Global Warming and Current Temperatures: The impacts on fishing grounds

Global warming- the aftermaths

Global warming is the direct consequence of anthropogenic activities where humans selfishly continue their pursuit of happiness and ultimately face the impact of their actions. Global warming occurs due to the increased amount of greenhouse gases in the atmosphere which functions as an unwanted extra blanket in summer preventing the Earths radiation from escaping. These gases not only hike the temperature of the Earth as a whole but lead to the melting of glaciers, snow caps and even changes in the sea level. Increased evaporation rates might also affect the salinity and the extra carbon dioxide absorbed by the biggest sink- sea will affect the acidity levels as well.

Climbing temperatures are the cause of an increase in sea level, increased stratification of the ocean, decreased extent of sea-ice, and altered patterns of ocean circulation, precipitation rates, and freshwater input from rivers. The increased temperatures and the and the changed ocean circulation will reduce the surface oxygen (Keelinget al.2010).  The changes in ocean temperature and thus chemistry may alter the physiological functioning, behaviour, and productivity of organisms. When the carbon dioxide content of the atmosphere is increased the amount absorbed by the oceans will also be increased. Sabin et al. (2004), records that the amount of carbon dioxide absorbed by the ocean is 2 billion tonnes per year. This leads to shifts in the structure and size and also seasonal change in number.  These shifts, in turn, pave the way to changes in species interactions and trophic paths as change penetrates from primary producers to upper-trophic-level fish, aquatic birds, and marine mammals, with climate signals thereby propagating through ecosystems in top to bottom and vice versa.

The impact of these changes creates a shift in the ecological rhythm of the entire world including the aquatic ecosystems. It affects even the wind pattern and circulation of ocean currents. Nelleman et al. (2008) mark five stressors as the threats to the oceans of the world. They are1) Climate change 2) Fragmentation and habitat loss 3) Over-harvesting from fisheries 4) Pollution (mainly coastal) 5) Invasive species.

 NASA documents that in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era. It also records that the temperature is continuously rising.  The oceans have absorbed much of these increased temperatures, with the upper 700 meters (about 2,300 feet) of ocean showing warming of 0.302 degrees Fahrenheit since as early as 1969(Levitus et al.2009).

 Concerns about the catch

       The climate change affects the marine and freshwater species very fast compared to terrestrial species. Climate change reduces the resilience and reproductive output of the fish species in general and weight of the population. The water temperature will affect the body temperature of fish; its growth and thus the weight. It also affects the reproductive capacity and even the swimming ability of the fish (http://www.gbrmpa.gov.au/managing-the-reef/threats-to-the-reef/climate-change).When the ocean is acidified due to climate change it will affect the fish egg hatching and the fish larvae). Ocean acidification results in the following changes

1)      Increase in CO₂ both aqueous

2)       Total inorganic carbon

3)       Reduced pH, carbonate ion, and reduced saturation states of calcium carbonate (Doney et al. 2009).

Cold water fish are extremely sensitive to temperature changes. When the water becomes warmer, they show slow growth rates and more susceptibility to pests and diseases. These changes will affect the mobility of juvenile fish.

The following are some of the threats to the fishing grounds

• Fish depend entirely on the dissolved oxygen, and this is the most limiting factor under increased temperatures. Metabolic activity in fish is hyped by 10% for every 1?C increased in temperature of the ocean environment. This implies that the fish require 10% more oxygen for every 1?C increase in temperature (Rahman 1992).
• In the aquatic environment Phytoplankton are primary producers and their growth depends on the nutrient concentration in the water and also on external factors such as temperature and light penetration (Scavia and Park 1976). The respiration and mortality rates of these planktons depend on the temperature of the water (Jorgensen 1983). Even the Zooplanktons which consume the Phytoplankton depend on the water temperature and dissolved oxygen based on which the rate of consumption changes.
• The macronutrients Nitrogen and Phosphorus depend a lot on the temperature maintenance of water. As these nutrients are important for the growth of producers and in turn affect the fish growth (Piedrahita 1984).
• The increase and decrease in the particulate organic matter which is very important for fish production are also affected by temperature (Piedrahita 1984).

Hannesson (2007) documented that the change in the catches of cod, herring, mackerel, anchovy and sardines in the Northeast Atlantic are in accordance with the variations in the ocean temperature. The studies prove that fish growth and production are affected by the water temperature (Patton and Hubert 1996), which in turn is directly affected by the increased global temperature. The temperature dynamics does affect the fish catch of the world.

Conclusion

When the world is burning with food security issues due to increasing population we need to make sure that our fish catch is at least retained if not improved. Though an increase in temperature favours some species, increase in temperature beyond a limit is never accepted by any of the organisms. We still can have hope as scientists say that an attempt to revert can at the least prevent a further hike in temperature. The challenge is to create awareness to reduce the amount of carbon dioxide and other greenhouse gases in the atmosphere by reducing the carbon foot print. We need to go back to more eco-friendly mode of living. That will help us to achieve the goal.