CONSULTANCY AND RESEARCH IN AQUACULTURE AND THE AQUATIC ENVIRONMENT

A Company in the NIVA-group

Environmental impacts of aquaculture

Aquaculture impacts

Impacts of aquaculture can be put into 3 categories Physical Chemical Biological

Aquaculture impacts

Physical– Physical structures, cages, pens, jetties– Visual– Net friction to exchange– Use of wetlands and mangroves for pond construction– Saline infiltration

Aquaculture impacts

Chemical– Oxygen depletion– Eutrophication– Antifoulants boats and nets– Medications and treatments

Aquaculture impacts

Biological– Faeces– Excretion– Waste food– Genetics and Biodiversity

Nutrient balance

Inputs, uptake and outputs

Only 40% of inputs are retained by the fish. The remainder go into the environment

Biological

Aquaculture produces wastes which may negatively affect the environment.

In intensive aquaculture, a considerable amount of organic wastes are produced in the form of

particulate (mainly the uneaten food, faeces) soluble substances (excreta) which increase biochemical

oxygen demand, nitrates and phosphates

Scale Issues

One of the critical issues is identifying the scale on which they appear. Some impacts appear only in the immediate vicinity of the operation, while others are more widely distributed, and although they may appear smaller, the large area that they affect makes them important.

There are three major time and space scales for the impacts of finfish farms:– Localised This is a very small scale in both space and time,

illustrated by depletion of oxygen in and near the pens at slack tide.

– Near field, such as the deposition of carbon and other wastes on the seabed in the vicinity of a fish farm.

– Far field, usually due to the release of soluble nutrients and disease organisms into the water column.

Primary versus Secondary Effects

It is sometimes difficult to separate the primary and secondary environmental impacts of aquaculture.

The rate at which nutrients are released into the water column can be estimated or measured.

This is a primary effect, but nutrient levels in themselves are not very important.

The secondary effects of the nutrient release are more important with nitrification leading to enhanced primary productivity, and in particular, harmful algal blooms.

Photo Transect

Crete, 02-July-2001, MediterraneanMaximum Depth 20 mDiplodus puntazzo, number = 90.000, mean weight = 350 gDicentrarchus labrax, number = 175.000, mean weight = 250 g

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Environmental impact

Local Impact

Widespread impact

Input equals output x2

The well being of the fish in the farm is totally dependent on – the operator (the management) – the water (the environment)

The inputs that are made will be converted– fish production– pollution under the cages

For one tonne of fish produced, there is one tonne of waste materials

Self pollution

Who suffers most from the pollution under the cages or pens?