Friday, November 01, 2024
   
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Over fishing

The appetite for fish is exceeding our ocean’s ecological limits. Marine ecologists and scientists across the world think that overfishing is the biggest threat to marine ecosystems today.
The modern fishing industry is dominated by fishing vessels that out-match nature's ability to replenish fish. Giant ships using state-of-the-art fish-finding sonar can pinpoint schools of fish quickly and accurately. These ships are like giant floating factories with fish processing and packing plants, huge freezing systems and powerful engines to drag enormous fishing gear through the ocean. Simply put: the fish don't stand a chance.
Populations of top predators are disappearing at a frightening rate. Ninety percent of the large fish such as tuna, swordfish, marlin, cod, halibut, skate, and flounder have been fished out since large scale industrial fishing began in the 1950s. Their depletion can cause a shift in entire oceans ecosystem where commercially valuable fish are replaced by smaller, plankton-feeding fish. These changes endanger the structure and functioning of marine ecosystems and hence the livelihoods of those dependent on them.

Climate change

Climate change is a cause of increasing concern to scientists and it will have dramatic effects on marine mammals. The increase of carbon dioxide and other greenhouse gases into the atmosphere are thought to be the main cause of climate change or global warming. Exactly how climate change will affect the ocean, which is home to marine mammals, is hard to predict since there are so many factors that affect ocean ecosystems. How all these, such as weather events and salinity, will interact is highly unpredictable. Using global climate models or GCMs scientists can get a general idea of how climate change will impact the ocean environment in the future.

Marine mammals have evolved to live in the ocean, but the effects of climate change may be altering their habitat more rapidly than they can adapt to the changes.

As levels of greenhouse gases in the atmosphere increase, they trap heat which causes an overall warming of the planet. During the last century, global average land and sea surface temperature has increased dramatically. Many marine mammal species require specific temperature ranges in which they must live. The warming of the ocean will cause changes in species range. Those species that cannot relocate due to some barrier will be forced to adapt to the increasingly warming sea waters or else risk going extinct. Many species ranges are being pushed further and further north as water temperatures increase and will soon have nowhere else to go.

Not surprisingly, glacier ice melt has increased while sea ice extent and thickness has decreased as temperatures keep rising. Rises in sea level affect coastal habitat and the species that rely on it. This habitat is often used as haul out sites for several pinniped species. In order to combat rising sea levels in areas inhabited by humans the construction of sea walls has been proposed, however, these walls may interfere with the migration routes of several marine mammal species. These routes can be very important for reaching feeding and breeding grounds.

Changes in temperature ranges will also change the location of areas with high primary productivity. These areas are important to marine mammals because primary producers are the food source of marine mammal prey or are the marine mammal prey themselves. Marine mammal distribution and abundance will be determined by the distribution and abundance of its prey. Migration of marine mammals may also be affected by the changes in primary productivity.

Increased glacier ice melt also impacts ocean circulation due to the increase of freshwater in the ocean. Salinity concentrations in the ocean are changing. Thermohaline circulation may be altered by increasing amounts of freshwater in the ocean. Thermohaline circulation is responsible for bringing up cold, nutrient rich water from the depths of the ocean, a process known as upwelling. This may effect regional temperatures and primary productivity.

Susceptibility to disease is also thought to increase while reproductive success may decrease with increasing ocean temperatures.

The worlds oceans absorb a large amount of carbon dioxide from the atmosphere and causes an increase in carbon dioxide concentrations and a decrease its overall pH, making it more acidic.

Pollution

The problem of marine pollution due to various types of contaminants such as organochlorine pesticides (OCP), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs) petroleum hydrocarbons (PHCs), polychlorinated dibenzo-dioxins (PCDDs), heavy metals (mercury, cadmium, arsenic, cobalt, manganese, etc.) and nutrient salts, has become a global concern because of the accumulation of their residues in the tissues of various species of marine organisms and their bio-magnification through the food-chain leading to hazards to human health.In case of nutrients, excessive concentrations of these salts in coastal waters can lead to eutrophication and proliferation of toxic algal blooms.
The study of the impact of such toxic compounds, in general, and toxic action of these contaminants, in particular is of great importance to understand their impact on the ecosystem. The toxicity of pollutants to aquatic eco-system largely depends on the chemical and physical state in which the pollutants exist, and the toxic effects depend on their uptake, distribution, elimination and bio-transformation. Moreover, the toxic potentials of various contaminants can be correlated with their active concentrations in the bio-phase (i.e. body compartment where the contaminant exerts its effect; the contaminant then turns into being a pollutant) leading to significant changes in the biological responses.