Triennial migration and philopatry in the critically endangered soupfin shark <i>Galeorhinus galeus</i>

Globally, one quarter of shark and ray species are threatened with extinction due to overfishing. Effective conservation management can facilitate population recoveries. However, these efforts depend on robust data movement patterns stock structure, which lacking for many species, including the Critically Endangered soupfin Galeorhinus galeus, a circumglobal coastal-pelagic species. Using passive acoustic telemetry, we continuously tracked 34 mature female sharks, surgically implanted coded transmitters, 7 years via 337 underwater receivers stationed along west coast North America. These sharks an additional six were also externally fitted spaghetti identification tags. Our tagging site was shallow rocky reef off La Jolla (San Diego County), California, USA, where adult females observed aggregate every summer. Tagged highly migratory America, between Washington, USA Baja California Sur, Mexico. 3 years, they returned waters Jolla, underwent gestation. This is first conclusive evidence triennial migration philopatry (‘home-loving’) in any animal, apparently driven by this species’ unusual reproductive cycle. Females other cycles likely exhibit philopatry. At least (15%) our tagged killed commercial gillnets Policy implications. Identifying multiennial reveal hidden structure form discrete breeding cohorts, spatially temporally segregated as cycle through different phases. Accounting complexity may improve performance structured assessment models, particularly when fishery removals heterogeneous, well inform spatiotemporal design fishery-independent surveys. In United States, neither actively managed nor recognized Highly Migratory Species; however, given behaviour report, designation should be revisited US Pacific Fishery Management Council. Finally, extensive Mexico, future must internationally cooperative.