Your first suggestion is correct. For your fitted model, the analysis of deviance (anodev) table is:
Source DF Deviance Mean Dev F
Model 3 105.93 35.31 10.6
Residual 47 156.52 3.33
Total 50 262.45
Here the total deviance is the null deviance ...
Abigail, have you tried using the rsq package available in R to compute the R-squared for your model?
Here is the R code you would need:
# fit quasipoisson model
quasips <- glm(formula = PiecesTD ~ offset(LVolumeTD) + flocation + fMonth,
family = quasipoisson, data = SA)
# compute variance-function-based R-squared