common - partly that's reflected by the fact we are not over-fishing in a way that we were 50, 60, 70 years ago.

"The fact we are seeing more of these animals and occasionally they are coming close to shore is, for once, a good news story."

A spokesperson for British Divers Marine Life Rescue said the dolphins were "most likely" to be following fish up the Orwell.

"Dolphins have and will always swim up rivers from time to time, we haven't seen a particular increase," they said.

Issues the pod could encounter include pollution, risk of stranding, entanglement, and boat strikes were "the same dangers they could face in the sea".

The only difference was that rivers were smaller, so "noise pollution could be more of an issue as dolphins are so acoustically sensitive", added the spokesperson.

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