Essex Rivers Hub

In May this year one of our reserve wardens, Bob Seago, was walking along the beach at Colne Point Nature Reserve when he came across an unusual object on the strandline. Further investigation revealed it to be a fish tag

, and its recovery provided an insight into the little known movements of fish species in the North Sea. Read Bob's account of the discovery below!


During my regular walks on the beach at Colne Point I carry a sack and litter picking tongs to keep on top of the regular sea borne rubbish. On 25th May this year I spotted a fluorescent orange object on the tidal strandline, expecting it to be a float as used by anglers. However this was different, having some writing describing it as a fish tag, which carried a reward, and contact details for CEFAS, the Centre for Environment, Fisheries and Aquaculture Science. It had a unique record code 11,260.

Clearly according to the size of the tag this would not have been put on a small fish, and I guessed, correctly as it turned out that it had become detached from a Thornback Ray. I was interested to find out the information stored on the device and after exchanging emails, sent it to the laboratory in Lowestoft. I also revisited some notes I had taken at a conference about species monitoring, and found information on the worldwide web.

Eventually I received a letter from CEFAS describing the history of the device. A hundred such tags were attached to Thornback Rays and Cod on 20th January 2015. The individual was a male 69 cm. in length on release. Recordings of depth and temperature were recorded every 20 seconds and the spatial distribution and migration were also recovered. A map was produced describing a slightly erratic movement in the four months between being released near Walton On the Naze, and apparently becoming detached from the fish near the Gunfleet Sands, possibly by being snagged on a net or perhaps caught by a Seal. In that time it had wandered almost half way across the North Sea. The research was commissioned to monitor the possible effect of wind turbine arrays on commercial fish species.

Most sea fish exhibit some migratory nature, and they travel from the depths to high in the water column in order to employ or indeed to avoid the faster current near the surface. I heard a story at the conference about a tag placed on a European Eel, which regularly changed its depth to avoid predators until it started to behave differently and the temperature was constant for an extended time. After the tag was recovered somewhere in the Atlantic Ocean it was speculated that the eel had been predated, perhaps by a shark.

CEFAS have retained my contact details and have promised to send reports of some of the findings of their research. The reward has duly been submitted to the Tendring local EWT group.

Thursday 3rd September 2015.

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