Mozambique · Since 2010

Mozambique Acoustic Telemetry Network

Underwater listening stations along 400 kilometers of Mozambique's coast follow tagged sharks and rays as they move, and show which places matter most for their protection.

400 kmof Mozambican coast covered, from Závora to Bazaruto

2,300 kmof coast monitored together with South Africa's network

30%of tracked reef manta rays crossed the border with South Africa

82%of Bazaruto bull sharks' core habitat lies inside protected areas

Many of the sharks and rays we study travel far beyond a single reef. MMF’s acoustic tracking work on Mozambique’s Inhambane coast began in 2010, and the network of underwater listening stations has grown since.

The receivers stretch from Závora in the south to the northern end of Bazaruto Island, and are most concentrated in and around the Bazaruto Archipelago National Park and the neighboring Santuário Bravio de Vilanculos. The network is shared by MMF, South Africa’s Oceanographic Research Institute, and Oceans Without Borders, and we share tracking data with South Africa’s Acoustic Tracking Array Platform, so an animal tagged in one country can be detected in the other.

Reef manta rays, bull sharks, bottlenose wedgefish, bowmouth guitarfish, smalleye stingrays, and leopard sharks all carry acoustic tags that the network can hear, as do tiger, blacktip, and gray reef sharks tagged by our partners.

Dr. Nakia Cullain fits an acoustic tag to a reef manta ray

What we've done

Tracked 42 acoustic tags on reef manta rays between 2010 and 2014: they visit cleaning stations mainly by day, a quarter moved between Tofo and Závora, and the national park covered only about a quarter of their estimated range.
Followed 48 reef manta rays tagged between 2022 and 2024, in a study led by MMF’s Dr. Nakia Cullain: about 30% crossed into South Africa, and Závora proved the key corridor along the coast.
Contributed to a study led by ORI’s Dr. Ryan Daly showing that most tracked bull, blacktip, and tiger sharks move back and forth between South Africa and Mozambique.
Showed, in a study led by MMF’s Dr. Stephanie Venables, that adult bull sharks use the Bazaruto Seascape year-round, with about 82% of their core habitat inside protected areas.

What's next

Publish the tracking results for bottlenose wedgefish, bowmouth guitarfish, smalleye stingrays, and leopard sharks; they will be added here once they are out.
Contribute bowmouth guitarfish data to Shark Ray 360, a collaborative study involving Shedd Aquarium and Georgia Aquarium.
Replace aging receivers and keep up the yearly battery changes and data downloads.

Keep the receivers listening

Some receivers are more than ten years old and starting to fail. Your gift helps replace them and keeps the tracking studies running.

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How the network works

Projects that use the network

The receivers serve several of our species and site projects in Mozambique, each with its own page:

Mozambique manta and devil rays
African manta rays, shared with South Africa
Rhino rays: bottlenose wedgefish and bowmouth guitarfish
Smalleye stingrays
Leopard sharks
Bull sharks (completed)
Bazaruto Seascape marine conservation
Závora marine conservation

How acoustic tracking works

Each acoustic tag sends out an underwater sound signal that identifies the animal carrying it. Receivers anchored on the seabed log the signal, with the date and time, when a tagged animal swims within range, usually a few hundred meters depending on conditions. When we retrieve a receiver and download its data, we can see which tagged animals visited that site and estimate how long they stayed nearby. The receivers record visits to monitored sites; they do not follow animals continuously.

Two MMF researchers on a boat hold receivers covered in marine growth after recovering them from the reef

Manta rays across borders

In the first study, MMF’s Dr. Stephanie Venables and colleagues found that reef manta rays rely on a few cleaning-station reefs, mostly outside protected areas, and recommended new protection at Tofo and Závora. A decade later, a team led by MMF’s Dr. Nakia Cullain followed manta rays tagged at Závora and in South Africa’s iSimangaliso Wetland Park. Of the 46 rays with enough data, 14 crossed the border; the longest recorded one-way trip was about 950 kilometers (590 miles), and one ray made a round trip of about 1,100 kilometers (680 miles) in just over a month. Of the rays detected in Mozambique, 90% were recorded outside marine protected areas.

Infographic of the first reef manta ray tracking study in Mozambique, showing receiver sites from Závora to the Bazaruto Archipelago

Sharks on the move

A study led by Dr. Ryan Daly of ORI, with MMF’s Dr. Stephanie Venables, tracked bull, blacktip, tiger, and gray reef sharks between 2018 and 2021. Of the 74 sharks with enough data, 63% of the bull sharks, 87% of the blacktips, and 94% of the tiger sharks crossed between South Africa and Mozambique, some migrating between 980 and 2,256 kilometers (610 and 1,400 miles). At Bazaruto, one female bull shark crossed the Mozambique Channel to Madagascar and back, a round trip of at least 1,730 kilometers (1,070 miles). Another bull shark detected at Bazaruto later rounded southern Africa and was caught off Nigeria, more than 7,290 kilometers (4,530 miles) away, the longest journey recorded for the species. (Photo: Uli Kunz.)

A diver films a tagged bull shark in the Bazaruto Seascape. Photo: Uli Kunz

Keeping the receivers listening

The team changes each receiver’s battery and downloads its data about once a year, often on dives of 18 to 35 meters (60 to 115 feet). Marine growth builds up on the equipment, and storms and floods have damaged some receivers. Some are more than ten years old and starting to fail, so replacing them is a priority. MMF’s Dr. Nakia Cullain and Dr. Clare Prebble jointly lead this project: Nakia oversees the network and its tracking data, and Clare manages receiver maintenance in Bazaruto Archipelago National Park and at San Sebastián.