Land use alteration is recognized as a threat for many aquatic species, but demographic drivers of land use associated declines are poorly studied. We examined hellbender, Cryptobranchus alleganiensis, demography in six stream reaches stratified across a land use gradient to understand how land use might influence a long-lived species. We used robust-design surveys (2014–2015) to estimate abundance and demographic structure, and all captures recorded between 2007 and 2015 to estimate demographic rates. Catchment-wide riparian (CWR) forest predicted demography better than catchment or local riparian forest. Across space, sub-adult/adult abundance declined and demographic structure became increasingly skewed towards older adults as CWR forest declined. Demographic rates indicated sub-adults/adults were being lost from each reach at a similar rate and most populations remained stable over the period for which data were available (1–8 years per reach). Our findings suggest recruitment (via births, juvenile survival and/or immigration) of young age classes facilitated stability of high-density populations when CWR forest was relatively high. When CWR forest was lower, survivorship and longevity of old adults facilitated persistence of low-density populations for multiple years while recruitment of young age classes suffered. Fine sediment was not correlated with land use but water temperature, conductivity and pH declined as CWR forest increased, highlighting water quality as a possible mechanism linking forest cover to hellbender demography. Our findings suggest maintaining forest in upstream riparian areas is critical for conserving downstream biota, and emphasize the difficulty of detecting declines in long-lived species when environmental alterations act specifically on recruitment of young age classes.
Biological Conservation – Elsevier
Published: Apr 1, 2018
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