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.