Examinando por Autor "Ortiz, Marco"

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    Ítem
    Exploring sustainable scenarios for the brown algae fishery in the intertidal zone along the central Chilean coast (Maule region)
    (Elsevier, 2025) Berrios, Fernando; Ortiz, Marco
    This work presents the outcomes from five semi-quantitative loop models of different levels of complexity, built to explore and quantify the stability and resilience (used as proxies for sustainability) of the ecological and eco-social systems where intensive artisanal fishing activity of the algae Durvillaea incurvata (Di) and Lessonia spicata (Ls) is occurring in central Chile (Maule Region). The average values for Routh-Hurwitz local stability criterion 1 (Fs) and for Levins’ criterion (Fn) showed that the model systems achieved the desired stability and resilience only when both algae exhibit asymmetric level of abundance (avoiding symmetric competition). Furthermore, both species should exhibit self-negative feedback, that is, their abundances should fluctuate between k/2 and maximum abundance (according to logistic growth). The latter results imply that both algae were the most sensitive to perturbations, regardless of their level of complexity, which limits exploitation strategies and emphasizes the need for integrated management. The substrate (S) also emerged as sensitive in the system. When fishers (F) and demand (D) are dominated by self-negative feedback, the average values of local stability (Fs) and resilience (Fn) were higher than when F and D exhibited self-positive feedback. Therefore, to ensure a sustainable exploitation of both algae, it would be necessary to: maintain the asymmetry of abundance (regardless of which of the two dominates), monitor the quality of the coastal rocky substrate to ensure the colonization of new plants, particularly L. spicata and D. incurvata, and design and implement policies that promote control over the activity of fishers and demand.
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    Modelling 22-years of changes in productivity of the red sea urchin Loxechinus albus in southern Chile using the pre-image population analysis: insights for fishery and conservation management
    (Elsevier, 2025) Ortiz, Marco; Diaz, Josue
    Pre-image population analysis (PPA) corresponds to a graphic method which allows modelling population dynamics, being able to estimate local population growth parameters using time series of biomass and/or abundance. In this work, PPA was performed using two different types of biomass time series of the exploited red sea urchin Loxechinus albus (Molina, 1782) that inhabit three geographical areas in southern Chile estimating changes in productivity over a period of 22 years. Although the magnitudes of biomass in the time series seem to fluctuate in the analyzed time period, the PPA model parameters in terms of x* (equilibrium values) and r (growth rate, used as a proxy for productivity) showed a reduction between ~15 - 37 % and ~60 - 71 % respectively, highlighting that the Aisen Region (XI) showed the lowest values in both model parameters. Despite the above, the productivity (r) exhibited chaotic dynamics, reaching a flat level in last years. Based on current outcomes, it is suggested to consider the inter-annual magnitudes of equilibrium values (x*) and productivity (r) when determining the exploitation levels for L. albus. Likewise, the direction of change in transient values of productivity (r) could facilitate the monitoring of local populations of L. albus, providing useful information for the adoption of management decisions, such as the setting of fishing quotas and bans. Therefore, PPA could be a useful and complementary technique in estimating dynamic reference points that improve fisheries-management and conservation programs. Finally, it is recommended that PPA could be used as an easy single-species technique to assess the population dynamics of exploited and protected species.