Two-thirds of African countries have access to the sea. Some are making good use of it through fishing and tourism. But the productivity of African waters is plummeting. Kenyan fishermen now catch an average of 3kg of lobster on each trip, compared with 28kg in the 1980s. Grouper fish appear to have become extinct in the Comoros in the 1970s. South Africa's fishy haul is lower today than in the 1950s.
The main reason is bad governance. African Union calls to fight overfishing with joint navy patrols and co-operation between fisheries have been ignored. Nigeria, among Africa's richest countries, lacks a serviceable navy. Some governments even collude in overfishing. Angolan fisheries officers rarely report the illegal catches of boats owned by politicians.
At the same time African states are failing to invest in much-needed marine research. They say it is a "donor activity", meaning they want foreigners to pay for it. The continent has only one large oceanography department, at the University of Cape Town, and that is underfunded.
Coastal wetlands have little protection and fishing grounds are especially vulnerable. In many countries lot of foreign boats operate in areas close to the shore supposedly reserved for locals in dugouts. Some vessels use banned methods like light-luring (attracting fish with floodlights) and pair-trawling (where nets strung between boats are dragged on the sea floor).
Industrial fishing has been encouraged by rising global demand. The European Union has a series of agreements for its boats to fish in African waters. China has moved in too. The Russian fishing fleet is resurgent. In many cases, says André Standing, a researcher into fisheries agreements in Africa, it is not clear how much money is being paid for licences, or to whom. Critics say Africa's failure to protect its ocean is political, the definition of a continent too weak to exert full control over its resources. A recent deal between Mauritania and China makes it hard to reduce the catch even if it is unsustainable.
Meanwhile the human footprint along Africa's vast coastline is growing. The UN says African seaside cities are spreading by more than 4% a year. By 2050, a corridor along the Gulf of Guinea from Côte d'Ivoire to Cameroon is likely to be one of the world's most densely populated areas. It may also be one of its most unstable. Many of the cities are vulnerable to rising sea levels predicted by climatologists.
Making the sea safer and more productive may be the best way to keep landlubbers peaceful. Experts have plenty of suggestions. Community initiatives could help get rid of dynamite-fishing and its ruinous effects. Conservation no-catch schemes such as one run by Blue Ventures, a Madagascan outfit, have proven their value. But there is too little money to scale them up. The best way to find the cash would be to point out the security costs of unhappy fishing communities to rich governments. Somalia's piracy problem began in part as an armed response to illegal fishing in Somali waters. Some banditry in Nigerian waters started as a protest against the threat to fishing from the oil industry.
Scientists would like to see more sanctuaries, starting with a big area in northern Mozambique. Mr Standing suggests that one radical idea might be to ban industrial fishing in the worst performing African countries for ten years, which would favour labour-intensive fishing from dhows (traditional sailing boats). But given the local and global hunger for protein, such schemes could only work if fish farms were expanded.
The tributaries of Africa's oceans are mostly clean and its mangroves in good condition, especially compared with those of Asia. But abuse is growing. With the sharks almost gone, Chinese diners are demanding manta rays and mobulid rays as ingredients for their expensive banquet stews. Frank Pope, an Africa-based writer on oceans, says that the slow-breeding rays could be gone even sooner than the sharks they used to swim alongside on the glittering reefs.