Viducic et al.: Reproductive characteristics for Prionace glauca in the North Atlantic Ocean 35 
clasper calcification and found that his estimate of size at 
median maturity of 183.0 cm FL is similar to our recalcu- 
lated estimate of 184.1 cm FL, indicating that our methods 
for calculating maturity were not the cause of the shift in 
Ls 9 between time periods. Therefore, we conclude on the 
basis of training and the consistency in results from use of 
old and new maturity criteria that the differences between 
time periods are not an artifact of method in dissection, 
personnel changes, or data analysis. 
Another factor that may influence the shift in L5, 
between time periods is sample size distribution and sam- 
ple availability. The interim period and TP2 both had a 
larger sample size of bigger sharks than TP1 and, thus, 
a higher likelihood of larger juvenile specimens, which 
is what we find in the data (Fig. 3). Because the large 
(>200 cm FL) juvenile specimens in the interim period 
were collected close to TP1, it is probable that these spec- 
imens were in the western North Atlantic Ocean during 
TP1, just not sampled, leading to an underestimate of size 
at maturity in Pratt (1979) and indicating that the real 
Lo was higher at that time and thus no significant change 
has actually occurred in male characteristics. 
We hypothesize that the initiation of shark management 
led to an increase in large samples in TP2 (Table 4). The 
increase in sampling of large fish meant that more large 
juveniles were sampled; large juveniles are proportionally 
low and were not sampled in TP1 because of a lower over- 
all number of large sharks. Fishing pressure and fisheries 
management have changed dramatically since the study of 
Pratt (1979) and were hypothesized to have influenced blue 
shark sample distribution between TP1 and TP2. Shark 
management did not start in earnest until the interim 
period between TP1 and TP2 of this study, meaning that 
data collection in TP1 was fairly unrestricted and varying 
size ranges were available. The majority of sampling in all 
years was conducted at recreational shark tournaments 
along the East Coast of the United States (Suppl. Table 1) 
(online only). Early in these tournaments there were no fed- 
eral, state, or in most cases even tournament catch restric- 
tions of size or number (Castro, 2011). It was not until 1993, 
when the National Marine Fisheries Service implemented 
the fishery management plan for sharks of the Atlantic 
Ocean (NMFS, 1993), that tournament and recreational 
bag and size limits were imposed (NMFS, 2006). Although 
some tournaments always had size minima, more of them 
began to implement size restrictions that were often far 
higher than those of the federal regulations once manage- 
ment was in place (L. Natanson, unpubl. data). Together, 
the restrictions of tournaments and federal regulations led 
to greater sampling of larger sharks. Because the majority 
of the sampling came from recreational fishermen at tour- 
naments, the sample distribution became skewed to large 
fish (Fig. 3). Additionally, this influx of large fish led to the 
increased likelihood of observing large juvenile fish, which 
are proportionally rarer than the mature fish of that size. 
The presence of large juveniles would influence the results 
of the ogive analysis, leading to a higher L;, as we have 
observed in this study. 
Typically, female elasmobranchs reach a larger size than 
males, presumably because of the need to accommodate 
gestation (Cortés, 2000). However, in global studies on the 
blue shark, males have been observed to be larger than 
females (McKenzie and Tibbo, 1964; Aasen, 1966; Skomal 
and Natanson, 2003). Similar to our results, median size 
at maturity of males was found to be greater than that of 
females in South Africa (Jolly et al., 2013). The L;,) from 
our study is greater than those found in other studies of 
blue sharks globally (Table 5). Pratt (1979) and Hazin 
and Lessa (2005) reported that both sexes reached first 
maturity at 5 years; whereas, we found 50% maturity 
at 5 years, indicating a lower age at maturity for this 
region. Jolly et al. (2013) reported on differences in age 
at maturity between the sexes, with males maturing at 
7 years as opposed to females maturing at 6 years, again 
indicating regional differences in life history character- 
istics despite genetic similarity of this species globally 
(Verissimo et al., 2017). 
Differences in growth rates between populations of the 
same species of sharks have been well-documented and 
found to occur both regionally (e.g., the blacknose shark, 
Table 5 
Comparison of lengths at median maturity (Z;.) of blue sharks (Prionace glauca) from 
various life history studies. Measurements of L;,. have been converted to fork length (FL) 
by using the relationships from Kohler et al. (1996). The estimated L;, of blue sharks in 
this study represents data collected between 1971 and 2016. NA=not available because 
a length for females was not reported in the source. 
Region 
Western North Atlantic Ocean 
Mediterranean Sea 
Baja California Sur, Mexico 
South-east Pacific Ocean 
South Africa 
New Zealand 
Source 
This study 
Megalofonou et al. (2009) 179.9 170.1 
Carrera-Fernandez et al. (2010) 164.3 154.4 
Bustamante and Bennett (2013) 167.0 159.6 
Jolly et al. (2013) 163.0 168.8 
Francis and Maolagain (2016) NA 179.4 
Length (cm FL) 
Female Male 
190.9 192.5 
