1. Many fish species of greatest conservation need (SGCN) in Iowa and Minnesota, USA, have been in decline for decades. A key reason for the decline is the alteration and degradation of naturally flowing streams owing to land use changes resulting from agricultural practices. Populations of several fishes have been adversely affected by widespread stream channelization that has resulted in more homogeneous stream habitats throughout Iowa and Minnesota.
2. The goal of this study was to determine the abiotic and fish assemblage characteristics associated with the presence of these rare fishes. Electrofishing and seining were used to sample fish assemblages and 43 abiotic characteristics were measured at 111 sites in the North Raccoon and Boone River basins in central Iowa and the Rock River and Beaver Creek basins in north-west Iowa and south-west Minnesota during 2016 and 2017.
3. Six SGCN, including the federally endangered Topeka shiner (Notropis topeka), were included in statistical modelling to determine habitat and fish assemblage characteristics associated with their presence.
4. Species-specific nonmetric multidimensional scaling ordinations indicated that abiotic characteristics and fish assemblages often differed between sites where SGCN were present and absent. Random forest and logistic regression models suggested that the presence of four of six SGCN were positively associated with species richness, whereas all other 10 important abiotic and fish assemblage variables were unique to only one or two of the six SGCN.
5. Topeka shiners were present at 36% of sites and were positively associated with orangespotted sunfish (Lepomis humilis) catch per unit effort while being negatively associated with canopy cover and fantail darter (Etheostoma flabellare) catch per unit effort.

中文翻译：

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与美国中西部溪流中六种最需要保护的鱼类分布相关的因素

1. 美国爱荷华州和明尼苏达州的许多最需要保护的鱼类（SGCN）几十年来一直在减少。下降的一个关键原因是由于农业实践导致土地利用变化，自然流动的河流发生了改变和退化。几种鱼类的种群受到广泛的河流渠道化的不利影响，导致整个爱荷华州和明尼苏达州的河流栖息地更加均匀。
2. 这项研究的目的是确定与这些稀有鱼类的存在相关的非生物和鱼类组合特征。2016 年，在爱荷华州中部的北浣熊和布恩河流域以及爱荷华州西北部和明尼苏达州西南部的罗克河和海狸溪流域的 111 个地点，使用电子捕鱼和围网对鱼类组合进行采样，并测量了 43 项非生物特征。 2017 年。
3. 六个 SGCN，包括联邦濒危的托皮卡鱼 ( Notropis topeka )，被纳入统计模型，以确定与其存在相关的栖息地和鱼类组合特征。
4. 物种特定的非度量多维尺度排序表明，SGCN 存在和不存在的地点之间的非生物特征和鱼类组合通常不同。随机森林和逻辑回归模型表明，六个 SGCN 中有四个的存在与物种丰富度呈正相关，而所有其他 10 个重要的非生物和鱼类组合变量对于六个 SGCN 中只有一两个是唯一的。
5. Topeka 发光鱼出现在 36% 的地点，与橙斑翻车鱼 ( Lepomis humilis ) 的单位努力捕获量呈正相关，而与冠层盖和扇尾飞镖 ( Etheostoma flabellare ) 的单位努力捕获量呈负相关。