Distribution patterns of fish biomass by acoustic survey in three Tunisian man-made lakes
| Autor: | H. Laouar, R. Toujani, I. Djemali |
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| Rok vydání: | 2010 |
| Předmět: | |
| Zdroj: | Journal of Applied Ichthyology. 26:390-396 |
| ISSN: | 1439-0426 0175-8659 |
| DOI: | 10.1111/j.1439-0426.2009.01353.x |
| Popis: | Summary In order to test the hypothesis that fish distribution is related to water depth, three exploited reservoirs were sampled at day and at night using a Simrad EK60 echosounder. Acoustic surveys were carried out between February and June 2008, which focused on the fish size, species density (fish per ha) and biomass (kg ha−1) along vertical and longitudinal gradients. It was evident in the surface layer (0–3 m) during daytime that the larger fish sizes occupy waters near the dam or the middle of Lakhmess and Sejnane reservoirs. In the upper layer at nighttime, a gradient of fish size is shown proportional to the depth at Lakhmess Reservoir and inversely proportional at the man-made Sejnane Lake. At Lakhmess and Laabid reservoirs, fish density was significantly higher in deep water (3926 ± 1409 and 624 ± 258 fish per ha) rather than in the upper layer (988 ± 2 and 8 ± 2 fish per ha in daytime, respectively), while at Sejnane Reservoir the number of fish per area was similar along the vertical gradient. The biomass was significantly higher in waters deeper than 3 m at Sejnane Reservoir whereas at Lakhmess it was higher in the surface layer. Fish biomass increased from upstream (0.16 ± 0.05 kg ha−1) to middle (3.07 ± 2.96 kg ha−1) and downstream (3.82 ± 2.30 kg ha−1 at night) areas in the man-made Laabid Lake while a similar longitudinal gradient occurred in the deepest Sejnane Reservoir. The vertical gradient in fish distribution is discussed. From the dam to the tributary of the entire water column, it was concluded that fish biomass distribution was governed by depth and was most abundant in areas with deep waters. |
| Databáze: | OpenAIRE |
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