Homing and site fidelity in the greasy grouper Epinephelus tauvina (Serranidae) within a marine protected area in coastal Kenya

Homing ability and site-fidelity in the greasy grouper Epinephelus tauvina (Serranidae) were studied at Malindi Marine Park (6.3 km2), coastal Kenya, from January to April 2002 using acoustic telemetry. Displacement experiments involving 12 groupers (mean size 57.9 cm) from multiple capture sites resulted in a 67% homing success. Upon release at displacement sites (0.5 to 2.6 km from the point of capture), most initial movements were small-scale and non-directional. Neither the tidal range nor time of day influenced the magnitude of these daily movements. Returns to the capture sites were sudden, occurring predominantly (88%) on spring tide dates. Fish displaced at the spring tide returned to capture sites faster (8.6 d) than those displaced at the neap tide (14.3 d). Time taken to return to capture sites ranged from 4 to 19 d (mean 9.6 d) and was not correlated with distance of displacement. However, time taken for the fish to home was negatively correlated with tidal range at displacement. Home ranges established after homing (0.07 to 0.73 km2) were stable and negatively correlated with fish size, suggesting an ontogenetic shift in home range development

Experimental evaluation of influence of FADs on community structure and fisheries in coastal Kenya

Fish aggregating devices (FADs) have been widely used by commercial fisheries to increase the catchability of pelagic stocks in the open sea. FADs have the potential to enhance nearshore small-scale fisheries where stocks are often overfished. This study examined changes in catch composition, abundance, catch and effort, and aspects of diversity in Kenya's nearshore coastal fisheries after deployment of anchored fish aggregating devices (AFADs). The study combined both fishery independent and dependent methods in assessing changes in fish assemblages post-deployment. Results showed orders of magnitude increase in length, weight, commercial value, and catch per unit effort (CPUE) of landed catch after deployment of FADs suggesting that FADs had a positive effect on the local fishery. Species richness at FAD sites increased post-deployment (n = 281) compared to pre-deployment values (n = 223). Simultaneous use of several complementary structural indices may be required in order to accurately describe and monitor fish assemblages around the FADs. The findings suggest that AFADs are capable of creating both short and long-term impacts on livelihoods, with the potential to deflect pressure on the overfished nearshore fish stocks. However, more research will be needed on redistribution of fish around FADs, design and placement configuration, and site selection amongst others

Testing a global standard for quantifying species recovery and assessing conservation impact.

Recognizing the imperative to evaluate species recovery and conservation impact, in 2012 the International Union for Conservation of Nature (IUCN) called for development of a "Green List of Species" (now the IUCN Green Status of Species). A draft Green Status framework for assessing species' progress toward recovery, published in 2018, proposed 2 separate but interlinked components: a standardized method (i.e., measurement against benchmarks of species' viability, functionality, and preimpact distribution) to determine current species recovery status (herein species recovery score) and application of that method to estimate past and potential future impacts of conservation based on 4 metrics (conservation legacy, conservation dependence, conservation gain, and recovery potential). We tested the framework with 181 species representing diverse taxa, life histories, biomes, and IUCN Red List categories (extinction risk). Based on the observed distribution of species' recovery scores, we propose the following species recovery categories: fully recovered, slightly depleted, moderately depleted, largely depleted, critically depleted, extinct in the wild, and indeterminate. Fifty-nine percent of tested species were considered largely or critically depleted. Although there was a negative relationship between extinction risk and species recovery score, variation was considerable. Some species in lower risk categories were assessed as farther from recovery than those at higher risk. This emphasizes that species recovery is conceptually different from extinction risk and reinforces the utility of the IUCN Green Status of Species to more fully understand species conservation status. Although extinction risk did not predict conservation legacy, conservation dependence, or conservation gain, it was positively correlated with recovery potential. Only 1.7% of tested species were categorized as zero across all 4 of these conservation impact metrics, indicating that conservation has, or will, play a role in improving or maintaining species status for the vast majority of these species. Based on our results, we devised an updated assessment framework that introduces the option of using a dynamic baseline to assess future impacts of conservation over the short term to avoid misleading results which were generated in a small number of cases, and redefines short term as 10 years to better align with conservation planning. These changes are reflected in the IUCN Green Status of Species Standard

Marine reserves and their influence on adjacent fisheries in coastal Kenya

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

Influence of Seasonality and Bathymetry on Assemblage Structure of Decapod Crustaceans in the Malindi-Ungwana Bay, Kenya

