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Beach Find on EWT Reserve Reveals Secrets of Migratory Fish

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.

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The topics below represent the pressures that many waterbodies in the Combined Essex catchment face. They have been divided into six main categories, but it is quite often that these categories can overlap as pressures relate to each other.

Diffuse pollution occurs as water moves across the land or through the ground and picks pollutants. These pollutants can come from a variety of places, including urban and field run off. The pollutants that enter the river can range from sediment to toxins to excess nutrients, meaning that diffuse pollution can cause a whole range of different issues. The variety in these pressure groups means that it is something that can be quite difficult to tackle. It requires groups of people, business and stakeholders to work together in order to solve this problem.

Fish should be able to travel up and down a river freely, allowing them to move and breed in the most suitable habitats for them. It is important that fish populations do not become isolated, as this makes them more susceptible to disease and puts pressure on their survival. Unfortunately, there are often many barriers along rivers that prevent fish from being able to migrate up and down stream. Where barriers have been identified, they will be seen as a ‘pressure’ on a waterbody. Thankfully, there are many solutions now that can be put in place to aid fish passage, even over large barriers.

The flow in a river can vary greatly throughout the year as rainfall and run off can have an effect. This is a natural process. It is when flow is impacted by non-natural processes that it can cause problems. Sometimes, water can be intercepted or removed from a system; this will reduce the flow, therefore changing the habitat conditions. Some species are happy in high energy rivers. This means that when flow is reduced, these species will no longer survive. The opposite of this can occur when excess water is entering a river, for example through increased runoff. Low energy systems then become high energy and displace the species that live there.

A species that is not meant to be found in a particular area is known as an invasive species. Invasive species can be from a different habitat or a different country altogether. Most of the invasive species that we find on our rivers have come from other countries – plants that people have imported for their gardens or animals that have been released for food or by animal rights activists. Control of invasive species requires a lot of time and effort. We are fortunate that we do have a range of methods to manage most of the invasive species that cause havoc on our rivers, but there are still some which we are still struggling to control.

Many of our rivers have been heavily modified over the years as rivers have been used for a wide range of purposes. Physical modification is one of the biggest factors that causes our rivers to be unhealthy. The issues that it can cause range from reducing habitat, preventing migration of mobile species, and even have an effect on the water quality. Where structures and modifications are no longer in use or necessary, they should be removed to allow the river to regain its natural state. Unfortunately, this action is not always taken which means that many of our rivers are over straightened and contain redundant structures. It is possible to return a lot of our rivers to their natural state, through one off projects, but in other cases it is not possible as the river has been changed to protect assets or manage flooding. It is recognised that some modifications cannot be removed without having severe negative impacts both socially and economically.

This is pollution that comes from a single identifiable source. The pollution entering the river could include a whole range of pollutants. Some point source pollution is known about and licences, for example sewage treatment works. Other sources are not licensed, and therefore work needs to be done with landowners to fix the problems that are allowing the pollution to enter the river. Point source pollution is more easily controlled than diffuse pollution as it often only takes one management approach to solve the issue.