SAIAB: High-tech research to shed light on fish migrations

by Mar 30, 2011Marine & Coastal

Surprisingly little is known about marine biodiversity on our planet and even less is understood about the migration patterns of marine animals.

This is about to change as a global network of marine scientists are currently pooling research efforts to learn more about the mysterious lives of underwater creatures. A project, named the Ocean Tracking Network (OTN), will electronically tag thousands of marine animals with the aim of demystifying their migration patterns and providing answers to global problems such as disappearing fish stocks and climate change.

Bennett (PhD student) surgically implanting a transmitter into a large white steenbras

The OTN project is a Canadian initiative based at Dalhousie University in Halifax and involves scientists working in all five of the world’s oceans; the Atlantic, Pacific, Indian, Southern and Arctic. This $168-million conservation mega-project will also enhance local research abilities. In South African waters a range of fish species and possibly other marine animals like turtles will be tagged with acoustic transmitters (coded ‘pingers’) and their whereabouts will monitored by a network of receivers that will be strategically be placed around the South African coastline.

The OTN receivers will compliment existing receiver arrays owned by independent researchers that are currently working on the movement patterns of species such as white sharks, raggedtooth sharks, dusky kob, leervis (garrick) and white steenbras.

After some two year’s of negotiation by Dr Paul Cowley, Principal Aquatic Biologist at the South African Institute for Aquatic Biodiversity (SAIAB), the recent signing of a Memorandum of Agreement with OTN has tasked SAIAB, which is a National Research Facility of the National Research Foundation (NRF), with the role of facilitating this project in South African waters. SAIAB will be responsible for deploying and servicing the OTN receivers, and to provide administrative and data management services.

The first deployment of OTN receivers is scheduled for June 2011, when lines consisting of approximately 20 receivers will be deployed from the backline down to about 100m in both Algoa and Mossel Bay. The receivers, spaced approximately 800m apart, will effectively create a gate or “listening curtain” that will log tagged animals as they swim by. Later deployments will also take place in False Bay and several other strategic sites along the south east coast into KwaZulu-Natal.

The tagging procedure involves either surgically implanting a transmitter into the body cavity of an anaesthetized small fish or externally attaching it to the dorsal region of bigger fish such as white sharks.

Surgically implanted tags do not harm the fish; the results of tag-effect experiments conducted on several species (e.g. shad/elf and dusky kob) have shown no ill effects. Once tagged and released, the presence of an animal in an area will be recorded when a listening station (receiver) logs the unique identification code of the tag together with the date and time. In this way the movement patterns of individual animals, including direction and speed, can be reconstructed using the time of detection at different receivers and other listening curtains. Additional data can also be obtained when the transmitters are equipped with temperature and/or depth sensors.

The data-logging receivers need be physically retrieved in order to download the data. This is will be done every 12 months in order to secure stored data, replace receiver batteries and remove any bio-fouling on the equipment.

In addition to the movement data obtained from tagged animals, many of the study sites are also subject to oceanographic monitoring. For example, a host of temperature probes and other logging instrumentation are moored in Algoa Bay, a sentinel long-term monitoring site of the South African Environmental Observation Network (SAEON). Consequently, the prospects of gaining a better understanding of the causes for observed movement patterns and potential climate change impacts will also become a reality.

Research using high-tech acoustic telemetry methods have already provided valuable insights into the management needs of several important fishery species in South Africa. For example, a study on white stumponose conducted in Langebaan Lagoon unequivocally showed the conservation value of the West Coast National Park no-take marine protected area. Similarly, studies on how and when species such as dusky kob and spotted grunter make use of estuarine nursery habitats has highlighted the need for improved management and care of these coastal ecosystems. More recently, a study on spotted grunter revealed the possible impacts of climate change effects on estuarine associated fishes. On two occasions mass movements of fish tagged from two

Eastern Cape estuaries were observed and both coincided with extreme rough sea events. The evacuation of established home ranges or premature departure from nursery habitats caused by such extreme events, which climate change researchers predict will occur more frequently, may have severe consequences for fishery resources. Many of these projects have involved researchers from SAIAB over the last 10-15 years.

The deployment of OTN receivers will greatly improve our ‘listening’ capabilities at a national level and shed light on the long-shore movements and migrations of studied animals. In particular, significant insights will be gained on the ‘greatest shoal on earth’: it is known that the magnitude of the sardine run is influenced by environmental conditions; hence, a warming sea may have catastrophic consequences for a host of predators that depend of this annual migration. Many important fishery species (e.g. geelbek) rely of this migrating food resource to reach their spawning grounds off KwaZulu-Natal. The livelihoods of many commercial fishers will also be affected if climate change disallows these spawning events.

It is now well known that marine resources are not infinite and that human activities have impacted on the abundance of many exploited species. Research opportunities created by the OTN project will allow for the innovative collection of new information which will hopefully assist in corrective management of the world’s oceans in the future.

The recent signing of a Memorandum of Agreement with OTN has tasked the South African Institute for Aquatic Biodiversity (SAIAB) with the role of facilitating this project in South African waters. SAIAB will be responsible for deploying and servicing the OTN receivers, and to provide administrative and data management services. For more information contact Dr Paul Cowley at SAIAB (Email: Tel: 046 603 5805).