Fisheries survey with a boom
The ‘boom boat’, otherwise known as the ‘Thames Trout’ has a generator on board which produces an electrical current. This is passed through anodes hanging off the bow via a control box, putting a mild electrical current through the water. This current has the effect of attracting and momentarily stunning the fish allowing them to be netted on each side of the boat.
There are several reasons why sampling takes place at night. The fish are more active and higher up in the water at that time which is important since the electric field from the ‘boom boat’ is only effective to a depth of around 6 ft or so. There’s also less boat traffic around at night so the survey boat can meander around areas where fish congregate without risk of collision with other vessels, or people who have a habit of swimming in the Thames during good weather!
Once caught, the fish are then placed in the aerated tank on board the boat before being measured, a scale sample taken and returned to the water as soon as possible. Using this method gives the number and weight of fish per caught per minute.
Matt Drew, Fisheries Officer in the West Thames Area said, ‘working at night does have the disadvantage of not being able to see very shallow areas so easily – we have had some interesting occasions in weir pools where we frequently run aground on gravel bars’.
The surveys are carried out to assess trends in fish populations over an annual and 6 yearly cycle. The results also help determine the status of waterbodies for WFD purposes. This year’s survey in the West Thames area revealed a healthy population of fish including Barbel, Roach, Dace, and Chub.