Movements, dispersion, and mixing of bigeye tuna (Thunnus obesus) tagged and released in the equatorial Central Pacific Ocean, with conventional and archival tags

Abstract

a b s t r a c tA total of 31,242 bigeye tuna was captured, tagged, and released, 30,793 with dart tags (DTs) and 449 with geolocating archival tags (ATs), in the equatorial central Pacific Ocean along the 140• W, 155• W, 170• W, and 180• meridians, during 2008 through 2012, of which 10,029 (32.1%) of the DTs and 74 (16.5%) of the ATs were returned. A subset of high-confidence filtered DT data was retained for 5807 fish at liberty for 30 d or more, for evaluating linear displacements from release to recapture positions. For the filtered DT data, days at liberty ranged from 30 to 1701 d (median = 187 d). Linear displacements ranged from 1 to 5372 nautical miles (M) (median = 936 M), with 71% eastward and 29% westward, and 95% within 3614 M of their release positions. The data indicate significant differences in the linear displacements by release locations, days at liberty, and fish length at release. An unscented Kalman filter model with sea-surface temperature measurements integrated (UKFsst) was used to process 48 AT data sets from bigeye tuna at liberty for 30 d or longer, to obtain most probable tracks, improved estimates of geographic positions, and movement parameters. The 95% volume contours surrounding the position estimates, along the most probable tracks from bigeye tuna releases along the 140• W, 155• W, 170• W, and 180• meridians show substantial overlap. For the pooled AT data sets, the median parameter estimates from the UKFsst model for errors in longitude ( x ) and latitude ( y ) were 0.52• and 1.75• , for directed eastward and northward movements (u and v) were −2.01 M/d and −1.41 M/d, and for dispersive movement (D) was 496.7 M 2 /d. The linear displacements and most probable tracks obtained from these tagging data demonstrate constrained latitudinal dispersion, some regional fidelity, some extensive eastward longitudinal dispersion, and substantial mixing of bigeye tuna between release longitudes. The amount of mixing of bigeye tuna among these release areas in the equatorial central Pacific Ocean, with those in adjacent areas of the equatorial eastern and western Pacific Ocean, is dependent on distances between areas, with, in general, the greatest mixing occurring between the areas that are closest to one another.

Environmental influence on the seasonal movements of satellite-tracked ocean sunfish Mola mola in the north-east Atlantic

“…Thus, sunfish PSAT tracks had similar spatial errors to those found previously [e.g. 44,45]. The remaining 10 fish were monitored continuously via Argos receivers on polar-orbiting satellites, with one tag (#14) also recording depth and temperature data (see 'Methods' section).…”

Vertical movements, behavior, and habitat of bigeye tuna (Thunnus obesus) in the equatorial central Pacific Ocean

“…The materials and methods used for the capture, tagging, and releasing bigeye tuna with archival tags are described by Schaefer and Fuller (2002), and Schaefer et al (2015).…”

“…1. The unscented Kalman filter model (Lam et al, 2008), with sea-surface temperature measurements integrated (UKFsst), was used to obtain the most probable tracks and improved estimates of geographic positions, as described by Schaefer et al (2015). The position estimates as shown in Fig.…”

“…A daily position was estimated along the movement paths for each of the 47 fish, based on the methodology described by Schaefer et al (2015), except when no position was available due to the lack of a light-based position estimate, a position was interpolated for that day. For analyses of behavior types, the time series data were truncated, and only the 7868 days of data recorded after fish had been separated from initial association with floating objects, including the tagging vessel, were utilized.…”

“…For the 279 associative events analyzed, depth records indicate that the association began at some point during the night, as at sunrise the fish remained above the thermocline for the majority of the day and there was no indication of association prior to sunset on the previous day. When bigeye tuna less than about 100 cm in length inhabit the EEPO east of 120 • W they are apparently subjected to greater fishing mortality by purse-seine vessels fishing on DFADs, than when inhabiting the ECPO between 120 • W and 180 • , when considering recapture rates of 43% vs. 32%, respectively, from bigeye tuna tagged and released with plastic dart tags Schaefer et al, 2015).…”