Quantum mechanics

Ecology

Biology

δ15N

Fish <Actinopterygii>

Fishery

Ocean gyre

Swordfish

Tuna

Geology

Oceanography

Physics

Geography

Isotope analysis

δ13C

Stable isotope ratio

Subtropics

Marine Ecology Progress Series

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 (δ 13 C) and nitrogen (δ 15 N) 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 δ 13 C and δ 15 N revealed no relationship between fish size and δ 15 N, 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.

Assessing residency and movement dynamics of swordfish Xiphias gladius in the Eastern North Pacific Ocean using stable isotope analysis