Karlou-Riga et al.: Sex change and oscillating growth pattern of Spicara smaris in the Saronikos Gulf (Greece) 
357 
supports the size-advantage model (Warner, 1988). 
This model is particularly effective in accounting for 
postmaturational protogynous sex change among tele- 
osts in which a few large males can monopolize mating 
within the population (Francis and Barlow, 1993; Eris- 
man et al., 2009). 
The L 50 ( 15.3 cm TL) of this study, which corre¬ 
sponds to an age of 3 years (A 50 =3.0 years), is in gen¬ 
eral agreement with previous reports (Salekhova, 1979; 
Tsangridis and Filippousis, 1992; Duldic et al., 2003). It 
is noted, however, that initial maturation was observed 
at about one-half year old, or about 10 cm TL (Suppl. 
Figs. 4 and 6 ). According to the dimensionless theory 
(Charnov and Skuladottir, 2000), the ratio of L 50 /L max 
is invariant. Allsop and West (2003a), who found sup¬ 
port for this theory across 52 fish species, estimated 
the relative ratio at 0.80, a ratio that is related neither 
to the mating system nor to the presence of EMMs. 
When the same authors extended the list of species and 
estimated the same ratio for 77 species of fish, echino- 
derms, crustaceans, and molluscs, they found a value 
equal to 0.72 and concluded that the time when sex 
change occurs, is invariant for all animals (Allsop and 
West, 2003b). The same authors, on the other hand, 
agree that the invariant value of L 50 /L max corresponds 
to those species when the following criteria are met: 1 ) 
the species should be a unidirectional sex changer and 
2) if it is diandrous, the proportion of EMMs should 
be low, <2% according to Allsop and West (2004b). In 
the case of picarel, the species is a unidirectional sex 
changer (the proportion of males is positively correlat¬ 
ed with body length), whereas the proportion of EMMs, 
estimated at 2.4%, which is close enough to 2%, can 
be considered low. More specifically, Allsop and West 
(2004b) agree that the value of 2% EMMs is the up¬ 
per limit for those species characterized as pure sex 
changers. The value of L 50 /L max estimated in this work 
(0.74), although is lower than the original estimated 
ratio (L 50 /L max =0.80), is close enough to the value of 
0.72 of the extended list of Allsop and West (2003b) 
and within the L 50 /L max range (from 0.62 to 0.84) es¬ 
timated by Allsop and West (2003a) for 4 (other than 
picarel) species of the Sparidae family. Thus, the di¬ 
mensionless theory could be potentially supported and 
it can be concluded that the animals change sex at a 
certain proportion of their L max . A number of studies, 
on the other hand, have implicated fishing pressure as 
a cause of decline in the size at sex change (Platten et 
al., 2002; Hamilton et al., 2007) and therefore it should 
be noted that sequential hermaphrodites are more sen¬ 
sitive to size-selective harvesting than separate-sex 
species (Hamilton et al., 2007). 
According to the sex allocation theory (Charnov et 
al., 1978), the population is compensating for decreases 
in reproductive capacity. Picarel exhibit male parental 
care, where the males guard the eggs in their nest un¬ 
til time of hatching (Harmelin and Harmelin-Vivien, 
1976). It seems that the picarel represents a rare exam¬ 
ple of a species that exhibits co-occurring protogynous 
sex change and parental care. Although this feature of 
synchronicity could reduce the potential reproductive 
rate of males and hence the selection for sex change 
(i.e, the selection of females undergoing a sex change) 
(Allsop and West, 2004a), it seems that for picarel, as 
for some labrids (Warner and Lejeune, 1985), the cost 
of minimal parental care is outweighed by the benefit 
of larger male size in attracting and spawning with 
multiple females. On the other hand, the production of 
EMMs, which depends on the structure of the mating 
system, increases with high population density. High 
densities destabilize the potential for mate monopoli¬ 
zation and therefore selection for sex change (Allsop 
and West, 2004a). Preliminary results of stock assess¬ 
ment in the area (Karlou-Riga and Anastopoulou, 2005) 
showed that the picarel stock is under or lightly ex¬ 
ploited (ratio of current spawning stock biomass to vir¬ 
gin stock biomass is about 80%). Therefore, high local 
population density is probably another potential factor, 
which could reduce the proportion of individuals un¬ 
dergoing a sex change and increase the proportion of 
EMMs. The findings of the present work most probably 
support the statement of Allsop and West (2004a), who 
suggested that the abundance of EMMs can be used as 
a measure of the amount of sex change taking place. 
Acknowledgments 
This work is a contribution to the “Management 
plans—Surveys in highly commercial fishing areas” Re¬ 
search Project, supported by the Hellenic Ministry of 
Rural Development and Food (Project Code 9686535). 
The authors wish to thank the staff of the Fisheries 
Laboratory of the Hellenic Ministry of Rural Develop¬ 
ment and Food, who collaborated on this project and 
in particular the three anonymous reviewers for criti¬ 
cally reading the manuscript, providing insightful com¬ 
ments, and suggesting substantial improvements. 
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