More fish – surely we just need to farm the sea?

Posted by Stephen Hall on 20 March 2012

“Mariculture certainly holds promise as part of the solution to meeting our need and demand for fish, but it’s not the obvious option that many people imagine”

Giant clam exclosure, Solomon Islands

Molluscs are the principal farmed marine product: giant clam exclosure, Solomon Islands. Photo by Mike McCoy

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When I talk about what I do for a living, it doesn’t take long for the conversation to turn to the question of how we are going to meet the world’s growing demand and need for fish. In these conversations I find most people imagine it will be mariculture – farming aquatic animals and plants in the sea – that does this. It’s a conclusion that’s understandable. After all, compared to our lands, the relatively uncluttered seascape offers apparently endless opportunities for aquaculture.

But is a large increase in sea farming the most likely response to our increasing demand? Or will aquaculture in fresh and brackishwater continue to dominate as it does now? And which is best? Are there any differences in the benefits to be had by the poor and food insecure between farming these two environments? Is one likely to prove more environmentally sustainable than the other? Given that aquaculture is about the fastest growing food production sector in the world, these are important questions to think about.

For those of you who imagine that sea farming is set to take over, it may be surprising to learn that the percentage of farmed fish that comes from the sea has actually fallen over the past 15 years. From a high of 38% in 1995, if you exclude seaweeds, the value is now around 32% [1]. While aquaculture production is growing in all environments, it’s growing faster in fresh and brackishwater – an annual average growth rate of about 6.8% for the last decade, compared to 4.8% for mariculture.

So why does aquaculture in land-based fresh and brackish water systems dominate, and why is the gap widening? I think there are several plausible hypotheses.

Netcage mariculture

Setting up a mariculture farm can be risky business, netcages in Kuching, Malaysia. Photo by Fred Weirowsky

The first is that security of property and exclusive access rights to land based systems is often relatively easy to obtain, whereas licensing and permitting arrangements for coastal waters of many countries are often complex, contentious and in a state of flux. Setting up and running a marine fish farm can be pretty risky – competing demands on coastal waters and uncertainties and difficulties of securing tenure often make it hard to get the necessary investment.

The second reason is biophysical; it is often much easier to access and manage a pond system than it is a cage system in open water. Bad weather, harmful algal blooms, chronically poor coastal water quality and acute pollution incidents are all threats to mariculture operations, but largely avoided, or more easily managed, in pond systems. This and the higher capital costs that are often associated with establishing a farm at sea, especially in more exposed areas, often tip the balance of risk and return in favour of land-based systems, especially for the small-scale farmers that dominate developing countries.

The third reason is because most of the growth in demand for aquaculture products is for finfish, little of which is grown in the sea. This is, perhaps, another surprising fact for many readers – of the 36 million tonnes of fin fish produced in 2009, less than 10% came from sea farming. While many of you will be familiar with the prevalence of farmed salmon in western supermarkets, on a global scale, it is the freshwater tilapia, catfish and carps that dominate.

Black lip oysters

Black lip oysters floating in the warm ocean currents of the Solomon Islands, South Pacific. Photo by Idris Lane.

In contrast, the principal marine farmed product is molluscs (oysters, mussels, and clams) [2]. Partly because demand for these shellfish products has not grown at the same rate as for fin fish, mariculture growth has been slower. For this to change we would need to find a tropical marine fin fish that is largely herbivorous, grows rapidly, and can secure the prices required to offset the often higher capital and operating costs of marine farming. As yet, there is little sign of such a species on the horizon.

Yet, while farming the sea produces less and is growing more slowly, it still has a key role to play in the food security and livelihoods of many people. Sea farmed molluscs, for example, are an important, highly nutritious, affordable and accessible food for many poor consumers in developing countries. Finding their way into sauces, stews and other dishes of poor households they provide an important source of micronutrients, especially for pregnant and lactating women, and children.

From an environmental sustainability perspective too, molluscs have a lot going for them. As filter feeders, relying on the natural productivity of the seas they require no external feed inputs and often help improve coastal water quality by absorbing excessive nutrients before they become a problem. We will no doubt see the area under mollusc culture grow further, particularly in the waters of several countries of southeast Asia where undeveloped coastline remain. Efforts to support the growth of this sector in ways that meet local food security and livelihood objectives deserve particular attention.

One should also bear in mind that, while fin fish culture may be a relatively minor component of total mariculture production, it offers important livelihood opportunities for poor farmers, for example, in coastal regions of China, Indonesia and Vietnam.

Fresh and Brackishwater aquaculture

Fresh and brackishwater based aquaculture dominate fish production. Breeding hapas, Zambia. Photo by Asafu Chijere

So, given current circumstances it looks like, for the foreseeable future, it is fresh and brackishwater production that will dominate global statistics. Both sectors are growing fast, however, and in differing ways must confront the challenge of improving efficiencies and environmental sustainability [3]. This will require governments, businesses, non-government actors and researchers taking steps together to improve production systems and techniques, investing in innovation, especially to reduce reliance on fish meal and oils, and strengthening regulation including improving monitoring and compliance.


If we do these things we can ensure aquaculture is a sustainable endeavor that uses biophysical resources prudently. That’s essential if it is to fully play its role in meeting our future needs for fish.

[1] FAO FishStat (accessed, March 2012).
[2] Molluscs comprise 76% of all marine farmed and 97% of total farmed production]
[3] Hall, S.J., A. Delaporte, M. J. Phillips, M. Beveridge and M. O’Keefe. 2011. Blue Frontiers: Managing the Environmental Costs of Aquaculture. The WorldFish Center, Penang, Malaysia.