76 
Fishery Bulletin 11 7(1 -2) 
pears to represent a portion of the population that had 
remained unsampled until now. 
Jensen et al. (2002) sampled porbeagles caught in 
commercial fisheries in an area of high abundance of 
porbeagles. They found that mature females in this 
area were either pregnant or ovulating, leading them 
to the conclusions that 1) this area is a mating ground 
and 2) porbeagles have annual reproduction. Further, 
the seasonality of spermatophore production, observa¬ 
tions of females with fresh mating scars, and observa¬ 
tions of males and females captured on the same long- 
line indicate that porbeagles mate in the fall, primarily 
between September and November on the Grand Banks 
of Newfoundland and the vicinity (Jensen et al., 2002). 
Jensen et al. (2002) also predicted a gestation period of 
8-9 months and pupping from April through June. Ac¬ 
cording to Jensen et al. (2002), mature females would 
be recently postpartum in July and recovering to the 
point of mating (oocytes with diameters of ~3-6 mm) 
by September. However, this timing appears unrealis¬ 
tic for the samples collected in our study, on the basis 
of the condition of the resting ovaries observed in the 
summer (Fig. 2A). In addition, this study observed only 
one recently postpartum individual (caught in Septem¬ 
ber), and the remainder of the individuals were recov¬ 
ered to the point where vitellogenesis had commenced. 
Therefore, on the basis of other lamnid studies and the 
known timing of porbeagle mating, oogenesis would re¬ 
quire a year before they would be in mating condition, 
further indication that this shark has a biennial rather 
than an annual reproductive cycle. 
An additional mating ground on Georges Bank has 
been indicated by the presence of “high catch rates of 
mature females, which did not appear to be feeding” 
in June 2007, observed by Campana et al. (2010a), al¬ 
though no detailed necropsy data were presented. How¬ 
ever, because no males were captured with this group 
of females and the data of Jensen et al. (2002) indi¬ 
cates a fall mating season, it is unlikely that a mating 
aggregation occurs on Georges Bank in summer. On 
the basis of the findings of our study, we suggest that 
this aggregation was more consistent with resting than 
mating, particularly in light of the fact that Georges 
Bank is in geographic proximity to Stellwagen Bank 
(Fig. 1). Further, females assumed to be mature on the 
basis of size and tagged on Georges Bank, primarily in 
July 2008, have been shown to migrate to the Sargas¬ 
so Sea. This migration was assumed to be for pupping 
(Campana et al., 2010b). On the basis of time of year, it 
is unlikely that these sharks were pregnant and would 
have had to travel to the mating area before pupping 
in the Sargasso Sea. The tracks of tagging data pre¬ 
sented by Campana et al. (2010b; fig. 1) indicate that 
the sharks in that study did not travel to known mat¬ 
ing grounds and were only assumed to be pregnant (no 
direct reproductive assessments were made). In light 
of the evidence from our study, for a resting area in 
Stellwagen Bank, and data from the Campana et al. 
(2010b) tagging study that indicate that porbeagles 
did not travel east of longitude 62°W but resided in 
the areas of the Gulf of Maine, Stellwagen Bank, and 
Georges Bank, it is possible that the females tagged 
by Campana et al. (2010b) were in a resting stage and 
transited to the Sargasso Sea for unknown reasons, 
possibly related to feeding. 
The discovery of a resting portion of the population 
of porbeagles in the western North Atlantic Ocean has 
important implications for fisheries management. The 
inclusion of a resting period in the reproductive cycle 
of the porbeagle means at least some portion of the 
female population is not reproducing annually. A de¬ 
crease in productivity on the basis of non-annual repro¬ 
duction needs to be considered because such a decrease 
would reduce the resilience of this species to direct 
and indirect fishing pressures. Continued research on 
the migrations and distribution of porbeagles by their 
adult maturity stage is necessary to provide effective 
management for this species. 
Acknowledgments 
We thank the various shark tournament officials and 
fishermen for allowing us access to their catch. We also 
thank the captain and crew of the F/V Eagle Eye II for 
allowing us to sail onboard and sample catch and C. 
McCandless for making maps. 
Literature cited 
Aasen, O. 
1963. Length and growth of the porbeagle (Lamna nasus, 
Bonnaterre) in the North West Atlantic. Fisk.dir. Skr., 
Havund. 13:20-37. 
Bansemer, C. S. 
2009. Population biology, distribution, movement pat¬ 
terns and conservation requirements of the grey nurse 
shark (Carcharias taurus Rafinesque, 1810) along the 
east coast of Australia. Ph.D. diss., 159 p. Univ. 
Queensland, Brisbane, Australia. 
Campana, S., W. Joyce, L. Marks, P. Hurley, L. J. Natanson, 
N. E. Kohler, C. F. Jensen, J. J. Mello, H. L. Pratt Jr., S. 
Myklevoll, et al. 
2008. The rise and fall (again) of the porbeagle shark 
population in the Northwest Atlantic. In Sharks of the 
open ocean: biology, fisheries and conservation (M. D. 
Camhi, E. K. Pikitch, and E. A. Babcock, eds.), p. 445- 
461. Blackwell Publishing, Ltd., Oxford, UK. 
Campana, S. E., A. J. F. Gibson, M. Fowler, A. Dorey, and W. 
Joyce. 
2010a. Population dynamics of porbeagle in the North¬ 
west Atlantic, with an assessment of status to 2009 and 
projections for recovery. Collect. Vol. Sci. Pap. ICCAT 
65(6):2109-2182. 
Campana, S. E., W. Joyce, and M. Fowler. 
2010b. Subtropical pupping ground for a cold-water shark. 
Can. J. Fish. Aquat. Sci. 67:769-773. 
Castro, J. I. 
2009. Observations on the reproductive cycle of some vi¬ 
viparous North American sharks. Aqua Int. J. Ichthyol. 
15:205-222. 
