SWIOFP Shallow-water prawn trawl survey in Kenyan waters

SWIOFP Shallow-water Prawn Trawl Survey in Kenya started on the afternoon of the 21^st of January with the departure of the MV Vega from Mombasa. In the evening of the same day, Kenya Scientists boarded the vessel at Malindi and sailed to survey first trawling station at the heart of Malindi bay.

With the objective of collecting information on shallow-water prawn resources in Ungwana/Malindi bay area, SWIOFP shallow-water prawn survey implemented in Kenyan waters is considered a study of great importance to the development and management of the fishery in this country. 

As scheduled the survey endured 15 days (including 2 days of steaming) and covered two areas identified as of great importance to Kenya prawn fishieries, the Kipini (Ungwana Bay) shallow wide shelf area (<30m) of the Tana River and the Malindi Bay deep narrow shelf area of Sabaki (see figure 1). The survey was stratified by depth (principally) and distance from shore (see figure 1).

Figure 1- Survey areas and stratification

Bottom trawls were undertaken at depths of -10 m; 10-20m; 20-50 m, 50-100 m. From the 13 planned fishing days, one day was lost duet to a net caught on one of the ship propellers, and from the 48 stations that were expected to be surveyed and sampled, 44 were surveyed and 41 were sampled to determine species composition and distribution of prioritized crustacean species. Among other information, tissue samples were  collected for genetic studies to determine stocks abundance and structure in relation to nation jurisdictions (i.e. does a stock belong to a specific country or is it shared between 2 or more countries in the region?). Specimens were collected and preserved (frozen/formalin) for reference collection for the National Museum of Kenya

After completing its 15 days of survey the MV Vega returned to its home port in Mombasa, Kenya, on the 4^th of February 2011, to prepare SWIOFP second crustacean survey to take place in Tanzania during this same month of February. Upon arrival to Mombasa, Kenya Scientist provided the project with their personal view on the implementation of this cruise:

“The survey was a success! No serious problems were encountered and survey main objectives were achieved, except for the estimation of discards since the SWIOFP contract with MV Vega stated that no discards were allowed”. Dr. Edward Kimani, survey Chief Scientist, KMFRI

“The survey went very well! Fishing operations were conducted according to the sailing order with only two days, 23 and 24 January, 2011 transects not completed due to gear damage and entanglement to the ship propeller. A total of 2817 kg of fish and 92kgs of prawns were retained after biological samples were taken for specimen, reproduction, ageing and genetics. Bird’s mortalities and entanglements never occurred even though mitigation measures were not observed. There were few interactions with marine mammals i.e bottlenose dolphins but no entanglements were verified.” Dixon Odongo, survey Cruise Leader, KMFRI

“My project aims at assessing decapod crustaceans off Kenyan Coast up to a depth of 600m. It entails determining the abundance, distribution and basic biological aspects of prawns, lobsters, langoustines and crabs in relation to depth and distance from the shore. This was a good opportunity towards my studies regarding crustaceans found off the Kenya Coast. I did manage to collect all available samples for prawns though I did not get enough samples for lobsters and crabs and non for langostines. Very few lobsters and crabs were captured during the survey, but I hope we shall get more samples in the next inshore survey.  There is also need to collect samples for all the crustaceans in the next survey so as to have comparison between the two season’s i.e The North East monsoon and the South East Monsoon.”. Collins Kambu Ndoro, Fisheries Department Kenya and SWIOFP MSc student at Moi University; Project name: “Assessment of decapod crustaceans off the Kenya coast”.

“The research survey was marvellous and very interesting. I managed to collect both my PhD samples and specimens for reference at the National Museums of Kenya Reference collection center. I managed to collect over 45 different fish species and a handful of macrophytes plus other unidentified species of fish, molluscs, bivalves and some crustaceans. I have a strong feeling that most of these species have not been data based as species present along the Kenyan coast and SWIOFP has provided this opportunity!”. Rashid Kaka (National Museums of Kenya), PhD Student University of Nairobi; Project name: «Genetic diversity and population abundance of the wild penaeid species of Malindi-Ungwana bay in Kenya: Implications for aquaculture and conservation”

A quick observation of the type of shallow water trawl landings in the just concluded SWIOFP surveys off the Malindi-Ungwana bay in Kenya is provided by Cosmas Munga (KMFRI), photos bellow. Cosmas  is a PhD student from Gent University, project name: “Assessment of the status of the artisanal fisheries in the Malindi-Ungwana bay after a ban on the semi-industrial trawling activity”.

Figure 2- This can be described as one of the most successful trawl catch with at least 30% comprising of the penaeid shrimps

Figure 3- Where are the penaeid shrimps? Fish in most cases formed more than 90% of the retained by-catch;

Figure 4- Some of the trawl stations yielded nothing, only sponges though ecologically important;

The survey aims to answer key questions such as

1) what is the genetic diversity of crustacean species in Kenya waters;

2) what is their abundance, species composition, distribution and associated environmental variables;

3) what by-catch levels (retained and discarded) can be associated with prawn trawling in this region; and

4) how efficient are Turtle Excluder Devices (TEDs) fitted to trawl nets used in shallow waters?

Prawns are recognised as an important economical and food resource found in varying quantities along the Kenya coast, and historical commercial landings show that they are most abundant in the Ungwana/Malindi Bay area in the north. SWIOFP Component 2 (Crustaceans) has identified several species (Penaeus indicus, P. monodon and Metapenaeus monoceros) as a high priority for fisheries and biological research, including a genetic population study to determine whether stocks are local and linked to specific estuarine nursery sites (i.e. the Tana and Sabaki River estuaries), or whether the stocks are regional (i.e. eggs and larvae are widely distributed by ocean currents) and shared by neighbouring countries of the Western Indian Ocean.

On board the Vega a team of 10 Kenyan scientists will be monitoring oceanographic and environmental information, sampling the prawn and fish caught in each trawl net, and collecting genetic samples and whole specimens to complete reference collections for several Kenya Institutions, such as the National Museum. Among the scientists on board the vessel are experts from Kenya Marine and Fisheries Research Institute (KMFRI), Fisheries Department of Kenya, Moi University and Kenya Natural Museum.

Figure 1: The fishing vessel MV Vega, chartered by SWIOFP to do research on shallow-water prawn stocks and their bycatch in the Ungwana / Malindi Bay area.