ZINB or ZIP for cetacean data with many zeros I am stuck in my thesis to conduct a GLM with cetacean data (count, density, effort and covariates). I have over 94% zeros in my dataset meaning I should be using a GLM with zero-inflated negative binomial/ or Poisson? Do I still need an offset within the equation?
In other journal papers regarding cetaceans I have never read about ZINB or ZIP. Would it not be very common?
Thanks for your help.
 A: Indeed having 94% of zeros sounds like a rather large proportion of zeros so your original idea of using a zero-inflated or a hurdle model is not unfounded. Any reasonable analyst would. :)
That said, as Stephan mentioned in his comments, the large proportion of zeros does not necessitate the need for a  zero-inflated or a hurdle model. I think it is very likely that you will indeed need a ZI count model (94% seems very large without any context).
I would suggest looking at some formal references for example: Hilbe's Modeling Count Data, Chapt. 7 "Problems with Zeros", is very nice and accessible. It mentions a number of approaches (e.g. Boundary likelihood ratio tests, Vuong tests, etc.) Zuur et al. Mixed Effects Models and Extensions in Ecology with R Chapt. 11 "Zero-Truncated and Zero-Inflated Models for Count Data" is also consider quite a standard reference.
Regarding the use of an offset: Using an offset is mostly relevant if it makes sense to view the response variable as part of  a rate instead of raw counts (e.g. number of infected individuals per 100K). Without knowing your exact research question one cannot answer this definitively; the interpretation of offset has been covered a couple of times in this forum, eg. see the following threads for more info:

*

*When to use an offset in a Poisson regression?

*In a Poisson model, what is the difference between using time as a covariate or an offset?
In any case, it would be good to consider using rootgrams to visualise your results. Kleiber & Zeileis (2014) Visualizing Count Data Regressions Using Rootograms is a good reference for the matter (free version here).
A final comment about the perceived lack of ZI model use in "journal papers regarding cetaceans": It might be the case that in the papers you have seen ZI/hurdle models were unnecessary, unable to be estimated correctly or were simply ignored; we don't know that. Do not hesitate using a "more sophisticated" model; ultimately it is a matter if such a model (hierarchical, spatial, zero-inflated, what have you) is relevant to our research question and if we can correctly estimate it.
