The reproductive biology of the porbeage shark (Lamna nasus) in the western North Atlantic Ocean

Reproductive organs from 393 male and 382 female porbeagles (Lamna nasus), caught in the western North Atlantic Ocean, were examined to determine size at maturity and reproductive cycle. Males ranged in size from 86 to 246 cm fork length (FL) and females ranged from 94 to 288 cm FL. Maturity in males was best described by an inflection in the relationship of clasper length to fork length when combined with clasper calcification. Males matured between 162 and 185 cm FL and 50% were mature at 174 cm FL. In females, all reproductive organ measurements related to body length showed a strong inflection around the size of maturity. Females matured between 210 and 230 cm FL and 50% were mature at 218 cm FL. After a protracted fall mating period (September–November), females give birth to an average of 4.0 young in spring (April−June). As in other lamnids, young are nourished through oophagy. Evidence from this study indicated a one-year reproductive cycle and gestation period lasting 8–9 months

Multiple paternity in the nurse shark, Ginglymostoma cirratum. Environ

Synopsis For over a decade, we have been studying the reproductive behavior of the nurse shark, Ginglymostoma cirratum, in the Dry Torugas off the Florida Keys, an important mating and nursery ground for this species. In the course of these studies, we have used a variety of tags and tagging protocols to monitor individual animals. Here we report the use of molecular methods for the genetic analysis of nurse sharks. Specifically we have analyzed genetic variation at the MHC II α locus using the polymerase chain reaction (PCR) followed by restriction fragment length polymorphism (RFLP) analysis of the amplified products. We found this technique to be a relatively rapid and reliable method for identifying genetic differences between individual sharks. Applying this method to a family of sharks consisting of a mother and 32 pups, we demonstrate that at least four fathers must have fathered this brood. Multiple paternity in the nurse shark suggests a mechanism by which populations of this species may maximize genetic variability. This seems especially valuable for philopatric species whose migratory movement, and thus potential for genetic diversity, is limited

Videos to BEH 3810

   Video 1. Slow straight-line swimming (Table 1, Section 3.1.2). Video 2. Self-body cleaning (Table 1, Section 3.1.10). Video 3. Courtship and Copulation (Table 2, Sections 3.2.8–3.2.12, 3.2.15, 3.2.18). Video 4a. Basking shark ram feeding on plankton (Table 3, Section 3.3.1). Video 4b. Reef manta rays ram feeding on plankton (Table 3, Section 3.3.6). Video 5. Saw Bite (Table 4, Section 3.4.5). Video 6. Vertical breach with prey seizure (Table 5, Section 3.5.4). Video 7. Horizontal bite and lateral head shake (Table 5, Sections 3.5.6, 3.5.8–3.5.9). Video 8. Scavenging on sea lion (Table 5, Section 3.5.14). Video 9. Schooling (Table 6, Section 3.6.7). Video 10. Swim by (Table 6, Section 3.6.10). Video 11. Aggressive behaviours (Table 7, Sections 3.7.2, 3.7.4–3.7.5, 3.7.7–3.7.8) Video 12. Tail slap (Table 7, Section 3.7.10). Video 13. Exaggerated tail beats and looping (Table 7, Section 3.7.12). Video 14. Reflex biting (Table 7, Section 3.7.24). Video 15. Anti-predatory biting (Table 8, Section 3.8.5).</p

Seasonal Distribution and Historic Trends in Abundance of White Sharks, <i>Carcharodon carcharias</i>, in the Western North Atlantic Ocean

<div><p>Despite recent advances in field research on white sharks (<i>Carcharodon carcharias</i>) in several regions around the world, opportunistic capture and sighting records remain the primary source of information on this species in the northwest Atlantic Ocean (NWA). Previous studies using limited datasets have suggested a precipitous decline in the abundance of white sharks from this region, but considerable uncertainty in these studies warrants additional investigation. This study builds upon previously published data combined with recent unpublished records and presents a synthesis of 649 confirmed white shark records from the NWA compiled over a 210-year period (1800-2010), resulting in the largest white shark dataset yet compiled from this region. These comprehensive records were used to update our understanding of their seasonal distribution, relative abundance trends, habitat use, and fisheries interactions. All life stages were present in continental shelf waters year-round, but median latitude of white shark occurrence varied seasonally. White sharks primarily occurred between Massachusetts and New Jersey during summer and off Florida during winter, with broad distribution along the coast during spring and fall. The majority of fishing gear interactions occurred with rod and reel, longline, and gillnet gears. Historic abundance trends from multiple sources support a significant decline in white shark abundance in the 1970s and 1980s, but there have been apparent increases in abundance since the 1990s when a variety of conservation measures were implemented. Though the white shark's inherent vulnerability to exploitation warrants continued protections, our results suggest a more optimistic outlook for the recovery of this iconic predator in the Atlantic.</p></div

White shark habitat use.

<p>Distribution of (a) bottom depths (N = 564) and (b) SST (N = 124) associated with NWA white shark captures/sightings.</p

Recent trends in white shark relative abundance.

<p>Estimates of relative change in abundance (filled circles) with 95% credible intervals (dashed lines) for any reference year between 1990 and 2008 assuming no change in observation effort (black plot), a 25% and 50% increase in observation effort (green and red plots, respectively), and a 25% and 50% decrease in observation effort (blue and purple plots, respectively) for the original sightings time series from 1990 to 2009 (a) and the time series with sightings that occurred near Monomoy Island during that time frame removed (b).</p

White shark relative decline in abundance.

<p>Estimates of relative decline in abundance (filled circles) with 95% credible intervals (dashed lines) for any reference year between 1960 and 1986 assuming no change in observation effort (black plot), a 25% and 50% increase in observation effort (green and red plots, respectively), and a 25% and 50% decrease in observation effort (blue and purple plots, respectively). Note that the scale for the y-axis has been reversed when compared to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099240#pone-0099240-g008" target="_blank">Figure 8</a> to visualize the declining trend in abundance during this time period.</p

Trend comparison of white shark relative abundance.

<p>(a) Estimated trend from the hierarchical analysis, and (b) estimated trend from the sightings analysis.</p

White shark seasonal distribution.

<p>Distribution of white shark presence records (white circles) in the NWA during (a) winter, (b) spring, (c) summer, and (d) fall. Positions are overlaid on seasonal average SST conditions (1985–2001). The 200 m bathymetric contour is displayed to delineate the edge of the continental shelf. CC  =  Cape Cod, NYB  =  New York Bight, CH  =  Cape Hatteras, FL  =  Florida, GOM  =  Gulf of Mexico, and CS  =  Caribbean Sea.</p

White shark relative abundance.

<p>White shark indices of abundance (index/mean) standardized using a zero-inflated Poisson model plotted by year for three time series: NEFSC LL  =  Northeast Fisheries Science Center fishery-independent longline surveys, TOURN  =  NEFSC tournament database, and OBS LL  =  observer program of the directed shark longline fishery. Trend lines are best fit regression models of the standardized data (second order polynomial for NEFSC LL and exponential for TOURN and OBS), using R² values and considering the biology of the white shark. The dashed red line indicates the year of the first fishery management plan (FMP) for Atlantic sharks in 1993 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099240#pone.0099240-National2" target="_blank">[77]</a> and the solid red line indicates the year that white sharks were listed as a NMFS prohibited species in 1997 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099240#pone.0099240-National1" target="_blank">[21]</a>.</p