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1. Large-scale shift in the structure of a kelp forest ecosystem co-occurs with an epizootic and marine heatwave

   https://doi.org/10.1038/s42003-021-01827-6  

   McPherson, Meredith L.; Finger, Dennis J.; Houskeeper, Henry F.; Bell, Tom W.; Carr, Mark H.; Rogers-Bennett, Laura; Kudela, Raphael M. (December 2021, Communications Biology)

   null (Ed.)

   Abstract Climate change is responsible for increased frequency, intensity, and duration of extreme events, such as marine heatwaves (MHWs). Within eastern boundary current systems, MHWs have profound impacts on temperature-nutrient dynamics that drive primary productivity. Bull kelp ( Nereocystis luetkeana ) forests, a vital nearshore habitat, experienced unprecedented losses along 350 km of coastline in northern California beginning in 2014 and continuing through 2019. These losses have had devastating consequences to northern California communities, economies, and fisheries. Using a suite of in situ and satellite-derived data, we demonstrate that the abrupt ecosystem shift initiated by a multi-year MHW was preceded by declines in keystone predator population densities. We show strong evidence that northern California kelp forests, while temporally dynamic, were historically resilient to fluctuating environmental conditions, even in the absence of key top predators, but that a series of coupled environmental and biological shifts between 2014 and 2016 resulted in the formation of a persistent, altered ecosystem state with low primary productivity. Based on our findings, we recommend the implementation of ecosystem-based and adaptive management strategies, such as (1) monitoring the status of key ecosystem attributes: kelp distribution and abundance, and densities of sea urchins and their predators, (2) developing management responses to threshold levels of these attributes, and (3) creating quantitative restoration suitability indices for informing kelp restoration efforts. 

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2. Environmental variability and fishing effects on the Pacific sardine fisheries in the Gulf of California

   https://doi.org/10.1139/cjfas-2020-0010  

   Giron-Nava, Alfredo; Ezcurra, Exequiel; Brias, Antoine; Velarde, Enriqueta; Deyle, Ethan; Cisneros-Montemayor, Andrés M.; Munch, Stephan B.; Sugihara, George; Aburto-Oropeza, Octavio (May 2021, Canadian Journal of Fisheries and Aquatic Sciences)

   null (Ed.)

   Small pelagic fish support some of the largest fisheries globally, yet there is an ongoing debate about the magnitude of the impacts of environmental processes and fishing activities on target species. We use a nonparametric, nonlinear approach to quantify these effects on the Pacific sardine (Sardinops sagax) in the Gulf of California. We show that the effect of fishing pressure and environmental variability are comparable. Furthermore, when predicting total catches, the best models account for both drivers. By using empirical dynamic programming with average environmental conditions, we calculated optimal policies to ensure long-term sustainable fisheries. The first policy, the equilibrium maximum sustainable yield, suggests that the fishery could sustain an annual catch of ∼2.16 × 10 5 tonnes. The second policy with dynamic optimal effort, reveals that the effort from 2 to 4 years ago impacts the current maximum sustainable effort. Consecutive years of high effort require a reduction to let the stock recover. Our work highlights a new framework that embraces the complex processes that drive fisheries population dynamics yet produces simple and robust advice to ensure long-term sustainable fisheries. 

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3. "So, where do you come from?" The impact of assumed spatial population structure on estimates of recruitment

   https://doi.org/https://doi:10.1016/j.fishres.2018.11.030  

   Cadrin, Steven X. (January 2019, Fisheries research)

   Understanding population dynamics is essential for achieving sustainable and productive fisheries. However, estimating recruitment in a stock assessment model involves the challenging task of identifying a self-sustaining population, which often includes representing complex geographic structure. A review of several case studies demonstrated that alternative stock assessment models can influence estimates of recruitment. Incorporating spatial population structure and connectivity into stock assessment models changed the perception of recruit- ment events for a wide diversity of fisheries, but the degree to which estimates were impacted depended on movement rates and relative stock sizes. For multiple population components, estimates of strong recruitment events and the productivity of smaller population units were often more sensitive to connectivity assumptions. Simulation testing, conditioned on these case studies, suggested that accurately accounting for population structure, either in management unit definitions or stock assessment model structure, improved recruitment estimates. An understanding of movement dynamics improved estimation of connected sub-populations. The challenge of representing geographic structure in stock assessment emphasizes the importance of defining self- sustaining management units to justify a unit-stock assumption. 

