The Warty Oreo Dory lives to over 200 years
Durban - The three species of fish found on the trawler – 8 701.81kg of Alfonsino, 6 067kg of Orange Roughy, and 1 352kg of Warty Oreo Dory – are in danger of being exploited to the point of extinction.
Some of these fish live to more than 200 years.
University of KwaZulu-Natal marine scientists, Gan Moodley and Dr Deborah Robertson-Andersson, said that many deep ocean fish such as these were severely threatened by over-fishing and the species’ ability to recover is constrained by the long lifespans and low reproductive success.
The species do not breed every year, and some take up to 30 or 40 years to reach maturity.
Deep-sea fish grow slowly because of limited food sources and slow metabolisms.
“When you buy these fish, you could be eating something even older than your grandfather!”
Over-fishing and destructive fishing methods (bottom trawling, beam trawling and gill netting), they said, were causing profound changes in the oceans.
“Fishermen are therefore changing their target species to other less desirable species. To make them more desirable to consumers, the names are often deliberately changed, hence Patagonian Toothfish became Chilean Seabass, while the Slimehead became the Orange Roughy.”
The Roughy (Hoplostethus atlanticus) had been categorised as “vulnerable to exploitation” by international monitoring body, the Marine Conservation Society.
It was the “in” fish of the 1980s, the scientists said, with a white flesh and mild flavour.
It lives in the open ocean at a depth of between 180m and 1 809m, but prefers 400m to 900m.
“Its length at first sexual maturity is 37cm, aged between 20 and 40 years old, with a max length of 75cm and a maximum weight of 7kg. It is very slow growing and with a maximum reported age of between 125 and 156 years, and is one of the longest lived fish species known.
“The fish is marketed fresh and frozen, and consumed steamed, fried, microwaved or baked.”
The scientists said because of its longevity, the Roughy might accumulate large amounts of mercury in its tissues (0.30 to 0.86 parts per million), compared with an average mercury level of 0.086ppm for other edible fish.
“According to the Seafood Network Information Centre, regular consumption of mercury-contaminated Orange Roughy could have adverse effects on health. Compared to most edible fish, Orange Roughy are a very poor source of omega-3 fatty acids, averaging less than 3.5g per kilogram.”
The Warty Oreo Dory (Allocyttus verrucosus) is also threatened by over-fishing.
“The global fishing capacity is now more than four times the amount of harvestable fish. According to the Food and Agriculture Organisation of the United Nations, over 70 percent of the world’s fisheries are either ‘fully exploited’, ‘over exploited’ or ‘significantly depleted’.”
Moodley and Robertson-Andersson said that some species had already been fished to commercial extinction.
“In South Africa, this includes the Seventy four (Polysteganus undulosus), Brindle bass (Promicrops lanceolatus) and Potato bass (Epinephelus tukula), among others.”
The Warty Oreo is found in all oceans at depths of up to 1 800m, but usually between 800m and 1 200m.
“It reaches a length of up to 42.5cm and its length at sexual maturity is 28cm and its maximum weight is 2kg. They are very long lived species with a reported age of 140 to 210 years.
“Young Warty Oreos reside in shallow waters of the oceans, less than a kilometre in depth. They eat other fish, as well as cephalopods (octupuses, for example) and shrimp. The eggs and larvae of Warty Oreos live on or near the surface of the sea.”
The Alfonsino (Beryx splendens) lives in temperate and tropical oceans worldwide, except the eastern Pacific.
Six species occur in South African waters.
“This fish inhabits depth ranges of between 25m and 1 300m (usually from 400m to 600m). It reaches a maximum reported age of 23 years and a maximum length of 75cm and a maximum weight of around 4kg. It reaches sexual maturity at 33cm.”