Thank you for the clues... Its very strange for me the way that this categorical variable is shown in the analysis and the fact that the null model is always selected. I tried to add the categories as dummy variables but the model gets too heavy, it doesn't even run.
dput(bonaci)
structure(list(nCPUE = c(0.06, -0.48, 0.97, 1.03, 0.22,
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