National Shark Research Consortium
Shark Research Program - Virginia Institute of Marine Science
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NSRC-supported Initiatives
Relative abundance and distribution studies
Coastal Population Monitoring: VIMS will continue its long-term (1973-2003) coastal longline surveys to track population
abundance, species composition, size and age distributions and sex ratios of sharks in the coastal ocean from Maryland to North
Carolina out to ca. 200m depth. These surveys entail standard longline sets with 100
hooks baited with menhaden and fished for 4 hours. Approximately eight stations will be occupied each month from May to October.
Virginia Nursery Grounds: VIMS will continue its long-term monitoring of
recruitment and relative abundance of juvenile sandbar sharks in Chesapeake Bay. In
addition, sampling has been expanded in the seaside Eastern Shore nursery grounds
where only ancillary studies have been conducted in the past. Eastern Shore sampling includes longline
sets comparable to those set in the Eastern Shore by the VIMS long term monitoring program beginning in 1995.
In addition juvenile sandbar shark movements and activity patterns will be studied using stationary acoustic stations
placed in a 5 km range in Wachapreague inlet. This information will be used to help determine daily space activity and
Essential Fish Habitat. The longline monitoring program in the nursery grounds will dove-tail with our long term (1973- present)
offshore longline monitoring program.
Alaska Salmon Shark Studies: VIMS scientists will collaborate with scientists from Alaska Fish and Game to
develop techniques using side scan sonar to assess salmon shark stocks in the fjords adjacent to Prince William Sound.
Preliminary studies in summer 2000 using sonically tagged sharks (known targets) suggested that an exploratory side scan
sonar survey using a line transect design would be possible in selected fjords in summer 2002. This exploratory research
was successful and will lead to more detailed surveys in 2004.
Age, growth and demographic studies
Knowledge of age, growth, and demographic parameters are essential to informed management of any elasmobranch species. Elasmobranch age and growth studies have been ongoing at VIMS since 1973. These data have been essential to modeling efforts by VIMS scientists as well as NMFS scientists at the NMFS Shark Evaluation Workshops which have formed the basis for NMFS shark fishing rules and regulations. In the coming year we plan to focus studies on the following species:
Sandbar shark: The theory of fishing assumes that as populations are harvested, and intraspecific competition declines fish populations will undergo compensation by increasing growth rates and perhaps maturing earlier. This has been shown to be true in many teleost species; however, when VIMS scientists compared growth rates for sandbar sharks before and after stock collapse from overfishing between 1980 and 1992, they found little growth compensation and no change in the age at maturity. Now in 2003 the sandbar shark population is still less than 50% of that in 1980 and compensation has had more time to become apparent (growth may be affected over more year classes). Therefore, VIMS scientists are examining sandbar shark growth rates (based on vertebral analysis) in 2001-2002 for comparison to published historical rates and those derived from archived vertebrae.
In addition, inter-population differences in shark growth may enlighten the debate about growth compensation. Therefore, VIMS scientists are working in cooperation with scientists from the University of Hawaii to collect sandbar shark vertebrae from the Hawaiian population which is purported to grow faster, mature younger, and reach a smaller maximum size.
Barndoor Skate: The barndoor skate has declined by more than 95% because it occurs as bycatch in the groundfisheries in Canada and New England. NMFS Office of Protected Resources has placed this species on the Candidate List under the Endangered Species Act. Age and growth of the species is unknown. VIMS scientists are studying the age and growth of barndoor skate by using vertebral ring analysis in cooperation with scientists at the NMFS Northeast Fishery Science Center (NEFSC). Results of this study will be used in population modeling. The results will be of value to NMFS, NEFSC, and Office of Protected Resources, as well as to the New England Fishery Management Council which is preparing a Skate Management Plan.
Squaloid sharks: The biology of deep-sea sharks is poorly understood at present. Several fisheries worldwide are landing squaloid sharks, as bycatch in deepwater trawls or longlines or in some cases (i.e. Centrophorus squamosus and Centroscymnus coelolepis) they are targeted for their livers, enriched in valuable squalene oil. Given the environment in which these sharks live, it is highly likely that they are very long-lived animals and are therefore exceptionally vulnerable to exploitation. In order to properly manage these sharks, age, growth, and demographics need to be studied. Ageing of elasmobranchs in general is difficult, but deep-sea sharks are particularly problematic since these animals do not experience "seasons" in the same way as coastal sharks. Also, calcium in the vertebrae is frequently recycled. Therefore calcified annuli in the vertebrae are not available for ageing these sharks. One of the primary goals of this project is to explore novel methods for aging deep-sea gulper sharks (Centrophorus granulosus),
using a variety of staining techniques with sections of fin spines.
