CAFA Publications

Author(s): Muhling, B. A., Brodie, S., Smith, J. A., Tommasi, D., Gaitan, C. F., Hazen, E. L., ... & Brodeur, R. D.

Project PI: Jacox
DOI: https://doi.org/10.3389/fmars.2020.00589

Spatial distributions of marine fauna are determined by complex interactions between environmental conditions and animal behaviors. As climate change leads to warmer, more acidic, and less oxygenated oceans, species are shifting away from their historical distribution ranges, and these trends are expected to continue into the future. Correlative Species Distribution Models (SDMs) can be used to project future habitat extent for marine species, with many different statistical methods available. However, it is vital to assess how different statistical methods behave under novel environmental conditions before using these models for management advice, and to consider whether future projections based on these techniques are biologically reasonable. In this study, we built SDMs for adults and larvae of two ecologically important pelagic fishes in the California Current System (CCS): Pacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax). We used five different SDM methods, ranging from simple [thermal niche model (TNM)] to complex (artificial neural networks). Our results show that some SDMs trained on data collected between 2003 and 2013 lost substantial predictive skill when applied to observations from more recent years, when ocean temperatures associated with a marine heatwave were outside the range of historical measurements. This decrease in skill was particularly apparent for adult sardine, which showed non-stationary relationships between catch locations and sea surface temperature (SST) through time. While sardine adults and larvae shifted their distributions markedly during the marine heatwave, anchovy largely maintained their historical spatiotemporal distributions. Our results suggest that correlative relationships between species and their environment can become unreliable during anomalous conditions. Understanding the underlying physiology of marine species is therefore essential for the construction of SDMs that are robust to rapidly changing environments. Developing distribution models that offer skillful predictions into the future for species such as sardine and anchovy, which are migratory and include separate sub-stocks, may be particularly challenging.

Author(s): Evans, N, Schroeder, ID, Pozo Buil, M, Jacox, MG, Bograd, SJ

Project PI: Jacox
DOI: https://doi.org/10.1029/2020GL089274

A confluence of subarctic, tropical, and subtropical water masses feed the California Current System (CCS), supporting a highly productive ecosystem and wide array of marine ecosystem services. Long-term declines in oxygen have been observed in this region, causing habitat compression and other ecosystem consequences. Here we quantify the water masses and processes causing deoxygenation in the subsurface CCS from 1993–2018, and we find that deoxygenation was caused both by changes in the advection of source waters and increased remineralization in the source waters. The historical deoxygenation trend can be attributed primarily (81%) to the Northern Equatorial Pacific Intermediate Water, the deep Pacific Equatorial Water mass transported in the California Undercurrent. We also find that advection and remineralization share nearly equal contributions to deoxygenation. This improved understanding of the mechanisms affecting the aerobic habitat of the CCS will inform projections of ecological impacts and mitigation of future deoxygenation.

Author(s): Smith, S. L., Golden, A. S., Ramenzoni, V., Zemeckis, D. R., & Jensen, O. P.

Project PI: Ramenzoni
DOI: https://doi.org/10.1371/journal.pone.0243886

Commercial fisheries globally experienced numerous and significant perturbations during the early months of the COVID-19 pandemic, affecting the livelihoods of millions of fishers worldwide. In the Northeast United States, fishers grappled with low prices and disruptions to export and domestic markets, leaving many tied to the dock, while others found ways to adapt to the changing circumstances brought about by the pandemic. This paper investigates the short-term impacts of the early months of the COVID-19 pandemic (March-June 2020) on commercial fishers in the Northeast U.S. to understand the effects of the pandemic on participation in the fishery and fishers’ economic outcomes, using data collected from an online survey of 258 Northeast U.S. commercial fishers. This research also assesses characteristics of those fishers who continued fishing and their adaptive strategies to the changing circumstances. Analysis of survey responses found the majority of fishers continued fishing during the early months of the pandemic, while a significant number had stopped fishing. Nearly all reported a loss of income, largely driven by disruptions of export markets, the loss of restaurant sales, and a resulting decline in seafood prices. Landings data demonstrate that while fishing pressure in 2020 was reduced for some species, it remained on track with previous years for others. Fishers reported engaging in a number of adaptation strategies, including direct sales of seafood, switching species, and supplementing their income with government payments or other sources of income. Many fishers who had stopped fishing indicated plans to return, suggesting refraining from fishing as a short-term adaptation strategy, rather than a plan to permanently stop fishing. Despite economic losses, fishers in the Northeast U.S. demonstrated resilience in the face of the pandemic by continuing to fish and implementing other adaptation strategies rather than switching to other livelihoods.

