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Fishery Bulletin 119(4) 
Monitoring recruitment to age 1 could provide an 
alternative method for investigation of bottlenecks to 
population growth that occur during reproduction and 
early life and could provide managers with forward- 
looking, quantitative measures for monitoring biological 
responses to restoration actions that target such bottle- 
necks (Pine et al., 2001; Schueller and Peterson, 2010). 
Indeed, some of the core goals of the Programmatic Dam- 
age Assessment and Restoration Plan (DHNRDAT”), 
which was developed to restore injury caused by the 
Deepwater Horizon Oil Spill of 2010, are to improve 
access to spawning habitats and to boost the reproduc- 
tive success of Gulf sturgeon by increasing rates of sur- 
vival during early life. 
One approach to gathering recruitment data for stur- 
geon species is to capture larval sturgeon as they disperse 
from spawning areas. This method has been used to col- 
lect larvae of several sturgeon species (Braaten et al., 
2008; Dumont et al., 2011; McAdam, 2011), although it 
requires precise knowledge of spawning locations and 
timing to effectively target larvae with fishing gear. 
Spawning has been confirmed at a handful of sites across 
the range of the Gulf sturgeon (Parauka and Giorgianni’; 
Heise et al., 2004; Kreiser et al., 2008; Flowers et al., 
2009; Sulak et al.*). However, larvae do not appear to 
disperse from spawning areas in a synchronized, pre- 
dictable fashion, as has been observed for other sturgeon 
species (Kynard and Parker, 2004), and it remains to be 
determined whether they can be reliably captured with 
drift nets. 
A second method for monitoring recruitment involves 
the capture of young-of-the-year (YOY) sturgeon by 
using bottom-trawling gear. This method has proven 
effective for large river species like the pallid stur- 
geon (Scaphirhynchus albus) and shovelnose sturgeon 
(S. platorynchus) (Herzog et al., 2005; Doyle et al., 2007), 
where occupied habitats have been identified (Braaten 
and Fuller, 2007). However, given the dispersal behavior 
of Gulf sturgeon, YOY are likely distributed through- 
out the entire system during their first summer after 
hatching (Kynard and Parker, 2004; Sulak et al., 2016), 
rendering capture with trawling gear unlikely. Indeed, 
efforts to capture Gulf sturgeon with bottom-trawling 
2 DHNRDAT (Deepwater Horizon Natural Resource Damage 
Assessment Trustees). 2016. Deepwater Horizon oil spill: final 
programmatic damage assessment and restoration plan and 
final programmatic environmental impact statement. [Avail- 
able from website.] 
3 Parauka, F. M., and M. Giorgianni. 2002. Availability of Gulf 
sturgeon spawning habitat in northwest Florida and southeast 
Alabama river systems, 77 p. [Unpublished technical report. 
Available from Panama City Field Off., U.S. Fish Wildl. Serv., 
1601 Balboa Ave., Panama City, FL 32405.] 
* Sulak, K. J., M. Randall, J. P. Clugston, and W. Clark. 2013. 
Critical spawning habitat, early life history requirements, and 
other life history and population attributes of the Gulf stur- 
geon (Acipenser oxyrinchus desotoi) in the Suwannee River, 
Florida, 99 p. Final report to the Florida Fish and Wildlife 
Conservation Commission. Proj. Rep. TAL-NG95-125-2013. 
[Available from the Fla. Fish Wildl. Conserv. Comm., 620 S. 
Meridian St., Tallahassee, FL 32399.] 
gear have had little success (Sulak and Clugston, 1999; 
Kirk and Killgore’). 
A third method for gathering recruitment data is to esti- 
mate the abundance of age-1 juveniles by using gill nets and 
a mark-recapture approach. This method is now routinely 
used to assess populations of Atlantic sturgeon (Acipenser 
oxyrinchus oxyrinchus) (Schueller and Peterson, 2010; Bahr 
and Peterson, 2016; Hale et al., 2016) and is also effective 
for monitoring small populations (e.g., Farrae et al., 2009). 
Despite success with Atlantic sturgeon, a fellow subspecies 
of A. oxyrinchus, quantitative estimation of age-1 juvenile 
recruitment has not been attempted for any population of 
Gulf sturgeon (USFWS and NMFS, 2009). Several research- 
ers have back-calculated recruitment by using data on the 
age structure of populations (Sulak and Clugston, 1999; 
Randall and Sulak, 2007; Pine and Martell®), but those 
studies provided only general information about historical 
population trends and shed no light on current trends in 
recruitment of Gulf sturgeon. 
In addition, little is known about the seasonal habitat 
requirements of juvenile Gulf sturgeon, although habi- 
tat and access may be impediments to species recovery 
(USFWS and GSMFC’; Zehfuss et al., 1999; Flowers et al., 
2009). During the summer months, both adult and juvenile 
(i.e., age 1 and older) Gulf sturgeon reside in main-channel 
aggregation sites of their natal rivers (Wooley and Crateau, 
1985; Hightower et al., 2002), and the majority of individ- 
uals do not actively forage (Sulak et al., 2012). During late 
fall, juvenile Gulf sturgeon move downriver to forage for 
benthic macrofauna in the estuary (Mason and Clugston, 
1993; Sulak and Clugston, 1999; Sulak et al., 2009), while 
adults disperse more widely to feed in the nearshore, 
marine waters of the Gulf of Mexico (Odenkirk, 1989; Sulak 
and Clugston, 1999). 
Abiotic conditions may limit habitat access and utiliza- 
tion by juveniles; young juveniles have a lower tolerance 
for salinity than older fish (Altinok et al., 1998; Kynard 
and Parker, 2004). Juvenile Gulf sturgeon may remain 
inshore for up to 6 years (Clugston et al., 1995), possibly 
because of an intolerance to full ocean salinity. Regarding 
one potential determinant of year-class strength of Gulf 
sturgeon, Randall and Sulak (2007) proposed the salinity 
barrier hypothesis, which is that growth and survival of 
juvenile sturgeon may be enhanced during years when 
elevated river discharge reduces the salinity of the receiv- 
ing estuary for longer durations, thereby providing juve- 
niles greater access to benthic resources during the 
foraging period. Monitoring the year-class strength of 
° Kirk, J. P,, and K. J. Killgore. 2008. Gulf sturgeon movements 
in and near the Mississippi River Gulf outlet. U.S. Army Corps 
Eng., ERDC/EL TR-08-18, 9 p. [Available from website.] 
° Pine, W. E., II, and S. Martell. 2009. Status of Gulf stur- 
geon Acipenser oxyrinchus desotoi in the Gulf of Mexico, 34 p. 
[Unpublished report prepared for 2009 Gulf sturgeon annual 
working group meeting; Cedar Key, 17-19 November.] 
7 USFWS and GSMFC (USS. Fish and Wildlife Service and the 
Gulf States Marine Fisheries Commission). 1995. Gulf sturgeon 
recovery/management plan, 170 p. Southeast Reg., USFWS, 
Atlanta, GA. [Available from website.] 
