I have data for the population of a number of different fish, sampled over a period of about 5 years, but in a very irregular pattern. Sometimes there are months between samples, sometimes there are several samples in one month. There are also many 0 counts

How to deal with such data?

I can graph it easily enough in R, but the graphs are not particularly illuminating, because they are very bumpy.

In terms of modeling - with species modeled as a function of various things - maybe a mixed model (aka multilevel model).

Any references or ideas welcome

Peter