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River discharge (m°/s) 
Figure 2 
The relationship of catch per unit of effort (CPUE) for sampling of 
Gulf sturgeon (Acipenser oxyrinchus desotoi) and discharge of the 
Apalachicola River in Florida between May and August in 2013— 
2018. Catch per unit of effort was calculated as number of stur- 
geon captured per hour of netting effort. River discharge data are 
from U.S. Geological Survey (USGS) stream gage 02359170 on the 
Apalachicola River near Sumatra, Florida. Data in this figure are a 
subset of all catch data, consisting of catch for the 2 sites most fre- 
quently sampled in the Brothers River tributary, which had a wide 
Fishery Bulletin 119(4) 
period) were expended in other areas of the Apala- 
chicola River system. Water quality in netting 
areas remained relatively consistent throughout 
all summer sampling periods (Suppl. Table 1) 
(online only). The interquartile temperature range 
was 26.7—29.1°C, and the interquartile range for 
dissolved oxygen was 4.34-5.79 mg/L. Salinity in 
all sampling locations was <0.1, with the exception 
of several sets in the lower Apalachicola River, 
from which no sturgeon were caught. 
Over the 6 years of sampling, 2029 Gulf stur- 
geon were captured in the Apalachicola and 
Brothers Rivers, including 1100 unique individ- 
uals (Table 2). Of those fish, 288 were identified 
as age-1 juveniles. Results of length—frequency 
analysis (validated by pectoral fin ray analysis) 
indicate that age-1 fish had FL of 370-530 mm, 
although there was some variation among years 
in median length (Suppl. Fig. 1) (online only). Most 
age-1 juveniles (number of samples [n]=282, 
97.9%) were captured within the Brothers River. 
During this study, only 6 age-1 fish were ever 
captured in other reaches of the Apalachicola 
River—all were observed just below the JWLD 
in 2017 and 2018 (although we sampled in that 
area in 2015-2018). 
In May and early June during 2014-2017, we 
variety of river discharge conditions in 2013-2018. 
sturgeon effectively when river discharge exceeded 
~850 m°/s (Fig. 2), we generally did not set nets when 
flows exceeded this threshold. Therefore, sampling period 
varied among study years, from just 4 weeks in 2013 to 
15 weeks in 2018 (Table 2). In 2013, netting locations 
were dispersed entirely within the Brothers River. During 
2014-2018, 192 net-hours (10% of all net-hours in the 
tagged 50 age-1 juveniles with acoustic trans- 
mitters (Fig. 3). All but 1 fish were captured 
within the Brothers River; the exception was a 
fish captured at the JWLD. We detected 76% 
(n=38) of tagged fish on our acoustic array after tag- 
ging; detection rates varied, with 42-100% of fish 
detected per study year and 21—25, 360 detections per 
fish. We also physically recaptured 16 acoustically 
tagged individuals within the year they were tagged or 
in subsequent years. In 2016, we found infections of the 
sutured surgery site on several tagged fish that were 
Table 2 
Effort, catch, and other details for sampling of Gulf sturgeon (Acipenser oxyrinchus desotoi) in the Apalachicola River, in 
Florida, during May—August in 2013-2018. The total number of Gulf sturgeon captured includes all ages and all recap- 
tured fish. Abundance of age-1 fish was calculated by using Huggins closed capture models, and values are presented as 
point estimates of number of individuals with 95% confidence intervals (CIs). We tested for closure of the age-1 population 
by using the program CloseTest; P-values <0.05 indicate statistical significance and a population that was not closed. 
Effort 
Total no. 
of fish 
captured 
Nets Net- 
set hours 
Sampling 
periods 
287 101 
465 602 
348 341 
270 333 
311 198 
524 156 
No. of age-1 juveniles 
Marked 
Abundance of age-1 fish 
CloseTest 
Recaptured Abundance 95% CI P-value 
12 0.34 
62 0.63 
6 0.75 
23 0.06 
22 0.72 
9 0.11 
