I am carrying out research to look at differences in fish density and fish species richness when using two different underwater visual census methods. My data was originally count data but then typically this is changed to fish density but I have still decided to use a Poisson GLM, which I hope is right.
model1 <- glm(g_den ~ method + site + depth, poisson)
My 3 predictor variables are method, site and depth which I ordered as factors when I input them.
My response variables are grouper species richness, grouper density and the same for other fish groups. I am aware that density is not an integer and it is numerical data e.g 1.34849. I am now however getting this error:
In dpois(y, mu, log = TRUE) : non-integer x = 0.037500
I've been reading up and many people suggest using an offset, is this the most advisable thing to do?