Yesterday, while snorkeling at the Port Noarlunga reef in near perfect conditions I was fortunate enough to encounter a South Australian endemic gastropod mollusk, the Black Cowry (Zoila friendii thersites). The animal I sighted was perched quite conspicuously on a large yellow/orange sponge in about three metres of water. I later discovered that a photograph taken by Greg Adams of one in the midst of laying eggs (also taken at Port Noarlunga) was published in October 2014 by ABC news.
I was first made aware of the Black Cowry by a friend who collects shells for a hobby several years ago. Evidently, the shells of the Black Cowry are quite sought after in collectors’ circles, though collectors can be quite fussy about the pattern on the shells. Rare, entirely black specimens are the most sought after.
More recently, I heard accounts of Black Cowries being sighted with ‘X’ marks intentionally carved into their shells. You can read a little on the topic in this DiveOz forum thread. While at first glance this may seem like an act of vandalism, the intentions of the divers responsible for these marks are generally good. A damaged shell quickly loses its commercial/collection value, and thus the likely survival of a marked individual (at least at the hands of human collectors) is improved.
When I looked for more background information on the species, I was pleased to find images and information confirming my specimen’s identification in Karen Gowlett-Holmes’s A Field Guide to the Marine Invertebrates of South Australia (published by Notomares in 2008). The book is a must-have for anyone interested in our wonderful marine invertebrate biodiversity here in SA.
Collecting and Conservation
Barry Wilson’s A Handbook to Australian Seashells on Seashores East to West and North to South (2002) does not feature Zoila friendii thersites specifically, but does include some general information on conservation of gastropod mollusks including Zoila. It warns that some species may be locally vulnerable due to collection and inshore and near-shore habitat loss and modification due to pollution. It states:
“Local populations… of Zoila cowries of Western and Southern Australia, have disappeared, possibly due to collecting… Another conservation issue is chronic pollution of inshore bays and estuaries that may affect whole communities of plants and animals.”
Wilson describes the conservation risks as the disruption to local ecosystems by the removal of certain species and the loss of genetic strains rather than species extinction itself. In the case of the Black Cowry, the species has the advantage of inhabiting a depth range from the shallows down to 160 metres. Wilson recommends against the collection of any specimens containing live animals, and also warns that live gastropod mollusks can be difficult to remove from their shells and release a nasty odor while decomposing.
Protection for a South Australian endemic?
There is no species-specific protection of Black Cowry in place in South Australia. The state’s fisheries regulator, PIRSA, allows recreational collection to a bag limit of one individual per day. There is no size limit, which could be a matter of some concern given the species longevity (in excess of 12 years). The younger animals’ shells match the colour of their preferred food sponge (Mycale sp.) with the dark mottled pattern emerging as they mature and their diet diversifies.
Commercial collection permits may also currently exist, though there is no current listing of these on PIRSA’s website. In 2002-2003 there was a single license holder for commercial specimen shell collection in South Australia, and in that year 61 shells were taken (including some Black Cowry). Recreational collection quantities can only be guessed at.
Gowlett-Holmes’ book A Field Guide to the Marine Invertebrates of South Australia refers to a ‘closed season’ on the collection of the species, but this protection may have lapsed. There appears to be no mention of it on PIRSA’s website as of January 2015.
The Black Cowry receives defacto protection through spatial ‘no take’ zones when it occurs within South Australia’s long-standing network of aquatic reserves (which have been in place since the 1970s) and more recent state Marine Park sanctuary zones (enacted in 2014). For the time being, provided that visitors and locals honour ‘no take’ zones and play by the rules, the Black Cowry can be seen by keen-eyed snorkelers and divers at a number of locations around South Australia.