The Full Picture

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Applications of remote sensing

in fisheries and aquaculture

Trevor Platt, Research Scientist; Shubha Sathyendranath, Executive Director, Partnership

for the Observation of the Global Oceans; Venetia Stuart, Project Scientist, International

Ocean Colour Coordinating Group, all of Bedford Institute of Oceanography, Nova Scotia, Canada

ollectively, human society is responsible for the well-being

of the oceans. Various commercial conflicting interests

are concerned that range from fisheries, aquaculture, and

mineral extraction to tourism and transportation. Non-commer-

cial issues, such as maintaining a healthy state of biodiversity,

are also signifcant.

Internationally, and intergovernmentally, a consensus has been

reached that, in meeting the responsibility for stewardship of the

oceans, an ecosystem-based approach should be followed. The impli-

cation is that management decisions should be made in such a way

that the integrity of the ocean ecosystem, its structure and vital func-

tion, should not be compromised. Ecosystem-based management is

the new paradigm.

But it is far from simple to restate the new principle in operational

terms. Here, the primary requirement is for information about the

ocean and its ecosystem. First, we need to know the

spatial structure. Next, we need to know how the ocean

changes in the short term (response to weather),

medium term (response to seasonality) and long term

(response to climate change). The green plants in the

ocean (the phytoplankton) are mostly microscopic and

they respond to short-term changes in the environment

more rapidly than do the plants on the land. Ideally, we

need our information about the ocean to be updated

daily if we are to understand the mechanisms underly-

ing ecosystem response to change.

Earth observation (EO) by remote sensing is the only

way in which we could hope to collect the information

required on the appropriate timescales at the spatial scale

of the ocean. And fortunately, there is a technology avail-

able (visible spectral radiometry, often called

ocean-colour remote sensing) that enables us to produce

maps of the quantitative distribution of plant biomass,

indexed as the concentration of chlorophyll, over the

broad swath of the ocean. Chlorophyll is a pigment

found in all green plants, including the microscopic ones

living in the sea: it provides the means by which the

ecosystem can interface with its energy source, the sun.

When we look at an image of the distribution of chloro-

phyll in the ocean, we are really looking at a map of

connectivity of the marine ecosystem to the source of

its sustenance. It is the most fundamental information

we could have about the marine ecosystem.

If information is the essential requirement, and if EO

is the method to acquire it, what is the best way to apply

it? One of the important applications is in the construc-

tion of ecological indicators. These are a suite of

objective, quantitative indices intended collectively to

capture in a few numbers the condition of the ecosystem

at a given time and place. The idea is to condense the

potentially-bewildering detailed information into an

economical set of quantitative indices that should be

more simple to assimilate. When the indicators are eval-

uated in a serial manner, they afford the possibility of

detecting, and quantifying, ecosystem changes in

response to perturbations such as pollution, over-fishing

or climate change. EO has many qualities advantageous

Photo: Meena Kumari, Central Institute for Fisheries Technology, Kochi, India

Local fish market in Nagapattinam, Tamilnadu, India

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