Label stacked bar chart with variable other than plotted Y

I'm working on some fish electroshocking data and looking at fish species abundance per transects in a river. Essentially, I have an abundance of different species per transect that I'm plotting in a stacked bar chart. But, what I would like to do is label the top of the bar, or underneath the x-axis tick mark with N = Total Preds for that particular transect. The abundance being plotted is the number of that particular species divided by the total number of fish (preds) that were caught at that transect. I am having trouble figuring out a way to do this since I don't want to label the plot with the actual y-value that is being plotted.

Excuse the crude code. I am newer to R and not super familiar with generating random datasets. The following is what I came up with. Obviously in my real data the abundance % per transect always adds up to 100 %, but the idea is to be able to label the graph with TotalPreds for a transect.

#random data
Transect<-c(1:20)
Habitat<-c("Sand","Gravel")
Species<-c("Smallmouth","Darter","Rock Bass","Chub")
Abund<-runif(20,0.0,100.0)
TotalPreds<-sample(1:139,20,replace=TRUE)
data<-data.frame(Transect,Habitat,Species,Abund,TotalPreds)

#Generate plot
AbundChart<-ggplot(data=data,aes(x=Transect,y=Abund,fill=Species))
AbundChart+labs(title="Shocking Fish Abundance")+theme_bw()+
scale_y_continuous("Relative Abundance (%)",expand=c(0.02,0),
  breaks=seq(0,100,by=20),labels=seq(0,100,by=20))+
scale_x_discrete("Transect",expand=c(0.03,0))+
theme(plot.title=element_text(face='bold',vjust=2,size=25))+
theme(legend.title=element_text(vjust=5,size=15))+
geom_bar(stat="identity",colour="black")+
facet_grid(~Habitat,labeller=label_both,scales="free_x")

I get this plot that I would like to label with TotalPreds as described previously.

Again my plot would have bars that reached 100% for abundance, and in my real data transects 1-10 are gravel and 11-20 are sand. Excuse my poor sample dataset.

*Update

My actual data looks like this:

Variable in this case is the fish species and value is the abundance of that species at that particular electroshocking transect. Total_Preds is repeated when the data moves to a new species, because total preds is indicative of the total preds caught at that particular transect (i.e. each transect only has 1 total preds value). Maybe the melt function wasn't the right way to analyze this, but I have like 17 fish species that were caught at different rates across these 20 transects. I guess habitat type is singular to a transect as well, with 1-10 being gravel and 11-20 being sand, and that is repeated in my dataset across fish species as well.