Department of Biological Sciences, Earth to Ocean Research Group, Simon Fraser University, Burnaby, British Columbia, Canada.
Fisheries and Ocean Canada, Pacific Science Enterprise Centre, West Vancouver, British Columbia, Canada.
PLoS One. 2020 Dec 17;15(12):e0237052. doi: 10.1371/journal.pone.0237052. eCollection 2020.
Over 1 billion USD are devoted annually to rehabilitating freshwater habitats to improve survival for the recovery of endangered salmon populations. Mitigation often requires the creation of new habitat (e.g. habitat offsetting) to compensate population losses from human activities, however offsetting schemes are rarely evaluated. Anadromous Pacific salmon are ecologically, culturally, and economically important in the US and Canada, and face numerous threats from degradation of freshwater habitats. Here we used a matrix population model of coho salmon (Oncorhynchus kisutch) to determine the amount of habitat offsetting needed to compensate mortality (2-20% per year) caused by a range of development activities. We simulated chronic mortality to three different life stages (egg, parr, smolt/adult), individually and simultaneously, to mimic impacts from development, and evaluated if the number of smolts produced from constructed side-channels demographically offset losses. We show that under ideal conditions, the typical size of a constructed side-channel in the Pacific Northwest (PNW) (3405 m2) is sufficient to compensate for only relatively low levels of chronic mortality to either the parr or smolt/adult stages (2-7% per year), but populations do not recover if mortality is >10% per year. When we assumed lower productivity (e.g.; 25th percentile), we found that constructed channels would need to be 2.5-4.5 fold larger as compared to the typical size built in the PNW, respectively, to maintain population sizes. Moreover, when we imposed mortality to parr and smolt/adult stages simultaneously, we found that constructed side-channels would need to be between 1.8- and 2.3- fold larger that if the extra chronic mortality was imposed to one life stage only. We conclude that habitat offsetting has the potential to mitigate chronic mortality to early life stages, but that realistic assumptions about productivity of constructed side-channels and cumulative effects of anthropogenic disturbances on multiple life stages need to be considered.
每年投入超过 10 亿美元用于修复淡水生境，以提高濒危鲑鱼种群的恢复存活率。缓解措施通常需要创造新的生境（例如生境补偿）来弥补人类活动造成的种群损失，但补偿计划很少得到评估。溯河洄游的太平洋鲑鱼在美国和加拿大具有生态、文化和经济重要性，面临着淡水生境退化的诸多威胁。在这里，我们使用银大麻哈鱼（Oncorhynchus kisutch）的矩阵种群模型来确定需要补偿多少生境补偿来弥补一系列发展活动造成的死亡率（每年 2-20%）。我们模拟了慢性死亡率对三个不同生命阶段（卵、幼鱼、幼鱼/成鱼）的影响，单独和同时进行，以模拟发展的影响，并评估从构建的旁道中产生的幼鱼数量是否在人口统计学上抵消了损失。我们表明，在理想条件下，太平洋西北（PNW）典型的旁道构建规模（3405 平方米）仅足以补偿幼鱼或幼鱼/成鱼阶段相对较低水平的慢性死亡率（每年 2-7%），但如果死亡率超过每年 10%，则种群无法恢复。当我们假设较低的生产力（例如；第 25 百分位数）时，我们发现与在 PNW 建造的典型尺寸相比，构建的通道需要分别扩大 2.5-4.5 倍，以维持种群规模。此外，当我们同时对幼鱼和幼鱼/成鱼阶段施加死亡率时，我们发现与仅对一个生命阶段施加额外慢性死亡率相比，构建的旁道需要分别扩大 1.8-2.3 倍。我们得出结论，生境补偿有可能减轻早期生命阶段的慢性死亡率，但需要考虑对构建旁道生产力的现实假设以及对多个生命阶段的人为干扰的累积影响。
