article · Fishes
Large reservoir fisheries are often managed under the assumption that fish populations are evenly distributed, ignoring complex embayment structures. An ecological study in Lake Nasser, Egypt, assessed how local bay systems, known as khors, affect two commercially important catfish species, Chrysichthys auratus and Chrysichthys rueppelli. Across six khors along a north to south gradient, standardised sampling yielded significant differences in fish abundance, size, and physical condition. Chrysichthys auratus demonstrated substantial variation in catch rates, reaching its highest numbers and best condition in Garf Hussein, alongside a significant female bias overall. Conversely, Chrysichthys rueppelli maintained stable catch rates across locations but achieved greater body length and weight in southern khors, with peak body condition recorded in Toshka. These variations confirm that embayment-level measurements capture crucial ecological trends that whole-lake averages obscure, providing essential detail for sustainable mega-reservoir management.
Managing large reservoirs using blanket averages risks overlooking localised stock depletion or habitat advantages. Demonstrating that fish populations vary markedly between specific bays enables fisheries authorities to tailor conservation and harvest policies to local conditions. This spatial precision supports better protection of breeding stocks, sustains commercial catches, and improves food security in regions reliant on major freshwater fisheries.
This research provides applied baseline evidence to inform spatial fisheries management and harvest quotas in large inland reservoirs. Primary users would be freshwater fisheries authorities, reservoir management bodies, and policy planners seeking to improve catch monitoring programmes. Because the findings represent field-tested ecological assessments rather than a deployable tool, operational use depends on authorities adopting these spatial monitoring protocols into existing regulatory frameworks.
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Global inland fisheries depend on large reservoirs, yet many assessments assume spatial homogeneity despite complex embayed morphometry. We tested whether khor-scale structure within Lake Nasser, Egypt, explains variation in two commercially important catfishes. Six distinct khors spanning the north–south axis (Ghazal, Sheniara, Garf Hussein, Amada, Toshka, and Hamedo) were sampled with standardized effort (72 net-nights; 12 per khor, 3 representative areas ≥ 500 m apart × 4 campaigns, March–June 2021), yielding 398 fish (268 Chrysichthysauratus, 130 C. rueppelli). Abundance was expressed as standardized CPUE (fish·net-night−1). C. auratus CPUE ranged from 2.83 (Ghazal) to 5.92 (Garf Hussein), while C. rueppelli CPUE was relatively uniform (1.50–1.92). C. auratus attained the largest TL in Ghazal (25.51 ± 2.9 cm) and the highest condition K in Garf Hussein (1.46 ± 0.18). C. rueppelli attained the greatest TL and weight in southern khors, especially Hamedo (23.3 ± 2.33 cm, 146.7 ± 30.5 g), while its highest condition was in Toshka (1.30 ± 0.15). Sex ratio was significantly female-biased for C. auratus (92 M:176 F, 1:1.91, p < 0.001) but not for C. rueppelli (55 M:75 F, 1:1.36, p = 0.079). Results show embayment-scale CPUE and condition, not whole-lake means, capture key population patterns, improving precision of mega-reservoir fisheries management.
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DOI: 10.3390/fishes11090523
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