Browsing by Author "Mgeleka, Said"

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Growth, mortality, exploitation rate and recruitment pattern of Octopus cyanea (Mollusca: Cephalopoda) in the WIO region: A case study from the Mafia Archipelago, Tanzania
(Western Indian Ocean Journal of Marine Science, 2021-08-24) Silas, Mathew; Kishe, Mary; Mshana, Johnson; Semba, Masumbuko; Mgeleka, Said; Kuboja, Bigeyo; Ngatunga, Benjamin; Chande, Muhaji; Matiku, Patroba
Octopus cyanea is a commercially important cephalopod in the Western Indian Ocean (WIO) region, but scientific information to inform management strategies for the species is limited. A study was conducted in 2014, 2015, 2017 and 2018 to investigate biological parameters including growth, mortality, exploitation rates and recruitment patterns in the sea around Mafia Archipelago, Tanzania. Virtual population analysis (VPA) indicated differential mortality between two sampling sites; the lowest and highest fishing mortality of F = 1.5yr-1 and F = 2.7yr-1 were observed in Bwejuu (Dorsal mantle length, DMT = 18-20 cm) and Jibondo (DMT = 8-12 cm) fishing villages, respec tively. The maximum exploitation rate (Emax), which gives the maximum relative yield per recruit, was estimated at 0.380 and 0.379 for Jibondo and Bwejuu, respectively. The exploitation rates E 0.5, which corresponded to 50% of the unexploited stock relative biomass per recruit, were estimated at 0.248 for Jibondo and 0.247 for Bwejuu. These values differ greatly from the exploitation rates of 0.53 and 0.41 for Jibondo and Bwejuu, respectively, sug gesting that the stock of O. cyanea is probably being overfished both in terms of yield per recruit and biomass per recruit. The stock-recruit pattern was observed to be continuous year-round, with the peak being between May and July. Since the peak in recruitment of both areas coincides with the south-east monsoon (SE Monsoon) and the level of maximum sustainable yield has been overshot, it is recommended that management plans are implemented that will reduce effort while increasing biomass, for example, implementing temporal octopus fishery closures at a village level.
Population genetics of the hound needlefish Tylosurus crocodilus (Belonidae) indicate high connectivity in Tanzanian coastal waters
(Taylor & Francis, 2023-07-13) Mgeleka, Said; Silas, Mathew; Mtonga, Cretus; Rumisha, Cyrus; Viinamäki, Elina; Polte, Patrick; Sköld, Mattias; Winder, Monika; Gullström, Martin
. The hound needlefishTylosurus crocodilus(Belonidae) is a highly demandedfish in the localmarkets of Tanzania, but the growing coastal population threatens its sustainability. As belonidsare highly migratoryfishes utilising various parts of the seascape, increasedfishing pressuremay disrupt connectivity patterns on different spatiotemporal scales and disaggregatepopulations. Using the COI gene, this study assessed the genetic population structure,connectivity patterns, and historical demography ofT. crocodiluscollected in seven sites spreadalong Tanzanian coastal waters. Results showed fourteen haplotypes with low overallnucleotide and haplotype diversity. Pairwise FSTcomparisons revealed no significant differencesamongthesampledsites,exceptforthenorthernmostsite(Tanga)andanislandinthesouth(Songosongo). Analysis of molecular variance (AMOVA) revealed a non-significant geneticstructure among populations (FST= 0.01782), suggesting thefishery across Tanzanian watersexploits the same population. Moreover, there was no correlative relationship between geneticand pairwise geographic distances, rejecting the isolation by distance hypothesis. However,neutrality tests and mismatch distribution analysis revealed that recent demographic expansionmight exist. Empirical evidence of panmixia suggests high genetic connectivity. In combinationwith low genetic diversity, management shouldbe directed to actions that prevent geneticdiversity loss and the effect of genetic drift on populations.
Using fishers’ local ecological knowledge for management of small-scale fisheries in data-poor regions: Comparing seasonal interview and field observation records in East Africa
(Elsevier, 2023-08) Silas, Mathew; Semba, Masumbuko; Mgeleka, Said; Well, Lisa; Linderholm, Hans; Gullström, Martin
Fishers, scientists and policy makers need to describe, understand and “agree on” variations in fish catches caused by exploitation and climate change for effective fisheries management. To achieve this, relevant data with sufficient spatiotemporal resolution is a necessity. In regions of the Global South, such as the Western Indian Ocean (WIO), fish catch data useful for management is scarce or non-existing. Still, the potential of local ecological knowledge to provide such information has not been fully utilised in these regions. In this study, we evaluated fishers’ local ecological knowledge (based on interviews) against detailed seasonal fish catch variability data based on catch per unit effort (CPUE) records. Because of the importance of the monsoon seasons for marine resource variability, differences in fish catches during the northeast (NE) and southeast (SE) monsoon seasons were investigated. Fishers’ perceptions generally agreed with catch data records, both showing that the NE monsoon season generally provides higher catch rates than the SE monsoon season. The fishers’ perceptions at two of the landing sites (Nyamisati and Shangani) contradict the recorded observations by showing highest fish catches during the SE monsoon season. It was clear, however, that fishers’ perceptions in these two sites focused on the most valuable target species (prawn and tuna in Nyamisati and Shangani, respectively) rather than total catches. In this particular case, fishers’ perceptions facilitated the significance of taking target species into consideration. The findings of this study highlight the importance of integrating local ecological knowledge into scientific research to help understand the complex dynamics of coastal fisheries and improve the management of data-poor fisheries.