Contributions to Management Strategies in the NE Atlantic Regarding the Life History and Population Structure of a Key Deep-Sea Fish (Mora Moro)

Trends in abundance indices derived from commercial fisheries for priority marine stocks in the Azores

Large-scale assessments of fish and shellfish populations may be valuable for identifying the impacts of fishing pressure on stocks, but they are rarely possible due to a lack of long-term datasets. In this study, a two-part mixed-effect model for lognormal data was used to obtain historical abundance indices for 16 priority fish and shellfish stocks in the Azores region derived from catch per unit effort (kg per day at sea per vessel) and landing per unit effort (kg per landing per vessel). This data was obtained over the past 30 years under the EC Data Collection Framework and, in addition to information on effort and catch, included details about the fishing operation such as quarter, vessel length and fishing gear. This information was analysed to investigate how abundance indices changed over the years, verify if trends from different data sources were different and, if possible, relate these results to the population and fishery dynamics. The abundance indices derived from both datasets were generally in agreement with each other. Declining trends have been observed for some commercially important species, such as forkbeard Phycis phycis, European conger Conger conger, parrotfish Sparisoma cretense, red scorpionfish Scorpaena scrofa, offshore rockfish Pontinus kuhlii, common spiny lobster Palinurus elephas, splendid alfonsino Beryx splendens and alfonsino B. decadactylus, which is concerning because they are particularly slow-growing, long-lived and have low natural mortality, making them susceptible to overfishing. The results of this study are very important and should help future stock assessment and management initiatives.

Life History and Fishing Aspects of the Deep-Sea Silver Scabbardfish Lepidopus caudatus in the Azores

Deep-sea fisheries are of important economic value. Therefore, it is necessary to generate biologically and ecologically based fishing plans to make this fishery sustainable over time. The silver scabbardfish, Lepidopus caudatus, is a worldwide-distributed demersal fish, commercially exploited in the Azores. Despite L. caudatus high landings and discharges in the region, information about its ecology, population structure, biology and fisheries remains little-known. This work analyzed scientific survey and fishery-dependent data from the past 30 years to understand the changes in abundance, spatial distribution and life history of this species. Lepidopus caudatus spatial distribution was associated with depths between 200 and 400 m, close to seamounts and islands, and on sandy bottoms. The size structure varied yearly, and the population was dominated by females (sex ratio, M:F = 0.46:1). Growth rates were between the estimated values in previous studies in the Azores and indicated a slow-grower species (L∞ = 171.62 cm, k = 0.12 year−1, Φ’ = 3.52). The abundance indices highlighted a declining tendency, and this result was backed by the high exploitation rate for the fish in the region (E = 0.53). Lack of management measurements and the species’ vulnerability could lead to the depletion of this species.

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

Simple Summary

Sharks, 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.

Abstract

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.