Habitat utilization and migration studies
VIMS scientists have been collaborating since 1973 with NMFS scientists with the Cooperative Tagging Program at Narragansett, RI to use NMFS tags on several species of sharks off Virginia. This study continues. In addition, we are continuing to tag juvenile sandbar sharks with nylon barbed "puppy" tags to describe movements and migration patterns of juveniles. These are the same tags that are used by Mote scientists on the Gulf Coast and by the NMFS scientists COASTSPAN program. Our juvenile tagging program is an integrated part of a NMFS Atlantic and Gulf Coast wide study of shark nursery habitats.
Although standard tags have provided a great deal of information so far on shark movements and migration,
they provide basically only two pieces of geographic information: point of release and point of capture. In the
summer months of 2003 VIMS scientists deployed 21 pop-off satellite transmitters on large juvenile sandbar sharks to further
define migration patterns and habitat utilization.
These tags will provide data on temperature, depth and approximate
geolocation (derived from light measurements) during migration. These transmitters are programmed to release in the winter
months of 2003/2004. Other shark species will be tagged with satellite tags as opportunity permits. Among those may be
whale sharks which aggregate off the mouth of the Mississippi River each summer. This work will be pursued primarily by
collaboration with Charter Boat fisherman (including a trained fishery scientist) based in Venice, LA. Whale sharks have been
on the Protected List for several years and their status is unclear. Nothing is known of their migratory movements in the
North Atlantic, and this collaboration may offer a rare opportunity to study behavior of whale sharks at a very minimum cost.
Alaskan studies: VIMS scientists will continue to collaborate with scientists from Alaska Department of Fish and Game and Hopkins Marine Station, Stanford University to attach pop-off satellite tags to salmon sharks in Prince William Sound and adjacent waters. These tags will help to define seasonal movements and habitat utilization for this species which is an important recreational species and which may also be capable of supporting a modest commercial harvest in Alaska.
Shark energetic and osmoregulatory studies
Chesapeake Bay serves as primary nursery ground for sandbar sharks (Carcharhinus plumbeus).
Previous VIMS research shows that sharks utilize areas in Chesapeake Bay down to about 20ppt salinity.
Analysis of our long-line data shows that large shark species which might prey on juvenile sandbar sharks
are rare in Chesapeake Bay. We hypothesize that this is because of the lower salinity there. In order to
test this hypothesis we plan to study the salinity tolerance of sandbar sharks as well as that of their predators,
blacktip (C. limbatus), dusky (C.obscurus), and sandtiger (Carcharias taurus) sharks. In addition, following up on
our energetics studies of last year, we plan to study the metabolic rates of juvenile sandbar sharks at different
salinities to determine the energetic cost of using the brackish Chesapeake Bay nursery ground.
Sandbar shark genetic studies
Although we have been able to estimate the abundance of juvenile sandbar sharks in Virginia nurseries, it has been impossible to estimate the numbers of females that pup in these nurseries each year. Pregnant females are in the nurseries only briefly, rarely feed during this period (so are unavailable to our longline gear), and quickly disperse offshore after pupping. Adult males remain offshore year round. Using modern genetic techniques (PCR, microsatellites) it will be possible to estimate both the effective population size as well as the effective number of breeders utilizing the Chesapeake Bay as a nursery. In addition comparisons can be made between recently collected samples and museum samples from the late 1970's to determine if there has been any significant loss of genetic variation during the last thirty years of exploitation.
In an attempt to assess the nature of gene flow in this species we will compare animals from the Chesapeake Bay nurseries with animals from the Delaware Bay nurseries. The comparison will be made using mitochondrial DNA sequences (mtDNA) as well as microsatellites. mtDNA is passed maternally so significant differences between nursery locations are evidence of philopatry. Microsatellites are passed biparentally. In a situation where gene flow is male mediated and dispersal is mediated by female philopatry we would expect significant differences between nurseries in mtDNA but not in microsatellites. In addition using these same markers we can assess the strictness of philopatry.
We should also be able to detect reproductive periodicity by finding kin groups that should appear in age classes corresponding to alternate years of pupping. We will also examine the possibility that aggregations of young of the year and juvenile sharks may be kin.
Page updated November 2003
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