Context: 

Recently, tens of thousands of dead fish washed up on multiple beaches of southeast Texas, USA. The incident took place due to a phenomenon called “fish kill”. 

About Fish Kill:

• It is the sudden and unexpected death of many fish or other aquatic animals over a short period and mostly within a particular area. 
• It occurs mainly due to low levels of dissolved oxygen in the water that causes suffocation of the fish.
• Fish kill phenomenon is not unusual. Texas experiences fish kills every year during summers, when the temperatures of the sea surface rise.

Reasons behind fish kill:

• Warm Water: 
  • When sea surface temperatures rise, it becomes difficult for the fish to breathe as oxygen dissolves easily in colder water in comparison to warmer water. 
  • A school of fish gets trapped in shallow water, which gets warmer more quickly. This causes fish to act more erratically, which in turn, further depletes the oxygen from the water.

• Calm Seas: 
  • One of the ways for oxygen to enter the water is by mixing with wind and waves. But in the past few weeks, the waves along the Texas Gulf Coast have been very calm, causing the depletion of dissolved oxygen.
  • Due to cloudy skies, phytoplankton were unable to carry out the process of photosynthesis, which is another way of producing oxygen in the water. 
    • Photosynthesis is driven by sunlight and it slows down on cloudy days, resulting in decreased dissolved oxygen concentration.

Impact of climate change on fish kill:

• Although experts haven’t found any relation between Texas fish kill and climate change, they say that with rising temperatures of oceans, such incidents will become more prevalent. 
• Warmer oceans will lead to less dissolved oxygen levels, causing more death of fish.

Other adverse effects of warming of the oceans:

• Studies have found that fish like sardines, pilchards and herring will become smaller in size and not be able to move to better environments. 
• Some fish species have started to leave their natural habitat in search of cooler waters, which has disrupted the fish industry.

News Source: Indian Express