Stock Structure Studies
Swordfish are highly migratory fish that seasonally inhabit the rich foraging grounds off Southern California. Each year swordfish can travel over 5,000 km as they move from their spawning grounds in the tropics to the feeding grounds off the West Coast. Although several tagging studies have tried to document movements for this species, annual migratory patterns remain poorly understood. This problem has been partially due to the lack of technology available for monitoring long-term movements in deep-diving species like swordfish.
In 2017 PIER began using several different tag types to assess longer-term, migratory movements of swordfish in the north Pacific. The primary goals have been to document inter-annual migration patterns and also identify where California swordfish spawn. One of the big questions we continue to address is whether current stock structure hypotheses are accurate in describing the movements of swordfish off California.
PIER has worked with collaborators and tag manufactures to develop new and innovative ways to document long-term migration patterns for swordfish. PIER is now deploying dorsal fin mounted SPOT tags, a relatively new technology that provides a position estimate every time the swordfish rises to the surface to bask. We are also working with the Alvarado-Bremer Laboratory at Texas A&M to genetically compare swordfish of known track trajectories. We are confident that the combining of different techniques and methods will help resolve stock structure questions for swordfish in this region.
This work is ongoing and has been supported by the NOAA Saltonstall Kennedy Program and the state of California (California Ocean Protection Council). Data from these studies continue to be provided to regional resource managers at the ISC, IATTC and PFMC.
Using Parasites to Assess Swordfish Stock Structure
Swordfish and other marine fish have both external and internal parasites that are often unique to a specific region.
The PIER team is working with cooperative fishers and local processors to identify the common parasites present in Southern California swordfish.
We plan to compare these results with ongoing tagging and genetics studies to assess if parasites can help determine which stock a fish belongs to.
Similar work has been done on other pelagic fish around the world. Our hopes are to use all available tools to help better understand swordfish population dynamics in the North Pacific.