A.M.Hoguane 1, E. L. Cuamba 2 & Tor Gammelsrød 3 1 School of Marine and Coastal Sciences, Eduardo Mondlane University, PO Box 128, Quelimane, Mozambique; hoguane@yahoo.com.br; 2 Centro de Pesquisa do Ambiente Marinho e Costeiro (CEPAM), P.O.Box 306, Pemba, Moçmbique, ntchamby@gmail.com; 3 Institute of Geophysics, University of Bergen, Allegt 70, 5007 Bergen, Norway, torg@gfi.uib.no
Content Introduction and objectives; Study area; Methodology; Result and discussion; Concluding remarks.
Introduction and objectives The artisanal catch contributed about 87% of the overall annual fish production in Mozambique, estimated to 115,000-140,000 tones; The artisanal fisheries involve on average about 70,000 to 100,000 fishermen and fish collectors per year, who operate in coastal waters using canoe and small boats, and a variety of fishing gear including bottom trawls, beach seines, gillnets, hand-lines, traps and spears. The availability of fish depends on a variety of factors among which the environment and fishing effort so that the traditional management measures based only on controlling the effort are no longer effective (Hoguane et al, 2002).
Introduction and objectives cont. Objectives: The present paper analyses the relationship between the fish abundance and the freshwater input into the coastal zone in the coastal districts of Moma, Angoche and Mongicoal, in northern Mozambique (Fig. 1).
Study area Latitudes 15 o 17 o S; Climate: tropical rain savannah climate, with two distinct seasons: - winter or dry and - summer or wet seasons. average annual precipitation is 1,200 mm; rainfall is mainly restricted to the warm season November to April. Fig.1. Area de estudo
Methodology The study was based in the artisanal catch statistics of northern Mozambique (Mongicual, Angoche and Moma), from 1998 to 2008; Monthly rainfall recorded at the Angoche meteorological station, from 1995 up to 2008; Since the fishing effort was determined by the number of active gears registered only once a year and there is no indication of how often the gears were applied, then the total catch was used as a measure of fish abundance instead of catch rate; Hence, the total annual catch of the artisanal fisheries was correlated with the annual rainfall recorded in Angoche, with time lags from zero to three years (Figure 2 and Table 1).
Result and discussion Dominant family groups were: Engraulididae, Carangidae,Clupeidae, Leiognathidae and Trichiuridade (over 40%). Familia Captura total (1998-2008) Percentagem (%) Engraulididae 11266 15 Carangidae 6422 9 Clupeidae 5680 8 Leiognathidae 4239 6 Trichiuridae 4181 6 With longevity of 2 to 4 years and/or attaining commercial size with age 2. Scombridae 3654 5 Sergestidae 3618 5 Pomatomidae 3137 4 Sciaenidae 2771 4 Haemulidae 2607 4 Mulidae 2373 3 Siganidae 1316 2
c) 1 Figure 3. Result of correlation between total catch and rainfall with different time lag (n=12) Coeficiente de correlacao (R2) 0.8 0.6 0.4 0.2 0-0.2 0 1 2 3 Faseamento d) Regression analysis between catch and precipitation with 2-years lag Capturas (tons) 18000 16000 14000 12000 10000 8000 6000 4000 2000 0 R² = 0.78 0 200 400 600 800 1000 1200 1400 1600 Precipitação (mm)
Desfasamento (Anos) r p 0-0.141 0.678 1 0.388 0.238 2 0.786 0.004 3 0.225 0.506 Table 1: Result of correlation between total catch and rainfall with different time lag (n=12) A positive and significant correlation between the rainfall and the artisanal total catch was found with two years lag between the rainfall and the total catch, with (r = 0.78; p=0.004, n=12) The result is consistent with the findings from other areas (e.g. Quiñones and Montes (2001) in Chile)
The positive correlation between the rainfall and productivity of coastal fisheries may be explained as follows: freshwater supplies nutrients into the coastal waters, which provides food for fish as explained by (Gammelsrød, 1992; Meynecke et al, 2006; e Ayub, 2010); freshwater input is associated with sediment load and relatively high turbidity in the coastal waters, providing suitable shelter for the larvae and juveniles from the predators; The two-year time lag may be explained by the fact that dominant family groups such as Engraulididae, Clupeidae and Leiognathidae, have longevity of 2 to 4 years and most of the family species such as Carangidae attain size caught by artisanal fishing gears at 2 years of age (Cabanban, 1991; Nelson, 1984; Whitehead et al., 1988).
Considering the fact that freshwater contributes to the survival rate of larvae and juveniles (Ayub, 2010), then the effect of abundant freshwater into the fisheries would be felt few years later, after recruitment (Meynecke et al, 2006) It seems that the artisanal fish abundance in Northern Mozambique may be predicted two years ahead based on the rainfall in the area (Figure 3)
18000 1600 Catch (Tons) 16000 14000 12000 10000 8000 6000 4000 2000 1400 1200 1000 800 600 400 200 Rainfall (mm) 0 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 0 Catch Rainfall Figure 3. Time series of the annual artisanal total catch in Mongicual, Angoche and Moma with the annual rainfall recorded at Angoche lagged two years
Concluding remarks A positive and significant correlation between the rainfall and the artisanal total catch was found with two years lag between the rainfall and the total catch, with (r = 0.78; p=0.004, n=12) The two-year time lag at which the significant correlation was found may be related to the fact that rainfall influences the earlier stage of the life cycles of most fish species The findings in this work may contribute to predict the fish production, and hence improve the management measures of the artisanal fisheries
Acknowledgement The artisanal catch and fishing effort data were provided by the National Institute of Fisheries Research. The rainfall data was provided by the National Institute of Meteorology. NOMA (Norwegian Maters Program) and SOED (Southern Ocean, Education and Development project) co-funded our participation in the WIOMSA Symposium
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Resultados e discussão 1600 1400 a) Precipitacao (mm) 1200 1000 800 600 400 200 0 Periodo (anos) Capturas (tons) 18000 16000 14000 12000 10000 8000 6000 4000 2000 0 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Periodo (Anos) b) Figura 2. Variacão da precipitação a) e das capturas b)
Cont. Percentagem (%) 16 14 12 10 8 6 4 2 0 Familias capturadas Figura 3. Grupo das familias das especies mais capturadas