• Amy Webber

World Rivers Day: how do rivers and stingrays go together?

Rivers are one of the foundational ecosystems that all life on Planet Earth relies on, so what could be more appropriate than celebrating World Rivers Day this upcoming Sunday. Each river’s journey is unique, but they all have a source, where wonderfully fresh water can be supplied from above as rainfall, from below as groundwater, or even from besides as the melt of snow or glaciers. This water can meander or rush downstream, pulled by gravity, where it will either join other rivers, lakes or dams, or eventually meet the ocean. When a river meets an ocean, a unique environment is created, called an estuary. These are constantly changing ecosystems, becoming more fresh with increased rains or more salty with incoming ocean tides. As no two rivers are alike, no two estuaries are the same, and they are diverse and exceptional ecosystems that support a plethora of animals, including sharks and rays!


One estuary we’ll explore in a bit more detail is the Keurbooms Estuary, part of the coastal town of Plettenberg Bay, where the 85km long Keurbooms River meets the Indian Ocean. It’s an ecosystem that holds importance to the local community; subsistence fishermen, recreational boaters, paddle boarders and daily walkers along the banks are a common site all year round. This estuary is being studied by ELMO’s very own project manager, Dr Chantel Elston, who specialises in stingray research.

The gorgeous Keurbooms Estuary, Plettenberg Bay, where the river meets the sea. Photo by Chantel Elston.


In August, ELMO intern Amy Webber joined Dr Elston to assist with fieldwork on the Keurbooms Estuary. This involved deploying a Baited Remote Underwater Video System (BRUVS) at various sites in the estuary. A BRUVS is a cheap and accessible tool to survey the underwater world that is non-intrusive to the animals and environment. It consists of a weighted rig that is placed on the ocean floor, with a bait bag on one end and a GoPro on the other, to see who calls the estuary home. This project aims to monitor the presence and abundance of fish, sharks and stingrays in the estuary over 2 years, and to determine whether physical conditions like temperature or salinity influences which species occur in the estuary. Dr Chantel Elston deploying the BRUVS in the

Keurbooms Estuary. Photo by Carmen Claire

van der Westhuizen.


Dr Elston has been collecting underwater footage of the Keurbooms Estuary almost weekly since April 2021, building over 172 hours of footage! They have seen that all kinds of animals call the estuary home, including over 25 species of fish, stingrays, sharks, octopus and cuttlefish. One of the most interesting findings has been the continual presence of the endangered eagle ray (Myliobatis aquila), and this is the first estuary in South Africa in which the the presence of stingrays has been recorded in every single month of the year. Many of the individuals sighted have been juveniles, suggesting the estuary provides a nursery habitat for rays to rest and feed in during this vulnerable age.

Still taken from the underwater video footage: a) common eagle ray, b) atlantic horse-mackerel, c) a cuttlefish in amongst strepies and a cape stumpnose, d) a smoothhound shark in amongst blacktail


Identifying the locations where these endangered species aggregate, breed and feed is vital to conservation efforts when used in policy making decisions. At the end of this research project, the data collected by Dr Elston will be shared with the local municipality who manage the relevant section of the estuary. Sharing this invaluable data creates an opportunity for the incorporation of the project’s findings into the municipality's Estuary Management Plan, allowing the environment to be maintained at the healthy state it currently is, further supporting the population of stingrays and ensuring their continued protection.


 

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