The shipping industry operates in an environment that is subject to weather conditions that range from calm water to enormous swells, strong wind and heavy rain; it operates in temperatures that range from well below zero in the Arctic areas to the heat and humidity of the tropics. Thus the marine environment influences shipping in many ways, that environment is central to the fishing industry that provides millions of tons of food each year.
To understand the delicate balance within marine ecosystems and food chains, study the diagram in the Grade 10 Section 10.4.2 of this website. You will see that one link in the food chain in the system relies on another for food, and each link keeps the numbers of the link below it at acceptable levels.
Damage caused to marine ecosystems by over-fishing and poaching
If one part of the marine ecosystem is disturbed (destroyed or depleted as would happen during uncontrolled fishing operations) another part of the system is affected. For example, if poachers take out large quantities of crayfish during the breeding season or undersized crayfish are caught without reserve, there will be fewer crayfish available to be caught during the next few seasons. In some areas of the south-western coast, abalone (perlemoen) has been taken out by poachers, totally destroying the abalone population.
In the period from about 1965 to 1990, overfishing on the west coast by foreign and local trawlers depleted the fish stocks, and resulted in several fish-processing plants having to close.
When one fish species (or even one link in the marine food chain) is disturbed, depleted or destroyed, another link in that food chain is affected. For example, if too many tuna are caught by fishing vessels, the tuna’s natural predators (seals, sharks) will have their food source depleted and therefore, those predators may move away, or turn to other levels of the food chain for their food. It may even raise the number of shark attacks on humans.
If too many sharks are killed for trophies for unscrupulous divers or tourists, their natural prey (e.g. seals) will multiply, and deplete the numbers of smaller fish species (e.g. pilchards) on which humans in a particular area depend for their food.
These examples underline the need to maintain the natural balances in the marine food chain. That can only be achieved by careful management of marine resources through measures such as :
- Setting of “catch quotas” for fishing companies and for individual fish species;
- Requiring all fishermen to have licences to catch a certain number of fish per day;
- Forbidding fishing for a particular species of fish during that species’ breeding season;
- Limiting the size of fish that may be caught to avoid young fish from being caught. (This is not always possible, especially during normal trawling operations.)
- Declaring known fish breeding areas to be fish sanctuaries where no fishing is allowed;
- Policing fishing operations properly to enforce the regulations;
- Imposing heavy penalties on those who do not comply with the fishing regulations. These penalties often include jail sentences, and/or fines and/or confiscation of any profits from illegal fishing and/or the confiscation of property (e.g. boat and equipment, vehicle towing the boat, fishing gear) that the offender used to commit marine-related crimes.
Marine pollution (including oil pollution, waste disposal at sea)
All ships produce waste – oily waste from the machinery, galley waste (including organic such as food leftovers or peels, and inorganic material such as plastic wrappers or boxes that contained food), grey water (water from showers and galley) and black water (sewage).
The Marine Anti-pollution Convention (Marpol) governs measures and procedures that ships need to introduce to avoid pollution involving the disposal of waste matter, the level of cleanliness of water that is to be disposed of at sea, and procedures that are to be taken in the event of an oil pollution incident. It also covers the design of tankers to prevent oil pollution.
Ships are equipped with an oil-water separator that will extract oil from water in the slop tanks or bilges and if the water is of a prescribed cleanliness, it may be discharged at sea. If its level of purity does not meet the requirements, it must be brought ashore and disposed of via proper measures.
Oil pollution is the form of marine pollution that evokes the greatest public response, especially when sea creatures become covered in oil. The two sources of oil pollution that are the main concern of maritime authorities, particularly after an accident:
- Crude oil or other toxic substances transported by tankers, and
- Fuel oil used by all ships.
The roles of maritime authorities and/or salvors are
- To PREVENT oil pollution of the sea and coast resulting from accidents to ships by reducing the risk of groundings, collisions and other accidents. (This requires careful planning of shipping routes, issuing of accurate weather forecasts, and, if an accident happens, the intervention by specialist salvors, tug operators and other personnel.)
- To REDUCE oil pollution of the sea and coast after a shipping accident has occurred and oil is leaking from a ship. (This also requires intervention by specialists.)
- The prevention of oil pollution by visible patrolling to discover any oil slicks before they can pollute the coast so that action can be taken, and to discourage deliberate dumping of pollutants in the sea, and to gather evidence to prosecute offenders. Visible patrolling is usually done by aircraft as there is a better chance to catch an offending vessel in the act, to identify the ship, and to capture images that can lead to the successful prosecution of those responsible aboard the offending vessel.
All ships – even fully laden vessels – require some ballast water to ensure that the ship is trimmed properly and also to minimise the ship’s rolling. The ballast water is taken onboard in one port and is discharged in another. In this process, and despite grills on intake valves, marine organisms that are taken in can easily be transferred from one port to another.
For example, a ship that discharges an iron ore cargo in China will take in ballast water before sailing from the Chinese port. That ballast water will contain small (even microscopic) marine organisms that live in the water in the Chinese port. If that water is kept in the ballast tanks until the ship arrives in Saldanha Bay to load her next cargo of iron ore, as the ballast water is discharged in Saldanha Bay, those foreign organisms will be discharged with the water. This means that foreign (exotic) organisms are introduced to the water in Saldanha Bay, a most undesirable situation.
However, if the ballast water is released into the sea en route between the Chinese port and Saldanha Bay, and replaced with new ballast water, the new intake of ballast water will contain organisms more like the Saldanha Bay marine life, and therefore less harmful to the environment. Ballast water exchange while at sea may only be done when the ship is a minimum of 200 nautical miles from shore and in water with a minimum depth of 200 metres. To exchange ballast water, the ship can use the “flow-through” or sequential (tank-by-tank) method. At least 95 percent of the total ballast water should be exchanged between ports.
To kill exotic organisms in ballast water, chemicals can be put into the ballast tanks or mechanical and electronic measures can be put in place such as ultra-violet radiation, filtering of water, deoxygenation of the water or heating of ballast water.
The Ballast Water Control Convention requires all ships to have a Ballast Water Management Plan that includes the accurate recording of amounts of ballast water taken in and discharged.
Unfortunately, ships occasionally have accidents – grounding, fire, collision, storm damage, or other problem. In these accidents, bunker tanks can be punctured or, in the case of damage to a tanker, her cargo tanks can be punctured, releasing fuel oil or crude oil respectively into the sea, and causing pollution. Other toxic cargo can be released into the sea as the result of an accident. If the ship sinks or breaks up, widespread pollution can occur with serious consequences for marine life and marine activities (e.g. fishing, leisure, tourism, etc.).