In this blog I will be providing some information about the changing climate’s effect 0n species that inhabit the Pacific Ocean. In this blog, we will talk about the way climate change is affecting several tuna species in the Pacific Ocean. These four species are the skipjack, yellowfin, bigeye, and South Pacific albacore tuna. These species of tuna are vitally important to the Pacific Island Countries and Territories. The total harvest of the these four species from the exclusive economic zone (EEZ) of the PICT had a total of more 1.5 million tonnes in 2016, which represented approximately 30 % of the total global harvest of tuna.
As we begin, it is important to understand that the abundance and distribution of tuna stocks are affected by climate variables such as the El Nino Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). These climate variables can influence the survival of larvae , thus affecting recruitment. The se climate variables can also cause a shift in the most suitable habitat for these tuna species. The influences resulting from climate variability are more easily seen in the skipjack tuna because it has a shorter lifespan than other species. Other tuna species that have a longer lifespan experience environmental variability over many age classes, making it more difficult to disseminate climate variability from other types of variability in species with a longer lifespan.
Climate change is expected to have a sizable affect on the physical environment in the tropical Pacific Ocean. Since 1900, average sea surface temperatures in the Western Pacific warm pool have increased by approximately 0.7 degrees Celcius. These temperatures are projected to rise to between 1.2–1.6 degrees Celcius by 2050 and 2.2 – 2.7 degrees Celcius by 2100. These projections are compared with 1980 – 1999 trends, under a scenario of high emissions. As we move forward, changes in ocean circulations are also expected. This will likely affect the timing, location, and extent of the upwelling process, which will impact primary reproductive processes for most oceanic species. Changes in the vertical structure of the water, along with changes in the depth and strength of the thermocline will also affect nutrient availability.
The presence of phytoplankton at the base of the food web help to support the tuna population. Because phytoplankton quickly diminishes the amount of nutrients at the surface, most primary production occurs only where deep, nutrient waters are lifted to the surface by upwelling and eddies, or when a shallower and/or weaker thermocline allows nutrients from the deep, nutrient waters to be diffused to the surface. Under a high emissions scenario, the IPSL–CM4 climate model predicts a 9 % decrease in phytoplankton in the Western Pacific warm pool by 2110, and a 20 – 30 % decrease in the archipelagic deep basin ecological province, located in the southwest part of the region.
The abundance of zooplankton in this region is also expected to decrease as a result of less upwelling in the tropical Pacific Ocean. This will likely result in a reduction in primary production. Tuna obtain a significant relationship with their environment. This factor, combined with their life history characteristics, leads to complex interactions, feedback loops, and non-linear effects. Earth climate models are used in order to simulate a projection of how climate change will affect tuna species in the future. These climate models are indicating that there will be a reduction in western Pacific tuna abundance and /or a distribution of the tuna to the eastern Pacific. The figure shown above gives a visual of some of the factors that affect tuna abundance and distribution..
These changes would be caused primarily by the weakening of equatorial upwelling and current systems, and the warming of waters related to the increase of water stratification in the western Pacific Ocean. This would result in lower primary production (Johnson et al. 2021). In addition, new research conducted by the University of Wollongong Australia also shows that climate change will affect tuna stocks in the tropical Pacific. The study states that as climate change warm the waters near the jurisdiction of the Pacific islands, causing the skipjack, yellowfin, and bigeye tuna are likely to migrate to open waters (See the video above for more information on how this effects the economy of the Pacific Islands). The location of these tuna depends mainly on the ENSO. During El Nino years, the tuna tend to inhabit waters further to the west, and during La Nina years they tend to move further to the east. As a result of climate change, water temperatures in the Pacific Ocean are likely to warm further, causing tuna to relocate further to the east (Bell et al 2021).
Tuna populations are believed to be particularly sensitive to changes in food web productivity. These changes include primary productivity and abundance of micronekton prey. In the future, micronekton is likely to decrease, thus increasing the natural mortality of tuna. Interestingly, higher resolution climate change simulations indicate that enhanced vertical shear mixing and an increase in vertical nutrient supply to the photic zone will lead to an increase in primary production. Any changes in primary productivity in the western tropical Pacific Ocean would likely impact only skipjack tuna (Johnson et al. 2021).
References
Johnson, Johanna et al. Effects of Climate Change on Ocean Fisheries Relevant to the Pacific Islands. Commonwealth Marine Economies Programme. 2018 Report Card. Web. Mar. 11, 2022. https://reliefweb.int/sites/reliefweb.int/files/resources/11_Oceanic_Fisheries.pdf
Bell, Johann et al. Climate change is causing tuna to migrate. University of Wollongong Australia. https://www.uow.edu.au/media/2021/climate-change-is-causing-tuna-to-migrate-.php Aug. 2, 2021. Web. Mar. 10, 2022.
Pacific Tuna: Feeling the Heat. (Video) YouTube. Retrieved Mar. 10, 2022. https://www.youtube.com/watch?v=JzYqoK-xaRk
Images:
https://reliefweb.int/sites/reliefweb.int/files/resources/11_Oceanic_Fisheries.pdf (Image). Retrieved March 17, 2022.
https://reliefweb.int/sites/reliefweb.int/files/resources/11_Oceanic_Fisheries.pdf (Image). Retrieved March 17, 2022.
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