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Mobile Bay Jubilee
Updated: Wednesday, October 30 2013, 09:31 AM CDT
Jubilee is the name used locally for a natural phenomenon that occurs sporadically on the shores of Mobile Bay, a large body of water on Alabama's Gulf Coast. During a jubilee many species of crab and shrimp, as well as flounder, eels, and other demersal fish will leave deeper waters and swarm—in large numbers and very high density—in a specific, shallower coastal area of the bay. A jubilee is a celebrated event in Mobile Bay, and it attracts large crowds, many drawn by the promise of abundant and easy-to-catch seafood.
Although similar events have been reported in other bodies of water, Mobile Bay is the only place where the regular appearance of this phenomenon has been documented.The Mobile Bay jubilee typically takes place at least annually, and sometimes several times per year; years without a jubilee have been recorded, but they are exceedingly rare. Many accounts of the jubilee exist, the oldest dating back to the 1860s.
The size, scope, and duration of the jubilee can vary greatly. Sometimes a 15-mile (24 km) stretch of coast representing most of the eastern shore can be affected, and at other times the extent can be limited to as little as 500 feet (150 m) of coastline.Most jubilees happen in the pre-dawn hours.
The large volume of crustacean and fish that a jubilee can produce is hard to overstate; author Archie Carr comments, "At a good jubilee you can quickly fill a washtub with shrimp. You can gig a hundred flounders and fill the back of your pickup truck a foot deep in crabs. In addition to the sheer mass of the animals present, harvesting them is made considerably easier by the effect that the oxygen deprivation has on the animals. Their behavior has been described as "depressed and moribund",or "unnatural";crabs are observed "climbing tree stumps to escape the water" and flounder "slither up the banks.
It was not until 1960 that the phenomenon was explored in-depth by marine biologist Harold Loesch for the journal Ecology. Locals and laymen had based some earlier attempts to explain the animals' strange behaviors on the interaction of sea- and fresh water during the incoming tide. After researching the oral histories and journalistic records of past jubilees, measuring physical and meteorologic conditions, and taking biological and chemical measurements, Loesch concluded that accumulated organic material on the bay floor could, under a certain set of conditions, result in a rapid depletion of oxygen (hypoxia) in parts of the bay, driving fish to the surface seeking oxygenated water.
Another, more comprehensive study by Edwin B. May in 1973, as well as smaller studies by the Alabama Department of Conservation and Natural Resources and the NOAA confirmed many of Loesch's hypotheses. If wind direction, surface temperature, salinity, and tidal variation interact in ways that allow or promote a jubilee, the situation can develop rather quickly. May sums up the mechanism of action thus:
“ Except during jubilees the water inside the 2 meter contour along the eastern shore is well oxygenated. This shallow water extends several hundred meters offshore. During jubilees fishes present there are trapped between the shore and an advancing water mass low in dissolved oxygen; the water at the surface and very close to shore usually has enough oxygen to support them for the short duration of most jubilees.