Biological Knowledge of Thornback Ray (Raja clavata) from the Azores: Improving Scientific Information for the Effectiveness of Species-Specific Management Measures

Régis Santos,Mário Pinho,Osman Crespo,Ana Novoa-Pabon,Wendell Medeiros-Leal

doi:10.3390/biology10070676

Régis Santos, Mário Pinho + Show 3 more

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https://doi.org/10.3390/biology10070676

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Journal: Biology	Publication Date: Jul 17, 2021
Citations: 10	License type: CC BY 4.0

Affiliation: University of the Azores, Institute of Marine Research

Abstract

Simple SummarySharks, rays, and skates are increasingly being recognized as endangered due to their life-history characteristics, fishing pressure, and habitat degradation. The thornback ray Raja clavata is one of the most commercially important skates in the seas of Northwest Europe. However, due to a lack of biological knowledge about this species in Azorean waters, the types of stock evaluations that can be performed are restricted. This study expands current knowledge on vertical distribution, size-frequency distributions, growth patterns, sex ratios, mortality rates, and reproduction of this species, and provides a baseline for further fishing monitoring.Elasmobranchs are globally recognized as vulnerable due to their life-history characteristics, fishing pressure, and habitat degradation. Among the skates and rays caught by commercial fisheries, the thornback ray Raja clavata is one of the most economically important in Northwest European seas. However, the scarcity of biological knowledge about this species in Azorean waters has limited the stock assessment types that can be conducted. To improve information on its habitat preferences, spatial distribution and movement pattern, growth, sex ratio, mortality, and reproduction, as well as to investigate long-term changes in abundance and size, this study analyzed approximately 25 years of fishery-dependent and independent data from the Azores. Raja clavata was mainly caught at depths up to 250 m. Most of the tagged fish were recaptured near the release point. A larger–deeper trend was found, and females were larger and more abundant than males. Life-history parameters showed that R. clavata has a long lifespan, large size, slow growth, and low natural mortality. The sustainability of its population is of concern to fisheries management and, while our findings suggested a relatively healthy stock in the Azores, a thorough increase in data quality is required to better understand the stock condition and prevent overexploitation.

Highlights

There is a lack of biological knowledge, such as life history, habitat use, movement patterns, and population structure, for most species
A total of 2846 individual thornback rays were sampled from the scientific surveys
The generalized additive models (GAMs) results indicated that the presence–absence model explained 37.9% of the variance, while the positive catches (Gaussian) model explained 16.3% (Table 1)

Summary

Introduction

Elasmobranchs (sharks, skates, and rays) are widely recognized as a fragile resource, more susceptible to decline and extinction than most teleost fishes, due to their life-history characteristics (low fecundity, late maturity, and slow growth rates), fishing pressure, and habitat degradation [1,2]. There is a lack of biological knowledge, such as life history, habitat use, movement patterns, and population structure, for most species. Such characteristics may have serious implications for the sustainability of elasmobranch fisheries, as science-based measures are important to avert population collapse [6]

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