Characterization of the benthic zone: towards the protection of zones of biological interest in the marine and coastal ecosystem of Cameroon
Thanks to the characterization of the benthic zone on the north coast, it is now possible to know the distribution of the different types of benthic seabeds that make up the north Cameroonian coast.
Coastal areas are the underwater continuation of continents and occupy only 10\\% of the oceans, but they contain around 90\\% of all marine species. In addition, coastal areas are the most nutrient rich parts of the oceans. The coast of Cameroon is no exception to these statistics with an abundant marine life (crustaceans, molluscs, bony fish, elasmobranchs, cetaceans, sea turtles,...) that the AMMCO fishermen's network has been recording since 2017. In addition, the Cameroonian coast is irrigated by several rivers that enrich its environment with nutrients. Animal and plant life abounds there and generates great economic activity. According to a study carried out on the legislation and regulations for the inspection of fishery products in Cameroon, the fishing sector generates a national revenue of 119.4 billion FCFA.
However, there is very little knowledge available on the habitat, distribution and abundance of key species such as cetaceans, elasmobranchs, sea turtles and sirenians, whose conservation plays a role in maintaining balance through the species approach. On the other hand, AMMCO is recording more and more cases of intentional or accidental captures of these threatened species (11 species of elasmobranch threatened with extinction), as well as their strandings at sea and on the beach (38 sea turtles and 8 cetaceans stranded in 5 years). This is partly due to the poor application of the laws, resulting in a weak spatial management of the marine environment of the Cameroonian coast, through the non-existent materialization of fishing and non-fishing zones. If nothing is done, the population of key species could continue to decline at the risk of causing a trophic cascade.
It is in this context that AMMCO initiated a pilot project on the north Cameroonian coast, located between the Mungo River and the Rio Del Rey, to characterize the benthic zone in order to identify the zones of biological interest for a future protection of sensitive habitats and feeding areas which directly and indirectly influence the distribution of these emblematic species and fisheries in general.
The characterization of the benthic zone is now simpler, thanks to the hydro-acoustic method. Using a rowboat equipped with an outboard motor, all that was needed was to attach the side scanning transducer to a metal rod below the boat, 50 cm from the propeller. The transducer is connected to the Lawrance HDS9 GEN3 device, equipped with a monitor that helps assess the type of substrate that the boat has traversed (sandy bottom, rocky, reef or grass). In 10 trips at sea, we scanned over 100 km of coastline, 61 transects each one km long, from Limbe to Bamusso with a stop in Idenau. During the benthic characterization, the side scanning transducer was submerged in water and the rowboat was traveling at 7 km/h, to improve the reading of the sound waves by the monitor.
With these sea trips completed, it emerges that there are 4 types of habitats on the transects that we visited, namely rocky, coral, sandy or grassy (see map below). In addition, the two segments of coast that we traveled, including Limbe-Idenau and Idenau-Bamusso, have different characteristics in terms of the structure of benthic habitats. From Idenau to Bamusso, we identified a benthic zone of only sandy bottom. On the other hand, between Limbe-Idenau, all the four identified habitat types are present.
This activity gave an idea of the distribution of the types of substrate found on this part of the Cameroonian coast. Carrying out benthic characterization is a significant step towards the protection of aquatic megafauna. It makes it possible to identify and map the types of habitats that constitute the seabed of the northern coast of Cameroon. For example, we can find out where the feeding sites of sea turtles are, or even identify the breeding areas of certain fish. The habitats sheltering the most sensitive species will become areas where the use of trawlers or passive fishing gear will be prohibited. AMMCO aims to scan a larger area in the years to establish a complete mapping of the benthic zone of the north Cameroonian coast with the goal to build up enough arguments to protect those zones.