Natanson et al.: Resting population of Lamna nasus in the western North Atlantic Ocean 
71 
Map showing the areas used by female porbeagles (Lamna na¬ 
sus) in different stages of maturity. The Grand Banks of New¬ 
foundland and the Gulf of Saint Lawrence, Canada, form a re¬ 
ported mating area for porbeagles (Jensen et ah, 2002). A por¬ 
tion of the Sargasso Sea has been identified as a pupping area 
(Campana et al., 2010b), and Stellwagen Bank is an area where 
females in a resting stage have been captured (this study). A 
portion of Georges Bank has been identified as a possible resting 
or mating area (Campana et al., 2010b; this study). Also shown 
are other locations where specimens were captured in this study. 
quires a large ovary with relatively high oocyte 
production and high ovulation rates (Gilmore 
et al., 2005). In the strictly oophagous species, 
such as the shortfin mako (Isurus oxyrinchus ) 
and the common thresher shark (Alopias vul- 
pinus), multiple embryos per uterus, long ges¬ 
tation periods, and long resting periods (the 
period between parturition and the next preg¬ 
nancy) with 1 or 2 years between pregnancies 
is typical (Mollet et al., 2000; Gilmore et al., 
2005; Natanson and Gervelis, 2013). 
Jensen et al. (2002) conducted a study on the 
reproduction of the porbeagle in the western 
North Atlantic Ocean, assessing sharks taken 
by the U.S. and Canadian commercial fishing 
industries and scientific research surveys in 
the late 1990s. The sampling for that study 
took place from the Grand Banks of Newfound¬ 
land to the Scotian Shelf and into the Gulf of 
Maine. Jensen et al. (2002) demonstrated that 
the majority of mature females caught in the 
Grand Banks portion of the study area (87 of 
88 porbeagles examined) were gravid after No¬ 
vember. On the basis of the observation that all 
mature female porbeagles are pregnant in fall 
in these areas, Jensen et al. (2002) suggested 
that, contrary to the reproduction of most oth¬ 
er lamnids, the reproductive cycle for the por¬ 
beagle is annual. In this paper, we report the 
previously undocumented presence of females 
in a resting stage of maturity. This discovery 
indicates that porbeagles exhibit a biennial re¬ 
productive cycle rather than an annual cycle 
in the western North Atlantic Ocean, substan¬ 
tially decreasing their resilience to direct and 
indirect fishing pressures. 
men began a limited fishery on porbeagles. In an at¬ 
tempt to avoid overfishing, the government of Canada 
imposed catch quotas for the commercial porbeagle 
fishery from 1995 into the early 2000s through the 
Canadian Atlantic Pelagic Shark Integrated Fisher¬ 
ies Management Plan (Campana et al. 2 ). In 2013, the 
fishery for porbeagles was closed in Atlantic Canada 
(Campana et al. 3 ). Similarly, in 2008, the National 
Marine Fisheries Service implemented Amendment 2 
to the Consolidated Atlantic Highly Migratory Species 
Fishery Management Plan (NMFS, 2007), which sig¬ 
nificantly reduced landings of porbeagles by U.S. com¬ 
mercial fisheries (Curtis et al., 2016). 
Reproduction of lamnid sharks is distinct from that 
of the majority of other elasmobranchs (Gilmore et al., 
2005). One unifying characteristic for this group is 
oophagy, as a means of embryonic nutrition, which re- 
3 Campana, S. E., M. Fowler, D. Houlihan, W. Joyce, M. Show- 
ell, M. Simpson, C. Miri, and M. Eagles. 2015. Recovery 
Potential Assessment for Porbeagle (Lamna nasus ) in Atlan¬ 
tic Canada. Dep. Fish. Oceans, Can. Sci. Advis. Seer. Res. 
Doc. 2015/041, 45 p. [Available from website.] 
Materials and methods 
Porbeagles were collected primarily from recreational 
fishermen at sportfishing tournaments held off Massa¬ 
chusetts and caught in the general vicinity of Stellwagen 
Bank or off Cape Cod (n- 23; Fig. 1). A small number of 
porbeagles were captured on pelagic longlines onboard 
a U.S. commercial fishing vessel off the Grand Banks 
of Newfoundland (n= 3). Sampling took place between 
2004 and 2018. Additionally, data collected from por¬ 
beagle specimens captured between the Grand Banks 
of Newfoundland and Georges Bank prior to 2004, and 
used in Jensen et al. (2002), were reexamined. 
Each shark was measured in fork length (FL), over 
the curve of the body from the tip of the nose to the 
fork of the tail, to the nearest millimeter and reported 
in centimeters. Whole weight was obtained when pos¬ 
sible to the nearest pound and converted to kilograms. 
A number of measurements and weights and infor¬ 
mation on conditions were taken from reproductive or¬ 
gans in female porbeagles to determine maturity stage. 
All specimens were measured fresh. Reproductive 
