Tails from the riverside
Tails from the riverside!
An intrepid band of merry volunteers entered the river Corran on Wednesday 19th August in search of evidence of aquatic life. This was part of the ongoing invertebrate survey, supported by the national Riverfly organisation, to assess the health of UK rivers. In addition, we were using this survey to introduce more volunteers to the scientific approach to river health analysis.
We had chosen the bank below Laugharne Castle to set up our counting equipment and entered the river from Green Banks to sample from the waterway between the Castle and Island House. One benefit we found quite quickly of this location was the number of passers-by who stopped to enquire about our activities, expressing support and interest in equal measure. Indeed, some individuals, especially two children of 10 or so years, were so absorbed that they stayed for some time, helping to sort and count the animals we recovered from the water. One young lady, Gracie, was heard to comment to her mum who was asking her to leave “no, this is way more interesting than yet another castle!”.
And so, to business:
The haul of organisms at this location was not as diverse as our previous foray further upstream, though still very interesting and informative.
Our kick sampling revealed just two of the Riverfly indicator species; freshwater shrimp, of which there were over a thousand in our sample, and cased caddisfly, of which our sample yielded 14 examples.
In addition to this, we did observe many rocks almost completely encrusted with caddisfly larvae cases, though these were found only upstream of the bend in the river.
In this location we also spotted an eel, about 35 – 40 cm or so in length, initially foraging for food and then hiding under a rock.
Our kick sampling also yielded a couple of elvers. We did try for quite a long time to capture one of the elvers for the photograph; this example was so elusive it earned the name “Heidi”. Eventually though, with Gracie’s help and guidance, we did eventually achieve our goal.
These little miracles of our waterways have made an amazing journey. Adult European eels (Anguilla anguilla) swim thousands of miles to the deep waters of the Sargasso sea to breed and lay eggs before dying. The hatched, flat, transparent larvae (leptocephali) drift passively on the gulf stream currents for up to three years towards Europe and the UK. As they reach the continental shelf they transform into transparent “glass eels”. When they arrive in the UK estuaries and move into freshwater rivers, they gain pigment becoming the juvenile form known as “elvers”.
We also had two fish fry in our sample, species to be identified.
At this stage of our studies it is not clear if the limited diversity of indicator species in this location is due to weather conditions, slow river flow, low river level, tidal influence, predation, intervention from human and canine presence or something else. That said, it is quite clear that the river here is still supporting aquatic wildlife despite any or all of these factors.
It is important to note that invertebrate indicator species will vary as a result of a variety of natural factors such as: changing seasons, sampling location, prevalence of predators, larval hatchings and more. Clearly, such changes can be heavily influenced by man-made factors too such as agricultural run-off and pollution events. Consequently, these sampling exercises will be repeated at intervals across the years so that we can build a baseline from which we can measure change. All of the results we generate are uploaded to a national database so that a national picture of river health can be established. We have another sampling exercise planned and will keep you posted of results accordingly.
With many thanks to our band of volunteers, both those who signed up as well as the ad hoc visitors who joined us on the day and swelled our ranks.
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