Tracking Pacific bluefin tuna (Thunnus thynnus orientalis)in the northeastern Pacific with an automated algorithm that estimates latitude by matching sea-surface-temperature data from satellites with temperature data from tags on fish

TLDR

Light‑based geolocation of tuna provides robust longitude but suffers large latitude errors, especially near equinoxes and low latitudes, and satellite sea‑surface temperature data have been proposed to improve latitude estimates. The authors developed PSAT Tracker, an algorithm that matches sea‑surface temperature recorded by satellite‑archival tags with satellite SST to refine latitude estimates for juvenile bluefin tuna. PSAT Tracker produced latitude estimates that agreed with light‑based methods and succeeded when those failed, yielding near one‑year tracks showing tuna ranging from the California–Oregon border to southern Baja California, spending most time off central Baja and migrating northward in summer–fall.

Abstract

Data recovered from 11 popup satellite archival tags and 3 surgically implanted archival tags were used to analyze the movement patterns of juvenile northern bluefin tuna (Thunnus thynnus orientalis) in the eastern Pacific. The light sensors on archival and pop-up satellite transmitting archival tags (PSATs) provide data on the time of sunrise and sunset, allowing the calculation of an approximate geographic position of the animal. Light-based estimates of longitude are relatively robust but latitude estimates are prone to large degrees of error, particularly near the times of the equinoxes and when the tag is at low latitudes. Estimating latitude remains a problem for researchers using light-based geolocation algorithms and it has been suggested that sea surface temperature data from satellites may be a useful tool for refining latitude estimates. Tag data from bluefin tuna were subjected to a newly developed algorithm, called “PSAT Tracker,” which automatically matches sea surface temperature data from the tags with sea surface temperatures recorded by satellites. The results of this algorithm compared favorably to the estimates of latitude calculated with the lightbased algorithms and allowed for estimation of fish positions during times of the year when the lightbased algorithms failed. Three near one-year tracks produced by PSAT tracker showed that the fish range from the California−Oregon border to southern Baja California, Mexico, and that the majority of time is spent off the coast of central Baja Mexico. A seasonal movement pattern was evident; the fish spend winter and spring off central Baja California, and summer through fall is spent moving northward to Oregon and returning to Baja California.