Jubilee: Mobile Bay’s Unique Ocean Phenomenon Equals Good Eating
A windfall of free seafood just for the taking! That's what a jubilee is. Source: (porterbriggs.com)
Mobile Bay in Alabama, a shallow arm of the Gulf of Mexico, is home to a strange and unique ocean phenomenon that, for hundreds of years, has been cause for celebration and feasting. It is called a Jubilee. On rare occasions, when conditions are just right, hundreds of fish, crabs, or shrimp from the deep waters of the bay move to the shallow waters just off a beach. The free seafood is so plentiful and easy to catch with nets or bare hands, that locals gather to stock up on the windfall. Then they celebrate the jubilee with a huge seafood feast. Let’s look at how this strange phenomenon occurs.
Areas of low water oxygen in Mobile Bay. Source: (aces.edu)
What Causes a Jubilee?
Conditions must be just right for a jubilee to occur. Basically, a jubilee is an upwelling of water from the floor of the bay to the surface. Bottom-dwelling creatures, like crabs and shrimp, are carried up with the bottom water to the shallow water of the beaches. The up-welling, however, is the result of a complex process that involves the salinity of the water. In the northern part of Mobile Bay, the salty sea water meets the fresh water from rivers. The salt water is heavier than the fresh water, resulting in salinity stratification, or layers of water with different levels of salt. Sometimes, pockets of lower salinity water are trapped in place by a layer of heavier salt water. A jubilee occurs when this salinity stratification is disrupted and the pockets of water rush to the surface.
Children play in the water at Mobile Bay in Fairhope, Alabama. Source: (Photo by Carol M. Highsmith/Buyenlarge/Getty Images)
Setting the Stage for a Jubilee
No one can accurately predict when a jubilee will occur, but researchers have been able to learn when the conditions are favorable for one to occur. Most commonly, jubilees occur in the summer months and happen just before sunrise. The weather in Mobile Bay the day before a jubilee is usually cloudy and overcast, with a light breeze blowing from the east. The rising tide seems to trigger the jubilee and cause the pockets of low-salinity water from the bay’s floor to rush to the surface, carrying shrimp, crabs, or fish with it. Researchers know that jubilees only occur when all of the conditions are just right.
A Mobile Bay jubilee. Source: (en.wikipedia.org)
Sea Life Thrives at the Bottom of the Bay
Plant material becomes trapped at the bottom of the bay because of the salinity stratification. It provides an ideal food source for bottom-dwelling ocean life, like shellfish and fish. But the water is also low in oxygen, which impacts the muscle development of sea life. Fish and crabs move slowly and are easy to catch. Deep at the bottom of the bay, they are safer from fishermen. During the jubilee, however, they can be caught with one's bare hands.
A jubilee that occurred in 1950. Source: (encyclopediaofalabama.org)
Historical Accounts of Jubilees
The jubilee phenomenon has been occurring since long before Europeans settled in the Mobile Bay area. The Mobile Press-Register newspaper contains accounts of them from as far back as 1867. Oral accounts claim that the poor, recently-freed former slaves of the South looked forward to the jubilees because they provided a surge of free fresh food, just for the taking. For them, free seafood was an unexpected gift.
The Jubilee Phenomenon Wasn’t Studied Until the Sixties
Marine biologist, Harold Loesch, was the first to study the strange jubilee phenomenon. Reviewing the historical accounts and oral stories of jubilee occurrences, Loesch tried to determine if the jubilee was the result of behavioral changes in the fish or in the currents in the bay. What he learned was that the layers of water in the shallow bay, each with a different salinity level, was what caused the event. In 1973, Loesch’s work was confirmed and continued by Edwin B. May, working for the Alabama Department of Conservation and Natural Resources.
Jubilees Happen Only Two Places on Earth
The mechanisms that make jubilees possible are so precise that this odd oceanic phenomenon only happens in two places on Earth. One is, of Mobile Bay in Alabama. The other is Japan’s Tokyo Bay. While people flock to the beaches when a jubilee occurs to help themselves to the free seafood, it is important to note that the crabs and fish are not dead and are not trying to beach themselves. Once the tide shifts, they all return to the depths of the bay and the Jubilee is over…except for the seafood feasts to come.