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Estimated mortalities and potential yield of freshwater shark (Wallago attu) from the 'Dhir beel' (riverine floodplain lake) ecosystem of the Brahmaputra basin, Assam, India

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Title Estimated mortalities and potential yield of
freshwater shark (Wallago attu) from the
'Dhir beel' (riverine floodplain lake) ecosystem
of the Brahmaputra basin, Assam, India
 
Creator Goswami, P K
Devaraj, M
 
Subject Freshwater Fisheries
Estimation
 
Description The annual instantaneous natural mortality as well as the total mortality rates
and the potential yield of Wallago attu (Bloch and Schneider) were estimated
from the 'Dhir beel' ecosystem of the Brahmaputra basin, Assam, India. The
instantaneous natural mortality (M) as estimated by different methods was
found to be 0.83 (Pauly) and 1.15 (Cushing). However, the realistic value of
M for W. attu in the 'Dhir beel' was found to be 1.55 (assumed value). The
average instantaneous total mortality (Z) values calculated by various methods
were 3.44 (Jackson), 3.50 (Jones and Van Zalinge) and 3.70 (Beverton and
Holt). The annual Z for the period 1980-'90 ranged from 1.45 (1988-'89) to
5.14 (1986-'87) for M = 0.83; 1.69 (1988-'89) to 4.95 (1986-'87) for M = 1.15
and 2.0 (1988-'89) to 4.67 (1986-'87) for M = 1.55. The potential yield per
recruit (Y1) for W. attu in the 'Dhir beel' was estimated to be 440.0 g
corresponding to a length (1) of 70.80 cm and age (t) of 1.16 year as per the
analytical model of Beverton and Holt. However, it was 427.78 g for 1 = 73.55
cm and t =1.22 year as per the Kutty and Qasim model. The biomass per
recruit attained a peak at 1 = 62.63 cm and t = 0.98 year as per Jones' length
cohort analysis. The potential yield per recruit was estimated for three
different values of natural mortality, M(=0.83, 1.15 and 1.55) as a function
of exploitation ratio (E) for the observed age at first capture, t = 0.36 year
corresponding to lc = 30.0 cm and also for the age at first recruitment, t =
0.21 year corresponding to lr = 17.5 cm. In view of the highly predatory habit,
the length a-; first capture, lc = 30.0 cm can be considered to be the optimum
size at first exploitation of W. attu in 'Dhir beel'. The maximum sustainable
yield (MSY) for W. attu has been estimated to be 10,458 kg for the optimum
effort at MSY (fmgy) of 182 men/day as per Schaefer and the MSY of 8,646
kg at fms of 182 men/day as per Fox. The fms of 182 men/day could be more
economical for the W. attu fishery in the 'Dhir beel'.
 
Publisher CMFRI/ICAR
 
Date 1996
 
Type Article
PeerReviewed
 
Format application/pdf
 
Language en
 
Identifier http://eprints.cmfri.org.in/235/1/Article_06.pdf
Goswami, P K and Devaraj, M (1996) Estimated mortalities and potential yield of freshwater shark (Wallago attu) from the 'Dhir beel' (riverine floodplain lake) ecosystem of the Brahmaputra basin, Assam, India. Indian Journal of Fisheries, 43 (2). pp. 127-136.