Shortnose Sturgeon Population Evaluation in the St. Johns River, Florida
Has there ever been a shortnose sturgeon population in Florida’s St. Johns River?
 |
| Photo Credit: FWC |
Sturgeon are a primitive family of fishes found mainly in cold to temperate regions of the northern hemisphere. Habitat loss threatens or endangers many species, including shortnose sturgeon (
Acipenser brevirostrum). Anadromous species, which move upriver from the sea to spawn, are particularly imperiled, because the damming of rivers blocks access to historic spawning habitat. Shortnose sturgeon are considered semi-anadromous, because they travel upstream to spawn but return only to the lower estuarine portion of a river. They typically do not use marine habitat, but some transient fish have been known to move between river systems. Historically found in major rivers along the Atlantic seaboard from the St. John River, Canada, south to the St. Johns River, Florida, current populations are generally much larger in northern rivers. Shortnose sturgeon have been listed as endangered since 1967. In the late 1980s and throughout the 1990s, sturgeon researchers along the eastern coast began to assimilate a recovery plan that was completed in 1998. However, population estimates for several systems within the listed range, including the St. Johns River, Florida, were inadequate or missing.
In the spring of 2001, researchers working in cooperation with the United States Fish and Wildlife Service began a study to determine current population levels of shortnose sturgeon in the St. Johns River, Florida. Most biologists who were familiar with the system believed the St. Johns River sturgeon population was extremely small or nonexistent. From 1949 through 1999, only eleven specimens had been positively identified from the system. Eight of these captures occurred between 1977 and 1981. In August 2000, a shrimper’s cast net captured a shortnose sturgeon near Racy Point just north of Palatka, the area where most previous captures had been made. The fish carried a tag that had been attached in March 1996 by personnel from the Georgia Department of Natural Resources near St. Simon Island, Georgia.
Using a protocol developed by the National Marine Fisheries Service (NMFS), researchers conducted gill-net sampling in the St. Johns River from January 2002 through June 2003. Sampling areas, which were chosen based on historical catches or potential spawning migrations, included the lower river from Welaka to Jacksonville. From January through May of 2002 and 2003, 100-meter gill nets were set for a total time of 3,672 hours. From May through August of the same two-year period, biologists spent 820.5 hours sampling the estuarine portion of the river. Only one shortnose sturgeon was collected during the entire period. It was captured on 22 January 2002, tagged with a passive integrated transponder (PIT) tag, and released. This fish measured 56 centimeters in fork length and weighed 1.5 kilograms. It was captured on the south side of Federal Point near Palatka, within two miles of the most common area of historical shortnose sturgeon catches.
No data analysis for population size was possible, because researchers captured only one specimen in 2002 and zero in 2003 despite an extensive amount of sampling. In addition, from 1980 through 1993, similar gill-nets were deployed by researchers to target other species in the same areas. In all, these nets were deployed for 21,381 hours, but no incidental sturgeon captures were reported. It is, therefore, unlikely that any sizable population of shortnose sturgeon currently exists in the St. Johns River. Shortnose sturgeon reproduction generally requires rocky or gravel substrate or limestone outcroppings—habitat rarely found in the St. Johns River or its tributaries. No reproduction of sturgeon in the St. Johns River has ever been documented, and no large adults have been positively identified (all known specimens have been less than ten pounds). In other southern rivers, the species uses thermal refuges, such as springs, but no sturgeon have been observed in the numerous springs available in the St. Johns River. Given the marginal habitat, it is possible that shortnose sturgeon have not actively spawned in the system and that infrequent captures are transients from other river systems. However, with so little data available, researchers may never know how many shortnose sturgeon historically resided in the Sunshine State.
