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Time (week) 
Figure 4 
Weekly survival (S) of gray triggerfish (Balistes capriscus) from natural mor- 
tality in the northern Gulf of Mexico from 2013 through 2017. The dashed 
lines indicate the proportions of fish surviving after each weekly interval. 
Instantaneous natural mortality rates were calculated from S after 1 year 
at liberty. Black points indicate conditional estimates of S for weekly time 
intervals when a mortality occurred. Error bars indicate standard errors. The 
annual natural mortality rate, calculated as —In0.32°?4), was 0.25 (95% con- 
Fishery Bulletin 120(2) 
the number of mortalities were estimated 
directly, independent of the number of 
tags returned by fishermen, because the 
fates of tagged individuals were known 
while they resided at VPS-monitored 
reef sites (Hightower et al., 2001; Heupel 
and Simpfendorfer, 2002; Bacheler et al., 
2009; Topping and Szedlmayer, 2013; 
Williams-Grove and Szedlmayer, 2016a). 
The estimated annual F from this 
study is 0.23 for the period of 2013-2017, 
a level lower than that from the previ- 
ous stock assessment in 2015, indicating 
that management efforts of amendment 
37 have been successful in reducing F 
(GMFMC, 2012). However, the F of 0.23 
from this study is still greater than the 
F of 0.12 estimated for 2013 in the pre- 
vious stock assessment (SEDAR, 2015). 
The greater F in this study indicates that 
the Gulf of Mexico stock of gray trigger- 
fish may still be experiencing overfish- 
ing because the value is greater than the 
maximum F threshold of 0.17 from the 
stock assessment in 2015; the threshold 
was based on a spawning potential ratio 
of 30% (SEDAR, 2015). The rebuilding 
fidence interval: 0.07—0.57) during the 241-week study period. 
CI: 0.05-1.95), 2014 (M=0.12; 95% CI: 0.02—0.69), 2015 
(M=0.41; 95% CI: 0.04-1.87), and 2016 (M=0.22; 95% CTI: 
0.03-1.17). Again, CIs overlap and indicate no significant 
difference in M among years. No natural mortalities were 
detected in 2017 (Table 1). 
Total S from Z (Sz) for all years of the study was 0.11 
(95% CI: 0.02—0.44), S; adjusted to annual S, calculated 
as Se= ONIN boas was 0.62, and annual Z, calculated as 
—]n0.62, was 0.48 (95% CI: 0.18—0.85) (Fig. 5). Total mor- 
tality ranged from 0.12 (in 2014) to 1.13 (in 2017), but 
again CIs overlap and indicate no significant difference in 
Z among years (Table 1). No false detections were recorded 
by receivers at VPS sites or surrounding reef sites after 
mortalities occurred. The lack of false detections, along 
with reports from fishermen of recaptured fish, verify all 
mortalities determined with the VPSs (deaths resulting 
from both natural causes and fishing). 
Discussion 
In this study, acoustic telemetry was applied to directly 
estimate instantaneous rates of F, M, and Z for gray trig- 
gerfish. The arrays of receivers at VPS sites allowed con- 
tinuous, long-term (up to 662 d), highly accurate (to <3 m) 
tracking of tagged gray triggerfish that resided around 
artificial reefs in the northern Gulf of Mexico. Importantly, 
plan developed in 2017 also noted that 
the Gulf of Mexico stock of gray trigger- 
fish was not rebuilding on target, possi- 
bly as a result of the sport fishery often 
exceeding annual catch limits, incompat- 
ibilities between the federal and state fishing seasons, and 
low annual recruitment (GMFMC, 2017b). 
Limits on catch of gray triggerfish were unchanged over 
the study period of 2013-2017. However, sport fishery 
acccuntability measures led to seasons of varying lengths 
(from 37 to 236 d) during 2013-2016, with a complete clo- 
sure in 2017 because of landings in 2016 exceeding the 
catch limit by 245% (GMFMC, 2017b). In this study, we 
did not detect a significant difference in annual F, as 
indicated by overlapping Cls. It is possible that no trends 
were observed because fishermen were unaware of season 
length and closure dates prior to the start of the annual 
fishing season because they were announced mid-season 
once annual catch limits were estimated to have been 
reached. Yet, as has been the case with most telemetry 
tagging studies, sample sizes were small in this study. 
Therefore, annual comparisons of F should be treated with 
caution because of the limited number of tagged fish that 
were available for recapture each year. 
Fishery regulations for target and non-target species 
may have unexpected consequences (Gislason, 2003; 
Walters et al., 2005). In this study, although no significant 
differences were detected for F among years, the trend in F 
indicates that the highest annual rate was 1.13 in 2017. 
Surprisingly, this level of F occurred when the federal sport 
fishery for gray triggerfish was completely closed because 
fishermen exceeded the quota for 2016 (GMFMC, 2017b). 