Decapod crustaceans support both artisanal and semi-industrial fisheries in the Western Indian Ocean (WIO) region. Despite their commercial value, data on assemblage structure is lacking in most of the WIO region but are important for stock management. This study provides information on seasonal and bathymetric variation in assemblage structure of decapod crustaceans in Malindi-Ungwana Bay, a biodiversity rich ecosystem in Kenya. Samples were collected during the northeast monsoon (NEM) and southeast monsoon (SEM) seasons during a two-week experimental bottom trawling survey in 2011 under the South West Indian Ocean Fisheries Project (SWIOFP). A total of 43 transects covering an estimated area of 546 nm2 were trawled in four depth zones (0-10, 10-20, 20-40 and 40-100 m) for both seasons. Twenty species of decapod crustaceans belonging to 7 families were sampled in both seasons. The species were distributed in the families; Penaeidae, Portunidae, Calappidae, Majidae, Matutidae, Palinuridae and Scyllaridae. The penaeid shrimps had higher relative numerical abundance both in the NEM (89.3%) and SEM (85.3%) seasons. Of the penaeid shrimps, Fenneropenaeus indicus, had the highest relative abundance both in the NEM (58%) and SEM (42%) season. ANOSIM test indicated significant difference in total crustacean abundance (individuals/km2) between the depth zones (R=0.375; P=0.001; considering all seasons) but no significant difference between the seasons (R= -0.031; P=0.602; considering all depths). Simple Correspondence Analyses segregated the population into SEM assemblages dominated by the Penaeidae and a mixed group NEM assemblage. Canonical Correspondence Analysis showed temperature, salinity, Secchi depth and dissolved oxygen to have seasonal influence on the bathymetric distribution of the crustaceans in the bay. The structure of the assemblages seems to be influenced more by depth profiles than by seasonality. It is recommended that variations in bathymetric distribution of the crustaceans be taken into consideration when developing a crustacean fishery management plan for the bay.

Experimental evaluation of influence of FADs on community structure and fisheries in coastal Kenya

Fish aggregating devices (FADs) have been widely used by commercial fisheries to increase the catchability of pelagic stocks in the open sea. FADs have the potential to enhance nearshore small-scale fisheries where stocks are often overfished. This study examined changes in catch composition, abundance, catch and effort, and aspects of diversity in Kenya's nearshore coastal fisheries after deployment of anchored fish aggregating devices (AFADs). The study combined both fishery independent and dependent methods in assessing changes in fish assemblages post-deployment. Results showed orders of magnitude increase in length, weight, commercial value, and catch per unit effort (CPUE) of landed catch after deployment of FADs suggesting that FADs had a positive effect on the local fishery. Species richness at FAD sites increased post-deployment (n = 281) compared to pre-deployment values (n = 223). Simultaneous use of several complementary structural indices may be required in order to accurately describe and monitor fish assemblages around the FADs. The findings suggest that AFADs are capable of creating both short and long-term impacts on livelihoods, with the potential to deflect pressure on the overfished nearshore fish stocks. However, more research will be needed on redistribution of fish around FADs, design and placement configuration, and site selection amongst others

Assessment of the Ecological Health of Afrotropical Rivers Using Fish Assemblages: A Case Study of Selected Rivers in the Lake Victoria Basin, Kenya

Streams and rivers are globally threatened ecosystems because of increasing levels of exploitation, habitat degradation and other anthropogenic pressures. In the Lake Victoria Basin (LVB) in East Africa, these threats are mostly caused by unsustainable land use; however, the monitoring of ecological integrity of river systems has been hampered by a lack of locally developed indices. This study assessed the health of four rivers (Nzoia, Nyando, Sondu–Miriu and Mara) on the Kenyan side of the LVB using physicochemical water quality parameters and a fish-based index of biotic integrity (IBI). Fish tolerance ranking was derived from principal component analysis of water quality parameters, and the concept of niche breadth (NB). The relationship between fish species and water quality parameters was examined with canonical correspondence analysis, whereas community metrics and stressors were evaluated through Pearson network correlation analysis. Fish species richness, trophic structures, taxonomic composition and species tolerance were used to generate the metrics for fish-based IBI. NB showed that most of the fish species were moderately tolerant to poor water. Moderately tolerant and intolerant fish species were negatively correlated with a high level of organic loading in the Mara River. Fish-based IBI scores for the rivers ranged from 26 to 34, with Sondu–Miriu scoring the lowest. Our results show that the cumulative effect of stressors can adequately rank fish species tolerance according to the disturbance gradients and further develop regional metrics to assess river health. Despite the fact that fish communities are declining, continual management and enforcement of environmental regulations are important, with conservation and management of headwaters and low-order streams being essential while they are still species rich