Swordfish are large, open water predators that are capable of inhabiting a wide range of environmental conditions from the warm surface waters to depths well beneath the thermocline (300 to >1,000 m), factors that have contributed to their near-cosmopolitan range. They possesses several adaptations for life down deep including intricate gills that are designed for efficient oxygen extraction, very large eyes, and a “brain heater” mechanism that maintains relatively high temperatures in the cranial region compared to the cold surrounding waters.  These adaptations contribute to the success of swordfish as one of the few large predators that can effectively live and hunt in the ocean depths.

PIER has been tagging swordfish and studying their movements and behaviors since 2010, the results of which have led to the development of a new sustainable fishing gear type to target US west coast swordfish, and a better understanding of migratory patterns and stock structure that is aiding managers and fishers in maintaining healthy, sustainable swordfish populations.

Since 2005, PIER has focused on assessing how fine-scale movements relate to local fisheries and bycatch reduction.  Understanding local, daily movements can help fishers increase gear selectivity and efficiency and also reduce unintended fishery impacts.  In the early years, PIER was tagging swordfish to collecting fine-scale depth data to assess whether the harpoon fishery could be improved or optimized.  Around 2009, the goals shifted towards commercial gear development and testing whether swordfish could be selectively targeted at depth during the day. The data collected from these early experiments set the stage for the development and testing of deep-set buoy gear (DSBG), a federal fishery developed by the PIER team that was recently authorized by the Pacific Fisheries Management Council (PFMC) in 2019.    

The fine-scale studies continue to use several different electronic tag types to document depth distribution and habitat utilization.  The PIER team continues to deploy archival and satellite based tags using both hook and line as well as harpoon-based techniques.  

Collaborations with several research and funding partners have helped contribute to the success of this work, including partners at NOAA, the George T. Pfleger Foundation, the Pew Foundation and The Nature Conservancy.   

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.