spinydogfish.org - Research

Publications A list of recent publications can be found here. Mark-Recapture Tagging Research Dr Roger A. Rulifson has conducted research on the spiny dogfish shark for over 13 years. A major focus of Dr Rulifson’s work has used FloyTags, flexible spaghetti-like tags that are implanted in muscle tissue near the dorsal fin. Each tag has a reward and an address for return, or you can get a Tag Return Form right here on this website. PLEASE return the tag. We are tracking the movements of spiny dogfish along the Eastern Seaboard of North America and your tag return is very important to us.
We are currently analyzing data from nearly 12 years of mark-recapture research on spiny dogfish. Over 38,000 tags have been released by East Carolina University researchers or collaborators. Of those tags, over 425 were returned, giving us a 1.1% return rate. The shortest recapture time occurred within a few hours of release, in North Carolina waters. The LONGEST time a tagged fish has been “at large” so far has been over 3,000 days. The spatial extent of recaptures is extensive, and ranges from South Carolina to Iceland! Tagged fish have also been returned by processors in Italy and France! These data have been entered into software called GIS, or Geographic Information System (ESRI, www.esri.com). GIS allows us to plot geographic coordinates and environmental data together on a map. We can then relate the recapture locations to variables such as days at large (time from release to recapture), depth of recovery, and water temperature at recovery. We can also use the biological information that you provide to us to measure how much the sharks have grown since their release. Taken together, the recapture data plotted on the map can answer some very interesting biological questions; the timing of migration, the extent of migration (how far north and south?), and the extent that dogfish groups move together.
Acoustic Telemetry The Rulifson lab initiated a project to look at spiny dogfish movements with acoustic telemetry over the winters of 2009 and 2010. Acoustic telemetry provides higher resolution data than the mark-recapture technique by using both active and passive acoustic tracking. Coastal waters between Kitty Hawk, NC and Cape Lookout, NC were sampled with a towable acoustic receiver to relocate tagged individuals. An acoustic line was also deployed south of Cape Hatteras to monitor the movement of sharks around the Cape. Environmental monitoring equipment (acoustic dopplar current profilers and hydrolabs) was deployed concurrently with acoustic receivers. Telemetry and ADCP data will be combined with buoy and satellite data to characterize the effect of environmental conditions on localized shark movements and to understand the complex oceanography of coastal North Carolina. The first year of sampling was completed in April 2009, and we successfully located several sharks using both active and passive sampling approaches. In addition 12 sharks were relocated between April and November 2009 in Delaware Bay, and one shark was detected off the coast of Cape Cod in August 2009. The second year of sampling was completed between January and May of 2010. Of 40 sharks tagged in 2010, 20 were redetected on passive and active acoustic sampling receivers. Five sharks tagged in 2009 were redetected in 2010 in North Carolina waters.
Fishery Management Issues A significant focus of the research completed by Dr Rulifson and his graduate students has been the accurate determination of spiny dogfish population size off the North Carolina coast. Spiny dogfish are reported in many different coastal habitats, from the sounds to off the continental slope. The National Marine Fisheries Service does not sample below Cape Hatteras, despite the fact that significant numbers of sharks have been reported by recreational and commercial fishermen in this area. Dr Rulifson, his students, and collaborating commercial fishermen have characterized the population south of Cape Hatteras. Dr Rulifson has also helped to improve population models by identifying mortality from trawl and gillnet capture (and from tagging studies!). Trawl and gillnet mortality estimates were found to be much lower than those used in federal stock assessment models. Federal biologists have since integrated the results of this research to reflect this new information. Current research in the laboratory includes efforts to calibrate gillnets and to assess the survey design of the NMFS trawl surveys in North Carolina.
Biological Data Other research completed by lab members includes identifying basic biological data needs. Spiny dogfish diet is known to vary by region, but the role of dogfish in the ecosystem is still unclear. Are spiny dogfish selecting habitat based on the presence or absence of prey? Do the vast movements of large schools of spiny dogfish drive fish into certain habitats? What are all of these sharks eating, and is it consistent year-to-year?
A New Paradigm? In fisheries management there is a confusing term -- “stock”. Stock can refer to a management unit, or it can refer to a group of genetically distinct individuals. A single stock of fish managed together as one jurisdictional unit could have many populations involved. For example, striped bass in Chesapeake Bay are referred to as the “Chesapeake Stock”, although there are fish from spawning populations in the Choptank, the Nanticoke, the Potomac, etc. A single-stock approach groups all populations of a species together (within a defined management area); in this case, harvest quotas are applied to the entire group. Striped bass from the Albemarle-Roanoke (“A-R”) stock, the Chesapeake Stock, and the Hudson Stock, can all be migrating along the US eastern seaboard, and these are referred to as the “Coast-wide Stock”, which is managed under one management unit but the unit itself considers the sub-units (Chesapeake, Hudson, Albemarle). Fisheries stock management, therefore, typically involves either a “multi-stock” approach or a “single-stock” approach. A “multi-stock” scenario is used to accommodate the range of behaviors and habitats used by populations of a species that can be separated into aggregates. In the case of spiny dogfish, the single-unit stock concept is largely supported by the lack of genetic distinction between potential sub-groups. However, recent research suggests that differences in migratory behavior between spiny dogfish at the northern and southern extremes of the range may be cause for using a multi-stock concept for management. The integration of survey and monitoring data, tagging research, and other fishery dependent and independent research in both the U.S. and Canada has allowed for the development of a new research paradigm that challenges the current management of spiny dogfish as a single-unit stock. In 2008 a collaborative group of researchers from the United States and Canada hypothesized the separation of the Atlantic coastal spiny dogfish population into the following behaviorally distinct sub-groups of dogfish (Campana 2007): 1) a U.S. mid-Atlantic migratory contingent that moves between overwinter grounds in North Carolina and summer habitats in Cape Cod and the Gulf of Maine (Group “1”); 2) a Gulf of Maine group that migrates in a gyre-like fashion around the basin (Group “2”); 3) an offshore-onshore migration population that lives on the Scotian Shelf (Group “3”); 4) a resident population off Newfoundland (Group “4”); and 5) a resident population in the Gulf of St. Lawrence (Group “5”). Future research efforts by the Rulifson lab will explore the segregation of these groups, with specific emphasis on the mid-Atlantic migratory contingent. If separate groups of dogfish are identified as biologically distinct, the management structure of the species could be dramatically affected. Over the past decade, harvest quotas have been set by fishing season and fishing region (north or south); more recently, the quota has been separated by region and historical landings by state. If a multi-stock approach is adopted, then the quota structure will likely change again to reflect the availability of dogfish throughout the range.
Funding Sources This work is funded by several sources including the North Carolina Fishery Resource Grant program administered by NC Sea Grant, the U.S. Fish and Wildlife Service, the National Marine Fisheries Service, and the Mid-Atlantic Fisheries Management Council. We thank all of these good folks for continuing to provide funding so that we can answer questions about population size, migration, and demographics of the spiny dogfish overwintering in North Carolina coastal waters.