Ecological and socio-economic assessment of Kenyan coastal fisheries: The case of Malindi-Ungwana Bay artisanal fisheries versus semi-industrial bottom trawling

Abstract

This Ph.D. study assessed the ecological and socio-economic aspects of the artisanal fishery and semi-industrial bottom trawling in the Malindi-Ungwana Bay, Kenya before and after the trawl ban. Bottom trawling targets shrimps but also produce bycatch. For several decades, these two fishery types were practiced in the bay. Later on, conflicts emerged ostensibly due to excess trawl bycatches otherwise targeted by artisanal fishers, perceived environmantal degradation, and damage of artisanal fishing gear by the trawlers. Retained trawler bycatches also flooded the local fish markets with cheap fish that competed unfairly with fish sold by the artisanal fishers. These problems persisted for sometime until a ban on bottom trawling was imposed in September 2006 to pave the way for the formulation of the existing shrimp fishery management plan, six years after the ban. This Ph.D. study therefore, drew its motivation to investigate the status of the Malindi-Ungwana Bay fisheries before and after the trawling ban and fulfilled the following specific objectives: i. the study determined the trends of the Malindi-Ungwana Bay artisanal fisheries and the semi-industrial bottom trawl landings before and after the trawl ban; ii. the study characterised the artisanal fisheries in terms of vessel-gear categories and catch composition, and proposed several management recommendations; iii. the study determined the spatio-temporal distribution patterns and composition of stocks (shrimps and bycatch of finfish species) before lifting of the trawling ban; iv. the study determined artisanal fishers’ perceptions on shrimp trawling activity and identified to what extent fishing activity contributed to the livelihoods of the artisanal fishers. While the broader framework and key features of this Ph.D. study are explained and introduced in Chapter 1, the general discussion and conclusions generated in this entire study, and recommendations for sustainability of the Malindi-Ungwana Bay fisheries, like other fisheries in the tropics are provided in Chapter 7. Therefore, the above fulfilled specific objectives involved: a retrospective analysis of the existing artisanal and trawl data before and after the ban, shore-based artisanal catch assessments after the trawl ban, experimental bottom trawl surveys to determine the status of shrimp stocks and finfish bycatches after the ban, and a socio-economic assessment of artisanal fishers’ alternative livelihoods and their perceptions of shrimp trawling in the bay after the trawl ban was lifted in July 2011. Results in Chapter 2 are therefore based on aggregated catch data from the Kenya Fisheries Department. The artisanal landings (catches) declined before the ban, but rapidly recovered within 2 years after the ban was imposed. However, shrimp landings in the artisanal fishery were already low before and after the ban. Commercial shrimp landings gradually declined before the ban from 550 t in 2001 to 250 t in 2006, and the shrimp/fish bycatch ratio was 1:1.5 compared to values in early reports of 1:7 in 1999. Before the ban, distinct artisanal catch composition was evident between Formosa/Tana and Malindi/Sabaki areas. This difference was attributed to more abundant freshwater fish families Claridae, Cichlidae and Protopteridae in Formosa, and more abundant marine fish groups of mixed pelagics and mixed demersals, and the families Carangidae, Siganidae, Carcharhinidae and Lethrinidae in Malindi. Chapter 3 described the artisanal finfish catch composition (total number of species caught, sizes and trophic levels), and catch-per-unit-effort (CPUE) for each of the most popular vessel-gear categories used in the bay. This was based on the fact that specific vessel-gear category combinations instead of the traditional gear-based approach, offers a better alternative for monitoring catches and thus supporting fisheries management. A total of 4,269 finfish belonging to 178 species and 66 families were sampled by the 5 most popular vessel-gear categories between 2009 and 2011. Significant differences in species composition existed between the different vessel-gear categories with highest number of species caught by the canoe-gillnets and lowest number by the foot-handline category. The CPUE was not significantly different between vessel-gear, although this was on the average highest for canoe-gillnet and mashua-gillnet, and lowest for foot-handline. The highest trophic level of 4.0 was recorded for the mashua-gillnet and the lowest of 3.4 and 3.2 for canoe-gillnet and foot-seine net respectively. This study, singled out the mashua-gillnet, canoe-gillnet and foot-seine net as most suitable units for monitoring the artisanal fisheries in Malindi-Ungwana Bay by virtue of landing highest mean trophic level and largest sized individuals for the mashua-gillnet, highest number of species caught for the canoe-gillnet, and smallest sized individuals for the foot-seine net. Shallow water experimental trawl surveys in Chapter 4 indicated distinct species composition and abundance patterns between the Tana and Sabaki estuaries, attributed mainly to depth, turbidity and season. Penaeus semisulcatus was more abundant at the Sabaki area, where it was deeper with a muddy bottom and less turbid waters. Fenneropenaeus indicus was more abundant in the Tana area, a shallower, more turbid area with sandy-mud sediments. Penaeus monodon, Penaeus japonicus and