Browsing by Author "Grayson, Johnson Mshana"

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    Fisheries of Meuthynnus Affinis and Scomberomorus Cmerson in relation to oceanographic and atmospheric parameters off the coastal waters of Dar es Salaam, Tanzania
    (University of Dar es Salaam, 2010) Grayson, Johnson Mshana
    The present study was conducted to assess how fisheries of E. affinis and S. commerson relate to seasonal variations in- and atmospheric parameters off the coastal waters of Dar es Sal Tanzania.. Fisheries data of the two species of fish, oceanographic and atmosphericparameters were collected between April to September 2008 and November 2008 to February 2009 during southeast monsoon (SEM) and northeast monsoon (NEM) seasons respectively. A total of 2,591 E. affinis and 722 S. commerson were collected in both NEM and SEM seasons. Significantly higher seasonal variations in the catch- per unit effort (CPUE) were observed for fishing trips undertaken during the day (p = 0.042) and at night (p = 0.045) for E. affinis and S. commerson (p = 0.004), respectively. Both oceanographic (seas surface temperature and salinity) and atmospheric (temperature, rainfall, solar radiation and wind speed) parameters showed a significant correlation to CPUE of E. affinis (r = range from - 0.58 to 0.98). For S. commerson, only the oceanographic parameters correlated significantly to CPUE (r = range from - 0.58 to - 0.79). The relationship between length-weight (exponent b) for samples of different sexes and seasons showed an isometric growth for both E. affinis and S. commerson. Gonad-somatic index revealed a year round spawning for both species. Mean stable isotopes of '3C and '5N values showed that the two species feed on marine fish at different trophic position and they varied significantly (p< 0.05) with negative values and a wide range of trophic level were season whereas the most neg observed in NEM for E. affinis and in SEM for S. commerson. In conclusion, the present "fluence of oceanographic and atmospheric parameters on the findings showed the in and S commerson implying that they have impacts on the population CPUE of E. affinis an . al indices of these species. Therefore, long term monitoring of the dynamics and biological and atmospheric parameters on the population impacts regarding ocean dices of E. affinis and S. commerson is recommended.
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    Genetic stock structure and life History of euthynnus affinis cantor (1849) and scomberomorus commerson lacepede (1800) fishes in the northern coastal waters of Tanzania
    (University of Dar es Salaam, 2016) Grayson, Johnson Mshana
    The population genetic structure and life history traits of Kawakawa Euthynnus affinis Cantor (1949) and Narrow barred Spanish mackerel Scomberomorus commerson Lacepede (1800) in the northern coastal waters of Tanzania, Western Indian Ocean were studied using sequence analysis of mitochondrial DNA (mtDNA) control region. A 475bp and 500bp segment of the control region was sequenced and analyzed (38 and 46 samples of Narrow barred Spanish mackerel and Kawakawa, respectively). The study revealed high levels of haplotype and nucleotide diversities. Analysis of molecular variance (AMOVAL), nearest neighboring statistic (Sm) and exact test of genetic differentiation did not show evidence for population subdivision (p>0.005); hence a null hypothesis that studied fish species constitute a single genetic stock in the northern Tanzania coastal waters could not be rejected. The Tajima’s D and Fu’s Fs models showed a significant deviation from neutral condition (p<0.005), indicative of a recent population expansion. The study revealed a single clade of individual fish species, suggestive of similar genealogical history. The genetic data were also supported by life history traits, which revealed geographical similarities in the spawning patterns, size at maturity and fish condition. In addition, number and size of eggs (µm) for females collected from Dar es Salaam was not statistically higher than those from Pangani (p>0.005). The Presence of genetic similarities for studied fish species was a result of gene flow, short geographical distance (IBD) and homogeneity in environmental distances (IBED, p>0.005). A single-stock model and regional shared management along with further similar research covering the whole Indian Ocean is therefore recommended.
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    Genetic stock structure and life History of euthynnus affinis cantor (1849) and scomberomorus commerson lacepede (1800) fishes in the northern coastal waters of Tanzania
    (University of Dar es Salaam, 2016) Grayson, Johnson Mshana
    The population genetic structure and life history traits of Kawakawa Euthynnus affinis Cantor (1949) and Narrow barred Spanish mackerel Scomberomorus commerson Lacepede (1800) in the northern coastal waters of Tanzania, Western Indian Ocean were studied using sequence analysis of mitochondrial DNA (mtDNA) control region. A 475bp and 500bp segment of the control region was sequenced and analyzed (38 and 46 samples of Narrow barred Spanish mackerel and Kawakawa, respectively). The study revealed high levels of haplotype and nucleotide diversities. Analysis of molecular variance (AMOVAL), nearest neighboring statistic (Sm) and exact test of genetic differentiation did not show evidence for population subdivision (p>0.005); hence a null hypothesis that studied fish species constitute a single genetic stock in the northern Tanzania coastal waters could not be rejected. The Tajima’s D and Fu’s Fs models showed a significant deviation from neutral condition (p<0.005), indicative of a recent population expansion. The study revealed a single clade of individual fish species, suggestive of similar genealogical history. The genetic data were also supported by life history traits, which revealed geographical similarities in the spawning patterns, size at maturity and fish condition. In addition, number and size of eggs (µm) for females collected from Dar es Salaam was not statistically higher than those from Pangani (p>0.005). The Presence of genetic similarities for studied fish species was a result of gene flow, short geographical distance (IBD) and homogeneity in environmental distances (IBED, p>0.005). A single-stock model and regional shared management along with further similar research covering the whole Indian Ocean is therefore recommended.