Having grown up in Martin county water skiing, tubing, swimming, boating and fishing, I was surprised to learn as an adult that the Indian River Lagoon is one of the most important bull shark nurseries along the US Atlantic Coast.
Obviously the young sharks must display a different behavior than some of the older ones we learn about, as bull sharks are listed in the top sharks that attack humans. From what I have read, there have been no reported attacks in the St Lucie/Indian River Lagoon itself.
Personally, I was fascinated with sharks as a kid, (I am from the movie JAWS generation,) and know they play an important role in the food web and in the health of our oceans. I respect them which, yes, holds a certain element of fear. But there is no fear to be had for the many baby and juvenile sharks living in the St Lucie River and Indian River Lagoon.
In 2011 a study was published by The American Fisheries Society by Tobey Curtis, Douglas Adams, and George Burgess entitled “Seasonal Distribution and Habitat Association of Bull Sharks in the Indian River Lagoon, Florida: A 30 Year Synthesis.” The study covers years 1975-2005. Impressive!
Major points of interest for me were:
1. In the spring, female bull sharks enter the lagoon through inlets, and have live baby sharks in the northern lagoon. The females’ gestation period is around 10-11 months. She does not enter the lagoon until she is ready to have birth and will bear between 1-13 “pups.” She leaves afterwards. The pups are on their own and will eat seagrass critters, rays, fishes, turtles, and even take chunks out of bottle-nosed dolphins.
2. These baby sharks show “site fidelity,” (they stay in certain areas,) but beginning in October or November they appear to migrate south. Catch and releases of these young sharks have been documented all the way south to the St Lucie River although the majority were found in the area of the Sebastian Inlet.
3. Sharks under three feet represent the “dominant size-class” in the lagoon.
4. “Sharks greater than about 190 centimeters, or just over 6 feet, appear to have reached the size at which they leave the nursery and fully transition to offshore adult habitats.” Yikes! 🙂 Sharks this size are thought to be sexually mature but data is sparse, and some studies note up to 15 years for sexual maturity. (Some of the largest documented bull sharks in the ocean are 9-11 feet and over 500 pounds and are estimated to live from 20 to 30 years but no one really knows yet.)
5. Bull sharks are tolerant of both salt and fresh water and known to go far up into the rivulets of estuaries.
6. Bull sharks slow growth and reproduction rate means they do not populate easily or rapidly. Bull sharks, as many sharks, are on the edge of “threatened status,” and should be protected.
7. Because baby bull sharks use inshore and nearshore systems like the SLR/IRL that are “suffering from dramatic anthropogenic alteration and habitat loss, this potentially affects the survival of the species.
8. Bull shark juveniles are frequently observed at heated power plant outfalls, brackish and saltwater creeks, around piers, over seagrass flats, open and muddy bottoms and in dredged channels.
9. The authors note that “although seagrasses in some areas are stable or increasing, seagrasses have declined up to 70% in some areas over a 50 year period. (And this paper was compiled before the crash of 60% seagrasses that occurred from 2011 to 2013 in the northern and central lagoon due to the super and brown tide algae blooms.)
10. The bull sharks of the Indian River Lagoon are their own genetic stock, unique from bull sharks of other areas.
The is no reason to be afraid and every reason to be fascinated! If you catch a baby bull shark please release it back into the lagoon. He or she has a long journey ahead to clean up our oceans and fulfill its destiny as a top predator of the sea.
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Seasonal Distribution and Habitat Association of Bull Sharks in the Indian River Lagoon, Florida: A 30 Year Synthesis: (http://research.myfwc.com/engine/download_redirection_process.asp?file=11curtis_2543.pdf&objid=61673&dltype=publication)
If above link will not load try this: (http://www.researchgate.net/publication/233147673_Seasonal_Distribution_and_Habitat_Associations_of_Bull_Sharks_in_the_Indian_River_Lagoon_Florida_A_30-Year_Synthesis)
FWC/Bull Sharks: (http://myfwc.com/research/saltwater/sharks-rays/shark-species/bull/)