Warmwater fish in rivers
In addition to the gears described in the previous version, this edition includes an updated water body definition that is inclusive of Mexico and Canada as well as standard methods for the use of cast nets in warmwater rivers. There were organizational changes in the trawling and hoop-net sections to make them consistent with the format for this edition, but the methods themselves have not been changed and no standardized gears (e.g., small-mesh and large-mesh trawls are still both present) have been removed. The diversity of warmwater rivers of North America owes to the mosaic of precipitation and geology spanning the continent from the arid systems of the Sonoran Desert to the humid forests of the Appalachian Mountains. The types of rivers discussed in this chapter are highly variable in size from headwaters to mouth but will include parts of rivers that are nonwadeable and larger. Here, we use this flexible definition because we found that regardless of how we classified a river as a whole, whether through basin area, discharge, or stream order, there is sufficient diversity across North America such that major rivers of some regions would be left out. We, therefore, chose to use site-level characterization because characteristics like target fish species and communities and habitat characteristics like water depth, velocity, and channel geomorphology drive or constrain our decisions in the field about what sampling gear to use rather than overall river or river basin characteristics.