Alopias vulpinus (Bonnaterre, 1788)

Spear, Luka N., Kohin, Suzanne, Mohan, John A. & David Wells, R. J., 2024, Insights into vertebral band pair deposition rate in the juvenile common thresher shark (Alopias vulpinus) in the northeastern Pacific Ocean, Journal of Fish Biology 104 (1), pp. 104-112 : 109

3.1 | Tagged and recaptured OTC-marked A. vulpinus

For the 14 A. vulpinus included in this study, average time at liberty was 2.14 years (±0.97 years SD), ranging from 1.08 to 3.81 years. All were juveniles ( Natanson et al., 2016; Natanson & Gervelis, 2013) with an average 101 cm LF (± 13.42 cm SD) at tagging. Study animals for whom a recapture length was provided (n = 9) averaged 137 cm LF (± 18.47 cm SD) at recapture ( Table 1 ).

3.2 | Age validation

We found no systematic age bias (p> 0.05) in all comparisons for POTC and POBB counts (χ 2 -tests of symmetry; Figure 4 ). Variability among reader counts across all three readers was lower after the BB with an APE of 7.32%, and an ACV of 9.51%, compared to an APE of 10.70% and an ACV of 14.00% for POTC counts. Among readers, all final band pair counts after the OTC were within one band pair of each other, and 93% (13 of 14) of the counts after the BB were within one band pair ( Table 1 ). The slopes of the linear regression analysis conducted for each reader ranged from 0.84 to 0.94 (95% confidence intervals ranging from 0.43 to 1.36, Table 2 ; Figure 5 ), and were not significantly different from each other based on an F -test (F = 0.3275, p = 0.8054). The goodness of fit of the linear relationships ranged from 0.60 to 0.76 ( Table 2 ; Figure 5 ), which indicates that the model explains 60% – 76% of the variability in the data around its mean, respectively.

Figures

FIGURE 4 Age-bias plots for all oxytetracycline (OTC)-marked Alopias vulpinus vertebrae to determine the number of band pairs distal to the birth band (left column), and number of band pairs distal to the OTC mark (right column). Readers 1, 2, and 3 read all sample vertebrae without knowledge of fish ID or time at liberty.

FIGURE 5 Number of vertebral band pairs after the oxytetracycline mark compared to days at liberty for Alopias vulpinus at liberty ≥1 year, tagged and recaptured in the northeastern Pacific Ocean (1998–2013) n = 14. The dashed lines represent the relationship of band pairs to days at liberty; the dotted line represents a 1:1 deposition rate of one band pair per year.