Swordfish Biology and Data Needs Off the California Coast
The swordfish is a large pelagic species that is capable of inhabiting a range of environmental conditions from the warm surface waters to depths well beneath the thermocline (300 to >1,000 m). This species possesses several adaptations for deep diving including intricate gills that are designed for oxygen extraction at depth, very large eyes and a brain heater that maintains the cranial region of this predator warm even when subjected to extremely cold temperatures.
Swordfish are a valuable commercial resource targeted world-wide in every ocean. In California, recent studies suggest that the stock is healthy and currently under-exploited by U.S. fishers. Off the California coast there are two primary fisheries that target swordfish, a traditional harpoon fishery (that targets swordfish when they bask at the surface) and the California drift-gillnet fishery. Both of these commercial fisheries have declined dramatically over the past 30 years despite healthy stocks and robust markets. With this decline California now relies heavily on foreign imports to fill market demand. Given the destructive nature of many foreign swordfish operations, one of PIER’s goals is to focus on our domestic swordfish fishery and identify ways to revitalize domestic production. We feel that this revitalization should be in the form of low-impact commercial operations that have minimal interactions with bycatch species.
Initially PIER’s work focused on using movement patterns to identify ways to enhance the harpoon fishery. This research was conceived and funded through the interests of Mr. Tom Pfleger, who was a fishery participant in the late 1970’s. To address this question, the PIER team set out to document the fine-scale movements of swordfish in the Southern California Bight by deploying short-term PSATs on basking swordfish. Although this work did not find a specific time of day that had higher basking rates, the study did identify a very consistent trends in the depth distribution during the day that has led the PIER team towards the development of gear types that selectively target swordfish during the day.
Currently the PIER team is exploring alternative gear configurations that target swordfish at depth during the day. The initial trials have focused on the development and design of deep-set buoy gear, a gear type that uses a simple hook and line configuration that branches from a vertical mainline. The alternative gear targets swordfish at depths well below the thermocline in order to reduce interactions with other species. Because only a few species (bigeye thresher sharks, opah) tolerate the cool, dark and low oxygen conditions at depth (300 to 500 m), we feel that this gear has the potential to selectively target swordfish. Read more about the PIER’s deep-set buoy gear studies.