Author(s): Chen, Z., & Curchitser, E. N. 

Project PI: Curchister
DOI:

The Mid-Atlantic Bight (MAB) Cold Pool is a bottom-trapped, cold (temperature below 10°C) and fresh (practical salinity below 34) water mass that is isolated from the surface by the seasonal thermocline and is located over the midshelf and outer shelf of the MAB. The interannual variability of the Cold Pool with regard to its persistence time, volume, temperature, and seasonal along-shelf propagation is investigated based on a long-term (1958–2007) high-resolution regional model of the northwest Atlantic Ocean. A Cold Pool Index is defined and computed in order to quantify the strength of the Cold Pool on the interannual timescale. Anomalous strong, weak, and normal years are categorized and compared based on the Cold Pool Index. A detailed quantitative study of the volume-averaged heat budget of the Cold Pool region (CPR) has been examined on the interannual timescale. Results suggest that the initial temperature and abnormal warming/cooling due to advection are the primary drivers in the interannual variability of the near-bottom CPR temperature anomaly during stratified seasons. The long persistence of temperature anomalies from winter to summer in the CPR also suggests a potential for seasonal predictability.

Author(s): Shin, S., and Alexander, M. A. 

Project PI: Curchister
DOI: http://https://doi.org/10.1175/JCLI-D-19-0483.1

Projected climate changes along the U.S. East and Gulf Coasts were examined using the eddy-resolvingRegional Ocean Modeling System (ROMS). First, a control (CTRL) ROMS simulation was performed usingboundary conditions derived from observations. Then climate change signals, obtained as mean seasonalcycle differences between the recent past (1976–2005) and future (2070–99) periods in a coupled global cli-mate model under the RCP8.5 greenhouse gas trajectory, were added to the initial and boundary conditionsof the CTRL in a second (RCP85) ROMS simulation. The differences between the RCP85 and CTRLsimulations were used to investigate the regional effects of climate change. Relative to the coarse-resolutioncoupled climate model, the downscaled projection shows that SST changes become more pronounced nearthe U.S. East Coast, and the Gulf Stream is further reduced in speed and shifted southward. Moreover, thedownscaled projection shows enhanced warming of ocean bottom temperatures along the U.S. East and Gulf Coasts, particularly in the Gulf of Maine and the Gulf of Saint Lawrence. The enhanced warming was relatedto an improved representation of the ocean circulation, including topographically trapped coastal oceancurrents and slope water intrusion through the Northeast Channel into the Gulf of Maine. In response toincreased radiative forcing, much warmer than present-day Labrador Subarctic Slope Waters entered the Gulf of Maine through the Northeast Channel, warming the deeper portions of the gulf by more than 48ºC.

Author(s): Hollowed, A. B., K. K. Holsman, A. Haynie, A. Hermann, A. Punt, K. Aydin, J. Ianelli, S. Kasperski, W. Cheng, A. Faig, K. Kearney, J. Reum, P. Spencer, I. Spies, W. Stockhausen, C. Szuwalski, G. A. Whitehouse, T. Wilderbuer.

