Age and growth of redfish (Sebastes marinus, S. mentella, and S. fasciatus) on the Flemish Cap (Northwest Atlantic)

Fran Saborido-Rey Dolores Garabana Santiago Cervin o Age determination of redfish is difficult. In this paper, the ages of Sebastes mentella on the Flemish Cap are validated by following year classes from 1991 to 2000. The criteria used for S. mentella are consistent and coherent. The growth of different year classes is described and compared, and density-dependence is demonstrated to influence the growth rate of the strong 1990 year class, growth of that year class being the slowest of those followed. The slow rate of growth prevented that year class from maturing at the anticipated age. Growth is also compared between sexes, of S. mentella, S. marinus, and S. fasciatus, revealing that females grow faster than males. Finally, growth rate is compared among species. S. marinus grows fastest and S. mentella slowest, although the influence of density-dependent growth in S. mentella needs to be taken into consideration. 1054-3139/ $30 Introduction analysis, and element analysis. Direct methods are difficult to implement in Sebastes owing to the low rate of survival when fish are caught. Frequency year-class progression analysis has been successfully used in North Atlantic Sebastes: Svalbard S. mentella (Nedreaas, 1990) and Gulf of Maine S. fasciatus (then known as S. marinus; Mayo et al., 1981). It is difficult to identify redfish accurately to species, so in many areas two or more species are considered as a single stock (Saborido-Rey, 1993), precluding the comparison of growth among species. For Flemish Cap redfish, Saborido Rey (1995) validated age readings and compared growth rates. However, the short time-series available for that study prevented accurate interpretation of the data, resulting in the necessity for the current revised and improved analyses. In this study, we first validate the age of S. mentella by following the strong 1990 year class or cohort over time. We follow this with analyses and comparisons of the growth rates of different S. mentella cohorts and both sexes, and of the three species found on the Flemish Cap. Material and methods S. marinus S. mentella S. fasciatus Females Males Females Males Females Males All years S. mentella S. marinus S. fasciatus regressions, one for each group (SSi) and one for the pooled data (SSpool). Thus, Results Age validation of S. mentella Growth of S. mentella Discussion Age 6 !0.001 !0.001 !0.001 !0.001 !0.001 e !0.001 0.020 0.328 0.325 !0.001 !0.001 !0.001 !0.001 !0.001 e !0.001 !0.001 0.009 !0.001 !0.001 !0.001 !0.001 !0.001 e !0.001 !0.001 !0.001 !0.001 !0.001 !0.001 !0.001 e !0.001 !0.001 !0.001 !0.001 0.018 !0.001 e Value S. mentella S. marinus S. fasciatus Parameter Males Females Males Females Males Females 46.40 0.104 Maximum age recorded (years) Comparison S. marinus S. mentella S. fasciatus Females Females vs. males Females vs. males Females vs. males S. marinus vs. S. mentella S. marinus vs. S. fasciatus S. mentella vs. S. fasciatus S. marinus vs. S. mentella S. marinus vs. S. fasciatus S. mentella vs. S. fasciatus 6 026 7 030 5 175 6 265 5 370 6 001 6 791 5 837 6 204 *Critical F 5:42 (a 0:001) for all tests. yDenominator d.f. (numerator d:f : 3 for all comparisons). Age (years) Mean length (cm) Mean length (cm) Length (cm) Female Proportion (%) S. marinus S. mentella S. fasciatus 47.06 47.20 49.23 46.57 47.84 46.04 45.68 37.39 37.02 51.14 59.52 60.00 100.00 94.12 100.00 48.50 46.34 47.96 48.18 48.84 50.60 56.90 82.72 90.00 90.91 100.00 12e14 15e17 18e20 21e23 24e26 27e29 30e32 33e35 36e38 39e41 42e44 45e47 48e50 51e53 54e57 *Significant at p!0:05. **Significant at p!0:01. Age (years) Mean length (cm) Mean length (cm) Age (years) Mean length (cm) Mean length (cm) *Significant at p!0:05. **Significant at p!0:01. *Significant at p!0:05. Acknowledgements (...truncated)