[Editor’s note: This article was written by Laura King. Laura is an ecologist currently on an extended conservation expedition in Mauritius, a tiny island off the coast of Eastern Africa. Follow her adventures on Twitter @LaurasWildlife]
Bait, lures, spinners, spoons, flies, pellets….we spend a lot of time thinking about what to use. But how often do we think about our bait affecting the ecology of a lake or stream? We do try to not dump live bait and to not use certain introduced species as bait as we know this could harm our favourite spots.
However, a recent study demonstrated interesting impacts to rivers in the UK from pellets. Pellets (in bait balls) are popular for cyprinid fishing (carp and barbel), and are very high in calories. Anglers often use more than 1 kg of pellets per day in these rivers, so pellets are essentially a superfood that would be regularly available to fish there.
Whenever we as humans introduce something new to any ecosystem, we never know exactly how the food web might shift. A new study looked at the diet of the European Barbel (or Common Barbel, Barbus barbus) in four rivers to see how much of its diet was made up of pellets, and if there were any other impacts from having so much extra food around.
To do their study, they went fishing (of course) and took 3-5 scales off each Barbel. They also kick-sampled in the rivers for invertebrates and small fish (important parts of the Barbel’s natural diet) and then used stable isotope analysis. Stable isotopes can identify these different prey items, and so the researchers could find out just what the Barbel had been eating for the last few months from just their scales.
They showed that the Barbel from the four different rivers ate completely different amounts of pellets. For some Barbel, the pellets made up only 9% of their diet, but in three of the four rivers, the proportion of pellets eaten by an individual Barbel could be in the 70% range, as high as 79% pellets! So, amazingly, some (but not all) Barbel are pretty much avoiding their ‘natural’ diet of invertebrates and small fish to eat delicious pellets instead. This probably shows us why anglers use pellets in the fist place!
What are the consequences of this much added ‘food’ in the system introduced by anglers? Well, the authors cite a different paper that showed that the thousands of tonnes of bait ended up changing water chemistry because it added so many nutrients to rivers in Germany. They don’t know what the effects are in these UK rivers, but that would be another even more interesting question that would be nice to see answered in the future. Interestingly, it also shows us how adaptable Barbel can be between different rivers because many end up shifting to pellets for their main food source. Given lots of easy and nutritious extra food (that can’t even get away from them!), Barbel seriously take advantage of their all-you-can-eat bait buffet.
Citation: T Basic et al. 2015. Angling baits and invasive crayfish as important trophic subsidies for a large cyprinid fish. Aquatic Sciences 77: 153-160. Find the paper here