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The long-lived trait is ecologically significant. Marlin and Swordfish can live for as long as 15 years, with breeding after 6 years. If they are overfished decreasing average age and shortage of breed stock will result, and fish stocks decline.

The situation is so serious for Bluefin Tuna that the fisheries are approaching collapse.

Effects of climate change on salt water fisheries

We have seen that overfishing is destroying fish-stocks. Climate change also plays a role. How? Growing CO 2 emissions mean that more greenhouse gasses CO 2 enter the atmosphere. Then about 1/3 of atmospheric CO 2 is taken up by oceans . Result: with more atmospheric CO2 the ocean becomes more acidic . This can become a serious issue in the life cycles of fish.

There are already dire predictions concerning the effects of increasing CO 2 in the atmosphere from fossil fuels, deforestation etc. This is especially serious for fisheries and the world’s poorest: 15% of their protein comes from fish.

The primary problem for fisheries arising from climate change that increases acidity in the world’s oceans is especially serious in the extreme southern and northern regions.

Recall from basic chemistry a lower PH number means more acidity in some ocean waters. A fall of one PH point represents a tenfold increase in acidity in some ocean waters. Vinegar, for example is quite acid. From the late 80s to 2012, acidity has increased from PH 8.11 to PH 8.06, largely as a result of higher atmospheric concentration of CO 2 .

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The fall of 0.5 points in PH in the last three decades represents a rise in ocean acidity of about 12%. Further, the best estimates suggest that there has been a 26% rise in acidity since 1820, when the industrial revolution began. The corrosive effect of rising ocean acidity on fisheries depends largely on how it affects aragonite. Aragonite is one of the forms of calcium carbonate. Coral reefs and virtually all mollusks (scallops, oysters, clams etc.) utilize much Aragonite in their skeletons. Omega is a number describing the threat of acidification to shellfish and coral. It depicts the aragonite saturation rate (see Figure 19-7). An Omega value of ONE is the critical level of acidity. Below a level of one , shells and skeletons made of calcium carbonate will dissolve.

Some sea animals, however, require a much higher omega level. Corals in particular require an omega level of 3 to grow their reef-making skeleton. Figure 19-7 shows that only relatively small portions of the Atlantic and Pacific are predicted to have omega levels>1.

In the mid-20th century near-pristine coral reefs hosted billions of fish, a favorite fish habitat. Ocean acidification is not the only reasons for the rapid decline of coral reefs worldwide. Deforestation in the Philippines, Thailand, Indonesia, Brazil and other nations has played a role as well. Growing deforestation leads to growing siltation of rivers. Ultimately this runoff reaches many coral reef formations in the ocean stifling reef growth. A final cause of coral reef decline has been dynamiting of reefs, where concussion from the explosions also kills fish on a large scale.

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Source:  OpenStax, Economic development for the 21st century. OpenStax CNX. Jun 05, 2015 Download for free at http://legacy.cnx.org/content/col11747/1.12
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