Unbeknownst to the millions of people who hustle along its banks every day, it seems London's River Thames has some tiny new residents these days: a cohort of rarely seen seahorses. Just one or two seahorses typically show up in the Thames each year, but researchers with the Zoological Society of London (ZSL) have encountered six in the past two months alone.

Short-snouted seahorse 2_credit Anna Cucknell-ZSL web 2.jpg
A short-snouted seahorse (Hippocampus hippocampus) was recently spotted during an ecological survey near Greenwich. Image: Zoological Society of London

The recent sightings suggest that two species – the short-snouted seahorse (Hippocampus hippocampus) and the long-snouted seahorse (Hippocampus guttulatus) – inhabit London's iconic waterway. And for a river with such a dirty history, that's certainly noteworthy news. 

"We're really excited to be finding more and more evidence suggesting seahorses are resident in the Thames," ZSL Estuaries & Wetlands Conservation Manager Anna Cucknell said in a press release. The most recent sighting, of a short-snouted seahorse, occurred near the area of Greenwich in a portion of the river exposed to daily tides.

The Thames was declared "biologically dead" after contamination from sewage and industrial dumping hit an all-time high in the 1950s. But in recent years, the river that once gave rise to the "Great Stink of London" has (quite literally) taken on new life. Over 100 species of fish, including the critically endangered European eel, now call the waterway home. Large mammals like seals, dolphins and other cetaceans also occasionally move through the area. Yet even with such progress underway, the seahorse encounters are a significant milestone in the river's recovery. 

Seahorses are extremely sensitive to water quality: even tiny changes can make them vulnerable to pathogens and parasites. This means the animals are picky about where they hang out – which in turn makes them great indicators of ecosystem health. The animals have been documented in the river only since 2008, and while we don't know exactly why they appear more abundant this year, the ZSL team is hoping their presence bodes well for future biodiversity in the Thames. 

Short-snouted seahorse 2_credit Anna Cucknell-ZSL web_0.jpg
Image: Zoological Society of London

What's more, it seems the seahorses are sticking around. 

"The fact that both species typically have small home ranges and don't tend to travel far gives reason to believe that the seahorses we've found recently are permanent residents rather than occasional visitors," says Cucknell. "There's currently a real lack of scientific data on the wider status and populations of these two seahorse species in the Thames and across their range, so we're hopeful these recent finds will attract the attention of funders to help us understand more about these amazing animals."

Members of the public can help document seahorses in the Thames by reporting their own sightings at iSeahorse.

Super Macro Related 2016 09 14


Top header image: Dmytro Kochetov/Flickr