So, what do barbel eat?

DIET STUDY on behalf of the Barbel Society

I thought my readers could find this interesting from the latest Barbel Society Newsletter.








Are angler baits and invasive crayfish important components of barbel diet in English rivers? 

The research project into barbel diet that we have supported is almost ready to be published, and is being peer-reviewed at present. Here is a summary of conclusions, which make really interesting reading!
Benthic macro-invertebrates are basically insect life, like shrimps, fly larvae and isotopes are forms of carbon and nitrogen that can be detected in the scales after being eaten as part of the diet, a dietary fingerprint of sorts.
We expect to support further as part of the two PhD projects we are also supporting both financially and logistically by providing funding. access to fisheries, and barbel scales we are collecting.
(Study completed at Queen Mary University of London and Bournemouth University.) 

The aim of the study was to assess how anglers baits - primarily fishmeal - based pellets - and invasive signal crayfish influence the diet composition of barbel in English rivers. Previous studies have suggested that barbel whilst being omnivorous mainly feed on benthic macro-invertebrates with small fish sometimes taken.
It was completed on four rivers the Rivers Kennet and Lee, where signal crayfish were present and the Rivers Teme and Hampshire Avon. where it they are largely absent! (or at least in very low abundance) .. Fieldwork was completed in summer 2013, when samples of macro-invertebrates and crayfiish were collected from each river (as appropriate) along with scales from angler - caught barbel.
To assess diet composition of barbel stomach, contents analysis was not used. This was because the method tends to be destructive  to the fish and can require large sample sizes in order for patterns to emerge. instead  a method known as stable isotope analysts was used. This uses material such as fish muscle, fin clips and/ or scales with  mass spectrometry to determine their ratios
of 12C:13C and 14N:15N. Allied with the same data from their likely food resources (i.e. macro-invertebrates, fishmeal pellets, small fish, crayfish)  then statistical models can predict the likely diet composition of the barbel with associated levels of confidence, on the basis of the differences in the isotopic values between the species. It’s an increasing ly common method used in ecology.
All the barbel analysed were  42 to 80 cm in length. i.e. no small barbel were used. In general fishmeal pellets generally made a large contribution to their diet (up to 59 % in each river!. In the Kennet and Lee, crayfish were also an important resource (up to 30%
of population diet). Importantly, the proportion of diet derived from macro-invertebrates (excluding crayfish) was substantially lower. Further modelling revealed considerable variability in barbel diet within  each river  In the Avon and Teme, where there were no crayfish, up to 79% of barbel diet 'was based on pellets. In the Kennet and Lee. where crayfish are present they effectively replaced and so reduced the contribution of pellets to individual fish diet.
In summary, the evidence from the stable isotope analyses revealed that from three of the four rivers (Teme Kennet, Avon) the barbel were heavily reliant (50%) upon angler-introduced baits, with the River Lee showing that invasive crayfish can also be an important dietary component.


Dr Robert Britton