Nancy E. Kohler’s research while affiliated with National Marine Fisheries Service and other places

Tiger sharks, Galeocerdo cuvier, are apex predators that may structure marine communities through predation. Despite a large number of studies in other areas such as the Pacific Ocean, there are no quantitative data on the diet of tiger sharks in the northwest Atlantic Ocean and Gulf of Mexico. Diet was assessed from 169 tiger sharks by life stage, area, and environmental factors. Fifteen prey groups were identified, with teleosts, molluscs, birds, cephalopods, and reptiles being the predominant prey categories. There was an ontogenetic shift in diet, prey size and diversity. Molluscs were the most common prey in smaller sharks, while teleosts and reptiles became more important in the diet of larger sharks. Dietary overlap was significant by area (Gulf of Mexico vs Atlantic Ocean) and among all life stages except for young-of-the-year and adult tiger sharks. Juvenile tiger sharks also demonstrated selective feeding by targeting gastropod feet over ingesting the entire animal. While results were similar to feeding studies conducted on tiger sharks in other ocean basins, an understanding of area-specific trophic interactions is necessary to inform decision support tools for ecosystem-based approaches to management.

Link to ftp://ftp.library.noaa.gov/BrownBags/McBride07102017.mp4 to hear and see this presentation. See attached for a summary.

Despite recent advances in field research on white sharks (Carcharodon carcharias) 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 This study builds upon previously published data combined with recent unpublished records and presents a synthesis of 649 confirmed white shark records from the NWA compiled over a 210-year period (1800-2010), resulting in the largest white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.

Abstract Despite recent advances in field research on white sharks (Carcharodon carcharias) 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.

Age and growth of the dusky shark Carcarhinus obscurus from the South-West Indian Ocean was determined from bands in the vertebrae of 42 individuals. Age to maturity was estimated at 20,5 years for males and between 17 and 24 years for females. The oldest fish examined was a 34-year-old female. The Von Bertalanffy parameters calculated for the sexes combined were: L ∞ = 334, K = 0,047 and t 0 = −5,18. The growth rate of dusky sharks from the South-West Indian Ocean was similar to that of the western North Atlantic population.

A comprehensive population dynamics analysis of porbeagle shark (Lamna nasus) in the Northwest Atlantic indicates that the population has collapsed for the second time in its 43-year fishing history. The virgin population in the early 1960s supported annual catches of over 9,000 metric tons (t) before the fishery collapsed in 1967. After a partial recovery over the next 25 years, annual catches of 1,000-2,000 t throughout the 1990s appear to have once again driven the population to record-low numbers. Both the size and the age composition of the catch have declined markedly since 1990, with relatively few large sharks left in the population. Commercial catch rates are now only 10-30% of those in the early 1990s. Both Petersen calculations based on tag recaptures and an age- and sexstructured population model suggest that recent biomass is 10-20% of that present in the virgin population. Porbeagle have a low pup production rate and mature considerably after the age at which they first appear in the fishery. In light of the very low numbers of mature females now found in the population, it is unlikely that even the strict quota management that has been implemented will allow the population to rebuild quickly. However, a 75% reduction in fishing mortality, accurate monitoring of catch, effort, and size composition, and area closures to protect mating aggregations have all been put into place to allow population recovery.

The morphological similarity of many commercially exploited sharks, coupled with the widespread practice of delivering often difficult-to-identify carcasses and detached fins to port, has made the collection of shark fishery catch data on a species-specific basis nearly impossible. We report here on the utility of a simple, rapid, accurate, and relatively inexpensive genetic assay for identifying tissues and body parts from five shark species (silky, dusky, sandbar, shortfin mako, longfin mako) commonly encountered in pelagic fisheries.