ABSTRACT

Contemporary surveys and analysis of previous data identified negative effects of fish stocking for recreational angling in 87% of 23 English lakes (0.2–26 ha and 1–11.9 m mean depth) protected for nature conservation as Sites of Special Scientific Interest (SSSI). All sites except one were in unfavourable condition, with 92% failing to meet targets for characteristic macrophyte species. No lake was judged to have a natural fish community, and 96% had been subjected to fish stocking. The naturalised alien common carp (Cyprinus carpio) was the most widely introduced (87%). The presence of further alien species indicated illegal activity. A combination of estimates from surveys and angler records suggested carp comprised 53% of overall fish biomass density, with values up to 1164 kg ha⁻¹ in individual lakes. Successful recruitment of carp, attributed to a warming climate, was recorded in 44% of the lakes in which it occurred. Consideration of fish impacts on lake ecology from the literature concluded that management of fish stocks, through biomanipulation, was required. The efficacy of biomanipulation was demonstrated by removal of fish from a large exclosure (29% of area) in one study lake and a resultant favourable response of water transparency and macrophyte growth. In the wider SSSI lakes series, we concluded that the retention of carp in any lake was an unacceptable risk to restoration of favourable condition, as were damaging angling practices. A ban on fish stocking in SSSI lakes is recommended, unless fish are introduced to restore natural communities.

摘要

当代调查和对先前数据的分析发现，在 23 个英国湖泊（0.2-26 公顷和 1-11.9 m 平均深度）中，有 87% 的湖泊因作为特殊科学兴趣点 (SSSI) 而受到自然保护，因此放养鱼类对休闲垂钓产生了负面影响。除一个以外的所有地点都处于不利条件，92% 的地点未能达到特征大型植物物种的目标。没有一个湖泊被判定为具有天然鱼类群落，96% 的湖泊都进行了鱼类放养。归化的外来鲤鱼（Cyprinus carpio）是最广泛引入的（87%）。更多外来物种的存在表明存在非法活动。调查和垂钓者记录的综合估计表明，鲤鱼占鱼类总生物量密度的 53%，值高达 1164 kg ha ^-1在个别湖泊中。由于气候变暖，鲤鱼的成功招募记录在 44% 的湖泊中。从文献中考虑鱼类对湖泊生态的影响得出结论，需要通过生物操纵来管理鱼类种群。生物操纵的功效通过从一个研究湖中的一个大范围（面积的 29%）中去除鱼类以及由此产生的对水透明度和大型植物生长的有利反应来证明。在更广泛的 SSSI 湖泊系列中，我们得出的结论是，在任何湖泊中保留鲤鱼对于恢复有利条件都是不可接受的风险，破坏性的钓鱼实践也是如此。建议禁止在 SSSI 湖泊中放养鱼类，除非引入鱼类以恢复自然群落。