Armour-plated, four metres long, and older than the dinosaurs.

Sturgeon are living fossils. Their skeleton is largely cartilage, their tail is shark-like with a longer upper lobe, and their mouth sits underneath the snout as a tube that can extend downward to vacuum food off the bottom.

Four sensitive barbels hang in front of that mouth, feeling and tasting the sediment for worms, shrimp, and small molluscs before the fish commits to a bite.

The Minas Basin's enormous mudflats are a buffet. Every tide reworks the sediment and exposes invertebrates, and satellite-tagged sturgeon from rivers as far away as the United States have been tracked travelling here to feed in summer before returning south.

That makes the bay internationally important for a species listed as threatened across much of its range.

Sturgeon take a long time to mature — often 15 years or more — and females may spawn only every few years. Populations crushed by 19th-century caviar fishing therefore rebuild very slowly, and bycatch in other fisheries remains a serious pressure.