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4. Methods for Combining Ichthyoplankton Datasets for Predicting Annual Larval Fish Abundances in the Gulf of Alaska

   Block, L N; Hopcroft, R R; Rogers, L A (May 2024, NOAA Technical Memorandum)

   NOAA’s Alaska Fisheries Science Center’s (AFSC) Ecosystems and Fisheries-Oceanography Coordinated Investigations (EcoFOCI) program has collected spring ichthyoplankton abundance data in the Gulf of Alaska since 1981. Collections were made nearly annually until 2011 when sampling was reduced to only odd years. This dataset is used to better understand population recruitment of major fish species in the GOA and provides early warning of potential year-class strength to inform fisheries management. However, gaps in the time series during even years have made it more difficult to interpret the interannual variability of ichthyoplankton abundance in such a dynamic ecosystem. Recent collaboration with the Northern Gulf of Alaska Long Term Ecological Research (NGA LTER) program has allowed for additional spring sampling of ichthyoplankton in the GOA annually since 2018. Larval fish data collected by the NGA LTER were combined with EcoFOCI data and used to estimate abundance in years when EcoFOCI had no field presence in the GOA. Five taxa were determined to be suitable for this approach based on their percent occurrence in both surveys. A generalized additive model (GAM) was fit to ichthyoplankton data from 1981 to 2022 collected by both EcoFOCI and NGA LTER and used to predict larval abundances in 2018, 2020, and 2022. For each species, models with two different error distributions were compared and shown to produce similar predictions of larval abundance. This report provides a model framework for predicting interannual larval fish abundance while controlling for differences in sampling methodologies, timing, and location, and identifies a subset of taxa for which this framework is currently appropriate. As additional years of concurrent sampling are added in future, this approach has the potential to improve our understanding of interannual variation in ichthyoplankton dynamics and provide more comprehensive indicators for ecosystem-based fisheries management. 

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5. Sensitivity of fishery resources to climate change in the warm-temperate Southwest Atlantic Ocean

   https://doi.org/10.1007/s10113-023-02049-8  

   Gianelli, Ignacio; Orlando, Luis; Cardoso, Luis Gustavo; Carranza, Alvar; Celentano, Eleonora; Correa, Patricia; de_la_Rosa, Andrés; Doño, Florencia; Haimovici, Manuel; Horta, Sebastián; et al (June 2023, Regional Environmental Change)

   Abstract Climate change impacts on fishery resources have been widely reported worldwide. Nevertheless, a knowledge gap remains for the warm-temperate Southwest Atlantic Ocean—a global warming hotspot that sustains important industrial and small-scale fisheries. By combining a trait-based framework and long-term landing records, we assessed species’ sensitivity to climate change and potential changes in the distribution of important fishery resources (n = 28; i.e., bony fishes, chondrichthyans, crustaceans, and mollusks) in Southern Brazil, Uruguay, and the northern shelf of Argentina. Most species showed moderate or high sensitivity, with mollusks (e.g., sedentary bivalves and snails) being the group with the highest sensitivity, followed by chondrichthyans. Bony fishes showed low and moderate sensitivities, while crustacean sensitivities were species-specific. The stock and/or conservation status overall contributed the most to higher sensitivity. Between 1989 and 2019, species with low and moderate sensitivity dominated regional landings, regardless of the jurisdiction analyzed. A considerable fraction of these landings consisted of species scoring high or very high on an indicator for potential to change their current distribution. These results suggest that although the bulk of past landings were from relatively climate-resilient species, future catches and even entire benthic fisheries may be jeopardized because (1) some exploited species showed high or very high sensitivities and (2) the increase in the relative representation of landings in species whose distribution may change. This paper provides novel results and insights relevant for fisheries management from a region where the effects of climate change have been overlooked, and which lacks a coordinated governance system for climate-resilient fisheries. 

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