Project PI: Hollowed
DOI: http://doi.org/10.3389/fmars.2019.00775

The Alaska Climate Integrated Modeling (ACLIM) project represents a comprehensive, multi-year, interdisciplinary effort to characterize and project climate-driven changes to the eastern Bering Sea (EBS) ecosystem, from physics to fishing communities. Results from the ACLIM project are being used to understand how different regional fisheries management approaches can help promote adaptation to climate-driven changes to sustain fish and shellfish populations and to inform managers and fishery dependent communities of the risks associated with different future climate scenarios. The project relies on iterative communications and outreaches with managers and fishery-dependent communities that have informed the selection of fishing scenarios. This iterative approach ensures that the research team focuses on policy relevant scenarios that explore realistic adaptation options for managers and communities. Within each iterative cycle, the interdisciplinary research team continues to improve: methods for downscaling climate models, climate-enhanced biological models, socio-economic modeling, and management strategy evaluation (MSE) within a common analytical framework. The evolving nature of the ACLIM framework ensures improved understanding of system responses and feedbacks are considered within the projections and that the fishing scenarios continue to reflect the management objectives of the regional fisheries management bodies. The multi-model approach used for projection of biological responses, facilitates the quantification of the relative contributions of climate forcing scenario, fishing scenario, parameter, and structural uncertainty with and between models. Ensemble means and variance within and between models inform risk assessments under different future scenarios. The first phase of projections of climate conditions to the end of the 21st century is complete, including projections of catch for core species under baseline (status quo) fishing conditions and two alternative fishing scenarios are discussed. The ACLIM modeling framework serves as a guide for multidisciplinary integrated climate impact and adaptation decision making in other large marine ecosystems.

Author(s): Holsman, K. K., A. Haynie, A. B. Hollowed, A. J. Hermann, W. Cheng, A. Faig, J. Ianelli, K. Kearney, A. Punt, J. Reum

Project PI: Hollowed
DOI: http://doi.org/10.1038/s41467-020-18300-3

Climate change is impacting fisheries worldwide with uncertain outcomes for food and nutritional security. Using management strategy evaluations for key US fisheries in the eastern Bering Sea we find that Ecosystem Based Fisheries Management (EBFM) measures forestall future declines under climate change over non-EBFM approaches. Yet, benefits are species-specific and decrease markedly after 2050. Under high-baseline carbon emission scenarios (RCP 8.5), end-of-century (2075–2100) pollock and Pacific cod fisheries collapse in >70% and >35% of all simulations, respectively. Our analysis suggests that 2.1–2.3 °C (modeled summer bottom temperature) is a tipping point of rapid decline in gadid biomass and catch. Multiyear stanzas above 2.1 °C become commonplace in projections from ~2030 onward, with higher agreement under RCP 8.5 than simulations with moderate carbon mitigation (i.e., RCP 4.5). We find that EBFM ameliorates climate change impacts on fisheries in the near-term, but long-term EBFM benefits are limited by the magnitude of anticipated change.

Author(s): Kearney, K., A. Hermann, W. Cheng, I. Ortiz, and K. Aydin.

Project PI: Hollowed
DOI: http://https://doi.org/10.5194/gmd-13-597-2020

The Bering Sea is a highly productive ecosystem, supporting a variety of fish, seabird, and marine mammal populations, as well as large commercial fisheries. Due to its unique shelf geometry and the presence of seasonal sea ice, the processes controlling productivity in the Bering Sea ecosystem span the pelagic water column, the benthic sea floor, and the sympagic sea ice environments. The Bering Ecosystem Study Nutrient-Phytoplankton-Zooplankton (BESTNPZ) model has been developed to simulate the lower-trophic-level processes throughout this region. Here, we present a version of this lower-trophic-level model coupled to a three-dimensional regional ocean model for the Bering Sea. We quantify the model's ability to reproduce key physical features of biological importance as well as its skill in capturing the seasonal and interannual variations in primary and secondary productivity over the past several decades. We find that the ocean model demonstrates considerable skill in replicating observed horizontal and vertical patterns of water movement, mixing, and stratification, as well as the temperature and salinity signatures of various water masses throughout the Bering Sea. Along the data-rich central portions of the southeastern Bering Sea shelf, it is also able to capture the mean seasonal cycle of primary production. However, its ability to replicate domain-wide patterns in nutrient cycling, primary production, and zooplankton community composition, particularly with respect to the interannual variations that are important when linking variation in productivity to changes in longer-lived upper-trophic-level species, remains limited. We therefore suggest that near-term application of this model should focus on the physical model outputs, while model development continues to elucidate potential mechanisms controlling nutrient cycling, bloom processes, and trophic dynamics.

Author(s): McHuron, E. A., K. Luxa, N. A. Pelland, K. Holsman, R. Ream, T. Zeppelin, and J. T. Sterling.

