 Dusky dolphins are also susceptible to parasitism by certain nematode, cestode, and trematode species, mostly the genera "Nasitrema" and "Anisakis", and "Phyllobothrium delphini", "Braunina cordiformis", and "Pholeter gasterophilus".Dusky dolphins live in a fission-fusion society, with most group size increases occurring during foraging and decreases in group sizes occurring during resting and traveling.In the Golfo San José off the Valdes Peninsula, dolphins commonly switch between small traveling groups and large sociosexual groups, and encounter a variety of associates.