Cameras reveal secret lives of mangrove stingrays

Embargoed until 00:01 AEST, Wednesday, July 31, 2019

James Cook University scientists have filmed stingray activity in mangroves for the first time, revealing how different species use the underwater forests and how important the environment is for the animal’s survival.

JCU PhD candidate Shiori Kanno led the study, which placed three cameras on mangrove beds at Orpheus Island and produced more than 400 hours of video featuring more than 600 stingrays. 

She said habitat use and behavioural patterns of stingrays within mangrove areas are poorly understood and the reason why some stingrays favour them is unclear.

“We urgently need this knowledge, especially for juvenile animals that are dependent on mangroves because habitat loss may have significant consequences for population survival,” said Ms Kanno.

The research team monitored mangrove use by juvenile mangrove whiprays and cowtail stingrays. It was the first time the video technique had been applied. It revealed mangrove whiprays lived up to their name and spent a lot more time in the mangrove forests than cowtail stingrays.

“Both species visited the mangroves and mangrove-edge habitats, but their dependency on mangroves was different. While the whiprays were frequently seen feeding within the mangroves, the cowtail rays only fed on sandflats away from the mangroves,” said Ms Kanno. 

She said the movement of sharks capable of preying on juvenile stingrays was also recorded and the scientists found the predators rarely swam amongst the mangrove roots.

“We saw no sharks amongst the mangroves over summer and only four in winter. So, predator avoidance is one possible driver of why whiprays use mangroves – sharks big enough to eat them just can’t get into the root system and it offers effective protection. 

“We think the cowtails have other ways of dealing with sharks – they are larger, with a big tail and they may prefer turbid water and grouping strategies that confuse predators.” 

She said the whiprays may also get the same benefits as many other species by using the shaded mangrove areas as a refuge from hotter water.

Ms Kanno said the study demonstrates maintenance or restoration of mangrove habitats is particularly important for juvenile stingrays, since at least some species are highly dependent on the trees and adjacent habitats.

“What we’ve shown here, yet again, is the importance of mangroves to the environment through the dependence of another species on their presence and well-being. 

“There is a pressing need for mangrove forests to be conserved and treated with the utmost care as a vital part of the planet’s health,” said Ms Kanno. 

Contacts:
Shiori Kanno. (Ms Kanno works at JCU’s Townsville campus).  
M: 0448 509 714
E: [email protected]
Twitter: @ShioriSharky

Link to paper here.

Link to video here.

Ms Kanno’s research here.