Freshwater mussels, Unionoida, are endangered across the globe due to recruitment failure. In the present study, with general linear mixed models, we investigated the relative effects of biotic (host fish density) and abiotic (water depth, fine sediment, water temperature, and water quality) factors on the recruitment of Margaritifera laevis in 10 streams of Hokkaido, northern Japan. We additionally examined the factors regulating the density of the host fish Oncorhynchus masou masou with general linear models. The proportion of juvenile mussels had a unimodal relationship with the host density, which was the most influential factor among the others examined. The positive relationship between mussel recruitment and host density can be attributed to an increased host fish infection rate. The negative correlation between mussel recruitment and host density at high fish densities may be due to reduced larval growth on host fish that are in poor physical condition. We also found that host fish density was negatively affected by nutrient enrichment. Our results suggest that mitigating water quality degradation to recover host fish density should be prioritized to improve mussel recruitment. Although stock enhancement is effective for increasing the salmon population density, excess stocking can further disturb mussel recruitment.

中文翻译：

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生物因子和非生物因子对淡水贻贝（Margaritifera laevis）招聘的相对影响

由于招募失败，淡水贻贝Unionoida在全球受到威胁。在本研究中，我们采用一般的线性混合模型，研究了生物（宿主鱼的密度）和非生物（水深，细沙，水温和水质）因素对玛格丽特弗拉海藻在10条河流中募集的相对影响。日本北部的北海道。我们还检查了调节寄主鱼Oncorhynchus masou  masou密度的因素。与一般的线性模型。贻贝幼鱼的比例与寄主密度呈单峰关系，这是受调查的其他因素中影响最大的因素。贻贝募集与寄主密度之间的正相关可归因于寄主鱼感染率的增加。高鱼密度时贻贝的募集与寄主密度之间的负相关性可能是由于身体状况较差的寄主鱼幼体生长减少所致。我们还发现，养鱼密度受到养分富集的负面影响。我们的结果表明，应优先考虑减轻水质退化以恢复寄主鱼的密度，以改善贻贝的繁殖。尽管增加种群数量对增加鲑鱼种群密度有效，但过多的种群数量可能进一步干扰贻贝的捕捞。