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Biology

How will climate change affect coastal fisheries production?

Barange, M., Merino, G., Blanchard, J. L., Scholtens, J., Harle, J., Allison, E. H., … & Jennings, S. (2014). Impacts of climate change on marine ecosystem production in societies dependent on fisheries. Nature Climate Change. Link

Previous estimates of climate change impacts to marine systems used general circulation models (GCMs) to predict changes to primary production and fisheries production.  These models used coarse resolution (1-2°) – too coarse to efficiently capture coastal processes (where a quarter of global primary production and most of global fish production comes from).  Barange et al. (2014) developed a high resolution model to capture fine scale processes in the continental shelf seas of 67 marine ecological exclusive economic zones (EEZs).  They used a GCM under the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment A1B scenario to generate ten-year mean outputs from the present day to 2050.  These outputs were used in a food web model to estimate the impacts of climate change on fish production potential.

GCM models indicated all shelf regions considered should warm by 2050, relative to the present day temperatures (Fig. 1a).  Thermal increases ranged from 0.2°C (Irish EEZ) to 2.9°C (off Korea and East China).  Average increases in predicted primary production were 14%, slightly greater but consistent with other estimates.  Ecosystems in higher latitudes are predicted to increase primary production while lower latitudes (closer to the equator) will decline (Fig. 1b).

Figure 1 (Barange et al., 2014)

Figure 2. Results of GCM modeling runs for 20 large marine ecosystems. (A) Change in temperature (°C) of the mixed layer and (B) total primary production in 2050 relative to the present day. (Each figure represents 10 years of model outputs from Merino et al., 2012)

Global fisheries production was estimated to increase moderately (3.4%) with regional variations.  In general, findings indicated that fisheries production follows the available primary production.  Most notably, Peruvian catch is projected to decline significantly whereas Norway and Iceland will increase.  Fishing production calculations were validated by performing the same analyses to compare with observed catch data with similar results (see Barange et al., 2013 for more detail).

Predictions for increased fisheries potential yield in high latitudes and decreases in the tropics were generally consistent with other studies using bioclimate envelope approaches.  However, when models were run for smaller spatial scales such as regional and national, some inconsistencies became apparent.  Modest differences between model outputs are to be expected between models used for different goals.  The higher resolution models for continental shelves used in this study are particularly good at describing the effects of coastal processes (e.g., upwelling).  The authors suggest using an ensemble method to combine various models; this process can be thought of as a sort of “model average.”

Figure 1 Barange et. al., 2014

Figure 2. National dependency on marine fisheries production in the regions considered.

What countries will be affected the most?  While many nations have significant interest in marine production (Fig. 2), countries of most concern are those that do not have diverse economies to supplement altered fisheries yield.  Nations for whom climate change impacts to marine resources will be of most concern include those in South and Southeast Asia, Southwest Africa, Peru, and various small island developing states.  In other words, the countries with highest overall dependency on fisheries and magnitude of decline in potential catch (Fig. 3).

Socio-economic impacts in these countries will be determined by a number of factors.  Fishing pressure in South and Southeast Asia is high and poorly regulated.  Better management practices could help mitigate the effects of declining ecosystem productivity.  Additionally, South and Southeast Asia has some of the world’s fastest growing aquaculture which may contribute to food security as aquaculture becomes less dependent on wild-caught fishmeal.  West African countries are predicted to increase productivity in 2050 (Fig. 3).  Barange et al. (2014) suggest that these nations work to protect local fishermen’s opportunities from distant nations encroachment.

Figure 3 Barange et al., 2014

Figure 3. Kobe plot of potential catch change and national dependency on fisheries per national EEZ (Barange et al., 2014).

Note that although climate change will alter the distribution of productivity (particularly between low and high latitudes), most of the regions addressed in this study will experience modest changes (+10%).  It is also important to remember that this study only projects to the year 2050, a relatively short time considering climate change affects many other processes on longer time scales and with uncertain impacts.  For example, coral reefs, other habitat-forming species, and most notably, ocean acidification.

The authors also used their predictions in a combination of scenarios with human population growth, trade of fish and fish oil, and aquaculture development to explore what conditions would allow current per capita fish consumption to persist in the future.  Their results suggest that current consumption rates are sustainable in a changing climate if a series of plausible changes are made.  Changes include: a transition towards sustainable fisheries management practices in all regions, less wild caught fish used in animal feed, and a stabilized fishmeal trade.  This study provides a platform for exploring complex interactions between climate change, ecosystem production, and fisheries sustainability in coastal regions.

 

Other references

Merino, G., Barange, M., Blanchard, J. L., Harle, J., Holmes, R., Allen, I., … & Rodwell, L. D. (2012). Can marine fisheries and aquaculture meet fish demand from a growing human population in a changing climate?. Global Environmental Change, 22(4), 795-806. Chicago

Additional figures 

Figure 2 Barange et al., 2014

Changes in physical and ecological parameters of national shelf seas (Figure 2, Barange et al., 2014).

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