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Jean Hervé with a big African brown snapper
Jean Hervé with a big African brown snapper
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Cruise diary 2: Increasing our understanding about the living resources

Gabon is most known by its forest, but it also holds more than 900 km of coast mainly composed by virgin never ending sandy beaches, big estuaries and coastal lagoons. Its waters are also peculiar, since the Equator divides the country, two big oceanographic systems converge, the warmer Guinea current, from the north, and the Benguela current from the south. This singular feature creates two main ecosystems north and south of cape Lopez, each one holding different oceanographic characteristics and species.

In Gabon, the demersal species are exploited by the industrial and artisanal fisheries. The artisanal fishery lands about the half of the total production of fish with a mean annual production of around 25 000 tonnes, with 80 percent composed of demersal species. The annual production of the industrial fishery was in 2008, around 13 000–14 000 tonnes.

Sorting the catch

Sorting the catch

The main species caught are croakers (Pseudotolithus senegalensis and Pseudoplesiops typus) and threadfin (Galeoides decadactylus). Other important species are seabreams (Dentex spp., Pagrus spp.), Atlantic spotted grunter (Pomadasys jubelini), bobo croaker (Pseudotolithus elongatus), catfish (Arius spp.), and the soles (Cynoglossus spp.). These bottom fish are also important for artisanal fishers. The artisanal fishery is carried out with canoes and different types of gear. Traditionally, gears such as purse seine and beach seine are distinguished from the more individual gears such as gillnet, handlines, longlines and castnets.

Data collection from the artisanal fishery started in the mid-1980s and was restructured in 1994 with the introduction of new storage and processing routines when new statistical tools were installed through a FAO Technical Cooperation Program. A daily sampling program for the fishing effort gives an estimate of the number of trips for each gear type.

Occasionally big fishes get caught

Occasionally big fishes get caught. Jean Paul and Marie Louise shows two big snappers.

The sampling at the landing sites consists in recording data on the catches (weight, number of fish for each fishing operation and price at landing). This sampling is carried out three days a week, taking into account the importance of the fishing activity. All collected data are sent to the “Bureau statistique” of the Fisheries Administration where they are processed. From 1995, the data on the industrial fishery were collected by the fisheries administration officers of Gabon from the ship owners at landings using a specially designed form. In 2003, an improved form was designed to be filled by the captains of the industrial fishing vessels. Before 1995, data was transcribed on a register. Since then, data is stored in a database and exported to an Excel file. However, the number of samples collected at each landing site or on board of vessels is not available to the various FAO/CECAF working groups on the Assessment of Demersal Resources and thus no analysis of sampling intensity could be made. Neither, the length data or other biological information has been presented for these working groups

The third meeting of the FAO/CECAF Working Group on the Assessment of Demersal Resources, was held in 2011.The overall objective of the Working Group is to contribute to improved management of demersal resources in the Southern CECAF area through assessment of the state of the stocks and fisheries to ensure optimal and sustainable use of the resources for the benefit of coastal countries. In these meetings information is provided on: the fisheries, sampling intensity, biological characteristics, stock identity, trends in data (catch, effort, biological data and abundance indices), assessment, management recommendations and future research. Trends and quality of the basic data (catch, effort and length frequencies) collected by each country, has been one the main topics of discussion during the Working Group meetings. The results of the assessments show that many of the stocks analyzed are fully to overexploited, and the working group thus recommended that fishing effort should be reduced for the overexploited stocks to avoid further depletion or not increased for the other stocks. For most of the stocks assessed, the only series of stock abundance indices available were commercial catch per unit effort (CPUE) data series. Commercial CPUE series are affected by changes in fleet size and fishing strategy. Consequently changes observed in the CPUEs do not necessarily reflect the variations in stock abundance. When possible, recommendations on catch levels are also indicated for each stock. Given that most demersal fisheries in the region are multispecific, an overall reduction in fishing effort is necessary.

Jean Hervé with a big royal spiny lobster

Jean Hervé with a big royal spiny lobster

Onboard the R/V Dr. Fridtjof Nansen we are currently performing an ecosystem survey that will help to increase our understanding about the living resources of the continental shelf, species assemblages  and their  linkages with the environment. To do so, we are conducting different studies during these 14 days of survey including acoustic assessment of pelagic fisheries, stratified assessment of demersal fisheries, sea-bottom impact of bottom trawling, oceanographic measures, plankton biomass estimation and sampling, marine mammals, birds and turtle’s distribution and the exploration of the sea-mountain and canyons off Cape Lopez. All these activities will generate a great amount of data that will need to be processed and analyzed once at land

Of particular interest is the study regarding the impact of bottom trawling that will be performed in waters of the National Park of Mayumba. Situated in the extreme south of Gabon, Mayumba is the only Marine National Park of Gabon and it extends for 60 kilometers until the Congolese border. It is not only the second most important nesting site for Leatherback turtles in the world, but other turtle species also use this beach as a nesting site and in its waters can be found humpback whales during their breeding migration, rays, sharks, dolphins and a rich coastal fishery intensively exploited by uncontrolled industrial fishing until just few years ago. A Great effort have been done to stop all illegal fishing activity inside the park and nowadays is a no-take area, whereas only regulated industrial fishing activity is performed outside park.

Marie Louise with a big Gorean snapper

Marie Louise with a big Gorean snapper

During the survey onboard the R/V Dr. Fridtjof Nansen, we will assess fisheries resources  and we will collect benthos samples, both inside and outside the Marine Park with the intention of monitoring changes in the ecosystem between a recently closed fishing zone, previously exploited, and a contiguous currently trawled area. Results from this and following surveys will help us to understand how ecosystems recover after the closure of fishing activities and what effects can bring the creation of new Marine Parks on the marine biodiversity of West Africa. Preliminary results from trawl catches suggest bigger size and higher species diversity inside the park, than outside. One distinguished difference is that inside the park we got several big royal spiny lobsters (Panulirus regius).

So far we have conducted almost 50 bottom trawl stations. In many trawl hauls 20 to 40 different species have been identified. Most of these have been below 30 cm, but occasionally some big individuals have been caught. One African brown snapper (Lutjanus dentatus) was above 1 m long and weighted almost 20 kg. A Gorean snapper (Lutjanus goreensis) was close to 1 m long and 12 kg. One day we got a big Green sea turtle (Chelonia mydas) during the trawl, it seemed to be in good shape and after measuring we could release it again to the sea.

Contact

Kathrine Michalsen
454 29 971