Scientists probe near extinct of Nile Perch

alain
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Messagepar alain » mar. 26 févr. 2019 09:25

Article récent trouvé sur la toile:

Scientists probe near extinct of Nile Perch

Fisheries researchers are investigating a sudden resurgence of some fish species that had been facing extinction after introduction of the giant Nile Perch in the early 1950s.

Scientists from Kenya, Uganda and Tanzania, together with those from the National Science Foundation (NSF) in the US have in the past few weeks been in the Lake Victoria trying to establish the link between the steady rise in population of smaller species such as the Haplochromine (fulu in Luo) and the diminishing volumes of the Nile Perch and Tilapia.

The four-year funded project has begun studies to find out why there is a sudden rise in small fish types like Omena and Haplochromines, while the big fishes are fast disappearing, hence rendering several people jobless after closure of fish processing industries. Sunday Standard reporters spent two days with researchers at the lake.

Nile Perch, a predatory fish has been known to be gobbling up the smaller species since its introduction into the lake and researchers now want to know if the upsurge in the population of Haplochromine could be a sign that the Nile Perch, whose exports have been earning Kenya about Sh8 billion annually, is disappearing from Africa’s largest fresh water lake.

If this proves to be true, it could spell doom to the largest lake in Africa. Stocks of Nile Perch, which has been the main fish type that have been providing East Africa with lucrative business ventures, have been decreasing as revealed by past surveys.

Closed down

During the Nile Perch, boom between 1970s and 2002, many fillet processing and exporting companies mushroomed in Homa Bay, Migori and Kisumu counties. The fishing industry, suddenly became the biggest employer in the lake region. Besides the fishermen working in the lake, hundreds were employed by middlemen and the factories.

Today however, most fish plants have been closed down due to a shortage of Nile Perch. One such company based in Kisumu, has laid off staff and drastically reduced production.

Catch Assessment Surveys Department at KMFRI, says Nile Perch and Tilapia catch decreased by 34.2 per cent - from 251,063.3 to 165,084.3 tonnes in 2014 and by about 65.9 per cent - from 59,681.3 to 20,371 tonnes in 2015.

Interestingly, Dagaa Haplochromine catch estimates increased by 11.2 per cent; from 509,598.1 tonnes in 2014 to 566,570 in November 2015.

Fish harvests from Lake Victoria have drastically gone down over the years, with numbers suddenly dropping from 5,000 metric tonnes to 2,600 metric tonnes yearly. Kisumu alone has a deficit of 4,000 metric tonnes of fish annually, necessitating the recent China imports.

The Haplochormine, unlike the Nile Perch is mainly sold to small scale consumers in the villagers and has insignificant financial might.

Despite closure of processing factories, many small scale traders are still involved in the Nile Perch trade. The few factories still operating in Kisumu and Nairobi still sell to slum traders skeletons (locally known as mgongo wazi).

Kenya Marine and Fisheries Research Institute’s (Kemfri) Assistant Director for Freshwater Systems Research Christopher Aura says the recently released Frame Survey 2016 indicates an increase in production of Omena.

There is a 11.2 per cent increase in catches - from 41,884.8 tonnes in May 2014 to 46,567.4 tonnes in November/December 2015 in total lake wide catches according to the regional catch assessment survey synthesis report.

At the same time, Haplochromine, is one of the key catches that has attracted the attention of scientists. The fish that is small and bony and is usually food for the Nile perch also revealed a 20.7 per cent increase from 6,045.7 tonnes in April 2014 to 7,292 tonnes in November/December 2015 survey conducted in the three partner states. “There is a paradigm shift from large fish to small ones like Haplochromines and Omena. We are interested in finding out why,” Mr Aura said.

The scientists are also conducting gill nets survey to find out biodiversity as regards the types of fish currently available in Lake Victoria. So far, the scientists attribute decline of Nile Perch in the lake to over-fishing, use of illegal sized nets that catch immature fish and destruction of breeding ground due to human activity.

