Offatts Bayou, a Locality with Recurrent Summer Mortality of Marine Organisms

Abstract

In July, 1939, the writer was called to Galveston to investigate the sudden mortality of marine organisms in Offats Bayou. Since then several trips have been made to the bayou, none longer than a few days. In 1939 I presented an hypothesis to explain the situation, and, since subsequent observations have tended to confirm it, the facts relating to this somewhat peculiar case seem to be worth recording. Offats Bayou is a blind neck or inlet of water on the bay side of Galveston Island, opening into West Galveston Bay. It is shown on the United States Coast and Geodetic Survey chart No. 1282: Galveston Bay and Approaches. It is two and a half miles long and most of it is approximately half a mile wide. The mouth is constricted to less than a quarter of a mile in width and the inner third is set off from the rest of the bayou by a second constriction of about the same width. The channel at the mouth is approximately twelve feet deep, this being the shallowest part of the bayou. At the inner end of the bayou the depth is said to be forty feet in some places. The greatest depth I encountered was thirty feet, but extensive soundings were not made. Mortality has occurred every summer since 1936, except 1940, and was unknown before. These facts were ascertained from residents of the area. I am especially indebted to Mr. J. U. Rogers, who has watched the vagaries of the bayou for several years, and who has cooperated as an observer on the spot since. 1939. The only event seemingly connected with the commencing of mortality was the dredging of the inner end of Offats Bayou for dirt to be used for the west end fill of Galveston. Death of animals in the bayou was not known before that time and has recurred every summer since. Dredging of the bayou has been carried on for many years (see Hopkins 1931, p. 60). Since 1931 the thirty-foot channel at the mouth of the bayou, mentioned by Hopkins, has shoaled up considerably. Mortality occurs very suddenly in the upper end of the bayou in midsummer. I have never been on hand at the precise time but have made observations a few days afterward. Fish, shrimp, oysters and crabs die, and the crabs have been reported to leave the water and crawl ashore. The species referred to is the common Blue Crab, Callinectes sapidus Rathbun, and such action is not normal for that animal. The suddenness with which mortality occurs and the fact that different phyla of animals are affected argues against epidemic disease as the cause of death and conversely indicates some kind of poisoning or chemical change in the environment. The mortality of animals seems to be connected with local disturbances in the water known to the people along the bayou as boils. They have been described to me by several fishermen. Areas up to thirty feet in diameter in the water boil furiously with escaping 'gas. The color of the water in these areas has been variously described as milky, red, and black. In the parlance of fisher631