Offshore Aquaculture in India: Site
Considerations and Challenges in Indian
Mohd Atif Siddiqui*
Buoyancy Consultants and Engineering LLP, India
Submission: February 02, 2018; Published: May 15, 2018
*Correspondence author: Mohd Atif Siddiqui, Buoyancy Consultants and Engineering LLP, Goa, India.
How to cite this article: Mohd Atif S. Offshore Aquaculture in India: Site Considerations and Challenges in Indian Coastal Conditions. Oceanogr Fish Open Access J. 2018; 7(3): 555714. DOI:10.19080/OFOAJ.2018.07.555714
Offshore aquaculture is the practice of marine farming where
the fish farm cages are placed further from the shores into deeper
ocean areas. This helps in increasing the size of farms, reduces
danger of accidents with marine traffic and the waste from cage
is easily washed away with stronger currents in the open ocean.
One major disadvantage is that such a cage requires sophisticated
technology and large investments. India has over 8000 km of
coastline with great potential for development of mariculture.
The exclusive economic zones which can extend up to at least 200
nautical miles from the coast, as shown in (Figure 1) (left), gives
India a vast area for developing mariculture. Most of this potential
remains underutilized as the locals and regional authorities lack
the technical know-how and transfer of technology from academia
to industry and local companies is extremely poor.
Offshore cage design present considerable challenges. These
range from physical conditions, socio-economic condition in the
region, legal regulations and viability of technical equipment and
knowledge. We will discuss the physical conditions in detail later.
If we look at the social and economic challenges for a country like
India, infrastructure and investment due to high risk factor, lack of
proper regulation and technical knowledge. This results in open sea
cage farming being mostly relegated to an unorganized sector.
These socio-economic challenges can be a factor that hinder
open ocean aquaculture but the major reason still remains the
technical challenges. Site selection is one of the most important
decisions that needs to be considered. There often has to be
a compromise between perfect offshore site conditions and
local infrastructure available at the nearest port or on-shore
establishments. Benetti et al.  has given an in-depth criteriabased
site selection study for aquaculture cages. Here, we will
mainly focus on the physical conditions at the site. Design wave
is the highest wave height which a structure can withstand. Pérez
et al.  do not recommend any cages, surface or submerged, for
situations where the significant wave height exceed 8-9 meters.
The critical loading on offshore cages, however, occurs due to a
combination of waves, currents and the direction between waves
and currents. (Table 1) shows the physical parameters to be
considered and preferable values.
The major parameters for forces on cages are wave height,
current velocity and depth consideration which in turn will affect
the mooring loads. Estimation of force on a structure in a certain
wave climate is a complex matter, and depends on geometry, flow
direction etc. Generally, simplifications are made with calculations
of forces and various loads. The modified Morison equation  can
be used to calculate the hydrodynamic forces acting on the cage
structure is shown in Eq. 1.
where ρ is the density of sea water, CD the drag coefficient, KM
the added mass coefficient, A projected area
Relative velocity, VR is defined as VR=V-R ̇. water particle
velocity V relative to cage velocity R ̇. The first term on the right
hand side of Eq. (1) is often regarded as the drag force, second term
describes the added mass and the third term is called the inertia
force. In addition to these wind forces must also be accounted for
but are genrally small compared to wave loads. These loads are
balanced by moorings to keep the cage within a suitable range.
The mooring tension will depend on depth and forces on the cage.
Siddiqui et al.  discussed forces on an experimental cage located
on the east coast. The study showed values for mooring forces and
estimates of wave loads on cage structures. Parameters like depth
of site, depth of cage, size of cage were varied. The results show
that forces on cage structure varies considerably with depth. This
makes the depth an imprtant criteria for site selection. (Figure 2)
show wave height (left) and current velocity (right) conditions at
a moored buoy on the west coast of India. These seem reasonable
values along with the fact that west coast fo india is far less prone to
cyclones as shown in (Figure 1) (right). Similar sites proviidng great
potetnial can be found along the west caost of India.
Sustainable aquaculture is currently the need in India as
elsewhere. According to the MPEDA, there does currently not exist
any cage-based production. This could be developed, as shown
by a simplified example of physical condition analysis. In India,
several experimental offshore cages for mariculture have been
installed at several sites along the Indian coast. While some have
been commercially successful, technical difficulties are often a
commonissue. Modification in the cage design is done by trial and
error to suit the local conditions. Training in mariculture is limited to
the Central Marine Fisheries Research Institute in Cochin. Offshore
aquaculture developments require a different cage design. Cages in
offshore sites have to withstand harsher weather conditions, and
the distance from the shore requires complex logistical systems.
In my opinion technology transfer, infrastructure development
and promotion by the government will help sustainable aquaculture
in India to feed a large part of the population. Careful site selection
and planning can go a long way in achieving this aim.
We used the moored buoy network established by the National
Institute of Ocean Technology, Chennai data available with the
Indian National Centre for Ocean information Services (INCOIS)
(Figure 2) to show a sample site.