Drones, thermal sensors provide precise UK grey seal census

drone thermal grey seals

Drones equipped with thermal sensors are being deployed in one of the UK’s largest-ever surveys of Atlantic grey seal pups as a less intrusive, faster, and cheaper alternative to manual counting.

Those census operations are underway over the Farne Islands, located off England’s northern coast between Newcastle and the Scottish border. The islands are home to one of the area’s largest grey seal populations. Images taken of pups by thermal sensors aboard drones canvassing the area are giving researchers a more accurate count of reproduction rates. After hunting decreased population levels to only around 500 individuals early last century, current estimates place the number of grey seals in the UK at 120,000, representing about 40% of the global total.

The UK’s National Trust, which manages and conserves places of historical interest and natural beauty, oversees the Farne Islands, where rangers are now deploying drones with thermal sensors for the second time in the grey seal counts. Their previous 2019 survey established the many advantages of using the craft over manual efforts. It also recorded a record number of 2,823 pups born since the 2014 census – an increase of 62%.

Before the embrace of drones, human observers had to get themselves out to remote grey seal reserves after the first pups had appeared, then physically wade into their midst to apply an innocuous vegetable dye to indicate the period of their birth. That, and subsequent monitoring, not only required disrupting the young creatures and their parents, but it also took too long to conduct anything more than counts of sample groups. Those had to be extrapolated into larger population estimates. 

Now, drones are allowing wildlife authorities to access a much wider range of locations, and get far more precise tallies of the grey seal pups they survey. 

“The drone gives us an excellent view of the islands and from the clear images we can count the total numbers of seal pups born on each island,” says Thomas Hendry, a ranger involved in the survey. “It also allows us to see onto the smaller islands more frequently which can be more challenging to visit at this time of year due to difficult sea conditions.”  

The new process involves a first drone with a regular camera overflying reproduction areas to capture standard footage. Then, a second craft passes over using its thermal sensor to take more precise images in which different ages of seals can be discerned. 

“Having the extra thermal imaging technology is particularly useful now that the islands are supporting more and more pups and the population is denser,” Hendry says. “It will hopefully also allow us to detect any seal pups that sadly don’t survive, so that they aren’t accidentally included in our numbers.”

Photo: Diana Parkhouse

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