Utilization of the upper Houston Ship Channel by fish and macroinvertebrates with respect to water quality trends

Abstract

Nektonic utilization of the upper Houston Ship Channel (HSC) was assessed through characterization of species composition, abundance and community structure of finfish and macroinvertebrate populations. Impact of basic water quality trends on utilization was evaluated. seine, gillnet and revolving screen collections from two deep-water and six shoreline sampling stations in upper HSC stream segments 1006 (downstream) and 1007 (upstream) during May 1988 through July 1989 yielded 33,042 nektonic organisms comprising 84 taxa. Spatial and temporal trends in catch statistics, species diversity, and hydrological variables were assessed for each sampling gear type. Seasonal composition by dominant taxa was determined and effect of temperature, salinity and dissolved oxygen on catch statistics examined. Mean surface (shoreline) water temperature and dissolved oxygen levels were similar between segments and followed expected seasonal trends. Mean bottom dissolved oxygen levels in segment 1007 during May through September were consistently 1 to 1.5 mg/l lower than segment 1006 and exhibited hypoxic conditions. Significantly greater catch and biomass were observed in segment 1007 as compared to those of segment 1006. Species diversity and number of taxa were comparable between segments. Distinct reductions in catch, number of taxa and species diversity characterized winter seine collections in segment 1006. Surface water temperatures appeared to exert the greatest hydrological influence on shoreline catch statistics. Revolving screen catches were greatest in Segment 1007 during November through March when bottom dissolved oxygen levels peaked and water temperatures ebbed. Significantly reduced catches in segment 1007 during May through October coincided with highest water temperatures and near-anoxic dissolved oxygen levels. By contrast, catch statistics from segment 1006 were highest during summer and early fall when mean bottom temperature and dissolved oxygen levels were highest and lowest, respectively. Cumulative number of taxa was highest in both segments during winter. HSC segment 1006 maintains healthy shoreline and bottom nekton communities year-round. Low dissolved oxygen in bottom waters restrict nekton utilization of segment 1007 during summer. Richness and abundance in segment 1007 during winter equaled or exceeded that of segment 1006.