Macchi et al.: Effects of skipped spawning on the reproductive potential of Merluccius hubbsi 
405 
by Rideout et al. (2005), only the resting stage can be 
found in the Patagonian stock. When SS was included 
in the estimate of the maturity ogives of Argentine 
hake, it was shown that both L 50 and A 50 were affect- 
ed by this phenomenon. After accounting for skipped 
spawning (i.e., considering females at resting stage 
to be functionally immature individuals), the size at 
first maturity increased by 2-3 cm TL compared with 
values obtained with the traditional interpretation of 
maturity assignment, where females in a resting stage 
are considered mature individuals. Even so, most L 50 
values estimated with the revised interpretation for 
the period 2005-2013 were close to 35 cm TL, which 
is the length class traditionally used to differentiate 
between juveniles and adults in commercial catches of 
Argentine hake to define protected areas for this spe- 
cies (Dato et al. 4 ). 
In the case of age at first maturity, this coefficient 
increased by 0.27-0.88 years when the proportion of 
females that would skip spawning was incorporated. 
This represents an increase between 10% and 25% 
over the value obtained with the traditional inter- 
pretation. However, these differences in A 50 were low 
compared with those reported for sablefish ( Anoplopo - 
ma fimbria) by Rodgveller et al. (2016), who estimated 
an increase of A 50 of approximately 30% when females 
that would skip spawning were considered to be func- 
tionally immature individuals. The maturity models 
for Argentine hake, both for size and age, showed a 
decrease of the slopes when the SS effect was includ- 
ed in the estimations, indicating that the age and size 
at which 100% of individuals reach sexual maturity 
are greater than those calculated by the traditional 
interpretation. 
Analysis of the size and age structure of Argentine 
hake confirms that nonreproductive adult females are 
mainly young specimens with sizes ranging between 40 
and 50 cm TL, corresponding primarily with 3-year-old 
fish, as was previously reported (Macchi et al., 2016). 
The 3-year-old age class constitutes approximately 
70% of the female Argentine hake that would skip 
spawning; therefore, it is the main age class affect- 
ing the reduction in egg production. If the estimates 
of A 50 (Table 3) are taken into account, it is possible 
that a large proportion of females that have already 
experienced their first annual spawning could skip the 
next spawning cycle, probably because of deficiencies 
in their nutritional condition (Macchi et al., 2016). It 
is also possible that some females that skip spawning 
are actually juveniles that had not yet reached sexual 
maturity. However, for the purposes of estimating L 50 
or A 50 , this error in determining maturity would gener- 
4 Dato, C., G. Alvarez Colombo, and G. J. Macchi. 2013. Evalu- 
ation de los juveniles y stock desovante de merluza ( Merluc- 
cius hubbsi) en la zona de cria norpatagonica. Resultados 
obtenidos en la campana de enero de 2013 y comparacion 
con los resultados del periodo 2005-2012. Inf. Tec. Of. 12, 25 
p. [Available from Institute Nacional de Investigacion y De- 
sarrollo Pesquero, Paseo Victoria Ocampo Nro. 1, B7602HSA 
Mar del Plata, Argentina] . 
ate the same bias as SS because juveniles and adults 
in the resting stage are both functionally immature. In 
other cases, when skipped spawning has been reported, 
it has been observed that this phenomenon affects pri- 
marily younger adult individuals, as in the case of At- 
lantic herring ( Clupea harengus; Engelhard and Heino, 
2005) and Atlantic cod ( Gadus morhua) from the Arctic 
(Jorgensen et al., 2006) and from the Atlantic (Rideout 
and Rose, 2006). 
The L 50 ogives of the Patagonian stock of Argen- 
tine hake from the resting period (August) were more 
similar to those based on the previous spawning peak 
of January, when fish that would skip spawning were 
classified as mature, than when fish that would skip 
spawning were classified as functionally immature. 
These results indicate that specimens identified as 
adults in January, during spawning, show the same 
maturity characteristics 7 months later (August), when 
the maturity ogive basically differentiates between ju- 
veniles and adults at the resting stage. This finding re- 
inforces the idea that females that would skip spawn- 
ing in January are adults, not juveniles. 
The difference in egg production values by age class 
estimated in January with the traditional criterion, 
and considering spawning omission, ranged between 
3.56% and 12.12% over the period 2005-2013. That is, 
if the objective is to estimate the reproductive poten- 
tial of Argentine hake by using the A 50 ogive, in some 
years there would be an overestimation close to 12% 
for this variable. However, when the egg production 
by length class during January is considered over the 
same period, the percentages of reductions in egg pro- 
duction resulting from SS were much lower than those 
estimated from the age-based model, ranging between 
2.70% and 6.80%. The differences between the length- 
and age-based models in the percentages of reduction 
in egg production caused by SS may be associated with 
the variability explained by each model. The A 50 model, 
which groups different length classes in each age class, 
embodies greater variability than the maturity rela- 
tionship with total length. On the other hand, fewer 
samples were used to estimate the A 50 curves than the 
number of samples used to determine L 50 (Tables 2 and 
3) and consequently would be expected to generate a 
better model fit for length over age. 
The relatively low levels of reduction in egg produc- 
tion caused by SS for Argentine hake in our study in- 
dicate that the effect of skipped spawning in the Pata- 
gonian stock may be less significant than that reported 
for other species. For example, regarding Atlantic cod, 
Rideout and Rose (2006) suggested an overestimation 
of reproductive potential near 40% if the proportion of 
SS was not taken into account. Kennedy et al. (2014) 
reported that failure to properly interpret the maturity 
scale in Greenland halibut ( Reinhardtius hippoglossoi- 
des) could lead to an overestimation of spawning stock 
biomass between 28% and 92%, depending on areas 
and years, whereas Nunez et al. (2015) calculated an 
overestimation of approximately 20% for the same spe- 
cies. In Argentine hake, it seems that the overestima- 
