Browsing by Author "Mtonga, Cretus"

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Mitochondrial DNA revealed a single stock structure of the Spotted sardinella Amblygaster sirm (Walbaum, 1792) (Teleostei; Clupeidae) in Tanzanian coastal waters
(Springer Berlin Heidelberg, 2023-06-12) Fabiani, Godfrey; Mtonga, Cretus; Chauka, Leonard; Rumisha, Cyrus; Muhando, Christopher
The Spotted sardinella Amblygaster sirm are small pelagic fish that are important protein source to coastal communities in the Indo-West Pacific. In this study, a cytochrome c oxidase subunit 1 (COI) gene of A. sirm from Tanzania was amplified to assess the species’ genetic structure and demographic history. All individuals collected were identified using both morphological examination and genetic barcoding as A. sirm. A total of 19 haplotypes were found in the dataset, with low overall nucleotide (π = 0.13 ± 0.001) and moderate haplotype diversities (h = 0.45 ± 0.07). AMOVA revealed a very low and non-significant genetic differentiation in the dataset (Fst = 0.002, Фst = −0.004, p > 0.05), indicating a lack of population structure. The minimum spanning haplotype network revealed additional evidence for the lack of population structure, which grouped all the sampled haplotypes into one cluster, regardless of their geographical regions. The Tajima’s D, Fu’s Fs tests, and mismatch distribution analyses supported a hypothesis of recent demographic expansion. The lack of population structure identified suggests that the fishery should be treated as a single-stock management unit, consistent with the existing management regime for the species in Mainland Tanzania that currently does not consider genetic structure in managing the fishery. The lack of population structure suggests that populations with low genetic diversity, such as Dar es Salaam, can rebuild by recruiting from other sites if regulations against unsustainable fishing are strictly enforced.
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.
Recent rise in exploitation of Tanzanian octopuses: a policy and management challenge
(AJOL, 2022-11-29) Mtonga, Cretus; Jiddawi, Narriman; Benjamen, Debora
The artisanal octopus fishery is important for the coastal communities in Tanzania. In this work the octopi landing data from the United Nations Food and Agriculture Organization (FAO), Ministry of Livestock and Fishery Development (MLFD) and trade statistics from Comtrade of the United Nations were analysed. The FAO dataset show that from 1980 to 2017 annual octopus landings stayed below 2000 tons until 2018 when the catch increased to 2864 tons, and doubled to 5,687 tons in 2019. FAO datasets show large catches in 1995, 2003 and 2019, with 2019 recording the largest catch. For both Comtrade and MLFD export statistics, approximately 5,818 and 2,254 tons of octopus were exported globally from 2018 to 2020 with an equivalent value of approximately 13 and 19 million US$ respectively. Portugal was the largest importer of Tanzanian octopi, followed by Turkey, Italy, Spain, Netherlands, Israel, France and Panama. The current management interventions relating to octopi are presented, including the challenges needed to be addressed for sustainability of the octopi fishery. Voluntary octopi closures indicated some signs of success, but an in-depth assessment of the associated effects is required. The study recommends a need for verification mechanisms to ensure consistency of FAO and MLFD statistics, stock assessments, in-situ research on recruitment patterns of octopi, as well as innovation and research in designing sustainable fishing gear to support development of policies for sustainability.