Impacts of Climate Change on Highly Migratory Species Prioritized in NMFS Management Plan - Oceana
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July 29, 2014

Impacts of Climate Change on Highly Migratory Species Prioritized in NMFS Management Plan

*** Local Caption *** Bluefin tuna (Thunnus thynnus) in a tuna cage near the surface. Malta. Marviva Med Mediterranean Expedition. June 2008. Atunes rojos (Thunnus thynnus) en jaula, cerca de la superficie. Malta. ExpediciÛn por el Mediterr·neo del Marviva Med. Junio 2008.


Many marine species face endless obstacles: Overfishing, pollution, and habitat destruction are large threats, as well as climate change and its associated negative impacts. Factors ranging from their habitat, food source, predator defense, migration routes, and breeding grounds are already changing from warming seas, and these impacts are so widespread that it’s caught fisheries managers’ attention.

In a document released this month, the Highly Migratory Species (HMS) Management Division of the National Marine Fisheries Service (NMFS) indicated that they intend to examine the influence of climate change on important migratory species such as sharks, tuna, swordfish, and billfish in the Atlantic Ocean. Specifically, they plan to look at how climate change affects range, migration, pupping grounds, and prey species for HMS in general.

It’s widely recognized that warming temperatures force animals to move closer to the poles, but this phenomenon is happening much faster in the ocean than on land. Researchers found that marine animals are moving 4.5 miles north per year, which is 10 times faster than terrestrial animals, according to Science. These kinds of changes are worrisome to those who depend on current knowledge and understanding of migration patterns and movements, such as fishermen.

Aside from species shifting north, another alarming trend is the decreasing size of fish. For years, this was fully recognized as a result of overfishing large and lucrative predatory fish until smaller fish remained. But, recent studies show that this trend is also partially attributed to warming water temperatures. Most fish are ectotherms—animals that regulate body temperature based on the surrounding environment— and therefore are subject to the temperature-size rule, where organisms may grow more slowly in warmer waters. Size plays a major role in fecundity, or reproductive abilities: Smaller fish have fewer and smaller offspring than larger fish. This means that as temperatures rise, marine animals will become smaller and less abundant. This will not bode well for fishermen who rely on resilient, large fish.

In addition, ocean acidification is another negative impact of climate change, which affect  growth and development in commercially important fish species.  A 2009 study tested the effects of increasing temperature and acidification on two coral fish species and found that that their aerobic capacities were almost halved compared to normal conditions. And, like temperature increases, ocean acidification also affects fish size.

These changes to our oceans are already underway, even before scientists can fully understand the commercial and ecological implications of climate change. Oceana applauds the National Marine Fisheries Service for their efforts to prioritize research that will help us learn more about how to manage large fish in changing oceans.