49 
In search of climate effects on Atlantic Croaker 
< Micropogonias undulatus) stock off the 
U.S. Atlantic coast with Bayesian state-space 
biomass dynamic models 
Joseph Munyandorero 
Email address for contact author: joseph munyandorero@myfwc.com 
Abstract— Atlantic Croaker (Micropo- 
gonias undulatus) production dynam- 
ics along the U.S. Atlantic coast are 
regulated by fishing and winter water 
temperature. Stakeholders for this re- 
source have recommended investigat- 
ing the effects of climate covariates in 
assessment models. This study used 
state-space biomass dynamic models 
without (model 1) and with (model 2) 
the minimum winter estuarine tem- 
perature (MWET) to examine MWET 
effects on Atlantic Croaker population 
dynamics during 1972-2008. In model 
2, MWET was introduced into the in- 
trinsic rate of population increase ( r ). 
For both models, a prior probability 
distribution (prior) was constructed for 
r or a scaling parameter (ro); imputs 
were the fishery removals, and fall bio- 
mass indices developed by using data 
from the Multispecies Bottom Trawl 
Survey of the Northeast Fisheries Sci- 
ence Center, National Marine Fisheries 
Service, and the Coastal Trawl Survey 
of the Southeast Area Monitoring and 
Assessment Program. Model sensitivity 
runs incorporated a uniform(0.01,1.5) 
prior for r or rg and bycatch data from 
the shrimp-trawl fishery. All model 
variants produced similar results and 
therefore supported the conclusion of 
low risk of overfishing for the Atlantic 
Croaker stock in the 2000s. However, 
the data statistically supported only 
model 1 and its configuration that 
included the shrimp-trawl fishery 
bycatch. The process errors of these 
models showed slightly positive and 
significant correlations with MWET, 
indicating that warmer winters would 
enhance Atlantic Croaker biomass pro- 
duction. Inconclusive, somewhat con- 
flicting results indicate that biomass 
dynamic models should not integrate 
MWET, pending, perhaps, accumula- 
tion of longer time series of the vari- 
ables controlling the production dy- 
namics of Atlantic Croaker, preferably 
including winter-induced estimates of 
Atlantic Croaker kills. 
Manuscript submitted 4 September 2012. 
Manuscript accepted 27 November 2013. 
Fish. Bull. 112:49-70 (2014). 
doi: 10.7755/FB.112.1.4 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necesarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Florida Fish and Wildlife Conservation Commission 
Florida Fish and Wildlife Research Institute 
100 8th Avenue SE, St. Petersburg, Florida 33701 
The Atlantic Croaker (Micropogo- 
nias undulatus) is a demersal sci- 
aenid species common in estuarine 
and coastal waters of the U.S. Atlan- 
tic coast (Chao and Musick, 1977). 
This species is abundant off the U.S. 
mid- and southeast Atlantic coast, 
where it forms a single genetic popu- 
lation and management stock-unit 
supporting important commercial 
and recreational fisheries (Atlantic 
States Marine Fisheries Commission 
[ASMFC] 1 ). Exploitation of Atlan- 
tic Croaker began in the 1800s, but 
coastwide (New Jersey-east Florida) 
commercial removals and bycatch 
estimates have been consistently 
reported only since 1950 and recre- 
ational harvests and catches since 
1981. These statistics show periodic, 
sudden highs and lows over the time 
series (Fig. 1A). 
Although fishing can have a signif- 
icant impact on the Atlantic Croaker 
population (ASMFC 1 ; Hare et ah, 
2010), Hare and Able (2007) advo- 
cated the hypothesis that population 
“outbursts” and harvest variability of 
Atlantic Croaker are largely driven 
by long-term trends in winter tem- 
1 ASMFC (Atlantic States Marine Fish- 
eries Commission). 2010. Atlantic 
Croaker 2010 benchmark stock assess- 
ment. ASMFC, Washington, D.C., 336 p. 
[Available from http://www.sefsc.noaa. 
gov/sedar/download/Atlantic%20Croak- 
er%20Stock%20Assessment%20Report. 
pdf?id=DOCUMENT, accessed January 
2012.1 
perature. This idea was consistent 
with the observations that juvenile 
(age-0) Atlantic Croaker spend their 
first winter (December-March) in 
estuarine nursery habitats where 
winter water temperatures appear 
to regulate juvenile Atlantic Croak- 
er survival and year-class strength 
(Norcross and Austin; 2 Lankford 
and Targett, 2001a, 2001b; Hare 
and Able, 2007; Hare et ah, 2010). 
The mechanistic link between abun- 
dance of juvenile Atlantic Croaker 
and water temperature led Hare and 
Able (2007) to develop a conceptual 
model in which sequential warm 
winters result in high juvenile sur- 
vival rates. Such high rates of juve- 
nile survival would in turn lead to 
large year-classes that increase the 
population size. The reverse would 
be true of cold winters. These au- 
thors found positive, often significant 
correlations between spring juvenile 
and adult (age-2) abundances and 
minimum winter estuarine tempera- 
ture (MWET) and between coastwide 
adult catch and either MWET or the 
North Atlantic Oscillation. 
2 Norcross, B.L., and H.M. Austin. 1981. 
Climate scale environmental factors af- 
fecting year class fluctuations of Chesa- 
peake Bay croaker, Micropogonias undu- 
latus. Special Scientific Report 110, 78 
p. Virginia Institute of Marine Science, 
College of William and Mary, Gloucester 
Point, VA. [Available from http://web. 
vims.edu/GreyLit/VIMS/ssrl 10. pdf.] 
