E. van Snik Gray | USGS Science

USGS2005

Bioassessment of fish communities of the upper Delaware River

We assessed the biotic integrity of the middle-to-upper Delaware River. We sampled fish and assembled water quality data for eight stations and three habitat types (pool, riffle, and submerged aquatic vegetation [SAV]) of the Delaware River and applied an existing index of biotic integrity (IBI) recently developed for the northern mid-Atlantic slope drainages. We used Spearman's correlation to test IBI scores against measures of water quality (WQI) and cultural pollution. IBI scores were not significantly correlated with WQI, but were significantly negatively correlated with sewage load of adjacent tributaries (rs = -0.647, p = 0.08). Sites ranged from good to fair in biotic integrity. Fish assemblage composition from all three habitat types was necessary in order to accurately characterize biotic integrity. Of the three habitat types, fish assemblages from SAV habitats had the greatest positive effect on biotic integrity. Continued application of the IBI may be useful as a long-term monitoring tool as this river corridor becomes increasingly urbanized.

Northeastern Naturalist↗

USGS1997

Food resource partitioning by nine sympatric darter species

We compared the diets among members of the diverse darter community of French Creek, Pennsylvania, in relation to seasonal prey availability, feeding ontogeny, and sex. Prey taxa and size attributes were characterized for nine syntopic darter species; taxon, size, and availability of macroinvertebrate prey were also analyzed from Surber samples. In general, darters fed opportunistically on immature insects; few taxa were consumed in greater proportions than they were found in the environment. Some variation in diet composition was expressed, however, among different life stages and species. Juvenile darters consumed smaller prey and more chironomids than did adults. Etheostoma blennioides and E. zonale consumed the fewest taxa (2–3), whereas E. maculatum , E. variatum , and Percina evides had the most diverse diets (7–10 taxa). Etheostoma maculatum , E. flabellare , E. variatum , and P. evides consumed larger prey (1–13 mm in standard length), whereas E. blennioides , E. caeruleum , E. camurum , E. tippecanoe , and E. zonale rarely consumed prey longer than 6 mm. Percina evides fed on larger prey, fewer chironomids, and more fish eggs than Etheostoma species. Females consumed more prey than males and overlapped less in diet composition with males during the spawning season than afterwards. Fish diets did not seem related to habitat use. Greater trophic partitioning was observed in April, when prey resources were scarce, than in July, when prey were abundant. Darter species fed opportunistically when prey were dense, whereas they partitioned food resources mainly through the prey size dimension when prey were less abundant. The divergence of darter diets during a period of low food availability may be attributed to interspecific competition. Alternatively, the greater abundance of large prey in April may have facilitated better prey size selectivity, resulting in less overlap among darter species.

Pennsylvania↗