Natanson et al.: Resting population of Lamna nasus in the western North Atlantic Ocean 
75 
Table 3 
Data from Jensen et al. (2002) reevaluated for this study for porbeagles (Lamna nasus) captured between 1989 and 1999 
in the general vicinity of Georges Bank to off the Grand Banks of Newfoundland, Canada. All organ measurements are 
presented in millimeters unless otherwise noted. The vaginal membrane was absent in all of these specimens. A dash 
indicates that there were no data for a field. 
Maturity status 
Date 
captured 
Fork 
length 
(cm) 
Weight 
(kg) 
Upper 
oviduct 
width 
Oviducal 
gland 
width 
Uterus 
width 
Uterus 
length 
(upper) 
Uterus 
length 
(total) 
Ovary 
width 
Ovary 
length 
Maximum 
yolked egg 
diameter 
Resting 
7/19/1989 
240.0 
172.4 
10.0 
27.0 
_ 
_ 
_ 
75.0 
195.0 
2.5 
4/2/1994 
220.0 
- 
8.0 
25.0 
- 
320.0 
- 
120.0 
155.0 
2.0 
4/6/1994 
218.0 
- 
8.0 
29.0 
- 
370.0 
- 
80.0 
180.0 
2.0 
4/7/1994 
231.0 
- 
- 
31.0 
- 
340.0 
- 
110.0 
150.0 
3.0 
10/23/1993 
244.0 
- 
- 
28.0 
- 
- 
- 
110.0 
150.0 
1.0 
Ready to ovulate 
11/26/1999 
217.0 
128.0 
11.3 
37.2 
37.5 
160.0 
450.0 
135.0 
175.0 
6.0 
Ovulating 
10/2/1999 
234.0 
155.0 
9.0 
30.0 
42.0 
184.0 
435.0 
139.0 
153.0 
4.0 
9/28/1999 
228.5 
- 
5.0 
28.0 
39.0 
235.0 
535.0 
126.0 
177.0 
6.0 
5/20/1999 
230.5 
118.5 
6.0 
21.0 
48.0 
235.0 
514.0 
122.0 
169.0 
3.0 
10/11/1999 
221.0 
- 
9.0 
35.0 
36.0 
205.0 
470.0 
180.0 
193.0 
6.0 
5/18/1999 
240.0 
144.0 
6.0 
24.0 
54.0 
228.0 
514.0 
111.0 
148.0 
- 
10/2/1999 
248.0 
8.0 
35.0 
30.0 
160.0 
515.0 
142.0 
181.0 
4.0 
5/18/1999 
229.5 
135.0 
9.0 
23.0 
39.0 
292.0 
605.0 
112.0 
136.0 
4.0 
6/1/1999 
228.0 
118.5 
8.0 
21.0 
51.0 
236.0 
615.0 
134.0 
169.0 
5.0 
5/6/1999 
241.0 
- 
26.5 
65.0 
465.0 
820.0 
135.0 
230.0 
4.0 
Postpartum 
5/5/1999 
230.0 
132.0 
8.0 
24.0 
54.0 
336.0 
568.0 
147.0 
165.0 
4.2 
5/6/1997 
221.2 
- 
8.7 
26.9 
- 
530.0 
- 
140.0 
170.0 
- 
Unable to be 
6/2/1999 
216.0 
- 
- 
21.0 
- 
- 
- 
130.0 
152.0 
- 
determined 
5/6/1999 
233.0 
145.0 
7.0 
21.5 
38.5 
296.0 
580.0 
114.0 
130.0 
- 
4/8/1999 
214.0 
— 
7.5 
21.5 
26.0 
182.0 
343.0 
104.0 
— 
foundland and the mouth of the Saint Lawrence River 
(Fig. 2; Jensen et al., 2002). 
Discussion 
An essential component for assessing and managing 
populations of sharks is determining each species’ re¬ 
productive biology (e.g., when sexual maturity occurs, 
the timing of seasonal cycles, or gestation length) 
(Walker, 2005a, 2005b). However, variability in these 
important reproductive parameters has been shown 
to occur within species (e.g., Lombardi-Carlson et al., 
2003; Sulikowski et al., 2007; Castro, 2009; Driggers 
and Hoffmayer, 2009), complicating the management 
process. Therefore, because of the importance of repro¬ 
ductive data as inputs in demographic and population 
models (Cortes, 2002), it is imperative to accurately de¬ 
scribe the life history of a species throughout its range. 
Castro (2009) describes the complexities of the typi¬ 
cal biennial reproductive cycle of the sand tiger (Car- 
charias taurus), a lamnid species that inhabits sub¬ 
tropical and temperate waters worldwide. It has been 
suggested that this species has a biennial cycle with 
consecutive vitellogenesis and gestation and with dis¬ 
continuous ovulation in specimens captured in waters 
of Australia and the southwest Atlantic Ocean (Luci- 
fora et al., 2002; Bansemer, 2009). However, in North 
America, information on reproductive cycle is inconclu¬ 
sive, and an annual instead of biennial cycle has been 
reported (Castro, 2009). Indeed, only annual reproduc¬ 
tion may be considered because of the inability of re¬ 
searchers to find the resting segment of the popula¬ 
tion of sand tigers that may be highly localized and 
unsampled to date (Castro, 2009). The existence of a 
previously unsampled resting portion of the population 
of porbeagles is indicated by the results of our study. 
As in other lamnid species, at some point during 
gestation, the ovaries of a female porbeagle become 
exhausted; by the time of parturition, an ovary is de¬ 
pleted and hematose and contains atretic oocytes. A 
depleted ovary must then recover to a condition ready 
for vitellogenesis (Fig. 2A). Because it has been sug¬ 
gested that birth occurs between April and June and 
that mating occurs in the fall, an ovary of a porbeagle 
is unlikely to recover enough to ovulate and sustain a 
new brood by September (Fig 2; Jensen et al., 2002; 
Castro, 2009). In addition, sampling for our study took 
place by recreational fishermen between July and Sep¬ 
tember in an area (primary area: Stellwagen Bank) 
geographically distinct from the primary sampling area 
of Jensen et al. (2002) in waters between Nova Scotia 
and the Grand Banks of Newfoundland (Fig. 1). There¬ 
fore, the observation of females in a resting phase ap- 
