Fernandes, J. A., Rutterford, L., Simpson, S. D., Butenschön, M., Frölicher, T. L., Yool, A., Cheung, W. W. L., & Grant, A. (2020). Can we project changes in fish abundance and distribution in response to climate? Global Change Biology, 26(7), 3891–3905. https://doi.org/https://doi.org/10.1111/gcb.15081
Large scale and long-term changes in fish abundance and distribution in response to climate change have been simulated using both statistical and process-based models. However, national and regional fisheries management requires also shorter-term projections on smaller spatial scales, and these need to be validated against fisheries data. A 26-year long time series of fish surveys with high spatial resolution in the North East Atlantic provides a unique opportunity to assess the ability of models to correctly simulate the changes in fish distribution and abundance that occurred in response to climate variability and change. In this study, a model forced by physical-biogeochemical output from eight ocean models was used to simulate changes in fish abundance and distribution at scales down to a spatial resolution of 0.5°. When comparing the model simulation with the available fish survey, authors concluded that predictions based on different biogeochemical models are often more similar to each other than they are to the survey data, except for some pelagic species. Additionally, the authors stressed that model results can be used to guide fisheries management at larger spatial scales, but more caution is needed at smaller scales.
Policy relevant message:
Large scale and long-term changes in fish abundance and distribution in response to climate change can be used to guide fisheries management.
Cael, B. B., Chase, A., & Boss, E. (2020). Information content of absorption spectra and implications for ocean color inversion. Appl. Opt., 59(13), 3971–3984. https://doi.org/10.1364/AO.389189
The increasing use of hyperspectral optical data in oceanography, both in situ and via remote sensing, holds the potential to significantly advance characterization of marine ecology and biogeochemistry because, in principle, it can provide much more detailed inferences of ecosystem properties via inversion. This study focuses on complementary approaches to quantify the degrees of freedom in hyperspectral measurements in the case of in situ particulate absorption measurements, though these approaches can also be used on other such data, e.g., ocean colour remote sensing.
Cheung, W. W. L., & Frölicher, T. L. (2020). Marine heatwaves exacerbate climate change impacts for fisheries in the northeast Pacific. Scientific Reports, 10 (1), 6678. https://doi.org/10.1038/s41598-020-63650-z
Marine heatwaves (MHWs) have occurred in all ocean basins with severe negative impacts on coastal and ocean ecosystems. The northeast Pacific 2013–2015 MHW received major societal concerns. Yet, the knowledge about how MHWs impact fish stocks is limited. The authors of this study combined various model outputs to simulate responses of major northeast Pacific fish stocks to MHWs and showed that MHWs cause biomass decrease and shifts in biogeography of fish stocks with projected a doubling of impact levels by 2050 amongst the most important fisheries species over previous assessments. The authors stress the additional challenges from MHWs for fisheries and their management under climate change.
Policy relevant message:
Marine Heat Waves have occurred in all ocean basins with severe negative impacts on coastal and ocean ecosystems. They cause biomass decrease and shifts in biogeography of fish stocks with projected a doubling of impact levels by 2050 amongst the most important fisheries species over previous assessments.
Hameau, A., Frölicher, T. L., Mignot, J., & Joos, F. (2020). Is deoxygenation detectable before warming in the thermocline? Biogeosciences, 17 (7), 1877–1895. https://doi.org/10.5194/bg-17-1877-2020
Anthropogenic greenhouse gas emissions cause ocean warming and oxygen depletion, with adverse impacts on marine organisms and ecosystems. Warming is one of the main indicators of anthropogenic climate change, but thermocline1, changes in oxygen and other biogeochemical tracers may be a result of natural variability prior to warming. In about a third (35±11 %) of the global thermocline deoxygenation emerges prior to warming. In these regions, both reduced ventilation and reduced solubility add to the oxygen decline. In addition, reduced ventilation slows the propagation of anthropogenic warming from the surface into the ocean interior, further contributing to the delayed emergence of warming compared to deoxygenation. This study underlines the importance of an ocean biogeochemical observing system and that the detection of anthropogenic impacts becomes more likely when using multi-tracer observations.
1Thermocline: a sudden temperature change in water column, distinct from temperature of a layer above and below.
Albouy, C., Delattre, V., Donati, G., Frölicher, T. L., Albouy-Boyer, S., Rufino, M., Pellissier, L., Mouillot, D., & Leprieur, F. (2020). Global vulnerability of marine mammals to global warming. Scientific Reports, 10 (1), 548. https://doi.org/10.1038/s41598-019-57280-3
Although extinctions due to climate change are still uncommon, they might surpass those caused by habitat loss or overexploitation over the next few decades. Among marine megafauna, mammals fulfil key and irreplaceable ecological roles in the ocean, and the collapse of their populations may therefore have irreversible consequences for ecosystem functioning and services. Using a model approach, this study assessed the vulnerability of all marine mammals to global warming under high and low greenhouse gas emission scenarios for the middle and the end of the 21st century. Furthermore, the North Pacific Ocean, the Greenland Sea and the Barents Sea host the species that are most vulnerable to global warming. The authors of this study stressed the importance of these regions in future conservation plans, where there are long histories of overexploitation and there are high levels of current threats to marine mammals. Beyond species loss, the potential extinctions of the marine mammals that were most vulnerable to global warming might induce a disproportionate loss of functional diversity, which may have profound impacts on the future functioning of marine ecosystems worldwide.
