Citizen Science: Results from new otter survey indicate healthier rivers

• Volunteers have been trained to survey for signs of European Otter Lutra lutra

• Results provide new evidence of the health of six tributaries in the south of Greater Manchester

During the winter of 2022 and spring of 2023, trained volunteers searched for field signs left by otters around bridges along six tributaries of the River Mersey in the south of Greater Manchester which are known to support otters.  Otter field signs were found on four of the tributaries, indicating the river environment was healthy enough to support them.

Otters tend to frequent landmarks such as bridges where they sometimes leave behind pawprints as well as territorial markings including spraint (the technical term for their poo).  This behaviour is utilised by the ‘Otter Survey of England’, which is carried out by experienced professional surveyors to estimate the national population (1).

Our survey was designed to understand if a similar bridge survey method could be of use when carried out by volunteers on a local level.

You can read the full report here (opens in a new tab)

Otter spraint found on the River Goyt

Otters are an apex predator and need a healthy food chain beneath them, and hence a good river environment to support that food chain.  Otters also travel widely within their large territories (which can stretch to 20km or more), therefore, they are likely to visit all the healthy rivers in the area in which they live.

The hypothesis was that in an area known to have otters living there, volunteers would be able to find field signs at bridges on the rivers to indicate a healthy river environment. Not finding field signs would suggest that something could be improved about that river.

Otter food chain – credit catchments.ie

Credit: Tuam Tidy Towns tells the story of the River Nanny – Catchments.ie – Catchments.ie (opens in a new tab)

Otters are shy and elusive creatures that are difficult to spot – however, their field signs are easier to find.  Accordingly, volunteers were trained in the survey method and search techniques by Natural Course Project Officer Mike Beard, and Natural Course Advisor and otter expert Dr. Lorna Drake

Volunteers being trained by Dr. Lorna Drake

Four of the six tributaries surveyed were found to support otters, indicating that they have a healthy river environment.

Surprisingly few field signs were found during winter 2022 so a second phase of the survey was held in spring 2023 (wet weather during the first survey may have washed away the field signs).  The volunteer team for Platt Brook experienced trouble accessing bridges so that tributary was replaced by the River Tame.  The second phase of the survey was much more successful, with five field signs being found compared to one during the first phase.

Survey findings summary table

The survey succeeded in demonstrating that volunteers can use the bridge survey method to find otter field signs, which is a useful indicator of a healthy river.  It was also interesting to note that rivers that are classified under the Water Framework Directive as heavily modified were still being used by otters.

During the survey otter sightings were reported on social media but were not translating to official records that could be collated and carefully shared by the Greater Manchester Records Centre (GMLRC) and go on to be used for various conservation purposes.  The best method of making a sighting official, so that it can be used to help otters, is to send the information directly to GMLRC by way of their Simple Recording Form (opens in a new tab)

Mike Beard (Natural Course Project Officer and Greater Manchester Environment Team) said…

 “Volunteers are keen to help care for our rivers and associated wildlife and this novel survey gave them the opportunity to provide a new indicator of the health of their local tributaries.    Even if members of the public are not part of organised surveys like this one, they can still help build our knowledge of our natural environment by recording their sightings of otters, and other wildlife, with the easy-to-use GMLRC Simple Recording Form.”

References:

(1) Crawford A. 2010. Fifth Otter Survey of England 2009-2010. Bristol, Environment Agency