Western Indian Ocean Journal of Marine Science

A first assessment of marine litter on a beach of an uninhabited island in the Mozambique Channel

Sébastien Jaquemet — Wed, 28 Feb 2024 00:00:00 +0000

Marine litter is ubiquitous and associated with both ecological and socio-economic consequences. Beaches are major sinks of marine litter and as such its assessment and monitoring are needed. An opportunistic marine litter survey was performed for 12 consecutive days on the island of Juan de Nova in the central Mozambique Channel in February 2007. Plastic dominated the marine beach litter with daily accumulation of plastic positively related to the tide height (R2 = 0.768, p<0.01). Annual deposits could reach an average of 1 t.km-1, suggesting that regular cleaning of the coastline should be conducted to limit the impact on the local wildlife of this protected area.

Age, growth and mortality characteristics of the Thumbprint Emperor (Lethrinus harak) in Zanzibar

Tumu Ali Mussa, Saleh A.S Yahya, Jose J Castro, Leonard J Chauka — Tue, 12 Mar 2024 00:00:00 +0000

The growth parameters of Lethrinus harak were studied in Zanzibar water from 308 samples collected between June 2019 to May 2020 at Unguja Ukuu and Mkokotoni landing sites. The annulus count indicated that the majority of fishes captured were of three and four years old and very few were five, six, and seven years of age with a mean length of 17.69 cm, 21.04 cm, 24.18 cm, 25.86 cm, and 28.15, respectively. The number of rings was counted on the whole otolith and the growth rings were revealed to be formed annually, with the opaque margins generated from December to February and the hyaline ones during the rest of the year. The growth parameters were estimated as L_∞=34.22cm, K=0.25 year-1, and t₀=0.00. The total mortality (Z) was estimated as 0.68 year^-1 and natural mortality (M) was estimated using Pauly's equation, as 0.65 per year^-1 and fishing mortality (F) was 0.03 year^-1, which gives an exploitation rate (E) of 0.04 year^-1. Although these values indicate the species to be underexploited, the absence of older individuals 15 years and smaller below three years might have affected our findings.

The viability of seagrass ecosystems for supporting dugong recovery in Kenya

Dr. Asma Awadh, Maarifa Ali Mwakumanya, Mohamed Omar — Mon, 25 Mar 2024 00:00:00 +0000

Seagrasses are the primary source of food for dugongs and a good indicator of marine ecosys- tem health. The East African dugong (Dugong dugon) population is listed as critically endan- gered under the IUCN Red List. This study aimed to document the status of seagrass beds and evaluate their potential for supporting dugong recovery in Kenya. A cross-sectional survey was conducted in December 2016 to March 2017, with data gathered through desktop reviews, inter- views, beach surveys and aerial surveys. Seven seagrass species were found at sampled sites, namely Syringodium isoetifolium, Thalassodendron ciliatum, Halophila ovalis, Zostera capensis, Thal- assia hemprichii, Cymodocea serrulata, and Halodule uninervis. Halodule and Halophila seagrass spe- cies are important in the diet of dugongs. Two dugongs were sighted during the aerial survey. The spread of sea urchins, unplanned infrastructure development, Illegal, Unreported and Unregulated fishing, and boat anchors negatively affected seagrass ecosystems and hence dugong distribution in Kenya.

Effects of climate change on mangrove-dependent livelihoods in Lamu County, Kenya

Solomon Njenga, Dan Olago, Evans Kituyi — Fri, 31 May 2024 00:00:00 +0000

The effects of climate change on mangrove-dependent livelihoods were examined in Lamu County, Kenya. Climatic instrumental, household survey, key informant interview, and focus group discussion data were collected from August to December 2021. Data analysis indicated a significantly increasing trend in annual air temperature between 1985 and 2020, with minimum and maximum temperatures increasing by 0.034 oC and 0.0281 oC, respectively. Rainfall dur- ing the seasonal long rains declined, but not significantly. In contrast, the seasonal ‘short rains’ increased significantly. The mean sea level rose significantly, from 7066 mm in 1985 to 7150 mm in 2020. The perception data showed an increasing effect of climate change on mangrove- dependent livelihoods in the last 10 years. Critical livelihood aspects that were affected included the destruction of property, displacement, the prevalence of waterborne infections, reduced mangrove products, increased salinity in underground waters, and destruction of fish habitats.

