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Friday, 20 May 2022 15:27

River Ant Hydro-Acoustic Surveys 2004 - 2021

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These historic reports hace been found in the EA archives and provide a sound reference point to fish assembles in the river Thurne. Hopefully the Agency can successfully complete a survey this year as a reference point..  

Notes for use of this data.  

These data represent a snapshot of the fish distribution along a river at the time of survey. Surveys capitalise on the natural distribution of fish during the hours of darkness.

Fish density.

The value shown for fish density represents the number of fish per 1000 m3 of water sampled. The colour of the circle denotes the fish density as described in the map legend. The volume of water sampled by the acoustic beam broadly depends on the channel profile and boat speed If the total volume sampled is less than 1000 m3 then the calculated fish density does not represent the actual fish density. Consequently within the data set a value of 0.0 would indicate insufficient sample volume.  Conversely a fish density value of 0.1 or higher indicates that sample volume is sufficient. In most cases insufficient sample volume is a consequence of channel width, depth and / or extensive weed growth.  

Fish size research shows that the strength of a return echo relates to the size of the object producing the return.

The equipment used during surveys is capable of recording return echoes from objects less than 3 mm in size. Objects providing return echoes of this size could include reed stems, weed fronds, fish fry and suspended debris. To avoid erroneous fish counts and density value, return echoes are filtered during post processing. Fish density value reflects this filtering and the return echo strength chosen ensures that the minimum theoretical fish size counted is 100 mm.

Jeff Compton Bsc Msc

Environment Monitoring officer (A&R) Fish

2004 Survey

2005 No Survey

2006 Survey

2007 No Survey

2008 No Survey

2009 No Survey

2010 No Survey

2011 Survey

2012  No Survey

2013 No Survey

2014 No Survey

2015 No Survey

2016 No Survey

2017 Survey (Data Corruption)

2018 Survey (Data Corruption)

2019 Survey (Undertaking after a salt surge)

2020 (No Survey due tio COVID)

2021 Survey

Click the ‘download attachment’ link below to download these reports as a PDF

East Anglia

Environment Agency,
Dragonfly House, 2 Gilders Way, Norwich, NR3 1JB

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