Fish condition in introduced tilapias of Ugandan crater lakes in relation to deforestation and fishing pressure
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Date
2009
Journal Title
Journal ISSN
Volume Title
Publisher
Environmental biology of fishes
Abstract
This study identifies environmental predictors
of the condition of two introduced tilapia species
(Oreochromis leucostictus and Tilapia zillii) that are
known to have divergent trophic niches (planktivore
and herbivore, respectively) in 17 crater lakes in
western Uganda. We asked whether fish condition
differs among lakes characterized by differences in
fishing pressure and catchment deforestation; and we
related relative condition factor to gradients of
environmental variation across lakes. Lakes characterized
by severe catchment deforestation tended to be
lakes with high fishing pressure, so it was difficult to
explore independent and interactive effects. However,
mean relative condition factor was higher in populations
with high fishing pressure compared to populations with
low fishing pressure for both O. leucostictus and
T. zillii. The condition of O. leucostictus populations
was higher in lakes with severely deforested catchments;
but mean relative condition factor of T. zillii did
not differ between deforestation categories. Principal
components analysis (PCA) was used to describe the
major environmental gradients of variation among the
lakes; and PCA factor scores were regressed against
relative fish condition. The association between fish
condition and environmental gradients was stronger for
O. leucostictus than for T. zillii. For O. leucostictus,
fish condition was related to PC1 (43% of the variance)
and factors that loaded most heavily included Chl-a,
water transparency, lake area and depth, suggesting
higher condition in lakes characterized by higher
primary productivity and smaller size. For T. zillii,
PC3 (11%) was the only axis related to fish condition;
and factors that loaded most heavily included lake area
(positive), and conductivity and total nitrogen (negative).
Some of the larger lakes are characterized by
higher availability of macrophytes that may positively
affect the food base for T. zillii.
Description
Keywords
Human disturbance, Fishing pressure, Environmental predictors, Primary productivity, Oreochromis leucostictus, Tilapia zillii, Length-weight relationships
Citation
Efitre, J., Chapman, L. J., & Murie, D. J. (2009). Fish condition in introduced tilapias of Ugandan crater lakes in relation to deforestation and fishing pressure. Environmental biology of fishes, 85(1), 63-75. DOI 10.1007/s10641-009-9461-z