Policy relevant message:
The North Pacific Ocean, the Greenland Sea and the Barents Sea host the species that are most vulnerable to global warming (e.g. the North Pacific right whale and the dugong), where there are long histories of overexploitation and there are high levels of current threats to marine mammals. These regions should receive special attention in future conservation plans. Beyond species loss, the potential extinctions of the marine mammals that were most vulnerable to global warming might induce a disproportionate loss of functional diversity, which may have profound impacts on the future functioning of marine ecosystems worldwide.
Kelly, S. J., Popova, E., Aksenov, Y., Marsh, R., & Yool, A. (2020). They Came From the Pacific: How Changing Arctic Currents Could Contribute to an Ecological Regime Shift in the Atlantic Ocean. Earth’s Future, 8 (4), e2019EF001394.
With a warming Arctic Ocean, it has been suggested that the ocean currents that connect the Pacific to the Atlantic may change. This could have potential biological consequences, including bringing Pacific species of plankton to the Atlantic. The authors investigated how the pathways bringing Pacific water to the Atlantic have changed, identify a pathway that takes less time that other routes to bring waters from Pacific to the Atlantic (but that is only occasionally available), and note that even the shortest timescales are over 2 years.
Smalås, A., Strøm, J. F., Amundsen, P.-A., Dieckmann, U., & Primicerio, R. (2020). Climate warming is predicted to enhance the negative effects of harvesting on high-latitude lake fish. Journal of Applied Ecology, 57 (2), 270–282. https://doi.org/https://doi.org/10.1111/1365-2664.13535
Ecosystems at high latitudes are exposed to some of the highest rates of climate warming on earth, and freshwater ecosystems in those regions are already experiencing extended ice‐free seasons and warmer waters. The dominant fish species in these ecosystems are cold‐water salmonids, which play a central ecological role in lake ecosystems, where they are often exposed to size‐selective fisheries, making them potentially vulnerable to both exploitation and environmental perturbations. This study employed a model approach to address the combined effects of climate‐induced water temperature increase and fishing, over the period from 1950 to 2100 on the growth, demography and vulnerability of Arctic charr Salvelinus alpinus (L.). The model predicted that higher water temperatures would increase the growth of Arctic charr, leading to larger body size at age and increased stock biomass: 80% increase in stock biomass in the absence of fishing, and 40% increase in biomass with fishing mortality of 0.3 year−1 in 2100 in comparison to 2000. In addition, climate warming will affect younger individuals more, thus elevating the vulnerability of the population to environmental perturbations. The model‐based analyses highlight the combined effects of climate change and size‐selective fishing, emphasizing the emerging vulnerability of fish populations to multiple stressors. The authors recommended careful climate‐adapted management strategies permitting only a narrow range of fishing mesh sizes for inland fisheries at high latitudes.
Policy relevant message:
High latitudes ecosystems have been exposed to some of the highest rates of climate warming on earth, with extended ice-free seasons already recorded. The dominant fish species in these ecosystems are cold‐water salmonids, which play a central ecological role in lake ecosystems. These species are often exposed to size‐selective fisheries, making them potentially vulnerable to both exploitation and environmental perturbations. Careful climate‐adapted management strategies permitting only a narrow range of fishing mesh sizes for inland fisheries at high latitudes are strongly recommended.
Flecha, S., Pérez, F. F., Murata, A., Makaoui, A., & Huertas, I. E. (2019). Decadal acidification in Atlantic and Mediterranean water masses exchanging at the Strait of Gibraltar. Scientific Reports, 9 (1), 15533. https://doi.org/10.1038/s41598-019-52084-x
Seawater pH is undergoing a decreasing trend due to the absorption of atmospheric CO2, a phenomenon known as ocean acidification (OA). Biogeochemical processes occurring naturally in the ocean also change pH and hence, for an accurate assessment of OA, the contribution of the natural component to the total pH variation must be quantified. In this work, authors used 11 years (2005–2015) of biogeochemical measurements collected at the Strait of Gibraltar to estimate decadal trends of pH in two major Mediterranean water masses, the Western Mediterranean Deep Water (WMDW) and the Levantine Intermediate Water (LIW) and assess the magnitude of natural and anthropogenic components on the total pH change. The assessment was also performed in the North Atlantic Central Water (NACW) feeding the Mediterranean Sea. The analysis revealed a significant human impact on all water masses in terms of accumulation of anthropogenic CO2. However, the decadal pH decline found in the WMDW and the NACW was markedly affected by natural processes, which accounted for by nearly 60% and 40% of the total pH decrease, respectively. The LIW did not exhibit a significant pH temporal trend although data indicated natural and anthropogenic perturbations on its biogeochemical signatures.
Published 14 October 2019: Senina, I.N. P. Lehodey, J. Hampton, and J.Sibert: Quantitative modelling of the spatial dynamics of South Pacific and Atlantic albacore tuna populations, Deep–Sea Research II, 175, 104667, 2020. https://doi.org/10.1016/j.dsr2.2019.104667
In this study a model approach was employed to estimate and predict the dynamics of highly migratory albacore tuna populations in the South Pacific and Atlantic oceans. This study successfully explored the capacity of previously used model to predict complex spatial dynamics of highly migratory species that are consistent with 30-year-long data and existing knowledge. The quantitative approach presented could be used to assist stock assessment and to improve management advice internationally.