Growth, distribution, and mortality of Light Dusky Rockfish and Harlequin Rockfish in the Aleutian Islands

Objective

Along the Aleutian Islands, Light Dusky Rockfish Sebastes variabilis and Harlequin Rockfish S. variegatus are two of the more abundant species within the “Other Rockfish” management complex of this region. Many Sebastes spp. are assessed in multispecies complexes due to a lack of basic biological information to inform management. In an effort to address data gaps, we investigated age, growth, and natural mortality for both species. The larger abundance of Light Dusky Rockfish allowed for an examination of distribution across different areas of the Aleutian Islands.

Methods

Otoliths from Light Dusky Rockfish and Harlequin Rockfish were used for age determination to describe growth parameters and subsequent maximum ages used for calculating rates of natural mortality from a mean of updated age-based estimators. Generalized linear models were developed to describe the depth distribution of Light Dusky Rockfish.

Result

Ages ranged from 3 to 79 years for Harlequin Rockfish and 3 to 70 years for Light Dusky Rockfish. Maximum ages were corroborated by multiple analyses providing estimates for natural mortality (Light Dusky Rockfish = 0.084; Harlequin Rockfish = 0.075). The von Bertalanffy growth model for Harlequin Rockfish indicated sex-specific differences, with females attaining larger maximum sizes and a lower growth coefficient. Light Dusky Rockfish showed no differences in growth by area or sex. Length distributions among areas for each species were different. Light Dusky Rockfish tended to occur in deeper water in the central and western areas of the Aleutian Islands. The presence of Light Dusky Rockfish in deeper water is influenced, through the effect in terms of odd ratios, by maturity status and area and is variable by year.

Conclusion

These results contribute to our understanding of the management and biology of Sebastes spp. within their complex, but additional investigations are needed, especially with how traits may differ within and between regions.