Improved accessibility and changing dynamics of small-scale fisheries and aquaculture activities in southwest Madagascar

Lisiane Soanomeiny JERRY, Jacqueline RAZANOELISOA — Fri, 31 May 2024 00:00:00 +0000

Small-scale fishing and aquaculture activities in the village of Andrevo in southwest (SW) Mad- agascar was investigated to assess changing dynamics during a period of improved road infra- structure and accessibility. Socio-economic surveys and fisheries monitoring were undertaken using a simple random sampling strategy. Stakeholders involved in the small-scale fisheries and aquaculture sectors were sampled. The main types of fishing gear were hook-and-line (includ- ing longline), harpoon, speargun, gill nets, bottom seine nets, mosquito and shark nets (called ZZ or Jarifa). Subsectors of the fishery were boat fishers (74 %), foot fishers (18 %), and combined (8 %). On average, 236 boats fish on a daily basis, with an overall catch rate (all gears combined) of 7.5 kg/trip/gear and total catch of approx. 47 tonnes/month. Mariculture of seaweed and sea cucumber farming constitute alternative income-generating activities. The production of dry seaweed varied from 9-70 tonnes/year, and sea cucumber production depended on the number of juveniles delivered. An ecosystem-based approach to managing fisheries and aquaculture at Andrevo is recommended, using locally-based measures such as co-management and marine protected areas (MPAs). The dynamics of the small-scale fishery and aquaculture activities are also discussed in this paper in relation to improved road infrastructure and accessibility in SW Madagascar.

Fish species, families and guilds recorded in selected estuaries of Mozambique

Alan Whitfield, Steven Weerts — Fri, 31 May 2024 00:00:00 +0000

This review documents the occurrence of fish species in a range of estuaries from Mozambique. Altogether 217 fish species were recorded, belonging to 77 families, and dominated in terms of species richness by Gobiidae, Carangidae and Mugilidae. A guild analysis was conducted to compare the occurrence and degree of estuary-association by the various species in tropical Mozambique, with that recorded from nearby predominantly subtropical and warm-temper- ate estuaries in South Africa. The major difference in guild occurrence between the two coun- tries centered on the higher representation of marine stragglers in Mozambique estuaries, a probable result of the wide mouths and macrotidal exchange of some of the larger systems along this coast. Estuarine lakes and lagoons within the Mozambique coastal region showed increasing reduction in marine connectivity with channel distance from the sea, and a concom- itant increase in freshwater fish species domination of these incipient coastal lakes and lagoons. Once these systems lose all connectivity with the sea, they become freshwater coastal lakes and lagoons, and all estuary-associated marine fish species disappear.

Meiofauna as bioindicators of organic and inorganic pollution of estuarine sediments in Kenya

Fri, 31 May 2024 00:00:00 +0000

Meiofaunal density, diversity, and community assemblages were studied at the highly con- taminated Tudor Creek and the less contaminated Mida Creek in Kenya to assess their poten- tial as bioindicators of marine pollution. Sampling during the dry (January/February 2017) and wet (November/December 2017) seasons indicated a significantly greater total organic matter content at Mida (23.7 and 23.9 %) than at Tudor Creek (6.6 and 5.9 %) in the dry and wet seasons. Heavy metal concentrations were always greater at Tudor Creek. Meiofaunal densi- ties were greater at Mida (2729 and 2804 ind.10 cm-2) than Tudor Creek (612 and 183 ind.10 cm-2) during both seasons. Meiofauna at Mida Creek (10 and 7 taxa in the dry and wet seasons) were dominated by nematodes, copepods, and turbellarians. Meiofauna at Tudor Creek (8 and 6 taxa) were dominated by nematodes, turbellarians and ostracods. Meiofaunal diversity was greater at Tudor Creek, but dominance was highest at Mida Creek. Community dissimilarities between the two sites were shown in a Bray-Curtis cluster analysis. There is a high likelihood that heavy metals affect meiofauna density and diversity in the sediments of the two studied creeks in Kenya.