Several dozen freshwater pearl mussels have been killed by poachers in Assynt in the north west Highlands.
Assynt Field Club said the shellfish were forced open in the “off chance” one or more might contain a pearl.
The group said the poaching had happened at some point during the last two months.
Freshwater pearl mussels, which are a protected species, play a part in healthy river ecosystems and are found in some of Assynt’s rivers.
Assynt Field Club urged anyone who believed they were witnessing illegal pearl hunting to call police, and not to approach the suspected poachers.
Other incidents of poaching in recent years have included more than 100 being killed at a river south of Lochinver in the Highlands.