The effects of a by-pass canal upon the marine animals occurring in the cooling canal system of the P.H. Robinson Generating Station.

The species diversity and abundance of fishes and invertebrates passing through the cooling canals associated with the P.H. Robinson Generating Station at Bacliff, Texas were studied before and after the addition of a by-pass canal to the cooling canal system. The temperature and salinity, as well as the species composition, of the canal waters were determined on a weekly basis during June, July, and August of 1971 and compared to a similar period in 1969. It was found that the higher salinities (23.6 to 29.8 %) encountered in 1971 as compared to those in 1969 (6.8 to 13.2%) probably accounted for changes in the relative abundance and diversity of various species. The use of the by-pass canal lowered the change in temperature of the cooling water passing through the generating station by about 2.4 C from 10.4 to 8.0 C and substantially decreased the mortality of Penaeus aztecus, Penaeus setiferus, Callinectes sapidus, and Callinectes similis, but did not appear to benefit 48 other species found during the summer of 1971. The best survival in the discharge canal was noted when the water temperature was 34 C, the coolest temperature seen in that canal during the study. Further study will be necessary to determine whether significant survival occurs at higher temperatures, and whether even lower temperatures would further enhance survival.