Understanding the spatio-temporal dynamics of Antarctic krill ( Euphausia superba ) productivity along the Western Antarctic Peninsula (WAP) requires the application of robust analytical approaches. Both design-based and model-based methodologies have been employed to address this challenge. The Spawning Potential Ratio (SPR) is a indicator that provides valuable insights about population productivity. In this study, we analyzed the spatial and temporal variability of the SPR for krill by modeling Length-Based Spawning Potential Ratio (LBSPR) with 20 years of fishery-dependent length composition data. Results showed spatial and temporal heterogeneity among five fishing strata in the WAP, where SPR in Gerlache Strait stratum was consistently lower than the 20% SPR reference point, compared with Elephant, Bransfield Strait, Southwest and Joinville Island strata. Moreover, we demonstrate the sensitivity of LBSPR to changes in growth parameters, such as k and L _inf , which are influenced by environmental variables like chlorophyll. Our findings underscore the value of incorporating environmental variability into stock assessment models, such as those based on SPR, to accurately assess krill stock conditions. Given the apparent spatial heterogeneity in intrinsic productivity identified through our SPR estimates, we propose using this approach to establish a management procedure based on a control rule for each stratum. This method adjusts the allocation of catch limits in line with the new management strategy of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). By integrating knowledge about spatial krill dynamics and its intrinsic productivity, advice can be recommended to promote the sustainable management of krill populations in Subarea 48.1.

Bivalve fisheries are of high ecological and economic relevance worldwide, and the wedge clam (Donax trunculus) sustains a valuable small-scale fishery in the Gulf of Cádiz. Management of this resource has historically relied on empirical measures such as Minimum Conservation Reference Size (MCRS) limits and seasonal closures, with limited capacity to evaluate stock status or the long-term consequences of alternative regulations. This study pursued two objectives: (i) to conduct the first integrated stock assessment of D. trunculus in the Gulf of Cádiz using a length-to-age framework, and (ii) to quantify the effects of alternative MCRS regulations on stock status and productivity based on model estimated population dynamics. The assessment integrated multiple data sources, including time series of landings, length-frequency data, and abundance indices, under a consistent set of biological assumptions. Five MCRS scenarios ranging from 22 to 26 mm were evaluated. Model estimates indicated a progressive reduction in stock depletion during 2023 under more restrictive MCRS. Specifically, depletion declined from 20% under the 22 mm scenario to 34% under the 25 mm scenario, stabilizing at 33% for the 26 mm scenario. These results reflect a positive stock response to higher size limits, driven by increased spawning biomass retention and reduced exploitation pressure on juvenile fractions. All scenarios remained below a potential target reference point of 40% of unfished biomass (B/B0 = 0.40), indicating that current stock depletion levels are consistently below this precautionary benchmark regardless of the MCRS applied. The observed differences among scenarios highlight the strong sensitivity of stock status to alternative Minimum Conservation Reference Size configurations and their implications for rebuilding potential. The results suggest that although lower MCRS values may provide short-term economic gains through increased immediate harvest, they are associated with elevated long-term risks to stock productivity and sustainability. Maintaining the current 25 mm MCRS is supported as a precautionary strategy. More generally, this study highlights the value of integrated assessment models for evaluating size-based management measures in data-moderate bivalve fisheries.

Understanding the spatio-temporal dynamics of Antarctic krill ( Euphausia superba ) productivity along the Western Antarctic Peninsula (WAP) requires the application of robust analytical approaches. Both design-based and model-based methodologies have been employed to address this challenge. The Spawning Potential Ratio (SPR) provides valuable insights about population indicators. In this study, we analyzed the spatial and temporal variability of the SPR for Antarctic krill by applying a Length-Based Spawning Potential Ratio (LBSPR) model to 20 years of fishery-dependent length composition data. Results showed spatial and temporal heterogeneity among fishing strata in the WAP, where Gerlache Strait stratum was consistently lower than the 20% SPR reference point, compared with Elephant, Bransfield Strait, South West and Joinville strata. Moreover, we demonstrate the sensitivity of LBSPR to changes in growth parameters, such as k and L _inf , which are influenced by environmental variables like chlorophyll. Our findings underscore the necessity of incorporating environmental variability into stock assessment models, such as those based on SPR, to accurately assess krill stock conditions. Given the apparent spatial heterogeneity in intrinsic productivity identified through our SPR estimates, we propose using this approach to establish a management procedure based on a control rule for each stratum. This method adjusts the allocation of catch limits in line with the new management strategy of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). By integrating knowledge about spatial krill dynamics and its intrinsic productivity, advice can be recommended to ensure the sustainable management of krill populations in Subarea 48.1.

Pygoscelis penguin populations in the Antarctic Peninsula have dropped dramatically in the last 50 years. The main probable cause is the reduction in Krill (Euphausia superba), the most important feeding item for Pygoscelis penguins during breeding. The scientific community has expressed concerns on the potential that competition with the fishery during periods of low krill availability might be exacerbating the effects of climate change. By bringing together data on breeding success of penguin colonies throughout the Antarctic Peninsula with information of krill availability from acoustic survey and krill fishery monitoring data, we were able to show that fishery has had in the past an effect over breeding success. That is a consequence of a management strategy based on a constant catch level enabling the fishery to maintain the same levels of production even when krill availability is low. The total catch limit may have represented a substantial amount of the available krill biomass in some years, and we detected that when the catch goes over 5% of the available biomass during summer, breeding success of penguins decreased by one third. We discuss the implications of our findings to the revised ecosystem-based management strategy of the krill fishery in Antarctica.