Decline of the Frecklebelly Madtom in the Pearl River Based on Contemporary and Historical Surveys

Abstract

The Pearl River has experienced numerous human‐caused disturbances since the 1950s, including completion of a navigation channel, reservoir construction, and channel modifications on the main stem of the river. These types of disturbances are known to negatively impact the biotic and abiotic components of riverine ecosystems. Since the 1960s, several fish species in the drainage have declined in abundance or have been extirpated from the drainage. We undertook this study to assess the current conservation status of the frecklebelly madtom Noturus munitus in the Pearl River drainage. A 1999 survey of 53 sites within the historic range of the frecklebelly madtom yielded only 13 specimens from eight localities. We also examined historical population trends for the frecklebelly madtom and other benthic fishes using archived museum material (1950– 1988). After standardizing for variation in collection effort, analysis of long‐term collection data indicated that frecklebelly madtom populations have declined significantly since the 1960s. Despite greater sampling effort in the postmodification period (1965–1988), frecklebelly madtoms were most abundant in samples during the modification period (1950–1964). Similar declines were observed for the brighteye darter Etheostoma lynceum , a gravel–riffle‐dependent species. Other percid taxa (including the crystal darter Crystallaria asprella (formerly Ammocrypta asprella ), the saddleback darter Percina vigil , the Gulf logperch P. suttkusi , and the dusky darter P. sciera ) showed no significant changes between modification and postmodification periods. However, benthic taxa (including the naked sand darter Ammocrypta beani , longnose shiner Notropis longirostris , channel catfish Ictalurus punctatus , hogchoker Trinectes maculatus , gulf darter E. swaini , speckled chub Macrhybopsis aestivalis , and silver chub M. storeriana ) increased in abundance between modification and postmodification study periods. We suggest that channel changes and the loss of gravel substrates are related and are contributing to the decline of the frecklebelly madtom in the Pearl River drainage.