Project PI: Hollowed
DOI: http://doi.org/10.3389/fmars.2020.597973

Food availability is a key concern for the conservation of marine top predators, particularly during a time when they face a rapidly changing environment and continued pressure from commercial fishing activities. Northern fur seals (Callorhinus ursinus) breeding on the Pribilof Islands in the eastern Bering Sea have experienced an unexplained population decline since the late-1990s. Dietary overlap with a large U.S. fishery for walleye pollock (Gadus chalcogrammus) in combination with changes in maternal foraging behavior and pup growth has led to the hypothesis that food limitation may be contributing to the population decline. We developed age- and sex-specific bioenergetic models to estimate fur seal energy intake from May–December in six target years, which were combined with diet data to quantify prey consumption. There was considerable sex- and age-specific variation in energy intake because of differences in body size, energetic costs, and behavior; net energy intake was lowest for juveniles (18.9 MJ sea-day^–1, 1,409.4 MJ season^–1) and highest for adult males (66.0 MJ sea-day^–1, 7,651.7 MJ season^–1). Population-level prey consumption ranged from 255,232 t (222,159 – 350,755 t, 95% CI) in 2006 to 500,039 t (453,720 – 555,205 t) in 1996, with pollock comprising between 41.4 and 76.5% of this biomass. Interannual variation in size-specific pollock consumption appeared largely driven by the availability of juvenile fish, with up to 81.6% of pollock biomass coming from mature pollock in years of poor age-1 recruitment. Relationships among metabolic rates, trip durations, pup growth rates, and energy intake of lactating females suggest the most feasible mechanism to increase pup growth rates is by increasing foraging efficiency through reductions in maternal foraging effort, which is unlikely to occur without increases in localized prey density. By quantifying year-specific fur seal consumption of pollock, our study provides a pathway to incorporate fur seals into multispecies pollock stock assessment models, which is critical for fur seal and fishery management given they were a significant source of mortality for both juvenile and mature pollock.

Author(s): Reum, J., J. L. Blanchard, K. K. Holsman, K. Aydin, A. B. Hollowed, A. Hermann, W. Cheng, A. Faig, A. Haynie, A. E. Punt.

Project PI: Hollowed
DOI: http://doi.org/10.3389/fmars.2020.00124

Characterization of uncertainty (variance) in ecosystem projections under climate change is still rare despite its importance for informing decision-making and prioritizing research. We developed an ensemble modeling framework to evaluate the relative importance of different uncertainty sources for food web projections of the eastern Bering Sea (EBS). Specifically, dynamically downscaled projections from Earth System Models (ESM) under different greenhouse gas emission scenarios (GHG) were used to force a multispecies size spectrum model (MSSM) of the EBS food web. In addition to ESM and GHG uncertainty, we incorporated uncertainty from different plausible fisheries management scenarios reflecting shifts in the total allowable catch of flatfish and gadids and different assumptions regarding temperature-dependencies on biological rates in the MSSM. Relative to historical averages (1994–2014), end-of-century (2080–2100 average) ensemble projections of community spawner stock biomass, catches, and mean body size (±standard deviation) decreased by 36% (±21%), 61% (±27%), and 38% (±25%), respectively. Long-term trends were, on average, also negative for the majority of species, but the level of trend consistency between ensemble projections was low for most species. Projection uncertainty for model outputs from ∼2020 to 2040 was driven by inter-annual climate variability for 85% of species and the community as a whole. Thereafter, structural uncertainty (different ESMs, temperature-dependency assumptions) dominated projection uncertainty. Fishery management and GHG emissions scenarios contributed little (<10%) to projection uncertainty, with the exception of catches for a subset of flatfishes which were dominated by fishery management scenarios. Long-term outcomes were improved in most cases under a moderate “mitigation” relative to a high “business-as-usual” GHG emissions scenario and we show how inclusion of temperature-dependencies on processes related to body growth and intrinsic (non-predation) natural mortality can strongly influence projections in potentially non-additive ways. Narrowing the spread of long-term projections in future ensemble simulations will depend primarily on whether the set of ESMs and food web models considered behave more or less similarly to one another relative to the present models sets. Further model skill assessment and data integration are needed to aid in the reduction and quantification of uncertainties if we are to advance predictive ecology.