[R] plotting magnitude

[dkowalske at umassd.edu]

I am plotting fishing vessel positions and want these points to be
relative in size to the catch at that point.  Is this possible? I am just
begining to use R and my search of the help section didnt help in this
area.  Heres what Im using so far

xyplot(data$latdeg~data$londeg |vessek , groups=vessek,
xlim=rev(range(69:77)),ylim=(range(35:42)), data=data,
	main=list ("Mackerel catches", cex=1.0),
		ylab="latitude", notch=T, varwidth=T,
		xlab="longitude", cex.axis=0.5,)
any info would be appreciated