The importance of trimming National Hydrography Dataset streamline networks when delineating potential habitats and species distributions for fish and amphibians in broad geographical applications

Abstract

Objective: Digital representations of stream networks are integral components of spatial analyses to describe species distributions and habitat extents, but users should understand their strengths and weaknesses. Here, we used two resolutions of the publicly available and widely applied National Hydrography Dataset (NHD) with large fish and amphibian occurrence data sets to highlight patterns of habitat occupancy relative to availability as described by the NHD.Methods: Data sets consisting of 37,318 occurrences for 10 species were linked to NHD reaches, attributed with reach slope and mean flow values that represented major habitat gradients, and used to develop cumulative distribution curves describing habitat use and species- specific habitat threshold values for networks in the northwestern USA.Results: The 10 species rarely, and usually never, occurred in headwater reaches with the smallest flows and steepest slopes, although these reaches composed significant portions of the NHD. Application of species- specific habitat threshold criteria within a single river basin indicated that of its 25,797 km, only 16-55% of this length was likely to be occupied by one of four native species. At a broader scale encompassing the state of Idaho, the medium- resolution NHD network depicted 141,902 km of streams, but this figure was reduced by 52% to 68,586 km once 16% reach slope, 0.2- ft3/s mean flow, and intermittency criteria were applied that excluded most species from portions of the statewide networkConclusions: Our results suggest that the NHD often overestimates the network extents used by many aquatic vertebrates and could be trimmed to improve accuracy in species- specific applications that involve estimating range extents, developing sampling designs for data collection, and applying predictive biological models in unsampled areas. Descriptors of reach slope, flow magnitude, and other attributes useful for representing habitat conditions are available for the NHD and are straightforward to apply.

Citation

Isaak, Daniel J.; Horan, Dona L.; Nagel, David E. 2025. The importance of trimming National Hydrography Dataset streamline networks when delineating potential habitats and species distributions for fish and amphibians in broad geographical applications. North American Journal of Fisheries Management. https://doi.org/10.1093/najfmt/vqaf014.