Where do fish go? Lessons from the De Hoop Marine Protected Area
Guest author: Dr John Filmalter
Researchers from the South African Institute for Aquatic Biodiversity (SAIAB) have been studying the movement patterns of several of South Africa’s iconic fishery species for the past 15 years. This research has taken Dr Paul Cowley and his team on a journey that started out in a single Eastern Cape estuary tracking the movements of a spotted grunter to the development of an array of automated tracking stations (known as the Acoustic Tracking Array Platform) that spans most of the South African coast. Currently this network monitors the movement of over 1000 tagged sharks, rays and fishes. This tracking system uses acoustic technology, where animals are tagged with acoustic transmitters, each with a unique ID code, that ping on a regular basis and are recorded as they move past receiver stations moored on the sea floor.
A recent development in this tracking work is the expansion of the receiver array into the De Hoop Marine Protected Area (MPA). Late in 2018, with the help of CapeNature staff, six acoustic receivers were deployed inside the MPA.
These receivers will not only increase the power of the existing national network but also form a critical part of a local study on the fishes of the nearby Breede Estuary. Over the past three years Dr JD Filmalter, a SAIAB postdoc researcher, has been investigating the movement behaviour of fishes in the Breede, with emphasis on large adult dusky kob (Argyrosomus japonicus) for which the estuary is famous. During this study more than 60 fishes of various species have been tagged. This work forms part of a larger national project in collaboration with SAIAB and the Norwegian Institute for Nature Research examining the coastal movements and connectivity of adult populations of species commonly found in estuaries.
By expanding this work into the De Hoop MPA, and tagging fishes within its boundaries, this project is examining how fishes move between the MPA and the adjacent Breede Estuary and investigating exchange between the two areas. Ultimately this work will create a better understanding of the role that the De Hoop MPA plays in contributing to local fish stocks.
To date 45 fishes and rays have been fitted with acoustic tags from the beaches of De Hoop. These include 24 dusky kob, 13 white steenbras, 5 blue stingrays and 3 duckbill rays. The tags used in this study will transmit for approximately eight years, so the movements of tagged animals will be monitored for many years to come.
The receivers monitoring their movements are downloaded twice a year and are due for their first download in the next few weeks, which will shed the first light on the movements of the tagged animals. This work not only provides important information on how these fishes use their environment but also provides critical insight into how we can improve conservation and management strategies to ensure their survival for generations to come.
Acknowledgements: This work is not possible without the support many organisations that assist with maintaining the nationwide ATAP receiver network. The National Research Foundation and the Ocean Tracking Network are thanked for hardware (receivers) support and funding for running expenses are provided by the Save Our Seas Foundation.