A stretch of scorching, windless weather in early August 2015 set off a wave of fish kills in the sheltered back-bay waters around Orange Beach, with city officials pointing to low oxygen levels rather than pollution or disease as the cause.
Orange Beach Coastal Resources Manager Phillip West said the combination of relentless heat and weak northerly winds had stopped the natural mixing that normally keeps bay water oxygenated. Without that mixing, the water in shallow, poorly flushed pockets grew stagnant just as large schools of small baitfish, likely alewife or menhaden, crowded into the same stressed waters.
“These are species that show up in huge numbers in water that’s already struggling for dissolved oxygen, and that combination is a recipe for a fish kill,” West explained.
The first major kill was spotted in Cotton Bayou, and sightings continued through the following days across a wide stretch of the coastline, from Robinson Island near Perdido Pass north to Bayou St. John, between Ono Island and Bear Point. Most of the dead fish recovered were small, in the four-to-seven-inch range, with the heaviest concentration found in Cotton Bayou itself.
West drew on research from longtime University of South Alabama marine sciences authority Bob Shipp, whose writing on Gulf of Mexico fish species describes how menhaden often gather in shallow, poorly circulated estuaries during summer months. Because the species cannot tolerate low-oxygen conditions, large die-offs can cascade once conditions turn stagnant. As dead fish decompose, they consume even more of the water’s remaining oxygen, feeding a cycle that produces still more kills.
“It’s kind of a textbook phenomenon based on the conditions we’re dealing with right now,” West said.
Residents who spent time on the water described the scale of the die-off as unusual. West recounted that one longtime resident walking along Cotton Bayou said he had not witnessed a kill of this size since a severe heat wave roughly a quarter-century earlier.
West said his own experience bore that out. While he had seen fish kills tied to red tide and other harmful algae blooms in the past, he called this event among the largest he had observed in the area’s estuaries, adding that an unusually hot, dry July likely set the stage for what followed.
With the heat wave showing no signs of breaking, officials warned additional kills were likely in the days ahead. The city responded by placing a large disposal bin at the Boggy Point boat launch so residents could dispose of dead fish, and the Orange Beach City Council was expected to weigh in on mobilizing the city’s debris removal contractor to help with cleanup efforts along the shoreline.