Emily Dennis, Calliste Fagard-Jenkin and Byron Morgan have created an R package for fitting the generalized abundance index to seasonal count data. The work has been published in Ecology and Evolution in the paper “rGAI: An R package for fitting the generalized abundance index to seasonal count data”.
The paper can be found at: https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.9200
The R package is available at: https://github.com/calliste-fagard-jenkin/rGAI