According to Kemfri’s Research Scientist Dr Chrisphine Nyamweya, they want to find out why Haplochromines, the preferred food for Nile Perch has started showing a significant increase, yet Nile Perch stocks are deteriorating.

Cast nets

“Haplochromines have been in the lake. Before introduction of Nile Perch, there were over 500 species. We want to understand the biology and ecology of Haplochromines to be able to find a sustainable way for Nile Perch stocks to thrive,” he said.

Secure Fisheries Project Officer Paige Roberts said the intention is to protect Haplochromines so that people do not eat them because they are special to Lake Victoria. “Many of the species have totally disappeared and we are on a fact-finding mission to ascertain which ones still exist,” she said.

“We cast nets in the lake. When we find Haplochromines, we take pictures because it is difficult to identify one by just looking at it. We also preserve the whole specimen for expert identification,” Ms Roberts said.

The research is also being done by relaying data collected through GPS to scientists at the NSF in the US.

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jiji18
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Messagepar jiji18 » mar. 26 févr. 2019 13:17

Salut Alain,

Cet article as une date 14/05 2017

A une époque il semblait que la perche du Nil était en regression .

Mais il y a comme souvent un manque d'information concernant les espèces haplochromines .

Merci pour cette article ;)
Dernière édition par jiji18 le mar. 26 févr. 2019 17:18, édité 2 fois.
Plus on a de connaissances , moins on connait de gens .

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L134
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Messagepar L134 » mar. 26 févr. 2019 14:43


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jiji18
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Messagepar jiji18 » mar. 26 févr. 2019 17:17

L134 a écrit :https://www.standardmedia.co.ke/business/article/2001239629/scientists-probe-near-extinct-of-nile-perch?fbclid=IwAR1mXMbXEil4SP5boX2wDoPKZnfC_avQqAktf-nzoL00sZT-9c0pOxw2zrM


:) Merci Thomas :)
Plus on a de connaissances , moins on connait de gens .

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Gael
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Messagepar Gael » mer. 27 févr. 2019 08:12

Erf je suis pas motivé se matin à lire en anglais

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Gael
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Messagepar Gael » mer. 27 févr. 2019 08:13

Erf je suis pas motivé ce matin à lire ene anglais

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L134
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Messagepar L134 » mer. 27 févr. 2019 08:42

Gael a écrit :Erf je suis pas motivé ce matin à lire ene anglais


clic droit puis traduire en français sur la page d'origine, ça fonctionne très bien :D

alain
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Messagepar alain » lun. 11 mars 2019 23:51

En fait ce qui se passe est normal, les populations de prédateurs sont cycliques, par exemple on constate des cycles de 7 à 10 pour des explosions de population de sandres en milieu fermé, style lac de petite taille ou grand étang (50 hectares)
Lorsque la population de nourriture est au sommet, les prédateurs se reproduisent très bien vu l'abondance de nourriture, et au fur à mesure de la baisse de proies les populations de prédateurs vont diminuer, ayant pour impact une hausse des populations de proies, et les prédateurs auront leur population qui remontera par la suite.
C'est du vécu sur étang et lac, et c'est d'une logique implacable...
J'ai constaté également ça sur différents biefs en Canal à grand gabarit, mais sur certains biefs ces cycles ne se font pas, car il y a des déversseents de blanchaille pour les concours internationnaux, donc les cycles n'ont pas lieu d'être

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Messagepar Marsupilami » lun. 25 mars 2019 10:04

Salut,
les cycles dont tu parles ne s'appliquent pas à toutes les espèces et toutes les situations. Dans le cas de la Perche du Nil, c'est clairement la surpêche qui pose problème... il y a trop de pêche illégale et quasi aucun contrôle... A cela s'ajoutent les déséquilibres croissants dans le lac (je ne parle pas de la raréfaction des proies, les Haplos reviennent), mais bien d'un dysfonctionnement global, avec eutrophisation, coulées de boue, etc.
Séb


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