It asks iNaturalist which oysters have been recorded near you in the last 20 years and sorts them by how often they turn up. Wherever you are in the world the answer is short — one to three species is typical, and eight is about the richest anywhere gets. So there is no rockpooling-or-diving question to answer here: there is simply the list.
True oysters and pearl oysters. Pen shells and horse mussels sit in the same order and are filtered out, being neither.
This matters more for oysters than for most things. The Pacific oyster, Magallana gigas, has been carried to almost every coast with a farm on it, and in many places it now outnumbers whatever was there first. Where iNaturalist knows the answer for your country, the card says so.
It only knows it relative to a place, so the app resolves your country from the pin before asking. If that fails the badge is simply absent, rather than guessed.
Worked out from GBIF's recorded depths, the same method the sea slug app uses and carrying the same caveat: depth is logged overwhelmingly by divers, so the data leans deep. The question asked is therefore whether a species is recorded shallow at all, which errs towards telling you it reaches the shore rather than hiding it. Anything too thin to call is left unknown.
This app will not tell you what is safe to eat, and should not be used that way. Shellfish concentrate biotoxins that cooking does not destroy and that nothing about the animal reveals — no smell, no taste, no appearance. Closures are issued by public health authorities and are the only thing worth trusting. Check them every time, and never gather near a sewage outfall, stormwater drain or marina.
Photographs come from iNaturalist and are shown only where the photographer has applied a Creative Commons licence. Each one is credited, and tapping any photo opens it large.
Finding a usable one takes three goes. A species' headline photo is often all rights reserved, so the app then checks the taxon's photo gallery, and if that is also restricted — or holds a single image, as happens more than you would think — it searches the observations themselves filtered by licence. A blank tile means all three came up empty, which is now rare.
Your position never leaves your device un-rounded — it is snapped to roughly 100 m before any search is sent, which makes no difference across a 50 km radius. It is not stored, and it never appears in the address bar, so nothing can pick it up from there either.
Tap anywhere — somewhere coastal works best.
Starts at 200 km, because oysters are sparse: most coasts have only one to three species, and a wider sweep simply finds more of the few there are. Narrow it if you want to know what is on your own stretch of shore.
