Friday, April 28, 2017

Certain activities associated with the fishing industry have undesired negative effects, among which can be mentioned overfishing of some species, by-catch of non commercial species, discards and the destruction of marine habitats due to inappropriate fishing gear.  Port activities, urban settlements on the coast, hydrocarbon exploitation, and maritime traffic can have negative impacts resulting in contamination of the sea.

 

Unsustainable fishing

Argentine hake catch – © D. González Zevallos (CENPAT-CONICET)

Some practices associated with unsustainable fishing activities are a serious threat to the ecosystem and biodiversity. Excessive fishing or overfishing takes place when the maximum catch recommended by the scientific authority of a certain fishery is exceeded, something that happens quite frequently in the region.   Argentine hake (Merluccius hubbsi) is one example of an overfished species and this has led to a severe decline in its total stock and biomass together with a lesser capacity to replace individuals that die on account of fishing and other factors.  This circumstance negatively impacts not only the ecosystem, but also all the people who live off fishing for it results in a “fishing crisis” such as the current situation in many ports of the region.  Other negative impacts related to certain fishing activities include by-catch, discards and the destruction of the seabed.   By-catch affects species or individuals captured accidentally, such as seabirds, mammals, turtles, invertebrates and several species of fish.   Many individuals caught up accidentally in fishing gear die even though they are returned to the sea.   Excessive discards happen when a large volumen of fish or invertebrates of low commercial value has been caught during fishing operations.  Due to the lack of monitoring and control, part of the catch (generally dead) which includes juveniles of species that are highly valued, is thrown back into to sea.  Sea beds are affected by bottom trawling in which enormous weighted nets and other devices are dragged near the seabed causing the destruction of benthic communities where dozens of species, such as bivalve mollusc banks, cold water corals and concentrations of sponges, live.

 

Discarding a skate –© D. González Zevallos (CENPAT-CONICET)

 

Pollution

The Patagonian Sea is exposed to many pollutants.   The following have been detected in its waters: hydrocarbons derived from oil, heavy metals, persistently toxic substances (PCB), discharged urban effluents which cause eutrophication and solid waste.

Contents from the stomach of a green turtle accidentally caught in the artisanal fishery off the Samborombon bay (Victoria González Carman, CONICET- INIDEP y, Aquamarina/PRICTMA).
Telgopor: styrofoam
Globo: balloon
Corcho: cork
Plástico: plastic
Celofan: cellophane
Banda elástica: elastic band

One of the issues of greatest concern is the enormous amount of solid waste, both from the fishing industry and from towns, deposited on the coast year after year.  Winds and rain carry lighter waste to the sea, while currents near the shore carry them to places far away where they sometimes accumulate.   Much of this waste is plastic materials, bottles, bags and other articles which have been thrown away and remain unaltered in the environment for a very long time.  Wild marine vertebrate species (especially turtles, birds and mammals) frequently ingest plastic waste mistaking it for food and this results in malnutrition, mobility problems, diseases and risk of death. Some marine animals such as birds, seals, elephant seals and cetaceans get entangled in certain waste materials, for example parts of fishing gear, which cause injuries making them suffer and eventually die.

A rockhopper penguin affected by oil pollutiion

Hydrocarbons which are a by-product of oil affect coastal and marine areas.   Chronic oil spills can be detected even in areas far from the direct influence of ports or oil tanker routes.  The transport of oil by sea generates contamination risks along coastal areas, not only due to the ordinary manoeuvres of vessels and handling of their cargo, but also due to accidents.  Spills also happen during loading and offshore drilling.  Among the main causes of massive seabird deaths is contamination resulting from large scale oil spills.  The Magellanic penguin is one of the birds most affected by oil contamination and thus a reliable indicator of the occurence of incidents.  Latterly, due to successful mitigation actions, the number of birds affected has declined significantly but, notwithstanding, spills continue to cause the death of penguins in some places along the Atlantic shore.

On the Atlantic coast, the presence of heavy metals is restricted to ports and places where there are mining activities.   Persistent toxic substances (PCB) can be found in heavily industrial coastal areas such as the outskirts of the city of Buenos Aires.

The disposal of urban waste and other waste such as that resulting from agribusiness, generates locally high concentration of organic substances,  phosphates and nitrates that alter marine environments and cause mortality of fauna by eutrophication.  Eutrophication due to sewage is associated with human diseases caused by pathogenic microorganisms.

Severe contamination in ports can lead to malformation and local extinction of coastal species.  For example the presence of tributyltin (TBT) causes breeding problems in sea snails on the Argentine coast.  TBT is a pollutant that comes from the special paint that is used to coat ship hulls.

 

Non-native species

At least 41 non-native species have been reported in the Patagonian Sea.   At least 20 of them have a negative impact on ecosystems as they are capable of invading new habitats ultimately transforming them.  All these species live in coastal areas.  Among these non-native species we can mention the brown algae Undaria pinnatifida (commonly known as wakame), sea worms, mussels, snails, barnacles, crabs and fish.   Wakame, which covers large extensions of the seabed in gulfs and bays in the Argentine coast of central Patagonia, causes changes in biodiversity and economic losses owing to the degradation of bivalve banks and tourist sites.  Possibly two non-native salmon species may have negative effects on penguin populations if competition for food is confirmed.

 

Harmful algal blooms and climate change

Harmful algal blooms (red tides) seem to be increasing in the area.  Recently massive seabird mortality, caused by toxins produced by these organisms, has been recorded.  Their impact could be even more significant in the face of global climate change.  Accordingly, the high mortality of southern right whale juveniles which is being recorded annually in the Patagonian Atlantic could be associated with, among other factors, the scarcity of prey in the species’ summer foraging area in the South Atlantic. Rising sea temperature is suspectful of being the cause of the lack of prey for adult female whales, potentially explaining the poor nutrition of whale calves in their first weeks of life.

 

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