Wednesday, October 10, 2018

A brand new method to infer stream fish abundance
Interview with Prof. Taal Levi
Prof. Taal Levi is an Assistant Professor at Oregon State University and has one of the most diverse research profiles that we’ve ever seen. His studies range from disease ecology to seed dispersal across all sorts of environments, from the Amazon Forest to Alaska. His main peculiarity is perhaps the use of empirical data to address applied issues, such as wildlife overexploitation, overfishing, climate change and anthropogenic impacts in general.
Now, one of his projects is focusing on estimating stream fish abundance using quantification of environmental DNA. Environmental DNA (or eDNA) is the technique of detecting DNA found in the environment, like water, soil or even from stomach contents, instead of trying to extract it directly from an individual.
Here he talks about this interesting and important project (we know how important it is to have reliable fish abundance measures for fishery management!):

FEME: How does this method work exactly?
Taal Levi: Detection of environmental DNA using real-time qPCR or digital PCR is already being used to identify species occurrence. But now we are testing its effectiveness to infer species abundance.
Firstly, it is necessary to design species-specific primers – so, you have to decide a species focus. We are mostly using mitochondrial markers, such as COI (cytochrome oxidase I). Then, you have to collect some water samples and amplify all the DNA of the target fish you find there. Finally, you make a relation between the concentration of DNA from your target and the species abundance.

FEME: What have you found so far?
Taal Levi: We already tested this method for two salmon species and for Eulachon (a smelt) in the state of Oregon. All of them are very economically and culturally important. Actually, the Eulachon is so important for the people in that region that the Oregon’s state name was given because of how the indigenous called that fish, Ourigan. For these three species the method seems very effective.

FEME: Is it possible to test its efficacy? How?
Taal Levi: We are testing it using different forms of counts. For the salmon species, we counted the number of individuals entering the streams every day for two years. For the Eulachon, we used a different approach, a mark-recapture abundance estimative.

FEME: What are the advantages of using this methodology?
Taal Levi: Several! One is the possibility of sampling more areas very fast, because the only thing you need to do is collect water. The other is to be able to work with endangered species - usually, doing research with endangered species is very complex, and this method is very cost-effective.

FEME: Is there any disadvantage?
Taal Levi: The eDNA is very local and time specific, so you can only infer abundance from a small area and for the last 1 or 2 days.

FEME: Do you think that this technique can be applied in Brazilian streams?
Taal Levi: Definitely yes, you will only have some more trouble to design the markers. With that being done, it is totally posible.

If you are interested in learning more about prof. Levi and/or the methods he’s been developing and applying, check his website and his last publication on eDNA.