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An assessment of a light-attraction fishery in southern Lake Malawi
Abstract
This study provides the first quantitative
assessment of the light-attraction component of a small-scale purse seine,
locally known as a chilimira net, fishery in two areas of southern Lake
Malawi. For monitoring purposes the shoreline of Lake Malawi is divided into
a
number of statistical strata. Two strata (‘2.1' in the southeast arm and ‘3.1'
in the southwest arm of the lake) were selected for this study. Catch per unit
effort in stratum 2.1 was generally lower than that recorded in stratum 3.1 but
nets in stratum 2.1 fished more frequently, leading to similar annual catches
in the two strata. Annual catch was estimated as 19.4 (CI = 15.9–23.5) tons net–1 year–1 in
stratum 2.1 and 23.5
(CI = 19.5–28.1) tons net–1
year–1 in
stratum 3.1 respectively. A total of 62 species from 28 cichlid genera, and 13
species from nine non-cichlid genera, were identified from the samples. Of the
37 genera identified, only five; Copadichromis, Dimidiochromis, Engraulicypris,
Oreochromis and Rhamphochromis, contributed more than 5% to the
total annual catch in either stratum. Their combined contribution to the annual
catch was in excess of 85% in both strata. Comparisons showed that
catch-composition was dependent on area. Length-frequency distributions of
major target species in the catch showed that the fishery targeted juveniles in
stratum 2.1, while in stratum 3.1 most individuals were harvested after
reaching their length-at-maturity. The dependence of catch-composition and
size-selection on area indicates that management interventions for this fishery
need to be area-specific. Since the fishery targets a diverse species
assemblage, effort limitation or area closure may be the only viable management
options, until such time as additional biological and fisheries data are
available for the application of stock assessment models.
African Journal of
Aquatic Science
2004, 29(1): 1–11
assessment of the light-attraction component of a small-scale purse seine,
locally known as a chilimira net, fishery in two areas of southern Lake
Malawi. For monitoring purposes the shoreline of Lake Malawi is divided into
a
number of statistical strata. Two strata (‘2.1' in the southeast arm and ‘3.1'
in the southwest arm of the lake) were selected for this study. Catch per unit
effort in stratum 2.1 was generally lower than that recorded in stratum 3.1 but
nets in stratum 2.1 fished more frequently, leading to similar annual catches
in the two strata. Annual catch was estimated as 19.4 (CI = 15.9–23.5) tons net–1 year–1 in
stratum 2.1 and 23.5
(CI = 19.5–28.1) tons net–1
year–1 in
stratum 3.1 respectively. A total of 62 species from 28 cichlid genera, and 13
species from nine non-cichlid genera, were identified from the samples. Of the
37 genera identified, only five; Copadichromis, Dimidiochromis, Engraulicypris,
Oreochromis and Rhamphochromis, contributed more than 5% to the
total annual catch in either stratum. Their combined contribution to the annual
catch was in excess of 85% in both strata. Comparisons showed that
catch-composition was dependent on area. Length-frequency distributions of
major target species in the catch showed that the fishery targeted juveniles in
stratum 2.1, while in stratum 3.1 most individuals were harvested after
reaching their length-at-maturity. The dependence of catch-composition and
size-selection on area indicates that management interventions for this fishery
need to be area-specific. Since the fishery targets a diverse species
assemblage, effort limitation or area closure may be the only viable management
options, until such time as additional biological and fisheries data are
available for the application of stock assessment models.
African Journal of
Aquatic Science
2004, 29(1): 1–11
