Marine reserves and their influence on adjacent fisheries in coastal Kenya

Arara, Boaz Kaunda (2003) Marine reserves and their influence on adjacent fisheries in coastal Kenya. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Analysis of more than two decades (1978 to 2001) of commercial fish catch data collected by the Kenya Fisheries Department indicates that a rapid overall decline in landings occurred in coastal Kenya during the last decade. The decline was most severe in the most populated Mombasa district. Amongst the commercial families, the groupers (family Serranidae) showed the steepest decline in landings and forecasts indicated a gradual decline in yields for the next decade (2002-2011). This thesis reports on the results of experiments to test the efficacy of two of the oldest marine parks in Kenya (Malindi, 6.3 km² and Watamu, 10 km², created in 1968) to restore such over-fished stocks and their potential to sustain adjacent sites through a spillover effect. A comparison of catch per unit effort (CPUE) and sizes of fish species across the park boundaries showed that species are orders of magnitude more abundant and larger inside the parks than the adjacent fished sites. However, higher seasonal abundance and even larger sizes of some species (e.g., the whitespotted rabbitfish, Siganus sutor and the seagrass parrotfish, Leptoscarus vaigensis) occur outside the parks (especially at Watamu). Results suggest that yields of some species in adjacent fished sites and perhaps beyond may have been sustained by a spillover effect from the parks. However, this effect appears to be species and site specific and affected by season and reef types. Size frequency distribution of commercial species showed a high proportion of small sized fish inside the parks, suggesting the parks additionally function as nursery grounds. -- A logistic decay model fit to species abundance (CPUE and #/500m²) data across the park boundaries showed steep gradients of fish abundance (especially for the sky emperor, Lethrinus mahsena) across a patch reef at Malindi, indicating limited dispersal across this reef type. However, the locally abundant whitespotted rabbitfish, Siganus sutor, had a shallow gradient of abundance across this reef indicating ability for dispersal. Inter-annual variations in patterns of abundance were evident. For example, S. sutor was more abundant outside Malindi Park during the SE monsoon of 200/2001 but was more abundant during the NE monsoon in 2001/2002. -- Tagging experiments showed higher spillover rates of commercial species, mostly of S. sutor and the emperors along fringing reefs at Malindi and Watamu Parks. Little spillover was suggested off the patch reef at Malindi. Most of tagged fish showed little out-migration from the parks and had multiple recaptures within the parks. Large-scale (30-180 km) movements were reported in three species (Gaterin flavomaculatus, S. sutor and L. mahsena) that were generally believed to be sedentary on home reefs. -- Reduction of fishing mortality within the parks may interact with species behavior to enhance conservation potential of the parks. For example, results of acoustic telemetry studies within Malindi Park, showed site fidelity and homing tendency in a commercial grouper (Epinephelus tauvina: Serranidae) displaced to multiple sites (0.5-2.6 km) within the park. Homing in this species is thought to be linked to tidal factors amongst others and to play a role in the preservation of spawning stock biomass within the parks. -- Estimates of demographic parameters (growth, mortality and survival rates) of some commercial reef fishes necessary for stock assessment and management are provided. These rates are largely unknown for most species, thus making cross-regional comparisons difficult. However, where data exist for other geographical areas, growth parameters (e.g., instantaneous annual growth rate, K, and absolute growth rates) were higher, especially for Siganus sutor and Lethrinus mahsena, on the Kenyan coast suggesting superior conditions for growth. -- The overall implication of these results to species conservation, and the function and design of marine parks are discussed in the thesis.

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