I'm having difficulty finding an appropriate test for my data.

The experiment is looking at the distance animals have moved from a translocation site over a 12 week period (measured weekly), where animals are divided into 3 treatments (ie. I am looking at whether the different treatments influenced the distance moved). So my dependent, repeated measures variable is 'distance', and my independent variable (between subjects factor) is 'treatment'. My within subjects factor is 'individual'. I also have gender as a factor but if it's easier to analyse without this factor then I can just run the test with only one sex.

The data is not normal (nor would I expect it to be as animals move away from their release site but then reach an asymptote after about 4 weeks) and transformations have not helped, therefore I am looking for a suitable non-parametric test. I've looked at the Friedman test but I have an unbalanced design and some missing values where animals were removed from the experiment part way through.

Any suggestions of tests that I could use would be much appreciated, thank you!