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.