Metapenaeus monoceros were found in both areas, suggesting wider tolerance to environmental conditions. Shrimp total biomass and catch rates were significantly greater during the wet Southeast Monsoon (SEM) season, and decreased with increasing depth. Small-sized M. monoceros and P. monodon individuals were abundant during the SEM season, whereas large ones with ripe and spent gonads were more common during the dry Northeast Monsoon (NEM) season. Seasonal patterns in gonad maturity were less clear for F. indicus and P. semisulcatus. The length at first maturity (L50) varied among species, suggesting that different species in the bay started spawning at different sizes, an important biological reference for sustainable resource exploitation. The same experimental trawl surveys in Chapter 5 indicated that the associated finfish bycatch rates and biomass were significantly higher in inshore than offshore and distinct in composition, while less pronounced differences were found between seasons. The Shannon-Wiener diversity index was significantly higher during the SEM season, but no differences were found between areas, nor was their a significant interaction effect. A total of 158 fish species in 61 families were identified during the NEM survey, and 161 species in 57 families during the SEM. However, only 7 families contributed for 66.6% by mass during the NEM whereas 10 families contributed for 59.7% during the SEM. Offshore trawl bycatches showed lower similarity with the composition of artisanal catches than inshore trawl bycatches. The similarity between inshore trawl bycatches and artisanal catches was mainly attributed to 7 common and most abundant artisanal target species confirming a localised inshore resource overlap. Whereas these 7 species were mostly absent in offshore trawl bycatches. Furthermore, significantly smaller sized individuals of these 7 species occurred in the trawl bycatches posing a potential risk for low recruitment with continued trawling. Also species diversity in both inshore and offshore trawl bycatches was significantly higher than in artisanal catches further confirming the possible resource overlap between the two fishery types in the Malindi-Ungwana Bay. The socio-economic study using questionnaires in semi-structured interviews of 151 artisanal fishers in Chapter 6 indicated that livelihood diversification in Malindi-Ungwana Bay was common. However, full time fishers were associated with relatively higher daily catches and incomes compared to fishers with additional livelihoods. Analysis of economic viability of the different artisanal fishing categories using the Net Present Value (NPV) was found to increase when artisanal fishers additionally undertook either fish trading and micro-business, part time paid-up jobs, or used acquired skills for making extra income. Economic viability was however, low when fishing was undertaken with subsistence farming or when full time fishing was undertaken alone. The majority of artisanal fishers from all fishing categories except those who engaged in part time paid-up jobs perceived a negative impact of shrimp trawling mostly due to its associated damage to artisanal fishing gear, fish habitat, and excessive bycatches that are otherwise targeted by the artisanal fishers. The main conclusions of this Ph.D. study are:  Bottom shrimp trawling in the bay before the September 2006 ban indicated some negative impact on the artisanal catches, and the target shrimp catches but not on artisanal shrimp catches.  The mashua-gillnet, canoe-gillnet and foot-seine net are suitable fishing units for monitoring the artisanal fisheries in Malindi-Ungwana Bay by virtue of landing highest mean trophic level and largest sized individuals for the mashua-gillnet, and highest number of fish species caught for the canoe-gillnet, and smallest sized individuals for the foot-seine net.  Shrimp catch rates and biomass in Malindi-Ungwana Bay, decreased with increase in depth and away from the shore, and were significantly higher during the wet Southeast Monsoon (SEM) season than the dry Northeast Monsoon (NEM). Also the Tana and Sabaki estuaries significantly differed in shrimp composition, with the shallower and more turbid Tana estuary characterised by more abundant Fenneropenaeus indicus and the deeper and and less turbid Sabaki estuary characterised by more abundant Penaeus semisulcatus.  The length at first maturity (L50) was determined for Fenneropenaeus indicus (37.4 mm), Penaeus monodon (41.9 mm), Metapenaeus monoceros (36.0 mm) and Penaeus semisulcatus (33.4 mm) as a biological indicator for monitoring.  The finfish species: Galeichthys feliceps, Pellona ditchela, Johnius amblycephalus, Leiognathus equulus, Pomadasys maculatus, Otolithes ruber and Lobotes surinamensis were more abundant both in artisanal and trawl bycatches and therefore, the potential species for resource overlap and conflict between bottom trawling and the artisanal fishery in the inshore area of the Malindi-Ungwana Bay.  The economic viability of artisanal fishing increased with additional livelihood sources such as fish trading and micro-business, part time paid-up jobs, and use of acquired skills for making extra income, but not with subsistence farming or when full time fishing was undertaken alone.  Majority of artisanal fishers from all fishing categories except those who engaged in part time paid-up jobs perceived a negative impact of shrimp trawling mostly due to its associated damage to artisanal fishing gear, fish habitat, and excessive bycatches that are otherwise targeted by artisanal fishers.