Balanced harvest (BH) refers to applying moderate fishing pressure across a broad range of species, trophic levels (TL), stocks, or sizes in an ecosystem in proportion to productivity (gross production per biomass unit) or production (total cumulated biomass over a given period) instead of exerting pressure on particular taxa or sizes. Both modelling and empirical studies have shown that BH can lead to higher fish yield than selective fishing, with minimal changes to ecosystem structure and function. This concept has stimulated considerable debate, and one question that needs to be addressed is how close or far fisheries are from being balanced. Here, we investigated whether fishing on Lake Victoria (East Africa), the world’s second largest inland fishery, is consistent with BH, and whether there is any link between past and present fishing patterns and life history traits of major commercially-exploited species: Nile perch (Lates niloticus) and Nile tilapia (Oreochromis niloticus). We found exploitation rates to be relatively higher in high TL groups than low TL groups; however, the overall fishing pattern has been consistent with BH until recently (from 2000 onwards). Exploitation rates (E) above 50% of annual production (“overexploitation”) were observed for large Nile perch, Nile tilapia, and other less productive demersal groups (for example, catfishes, squeakers, and lungfish). Unexpectedly, there was no evidence of significant reduction in body size of Nile perch associated with this fishing pattern, which may be attributed to limited compliance of minimum size regulations. On the other hand, we found a significant reduction in body size of Nile tilapia, which tended to be associated with high fishing pressure. We conclude that the fishery is currently inefficiently utilized in terms of food energy value, whereby groups with highest production (including small Nile perch) are underexploited (E < 10%). However, moving towards BH in the case of Lake Victoria, and generally in many inland fisheries, will require a paradigm shift both in mindset and the law.

平衡收获 (BH) 是指对生态系统中广泛的物种、营养级 (TL)、种群或大小施加适度的捕捞压力，与生产力（每生物量单位的总产量）或产量（总累积生物量）成比例。给定时期）而不是对特定的分类群或大小施加压力。建模和实证研究都表明，与选择性捕捞相比，BH 可以导致更高的鱼类产量，而对生态系统结构和功能的影响很小。这一概念引发了相当多的争论，需要解决的一个问题是渔业距离平衡有多近或多远。在这里，我们调查了在世界第二大内陆渔业维多利亚湖（东非）捕鱼是否与 BH 一致，尼罗罗非鱼）和尼罗罗非鱼（Oreochromis niloticus）。我们发现高 TL 组的剥削率比低 TL 组高；然而，直到最近（从 2000 年开始），整体捕鱼模式一直与 BH 一致。观察到大型尼罗河鲈鱼、尼罗罗非鱼和其他低产底层种群（例如鲶鱼、尖尾鱼和肺鱼）的开发率 (E) 超过年产量的 50%（“过度开发”）。出乎意料的是，没有证据表明尼罗河鲈鱼的体型与这种捕捞方式有关，这可能是由于对最小尺寸规定的遵守有限。另一方面，我们发现尼罗罗非鱼的体型显着减小，这往往与高捕捞压力有关。我们得出结论，目前渔业在食物能源价值方面的利用效率低下，其中产量最高的群体（包括小型尼罗河鲈鱼）未被充分开发（E < 10%）。然而，在维多利亚湖以及许多内陆渔业中，转向 BH 将需要思维方式和法律的范式转变。