MEPS 645:171-185 (2020)  -  DOI: https://doi.org/10.3354/meps13363

ABSTRACT: Swordfish are migratory fish that inhabit tropical to temperate waters, but little is known about movement patterns or mixing between subpopulations of this species. This study examines carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios in growth rings of the anal fin spine and muscle tissue of swordfish from 3 different areas of the Eastern North Pacific Ocean (ENPO)—off Baja California Sur (Mexico) and California (USA), and in the North Pacific Subtropical Gyre (NPSG)—to assess swordfish movements between these areas. The analysis of δ¹³C and δ¹⁵N revealed no relationship between fish size and δ¹⁵N, suggesting a consistent consumption of prey items by this species over time. Differences between the anal fin spine and muscle were found, but interpreting these isotopic differences requires information on tissue-specific isotope turnover rates. The spatial pattern suggests that swordfish populations from these areas in the ENPO exhibit a relatively unexpected homing behavior at the temporal scale, according to anal spine and muscle turnover rates. Our findings support that swordfish may show site fidelity, which has important implications for their management and stock assessments.

KEY WORDS: Billfish · δ¹³C · δ¹⁵N · Muscle · Anal fin spine