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The Vessel in Port Gentil, Gabon
The Vessel in Port Gentil, Gabon
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Cruise diary: Recruitment studies on sardinella in the coastal waters of Gabon, Congo and northern Angola

RV Dr. Fridtjof Nansen left port from Port Gentil in Gabon on the evening of the 24th of May, heading south to Congo and Angola for a 25 day cruise along the coast of these three countries. The cruise ends in Luanda, Angola.

The scope of the cruise is to identify the distribution area of eggs and larvae from the pelagic species Sardinella (Sardinella maderensis and Sardinella aurita) in order to understand the spawning behaviour of the fish and the retention mechanisms for their eggs and larvae. In addition to collecting salinity, temperature and oxygen data, plankton samples are collected at the stations and multinets are used to catch fish eggs and larvae. Acoustic analyses are carried out throughout the survey to map the distribution of the adult fish and features that might explain distribution of eggs and larvae. Trawling is made on acoustic registrations to identify the species and to observe the gonad stages of the adult fish.

Sorting fish after trawling

Sorting fish after trawling

Gabon, Congo and Angola share the stock of sardinella, which is among the most important pelagic recourses in South-West Africa, with Angola being the primary industrial utilizer between the three countries. In Congo and Gabon, this fish is mostly caught by the artisanal fisheries.

Searching for fish larvae

Searching for fish larvae

Even though the habitats of adult sardinella are well known, the spawning mechanisms and the retention and distribution of eggs and larvae are yet to be thoroughly investigated. This knowledge is important in management terms, not least due to the heavy activity by the petroleum industry in the region and consequences of possible pollutant spills.

Taking chlorophyll samples

Taking chlorophyll samples

The first couple of days on the cruise were spent mainly with training of the local scientists. On this cruise, we have four Congolese, three from Gabon and two Angolans on board the vessel. Most have been on board Dr. Fridtjof Nansen prior to this cruise, while some have their first journey with the boat. Most of the local scientists have extensive experience in working with fish, but less so with plankton analyses. Nevertheless, the two teams quickly learned the drill, and have been working impressively efficient from just a few days after we left port. The atmosphere is great and despite some language challenges, all on board are communicating fine with an improvised combination of English, French and Portuguese.

Cruise leader and local scientist looking for sardinella eggs in the microscope

Cruise leader and local scientist looking for sardinella eggs in the microscope

After some days with little action in the microscopes, we entered an area with large abundance of both eggs and larvae as we were getting closer to the border between Gabon and Congo. It is known that juvenile sardinella is found off the northern Gabonese shore, quite some distance north of where we first found eggs and larvae. These are probably migrating northwards with the River Congo currents from the spawning region. We do find spawning sardinella in the trawl hauls, but it is yet to be determined exactly where the spawning is taking place. Hopefully this is knowledge that this cruise will contribute to find the answer to.

Waiting for water samples in the CTD room

Waiting for water samples in the CTD room

The ship is now on its way to Point Noire in Congo for a crew change before heading southwards to Angola for the second leg of the cruise – ending in Luanda on the 13th of June.

Eggs from sardinella and other species

Eggs from sardinella and other species


Sardinella eggs

Sardinella eggs

As we’re close to equator, the weather is steady, temperatures ranging from 25 to 28 degrees, day and night, and practically no wind. The dry season has just begun, and apart from a heavy shower in Port Gentil, we’ve had no rain, although it’s mostly cloudy.

Concentration in the lab

Concentration in the lab

This has been my first cruise on a research vessel. It’s been a fantastic experience to see how the research and training is carried out on board Dr. Fridtjof Nansen. I’ve been working closely with the EAF Nansen project for some years now, and I am thrilled to see how the activities on board work. With the ongoing debate back home about the organization of the Norwegian development cooperation in mind, I am convinced that the model of the EAF Nansen project – establishing scientific knowledge that is crucial for management purposes and at the same time training local scientists and managers in how to find and use such knowledge – is an example of a very good set-up for development cooperation projects.

Length measurements of fish after trawl

Length – measurements of fish after trawl