Harbour pollution

Picture credit: Transportworldafrica.co.za

South Africa has seven commercial ports along its 3000 km coastline.  Of these only two are on the West Coast:  Table Bay (Cape Town) and Saldanha Bay.  The West Coast is better known for its large number of small–boat harbours for fishing vessels, ski-boats and yachts.

Harbours are an important hub for development and commercial activity, but have a reputation for being some of the most polluted of all marine environments.  They are affected by both marine and land-based pollution sources, including shipping, surrounding industries and storm water runoff, all of which contribute to deteriorating water quality and unsightly litter.  The problem is compounded by the fact that harbours are generally not as well flushed as other waters along our high energy coastline, since they are designed to provide shelter from wind and waves.  This means that pollutants may accumulate to the point that they become toxic to marine life.

Picture credit: Garth Johnstone, Durban harbour 19 October 2017

The main pollutants affecting harbours are organic waste, litter, petroleum hydrocarbons and toxic chemicals.  Raw sewage is generally not discharged into harbours deliberately, but bacteriological monitoring of faecal coliforms reveals that human waste does indeed find its way into harbours via storm water runoff.  Heavy metals such as zinc, copper, lead, tin, mercury and cadmium are often introduced into harbours from maintenance activities such as painting, scraping and grit-blasting.  Furthermore, TBT (tributyltin), an anti-fouling paint used on boats to prevent the settlement of mussels, barnacles and seaweeds, is highly toxic to marine life and may put human consumers of seafood at risk.  Litter enters harbours through storm water drains from being blown off the quay by wind.  Plastic materials take many years to break down, and may kill or injure marine animals that become entangled in this litter or mistake it as food.

Picture credit: Garth Johnstone, Durban harbour 19 October 2017

Cape Town Harbour is a large, busy port, subject to pollution from a number of sources.  However, with the development of the V&A Waterfront, one of the Cape`s most popular tourist attractions, it was litter pollution that came under the spotlight.  Floating plastic and windblown litter is now swept off the surface of the water daily by a sweeper barge, but the problem is ongoing because the harbour is the discharge point for storm water systems draining the City Bowl.  Harbour authorities have attempted to contain the litter by covering storm water outfalls with large nets that can be periodically cleared, but these often burst during heavy rainstorms.  Some of the litter comes from sources within the harbour itself.  Fishing line and nets, as well as nylon strapping used to secure fish boxes, are regularly lost overboard or blown off the quay outside fishing companies operating within the harbour.  Seals often become entangled in these items, which cut into the flesh, causing deep wounds.  A team from Marine and Coastal Management visit the seals' favourite haul-out site each day to remove such items from entangled animals, and treat the injured where possible.

Source: SA Coast – Sue Matthews