Fogg et al.: Age and growth of invasive Pterois volitans in the northern Gulf of Mexico 
135 
for a fish collected in November 2012, and the data from 
our study confirm the presence of red lionfish in the north¬ 
ern GOM as early as 2008, 2 years prior to the first detec¬ 
tion in the region in 2010. Edwards et al. (2014) also found 
a single lionfish (Pterois sp.) with an estimated age that 
indicates it was present in the Caribbean Sea before the 
first detection off Little Cayman in 2010. Such delays in 
documented detections are expected because invasive spe¬ 
cies often are not detected immediately after introduction 
because of lag times associated with species expansion 
(Crooks and Soule, 1999). 
Age distribution of marine fish species is an important 
factor for assessing the health of a population (Berkeley 
et al., 2004). Typically, an established, healthy population 
will exhibit a “well-balanced” age structure (Brunei and 
Piet, 2013) with numerous larger, older individuals. In 
the northern GOM, 93% of red lionfish in our study were 
<2 years old in all 3 ecoregions. Similar results have been 
reported off Little Cayman (Edwards et al., 2014) and in 
the Atlantic Ocean off northeast Florida (Johnson and 
Swenarton, 2016) and North Carolina (Barbour et al., 
2011), where the majority (>90%) of lionfish were <3 years 
old. The higher proportion of fish between the ages of 
2 and 3 years found in Little Cayman and off northeast 
Florida and North Carolina is likely the result of lionfish 
having invaded those locations earlier than the northern 
GOM (Schofield, 2010). 
Although red lionfish can live much longer than what 
has been described in this study and in studies in other 
invaded geographic areas, the truncated age-class distri¬ 
bution observed in this study is a further indication that 
the population of red lionfish in the northern GOM may 
still be stabilizing in the region because older individu¬ 
als are not present or not captured. Red lionfish from 
the southern GOM that were aged in 2012 appeared to be 
much younger, with age and growth parameters that were 
much lower than those reported for this study and pre¬ 
vious studies (Rodriguez-Cortes et al., 2015). This differ¬ 
ence in age structure is likely a result of red lionfish being 
collected within the first 2 years of their invasion in the 
southern GOM. The difference also could be due to aging 
techniques: we determined age on the basis of otolith anal¬ 
ysis, but Rodriguez-Cortes et al. (2015) estimated ages on 
the basis of size-frequency analysis that was not verified 
by using otoliths. It is important to now establish up-to- 
date region- and sex-specific age and growth parameters 
so that, in the future when the invasion of red lionfish the¬ 
oretically has stabilized across the region (Benkwitt et al., 
2017; Cote and Smith, 2018), the same parameters can be 
estimated to evaluate the success of the invasion. 
There was an inconsistent pattern of differences in 
weight-length relationships among ecoregions with only 
males in the southeast ecoregion being heavier per length 
than males in the northeast ecoregion. In contrast, dif¬ 
ferences were found in females in all pairwise compari¬ 
sons between ecoregions, except for the comparison of the 
southeast and central ecoregions. Overall, weight-length 
relationships based on data pooled for males and females 
and on estimated marginal means adjusted for TL indicate 
minor differences in weight among ecoregions: 18.21 g for 
females and 22.75 g for males. 
Differences in weight-length relationships of lionfish 
have been reported throughout the range of the invasion 
among regions that are larger than the ecoregions used 
in our study (Suppl. Table) (online only). Some published 
comparisons of weight-length relationships have been 
based on data pooled across a range of locations within the 
sampled region (Barbour et al., 2011; Edwards et al., 2014; 
Sabido-Itza et al., 2016), and the relationships derived 
from those pooled data differ from those presented here 
for the northern GOM. Another study compared weight- 
length data pooled by year, reporting a significant differ¬ 
ence between the first and last year (2011-2013) (Dahl 
and Patterson, 2014). In contrast, Benkwitt et al. (2017) 
documented no changes in size structure in lionfish from 
the Bahamas over a 10-year period. Recently, Pusack et al. 
(2016) reported that red lionfish in their native range 
grow at a slower rate and achieve smaller maximum sizes 
than those in the range of their invasion. Finally, lionfish 
in the range they have invaded may be less susceptible to 
predation because of their larger size and would also be 
able to consume larger prey items (see review in Cote and 
Smith, 2018). 
In this study, male red lionfish found in the northern 
GOM achieved greater weight and length than females. 
In contrast, results from early work in the northern GOM 
(Fogg et al., 2013) indicate no significant differences in 
weight-length relationships by sex for red lionfish. One 
explanation for these differences between studies may be 
that the data from Fogg et al. (2013) came from early in 
the invasion and, therefore, likely had not yet reached an 
asymptotic value. Although von Bertalanffy growth param¬ 
eters were not reported by sex in other age and growth 
studies on invasive lionfish species (e.g., Potts et al. 2010; 
Barbour et al. 2011; Rodriguez-Cortes et al. 2015; Johnson 
and Swenarton 2016), age and growth and weight-length 
data quantified in our study confirm that sexual dimor¬ 
phism exists with males growing larger and faster than 
females. Sexual dimorphic growth was documented also 
for invasive lionfish in Little Cayman by using otolith 
analysis, but weight-length relationships were not evalu¬ 
ated (Edwards et al., 2014). Males in our study achieved a 
greater length-at-age than females and, similar to males 
examined by Edwards et al. (2014), had significantly larger 
K and L rjo values than females. Males of the related scor- 
peanid species, blackbelly rosefish, also appear to grow 
faster and slightly larger than females (White et al., 1998). 
In contrast, female black scorpionfish, native to the eastern 
Atlantic Ocean, Mediterranean Sea, and Black Sea, attain 
larger sizes than males (Bilgin and Qelik, 2009). 
The differences observed between male and female 
red lionfish in age and growth and in weight-length 
relationships are likely a result of the greater resources 
that females allocate to reproductive output (Gadgil and 
Bossert, 1970). Female red lionfish mature in their first 
year of life and are capable of reproducing every few days 
during 11 months of the year (Fogg et al., 2017). These ele¬ 
vated and constant reproductive rates likely result in more 
