Dante Queirolo

Dipturus chilensis and D. trachyderma are two species of skates found on the continental shelf and slope around the southern tip of South America. As another batoids, their life traits make them more susceptible to overfishing. In Chile, the skate fishery covers around twenty latitudinal degrees and is captured as a target species by artisanal vessels from the central-south zone to the Patagonian fjords (south of 41°S). Seven individuals of D. chilensis and three of D. trachyderma, 75-110 cm total length (TL), were tagged with pop-up satellite tags programmed to detach 60 days post-tagging. The skates were tracked in two areas of southern Chile, one exposed to the Pacific Ocean (Bahía Mansa) and another within the Patagonian fjords of the Chiloe inland sea (Comau Channel). Bathymetric ranges of 9-512 m and temperatures of 7.7-11.5°C for D. chilensis and depths of 111-513 m with temperatures of 10.5-11.5°C for D. trachyderma were detected. The minimum horizontal movement varied between 0.84 and 35.95 km in D. chilensis and 2.59 and 33.90 km in D. trachyderma. Notably, D. chilensis was found at significantly shallower depths at night, with differences between zones and higher levels of vertical activity in Comau. Both species showed daily vertical movements of up to 1.4 km, displaying movement patterns associated with different modalities of foraging. The median vertical speed was up to 0.18 TL s-1, suggesting that both species could primarily utilize nektobenthic diel vertical migration to move to and from the coast.

This study investigates the interactions between South American sea lions (Otaria byronia) and trawling fisheries in central‐southern Chile, using underwater video technology. From August 2017 to August 2018, a total of 32 underwater filming sessions were conducted across trawl fisheries targeting Patagonian grenadier (Macruronus magellanicus), nylon shrimp (Heterocarpus reedi), and Chilean hake (Merluccius gayi gayi). The records revealed a total of 15 sea lions, including adult and subadult males and females. These individuals were observed engaging in specific behaviors, such as swimming within the trawl nets and feeding at escape panels of bycatch reduction devices (BRDs). Notably, we documented one subadult male reaching 425 meters. This finding suggests a probable significant adaptability and potential predation behavior at extreme depths. Our findings highlight the importance of further monitoring and research to address conflicts between marine mammal populations and the fishing industry, while enhancing the of conservation strategies to ensure their effectiveness.

PDF Abstract Chilean hake (Merluccius gayi gayi) is one of central Chile's most important demersal resources, and its fishery involves an artisanal fleet that mainly uses gillnets. In the recent history of the fishery, there has been a decrease in catch sizes and a progressive reduction in mesh sizes. This study aimed to analyze the factors that influenced the mean catch sizes of Chilean hake between 2001 and 2018 to understand this situation, correlating the response of fishermen with the capture efficiency of the nets used. Applying a generalized linear model, a significant effect of the factors year, port (zone), and mesh size were observed on the mean size of individuals caught. The model explained 85% of the deviation, the greatest relative contributions being made by the factors year (53.6%) and port (30.2%). A lower effect was estimated for the mesh size factor with 1.2% deviance. These findings suggest that the progressive reduction in mesh sizes is associated with a response to the demographic change in the stock. Differentiated management measures by zones could be considered in the fishery, given the estimated differences.

Natural mortality (M) is a key parameter for understanding population dynamics, especially in relation to harvested populations. Direct observations of M in crustaceans are scarce, due to the moulting process. Indirect methods to estimate M with easier-to-obtain life history attributes are therefore used routinely. Given their theoretical background, we reviewed the applicability of these methods for crustaceans. We applied the selected methods to two crustacean species harvested in Chilean waters: the yellow squat lobster (Cervimunida johni) and red squat lobster (Pleuroncodes monodon). Uncertainty of each M estimate was incorporated in the life history parameters that input into the indirect method (trait-error) and parameters defining the indirect method (coefficient-trait-error). Methods based on the relationship between total mortality and maximum age, or with different ages and based on life history theory were the most appropriate for crustaceans since they apply across taxa. M estimates showed high variability between species, sexes and areas. Estimations of M for C. johni varied from 0.13 to 0.28 (year⁻¹) for males and 0.17 to 0.51 (year⁻¹) for females. For P. monodon values for the north varied from 0.26 to 0.37 (year⁻¹) for males and 0.24 to 0.45 (year⁻¹) for females. In the south, values of M were higher for both males (0.43–0.68 year⁻¹) and females (0.41–1.06 year⁻¹). High variability in the M estimates was associated with the method and number of parameters, their uncertainty, theoretical background and probability distribution. M estimates are not comparable, raising the need to propagate the uncertainty of M into the stock assessment of Chilean squat lobsters.