Importance of water quality to nekton habitat use in a North Carolina Branch estuary

Abstract

Nekton abundance and water quality were examined over 8 yr (1986–1993) in Isaac Creek, a small (2.5 km long), shallow (1–2 m), estuarine creek draining to Adams Creek (Neuse River system), North Carolina, United States. Water quality and nekton were sampled at 8 to 12 stations at 2–3 wk intervals from April to October (76 dates). The nekton assemblage, sampled by trawl, included 42 taxa but was dominated by 11 species (7 fish and 4 decapod crustaceans). Nekton and water quality (temperature, salinity, dissolved oxygen [DO], salinity gradient) data were grouped and analyzed by three (upper, middle, and lower) creek zones to determine if estimated abundance was correlated with water quality. Potentially stressful water quality conditions for salinity ( 30°C in morning), and DO (<2 mg 1−1) mainly occurred in the upper and middle zones. The most frequent occurrence of potentially stressful conditions for salinity was in the spring and for dissolved oxygen and temperature in middle to late summer. The frequency of potentially stressful conditions increased during a 3-yr period following timber harvest of a large portion of the watershed. Canonical correspondence analysis (CCA) suggested little correlation between the top 11 species and water quality and indicated an assemblage with regular seasonal changes. Comparison of nekton use of the middle and upper zones of the creek for 3-yr pre- and post-harvest periods showed an increase in proportion of nekton caught in those zones, despite the higher frequency of potentially stressful water quality conditions. This observation suggests that a complex set of factors, including water quality, influence the pattern of nekton use in Isaac Creek.