try this to find which files are big and see if you can delete them or copy them some where else:

du -k /var/mqm | sort -rn | more

... perhaps you should consider using the 'logrotate' utility to manage the above mentioned logs.

Find an rpm for AIX here:

http://www.oss4aix.org/download/RPMS/logrotate/

It should run under AIX 5.3 (at least it does for me), although its 'officialy' the version for AIX 5.1 (there is no other one, afaik).

wmp

... and one more:

When I wrote 'move away' in my first post, this was a bit inarticulate.
A safe way to 'move away', particularly if you can't pause your websphere application
is to first copy the file, then, if this was successful, to empty it using a '>' :

'cp -p [file] [/target/location] && > [file]'

wmp

One of the files that keeps growing is the /var/adm/wtmp file that contains login / logoff records.
You should somehow control this file. I use /usr/sbin/acct/fwtmp command (and its parameters i & c) in a script that runs monthly.
Here is what the script does:

1- Backs up & compresses wtmp file to a different location where I have enough space for archiving.
2- Converts the wtmp binary file to ASCII (text file)
3- Gets the last 500 lines in the text file into a new text file
4- Converts the new text file (500 lines - about 32K when converted to binary) again to binary (just to keep the most recent records in case I might need them)
5- Replaces the original wtmp binary file with the new smaller binary file.

If you are not familiar with fwtmp, try this to see what it displays on standard output:
/usr/sbin/acct/fwtmp < /var/adm/wtmp