No abstract

Sediment disturbance in marine environments is caused by activities including polychaete bait harvesting, trawling, dredging, sediment erosion and treading. These activities affect the benthic communities by changing the densities, community assemblage and diversity. The aim of this study was to evaluate the potential of nematodes as indicators of sediments disturbance following polychaete bait harvesting. The study was conducted in three sites experiencing different bait harvesting intensities in Mida Creek, Kenya. Sediment samples were collected from the mudflats during low tide, preserved in 5% formalin and transported to the laboratory for processing and identification of nematodes. The highly disturbed site recorded the lowest nematode genus richness while the less disturbed sites had the highest. Overall, the most abundant nematode genera in the non-disturbed (Dabaso) and less disturbed sites (Kirepwe) were selective deposit feeders (Spirinia and Terschellingia), while most disturbed sites (e.g. Mayonda) had predators/omnivores (Pheronus, Aporcelaimellus) and selected members of the genus Spirinia. The disturbed site was characterised by low nematode diversity (H’) and low dominance (D) while the non-disturbed and less disturbed sites had higher diversity and dominance. Clearly, nematode community assemblage, diversity and feeding guilds changed following disturbance to a low diversity that favoured higher proportions of predator/omnivore taxa.

No abstract

Traditionally basket traps, baited with gastropods, seagrass, among others, deployed in nearshore fishery, are typical to tropical coastlines. Although fish landings from such fishery are documented, bait utilized remains sketchy. The Indo-Pacific Mangrove mudwhelk (Terebralia palustris) are keystone species, threatened by habitat degradation but also the poorly documented human harvesting. Forest bait harvesting is comparable to tropical forest hunting but has received scant attention in spite of potential impacts. This study elucidates mudwhelk baited trap harvest and subsequent use in basket trap fishery at the Mida creek. Bait and fish landings and effort, and habitat attributes at sites at the Mida creek, are determined and variations described. Results show 0.64 kg.m-2 of mudwhelk occur at Mida creek, with higher biomass (P<0.05) at the more complex Dabaso forest. Harvesters targeted larger individuals (10.38 cm), extracting 9.26 kg.harvest-1 at a rate of 0.12 kg.min-1, with higher harvest (P<0.001), at the less complex Kirepwe forest. The mudwhelk bait, were used to land 0.69 kg.fisher-1 of fish with relatively low landing efficiency (>1.0 kg fish.kg-1 bait), but higher (P<0.001) landings at Kirepwe. We tentatively estimate Mida creek mudwhelk harvest of 5.9 t.yr-1, corresponding to 5.2% of stock (115.2 t), but may mask localized overharvesting at sites with higher trap fishery participation and require more testing to guide sustainable management.

Humanistic valuation of resources is critical to understanding drivers to patterns and impacts, however, value of non-traded intertidal tropical bait, such as polychaetes and hermit crabs, used by artisanal fishers, is unknown. Bait harvested from intertidal habitats and used for fishing at Mida Creek, were quantified, and variable and fixed cost incurred determined, income and profitability, were computed and compared. Fishers harvest and use 58 baits pieces, to land 2.4 kg of fish with an average earning of 3.8$.d-1. Bait values were similar among bait types and sites, but income (3.3$), earning (4.1$) and profitability (255%), were significantly higher for polychaete bait fishers. This was attributed to lower bait harvesting and fishing expenditure. Bait fishery is a labour intensive, and profitable enterprise, that is, however, comparable to semi-skilled wage livelihood options, in the region. Improvement in profits, may be achieved by increasing fishery yield, by adoption of alternative fishery and livelihoods.