220 
Fishery Bulletin 116(3-4) 
within the DPS for the southeastern United States re¬ 
main severely depressed or possibly extirpated (ASSRT, 
1998; ASSRT, 2007). Despite federal protections, many 
of these populations continue to suffer from degraded 
habitats in natal river systems, and from incidental by- 
catch in commercial fisheries that target other coastal 
or estuarine species (ASSRT, 1998; Collins et ah, 2000; 
ASSRT, 2007). The implementation of modern environ¬ 
mental regulations has helped reduce point sources of 
pollution in many river systems in the southeastern 
United States, but nonpoint sources continue to de¬ 
grade water quality, particularly in the lower rivers 
and estuarine habitats that were historically inhabited 
by juvenile Atlantic sturgeon (ASSRT, 2007). 
As an anadromous fish, Atlantic sturgeon adults 
typically reside in marine environments but migrate 
into freshwater rivers to spawn (Vladykov and Gree¬ 
ley, 1963). In northern populations, spawning occurs in 
the spring (Bain, 1997), whereas the results of recent 
studies indicate that at least some central and south¬ 
ern populations spawn in the fall (Hager et al., 2014; 
Smith et al., 2015; Ingram and Peterson, 2016). During 
the first several years of life, the young fish, known 
as river-resident juveniles (RRJs), occupy estuarine 
habitats near the freshwater-saltwater interface. The 
period of river residency varies depending on latitude, 
but in southern populations the RRJs typically remain 
in their natal system for 2-4 years before transition¬ 
ing to nearshore marine habitats as marine-migrato¬ 
ry juveniles (MMJs) (Bain, 1997). Consequently, the 
presence of RRJs within a river system is considered 
strong evidence of an extant population, especially in 
depressed populations in which adult spawners may be 
rare (Schueller and Peterson, 2010). 
The St. Johns River in Florida is considered the 
southernmost river system historically occupied by At¬ 
lantic sturgeon (ASMFC 1 ; ASSRT, 2007). Throughout 
the 20th century, sturgeon were commonly reported 
as bycatch in commercial fisheries that operate on the 
St. Johns River (Cox and Moody 2 ); however, reports 
of small juveniles are rare and spawning has never 
been confirmed there (McLane, 1955; Gilbert, 1992a). 
Furthermore, the construction of Rodman Dam (now 
called Kirkpatrick Dam) in 1968 blocked adults from 
accessing some of the best potential spawning habitats 
in the Ocklawaha tributary (Gilbert, 1992a; ASMFC 1 ; 
ASSRT, 2007). The current status of Atlantic sturgeon, 
however, remains unknown within the St. Johns Riv¬ 
er system. The most recent survey of this population, 
conducted from 2002 to 2003 by the Florida Fish and 
1 ASMFC (Atlantic States Marine Fisheries Commis¬ 
sion). 1998. Amendment 1 to the interstate fishery man¬ 
agement plan for Atlantic sturgeon. Fish. Manage. Rep. 31, 
42 p. ASMFC, Washington, DC. [Available from website.] 
2 Cox, D. T., and H. L. Moody. 1981. St. Johns River fisher¬ 
ies resources. Completion report. Study I. Ecological aspects 
of the fishery. Florida Game Fresh Water Fish Comm., Tal¬ 
lahassee, FL. [Available from Florida Fish Wildl. Conserv. 
Comm., Farris Bryant Bldg., 620 S. Meridian St., Tallahas¬ 
see, FL 32399-1600.] 
Wildlife Commission, yielded zero Atlantic sturgeon 
despite hundreds of hours of directed sampling effort 
(Holder et al. 3 ). The results of that study indicate that 
Atlantic sturgeon likely have been extirpated from St. 
Johns River, although rare but recurring captures of 
adult and subadult individuals by local anglers indi¬ 
cate that a small population could be present or that 
migrants from other systems are regularly occupying 
the estuary. 
Extirpation of any fish population is difficult to es¬ 
tablish conclusively, but it is especially difficult with 
sturgeons because of their cryptic nature, complex mi¬ 
gratory life history, and periodic reproductive strategy. 
Given the uncertain status of Atlantic sturgeon within 
the St. Johns River, the objectives of this study were 1) 
to document seasonal occurrence of Atlantic sturgeon 
in the lower estuary and 2) to sample for RRJs as evi¬ 
dence of an extant population of Atlantic sturgeon in 
the St. Johns River. 
Materials and methods 
Study site 
The St. Johns River is a large, blackwater river in 
northeast Florida, characterized by tannic waters and 
a very low mean gradient (~2.0 cm/km) (Whitney et 
al., 2004). It flows for 500 km to the Atlantic Ocean, 
draining several subbasins and associated tributaries 
that have in total a combined watershed area of ap¬ 
proximately 22,900 km 2 . Nontidal flow at the mouth 
averages 420 cm/s, but the rate may exceed 4220 cm/s 
after heavy rains. Much of the St. Johns River basin is 
urbanized and developed, and the river itself has been 
modified by dam construction and dredging (EPB 4 ). 
Sampling of sturgeon 
All sampling was conducted in the lower St. Johns Riv¬ 
er estuary below the head of tide, between river kilo¬ 
meter (rkm) 25 and rkm 115. Sampling occurred during 
summer months because this season is the most effec¬ 
tive time to capture RRJ Atlantic sturgeon (Schueller 
and Peterson, 2010; Bahr and Peterson, 2016). Specific 
netting locations within this zone (Fig. 1) were select¬ 
ed by using navigational charts and preliminary sonar 
surveys to find areas with depths of at least 2.5 m and 
3 Holder,J.C.,R.E.Lundy,A.R.Hyle,andL.West. 2005. Com¬ 
pletion report: St. Johns River fisheries resources, Lower St. 
Johns River resource development. Florida Fish Wildl. Con¬ 
serv. Comm., Tallahassee, FL. [Available from Florida Fish 
Wildl. Conserv. Comm., Farris Bryant Bldg., 620 S. Meridian 
St., Tallahassee, FL 32399-1600.] 
4 EPB (Environmental Protection Board). 2014. State 
of the river report for the lower St. Johns River basin, 
Florida: water quality, fisheries, aquatic life, and con¬ 
taminants 2014. State River Rep. 7, 301 p. EPB, 
City of Jacksonville; Univ. North Florida; and Jack¬ 
sonville Univ., Jacksonville, FL. [Available from 
website.] 
