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

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.