Koranteng, Kwame Abu (1998) The impacts of environmental forcing on the dynamics of demersal fishery resources of Ghana. PhD thesis, University of Warwick.

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Abstract

The dynamics of demersal fish species assemblages and stocks on the continental
shelf of Ghana, West Africa were investigated using data from trawl surveys
conducted between 1963 and 1990, and in relation to marine environmental and nearshore
forcing factors.
Time series analysis was used to examine the dynamics of the marine environment.
Classification and ordination methods were used to identify fish assemblages and to
identify factors that determine assemblage formation and dynamics. The response of
the identified assemblages to changes in the Ghanaian shelf ecosystem were assessed.
Between 1964 and 1992, three distinct environmental time blocks (ETBs) in the
continental shelf ecosystem off Ghana were recognised. In the first ETB (i. e. before
1972) sea surface and bottom temperatures were relatively high and salinity was low.
The second ETB (1972 - 1982) was characterised by low temperatures, high but
stable salinity, reduced rainfall and freshwater input into the sea. In the third ETB
(1982 - 1992), the system bore a resemblance to the first block with rising
temperatures and decreasing salinity.
Six fish species assemblages were identified, namely the supra-thermocline sciaenid
and lutjanid assemblages, two sparid assemblages (shallow and deep elements), the
deep shelf assemblage and the upper slope assemblage. During ETB I and ETB3, the
assemblages were easier to identify using ordination techniques, than during ETB2.
Species diversity also decreased during ETB2 especially in waters between 10 and 50
m deep. This behaviour of the assemblagesis attributed to the increase in abundance
of Balistes capriscus, a species that dominated the ecosystem for nearly 20 years
from about 1971, and the observed environmental changes.
The estimated density of demersal fish was higher in the upwelling season than in the
thermocline season and decreased from 50 kg ha-1 in 1963-64 to 32.4 kg ha-1 in 1990.
The density reached its lowest value of 22.5 kg ha-1 in the period between 1973 and
1977.
The potential yield of the total demersal biomass (excluding triggerfish) is estimated
to be 36,000 - 55,000 mt per annum. With landed catches exceeding 60,000 mt in
some years, it is apparent that the resource is over-exploited. A number of policy
options are discussed and recommendations for the management of the fishery are
made.

Item Type:	Thesis (PhD)
Subjects:	S Agriculture > SH Aquaculture. Fisheries. Angling
Library of Congress Subject Headings (LCSH):	Marine ecosystem health -- Ghana, Fishing -- Ghana, Fishery management -- Ghana, Fish communities -- Ghana
Official Date:	January 1998
Dates:	Date Event January 1998 Submitted
Institution:	University of Warwick
Theses Department:	Department of Biological Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	McGlade, J. M. (Jacqueline Myriam), 1955- ; Price, Andrew, 1950- ; Wellington, E. M. H. (Elizabeth M. H.), 1954-
Sponsors:	O.R.S.T.O.M. (Agency : France) ; European Commission (EC)
Extent:	xxv, 377 leaves
Language:	eng

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