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The biology of Barbus mattozi Guimaraes (Teleostei, Cyprinidae) in a Zimbabwean reservoir. 3. Numbers, biomass and mortality
Abstract
The population of B. mattozi in the
Mtsheleli Dam, Zimbabwe, was estimated to be about 55 000 fish in July 1974 but
fell to about 370 by June 1975. The total biomass followed a similar trend,
reaching 2 000kg (43kg ha–1) in July and falling to 130kg (2.8kg ha–1)
after one year. The mortality rate was very high (Z = 5.00) and considerably
higher than in a number of other fishes, many of them considerably smaller than
B. mattozi. The reasons for this decline are discussed and they include
the effects of humans who removed about 17.5% of the total population,
cannibalism, otters and birds. A remarkable feature of the population was the
lack of small fish (<12cm FL), which was attributed to a failure of spawning
during a serious drought in 1972–1973. The numbers of small fish began to
increase from June 1975 and these were most likely the cohort spawned during
the good rains of 1973–1974. Fluvial fishes in semi-arid parts of southern
Africa are likely to experience wide variations in numbers determined by the
success or failure of spawning in wet or dry years.
African Journal of Aquatic Science
2004, 29(1): 103–106
Mtsheleli Dam, Zimbabwe, was estimated to be about 55 000 fish in July 1974 but
fell to about 370 by June 1975. The total biomass followed a similar trend,
reaching 2 000kg (43kg ha–1) in July and falling to 130kg (2.8kg ha–1)
after one year. The mortality rate was very high (Z = 5.00) and considerably
higher than in a number of other fishes, many of them considerably smaller than
B. mattozi. The reasons for this decline are discussed and they include
the effects of humans who removed about 17.5% of the total population,
cannibalism, otters and birds. A remarkable feature of the population was the
lack of small fish (<12cm FL), which was attributed to a failure of spawning
during a serious drought in 1972–1973. The numbers of small fish began to
increase from June 1975 and these were most likely the cohort spawned during
the good rains of 1973–1974. Fluvial fishes in semi-arid parts of southern
Africa are likely to experience wide variations in numbers determined by the
success or failure of spawning in wet or dry years.
African Journal of Aquatic Science
2004, 29(1): 103–106
