Estuary Stingray

Fascinating facts about the Estuary Stingray

• A 1908 description by James Douglas Ogilby was based on a specimen caught in the Brisbane River, marking the first formal scientific record of this ray. The name fluviorum literally means “of the rivers,” highlighting its strong tie to tidal waterways. This historic link shows how long humans have noticed its presence in estuaries.
• When it slides into a mudflat at high tide, the ray can reach a disc width of up to 1.2 m (3.9 ft) and weigh as much as 6.1 kg (13 lb). Those dimensions make it one of the largest stingrays that still lives in shallow, mangrove-lined rivers, proving that size isn’t limited to open oceans.
• Males don’t reach reproductive size until they’re about 41 cm (16 in) across and seven years old, while females wait until 63 cm (25 in) and 13 years. This 22-centimetre gap is among the widest known for stingrays, reminding us that sex can shape life-history strategies dramatically.
• In Moreton Bay, the ray’s favorite snack isn’t oysters at all, it prefers soldier crabs (Mictyris longicarpus) and polychaete worms.
• Surveys have found that over 10 % of individuals in Moreton Bay bear embedded hooks or mutilated tails from recreational and commercial fishing. Those injuries signal how vulnerable a species with such specific habitat needs can be to human activity, underscoring the urgent need for better protection measures.

At a glance

About the Estuary Stingray

The estuary stingray (Hemitrygon fluviorum) glides through the mangrove-lined tidal rivers and shallow bays of southern Queensland and New South Wales, its diamond-shaped disc a muted canvas of yellow-brown to olive that fades toward the edges and deepens over the sting. At up to 93 cm (37 in) across, and possibly 1.2 m (3.9 ft) wide, the ray’s broad pectoral wings sweep over sandy-mud bottoms while a whip-like tail, twice the disc length, bears one or two serrated stingers and a low ventral fin fold. A row of enlarged thorns runs along the midline of its back, and long, narrow nostrils framed by a short, fringed skin “skirt” give it a distinctive profile. By day it lies partially buried, but at high tide it ventures onto intertidal flats, hunting chiefly crustaceans such as the soldier crab (Mictyris longicarpus) and polychaete worms, only occasionally raiding oyster beds, a reputation that belies its true diet. A surprising trait is its aplacental viviparity: embryos first draw on yolk, then switch to maternal “uterine milk,” a histotroph that sustains them until birth, producing litters each year in sheltered nursery waters of rivers like the Nerang and Macleay.

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