| 22 June 2010
Guest Editorial by Dr. Grant Gilmore
We had been setting traps in thirty inch diameter culverts connecting the Indian River Lagoon to the impounded Jack Island State Park mangrove forest. Each fall the culverts are opened to allow tides and fish to migrate from the forest to the Lagoon and back. We set the traps for three hours on ebb, flood tides both during the day and at night. On 27 Novermber 1085, 3,104 juvenile snook between 0.5 and 2 inches in length were captured moving against and with the tide in culvert traps around this imoundment. Over two thousand came from one trap.
Jack Island State Park is an impounded mangrove swamp. Jack Island covers 398 acres but 68% of the little snook came from the smallest cell occupying less than 63 acres, not counting another 200 juvenile snook captured in a seine within the forest at the same time.
Juvenile Snook, Red Drum and numerous other inshore gamefish are found together in mangrove creeks So if we captured 2,300 juvenile snook at two small locations within the 63 acre cell, how many snook were actually in that entire impoundment on 27 November 1985? Even if only the perimeter canal or ditch of this impoundment was considered optimum snook habitat, we would have sampled less than 1T of this ditch. It is not likely that snook occurred throughout this entire ditch, but if they did, there was a potential for 200,000 juvenile snook to have been there at that time, 3,175 snook per acre. Since that 63 acre cell only represented 16% of the area of Jack Island, there could have been hundred of thousands of additional juvenile snook in the 398 acre impounded mangrove forest in lat November, 1985.
Mangroves provide the backdrop for so many of our best memoriesSo how valuable is an acre of mangrove forest to snook? Extremely.
I do not have the space here to give statistics for tarpon, striped mullet, gray snapper, red and black drum captured at the same location during this historical study, but if I did, you would certainly see how very valuable an acre of mangrove forest is to all these fisheries based on the Jack Island studies conducted from 1984 to 1986.
Other Jack Island studies demonstrated that snook feed primarily on diminutive mosquitofish when they first recruit to mangroves. Mosquitofish populatins are capable of rapidly producing thousands of progeny in a short period of time. We captured hundreds of thousands of mosquitofish during these studies. The mangrove forest was the principal habitat for mosquitofish. An acre of mangroves can produce tens of thousands of mosquitofish on an annual basis, feeding thousands of snook.
Indian River is the longest saltwater lagoon in Florida; because of the productivity of its mangrove fish nurseries it draws anglers from around the world to its shores.Tarpon are not as numerous as snook but depend on this habitat too during their earliest development when they are most vulnerable to predation. Tarpon seek locations with much higher elevation than snookk, often locations that end up under homes, condominiums, roads and parking lots. This actually happened to one of our prime tarpon capture sites on South Hutchinson Island in St. Lucie County.
Every acre of mangrove forest habitat is valuable in producing our snook and tarpon fisheries now and years into the future at little or no cost. Since both these species suffered major mortality this past winter, it is truly time to eliminate any further loss of mangrove acreage for any reason in south Florida today.
So what is an acre of mangrove worth to the Florida snook and tarpon fishery?
About the Author: Dr. R. Grant Gilmore is a Senior Scientist with Estuarine, Coastal and Ocean Science, Inc., (ECOS). Dr. Gilmore founded ECOS in 2004 after spending 32 years with the Harbor Branch Oceanographic Institution, Fort Pierce, Florida and Dynamac Corp. at the Kennedy Space Center.
Dr. Gilmore has been studying the fish community and ecology of Florida and Caribbean Sea for the past 35 years. He has published over 70 technical and popular papers on fish ecology and life history including reproductive habits of spotted seatrout, snook, groupers, and sharks. He has appeared on 16 nationally and internationally televised programs. His appearances include programs on the Discovery Channel, and the National Geographic Ocean Science Documentary on the first American research expedition into Cuban waters since the revolution. Dr. Gilmore received his Ph.D., from the Florida Institute of Technology in 1988.
