the hut that is Animal Welfare Foundation by Chesterfield's? very legitimate..do good work
also here is the link to the only local shelter on the island on the French side.It is a no kill shelter.
you can donate online or go visit the shelter and donate.
http://www.ilovemyislanddog.org/home
they do such good work and can use any and all donations.
there are other organizations also on the island that try to alleviate the problem