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current posts

 
Thu 9th January 2020 11:45 by Ian Mathieson
Paul. This is very boring and very unscientific but I shall try and explain how I obtain my rankings. In 2003 I started recording here. At the end of the year I selected the 20 most abundant Somerset species according to the atlas of the time. The number of each species I had caught that year became my base figure of 100%. The following year I compared the number I had recorded that year against the base figure to give me a new percentage. The minimum, if I had not recorded any, would be 0% so I fixed the maximum, if I recorded twice as many, as 200%. By doing this for all 20 species and averaging the percentages I got a new percentage. If it had been quieter than 2003 it would be less than 100% but if the year had been more productive then the percentage would be higher than 100%.
In 2003 I recorded 250 different macro species. This number was multiplied by the percentage figure and gave me a base number in that year of 25000. The following years I've done the same. In 2019 my percentage catches was 90% of the 2003 figures but I recorded 289 different species. 90 multiplied by 289 is 26010 which is 104% of the base number of 25000. Therefore 2019 has a rating of 104 and can be ranked alongside the other years.
What it doesn't take account of is the amount of trapping I am able to do or the fact that I now often operate both an MV trap and an actinic. This would be why I regularly record more species than 2003 when I only had an MV trap.
As I keep repeating it is very unscientific but I believe that anybody who has been trapping for a number of years would accept that 2004, 2005 and 2006 were better for moths than 2007,2012 and 2016.
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