Elasmobranch Census

Project Overview.

Globally, a quarter of all shark and ray species are considered threatened with extinction by overfishing. Moreover, a recent worldwide study co-authored by MMF scientists surveyed 371 reefs across 58 countries to assess shark abundance. Sharks were not observed on almost 20% of these reefs, indicating a widespread decline. We are now using similar techniques for detailed surveys of the Mozambique coast.

Shark & Ray Research in Mozambique

The Inhambane Province is recognized as an area of outstanding shark and ray diversity, supporting numerous species of ecologically important elasmobranchs, largely as a result of MMFs long-running research programs in the region. MMF scientists have collected over a decade of elasmobranch sightings data during survey dives (up to 20 years in some regions). These data have enabled estimates of abundance and trends over time, and identified a number of key aggregation sites and important habitats for manta rays and whale sharks. At the same time, our researchers were collecting abundance data on other shark and ray species encountered on these survey dives. 

Aims of the Mozambican Elasmobranch Census

We are now collating and adding to this dataset to create detailed census information to identify and document where certain species can be found, and how many of them inhabit particular areas at certain times, particularly for endangered and data-deficient species. Unfortunately, many of these species are still caught in artisanal and commercial fisheries throughout the province, particularly as bycatch in non-selective fishing methods such as gill-nets. This poses a primary threat to elasmobranch populations in southern Mozambique, and to the overall health of regional marine ecosystems.

How this Helps Shark & Ray Conservation

Effective management and protection require baseline data on species diversity and abundance, along with the identification of critical habitats and aggregation sites. However, for mobile, rare or elusive species this information can be difficult and time-consuming to collect through diver surveys alone. Therefore, MMF scientists are developing and integrating emerging and innovative research techniques to rapidly gather much-needed census information for sharks and rays throughout the Inhambane Province. This includes the use of baited remote underwater video (BRUV) set-ups, remote cameras, and environmental DNA (eDNA) in addition to in-water and aerial surveys. A particular focus area is the Bazaruto Seascape.

Research Techniques.

In addition to continuing our long-term diver surveys, we are expanding our use of remote monitoring techniques on reefs in the Inhambane Province.

Data from these combined research methods allow us to establish an understanding of the abundance and diversity of elasmobranch species throughout the province. We utilize a multi-pronged research strategy, including the use of:

• Baited remote underwater video (BRUV) cameras. BRUVs are unmanned drop cameras that use bait to attract predatory species, which can then be identified and quantified during video analysis.

• Remote ‘camera traps’. These un-baited cameras can be placed on the seabed or reef by divers, left to record for ~2 hours, and collected. This allows for species counts and the observation of animal behavior in the absence of divers. 

• Environmental DNA (eDNA). eDNA techniques enable the detection of species through tiny molecules of DNA that are present in the water column in the form of waste products, skin cells, or mucus of marine organisms. This is an emerging and promising technique that can detect multiple species without direct observation.

Employing multiple complementary techniques allows our researchers to compare and contrast techniques, effectively fact-checking our own data to ensure we are obtaining the most accurate information possible.