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Sturgeon in the Florida Panhandle

This is one strange, primitive, dinosaur-looking fish.  They have large scutes embedded in their skin that give them an armored look.  They are big – reaching 14 feet in length and 800 pounds (though the Gulf sturgeon does not reach the large size of their cousin the Atlantic sturgeon).  They resemble sharks with their heterocercal caudal fin and possess long whiskers (barbels) suggesting a benthic mode of feeding.

Sturgeon are large fish. Note the shovel shaped head and barbels indicating this is a benthic feeder. Also note the large ganoid scales giving this creature a pre-historic look.
Photo: U.S. Fish and Wildlife Service.

 

Panhandle residents know them from their impressive leaps as they head upriver for spawning in the spring.  The loud splash from one of these leaps can be heard for a long distance and is a concern for boaters who may be zipping up and down one of the local rivers on a jet sky, or even a bass boat.  When in college, we asked one of the professors – “why do mullet jump?”.  He paused for a second and responded – “for the same reason manta rays jump”.  There was another longer pause.  Understanding what was going on we took the bait and asked – “okay… why do manta rays jump?” – “we don’t know”.  However, that was in 1980 and a lot has been learned since.  We know that not only do mullet and mantas leap, but baleen whales and sturgeon do as well.  It is believed that baleen whales leap to communicate during the breeding season.  Since sturgeon breed in panhandle rivers, it is believed that this is the reason they may do so.  Scientists have also found it helps adjust their swim bladders with internal gas making them more buoyant in the water.

 

Like salmon, sturgeon swim up rivers to breed and spawn in the spring.  Fertilization is external and the gray-black eggs are laid on the substrate at the bottom.  The newborn and adults spend the remaining spring in the rivers, and the adults do not feed at this time.  In summer all head for the estuaries where the adults begin feeding with a vengeance.  They feed on a variety of benthic invertebrates and prefer sections of the bay that are well oxygenated.  Sturgeon spend the summer and much of the fall in the bays until the temperatures begins to drop at which time they head into the open Gulf of Mexico.  The spring, they find their breeding rivers and the reproductive cycle begins again.  This is a long-lived fish, reaching up to 50 years in age.

 

As far as the biogeography of this species, it is an interesting one.  They have been around for about 200 million years.  This was about the time the whole “Pangea” movement was going on – Florida did not look like Florida then.  There was an opening between what is now the southeastern United States and the Florida peninsula.  The water moving through this was called the Georgia Seaway or the Suwannee Channel.  This allowed marine species to easily move from the Atlantic to the Gulf of Mexico.  It was believed the current in this seaway was significant enough to keep silt and clays from reaching what would be become peninsula Florida, which was probably a submerged region of islands at the time.

 

During those times the Atlantic sturgeon (Acipenser oxyrinchus) inhabited this region, using southeast rivers for breeding.  About 25 million years ago global land mass changes began a period of ice formation that encouraged sea level to drop and the peninsula portion of Florida was exposed – the Florida people know today.  However, this new peninsula isolated populations of sturgeon (and other fish at that time) from reaching each other.  As time moved on, different genetic changes occurred in both populations to produce offspring that varied from each other.  These external morphological changes were enough to let you know they were different, but genetically they are close enough to still breed.  In these situations, they have deemed “subspecies” of each other.  The Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) and the Gulf sturgeon (Acipenser oxyrinchus desotoi).  It is the Gulf sturgeon we find along the panhandle.  This process of producing new subspecies and species due to population isolation over time is called speciation.

 

Another interesting trend is the original range of the Gulf sturgeon was from the Texas/Louisiana border to about Tampa Bay.  This suggest that the fish took advantage of numerous rivers for breeding but there was a barrier as you reach the tropics.  Whether that barrier was climatic (temperature) biological (food source) or something else I am not sure.  With the high concentration of sturgeon in the panhandle you might think they require the alluvial rivers of this region.  But sturgeon are as common in tannic rivers, such as the Suwannee and Yellow Rivers, as they are in those alluvial ones, such as the Escambia and Apalachicola.

 

Today, their range is even smaller.  They are now found only in the rivers between Louisiana/Mississippi border to the Suwannee River.  This range reduction is probably due to habitat alteration (much of it human induced – such as dams) and overharvesting (the eggs of the sturgeon are used for caviar).  Today all species and subspecies of sturgeon are protected by the endangered species act.

 

Because this is an ancient fish, the biogeographic story of the sturgeon is an interesting one and shows how speciation occurs over time with all life.  They are really cool fish and, if you have not seen one leap yet, I hope you get to.  It is pretty amazing.

 

 

References

 

Florida’s Geologic History, University of Florida IFAS, https://edis.ifas.ufl.edu/publication/UW208.

 

NOAA Species Directory, Gulf Sturgeon, https://www.fisheries.noaa.gov/species/gulf-sturgeon.

 

NOAA Species Directory, Atlantic Sturgeon, https://www.fisheries.noaa.gov/species/atlantic-sturgeon.

 

Sturgeon, Florida Fish and Wildlife Conservation Commission, https://myfwc.com/conservation/you-conserve/wildlife/sturgeon/#:~:text=When%20the%20ambient%20pressure%20changes,to%20communicate%20with%20other%20sturgeon..