The fish community of Hamilton Harbour, Lake Ontario: Status, stressors, and remediation over 25 years

Hamilton Harbour is a large (21 km²) protected harbour located at the western end of Lake Ontario that was designated as an Area of Concern in 1985 by the International Joint Commission. As part of the designation, the fish community was deemed “impaired.” One of the long-term goals of the Hamilton Harbour Remedial Action Plan is to rehabilitate the fishery to a state, at least in part, to what it was prior to the degrading effects of industrial and municipal pollution, habitat loss, and invasive species. Since the Area of Concern designation, the nearshore fish community has been monitored regularly via a federal boat electrofishing program (1988–2013) and more recently, by a trap net program (2006–2012). During the study period, the harbour underwent significant physical and biological change which was related to both lake-wide (e.g. Dreissenids) and localized harbour events (e.g. habitat restoration). The fish community was assessed temporally using two indices of ecosystem health, the Great Lakes Index of Biotic Integrity and Proportion of Piscivore Biomass, and species-specific catch trends at unaltered sites or sites modified by habitat restoration. Early on, the fish community was dominated by tolerant species characteristic of degraded, eutrophic environments and piscivore abundance was low. The fish community responded positively to ecosystem actions during the first decade that improved water quality, increased physical habitat and reduced invasive species, but further progress was confounded by the interactions with other factors in the last decade that included new invasive species and a decline in water quality. Fish community assessments in the last decade, using both the indices found that the fish community was still impaired and dominated by non-native and pollution tolerant species. The Index of Biotic Integrity was a suitable indicator of ecosystem health strengthened by a consistent assessment with the Proportion of Piscivore Biomass index. A science based refinement of the existing Index in the future would benefit the ability to assess nearshore fish assemblages in the context of conservation goals.

汉密尔顿港（Hamilton Harbour）是一处面积达21平方千米的受保护大型港湾，坐落于安大略湖（Lake Ontario）西端，1985年被国际联合委员会（International Joint Commission）列为关注区域（Area of Concern）。随该划定一同出台的评估结论显示，其鱼类群落（fish community）被认定为“受损”。汉密尔顿港补救行动计划（Hamilton Harbour Remedial Action Plan）的长期目标之一，是将渔业恢复至工业与城市污染、栖息地丧失以及外来入侵物种造成退化之前的状态，至少实现部分恢复。
自该区域被列为关注区域以来，科研人员依托联邦船只电捕鱼项目（boat electrofishing，1988—2013年）及近期的诱捕网项目（trap net，2006—2012年），对近岸鱼类群落开展了常态化监测。研究周期内，该港湾经历了显著的物理与生物变化，这些变化既与全湖尺度的事件（如饰贝属（Dreissenids）入侵）相关，也与港湾本地事件（如栖息地修复）有关。
研究团队通过两项生态系统健康指数——大湖生物完整性指数（Great Lakes Index of Biotic Integrity）与食鱼生物生物量占比（Proportion of Piscivore Biomass），以及未受干扰位点或经栖息地修复改造位点的物种特异性捕捞趋势，对鱼类群落进行了时序评估。
研究初期，鱼类群落以适应退化富营养化环境的耐污物种为主，食鱼生物的丰度较低。
在首个十年间，随着水质改善、物理栖息地优化以及入侵物种防控，鱼类群落呈现出积极的恢复响应；但在随后的十年中，由于新的外来入侵物种出现及水质下降等多重因素的交互影响，恢复进程进一步受阻。
近十年的鱼类群落评估结果显示，依托两项指数均可发现，该港湾的鱼类群落仍处于受损状态，仍以外来物种及耐污物种为主。
大湖生物完整性指数是合适的生态系统健康指示物，结合食鱼生物生物量占比指数开展的一致性评估进一步强化了这一结论的可靠性。
未来可基于科学依据对现有指数进行优化，以更好地围绕保护目标评估近岸鱼类群落（fish assemblages）。