This study focused on the optimisation of offshore marine fish-cage farming in
Tenerife, Canary Islands. The main objective was to select the most suitable sites
for offshore cage culture. This is a key factor in any aquaculture operation,
affecting both success and sustainability. Moreover, it can solve conflicts between
different coastal activities, making a rational use of the coastal space. Site
selection was achieved by using Geographical Information Systems (GIS) based
models and related technology, such as satellite images and Global Positioning
System (GPS), to support the decision-making process. Three different cage
systems were selected and proposed for different areas around Tenerife. Finally, a
particulate waste distribution model (uneaten feed and faeces) was developed,
also using GIS, for future prediction of the dispersive nature of selected sites. This
can reduce the number of sites previously identified as most suitable, by predicting
possible environmental impacts on the benthos if aquaculture was to be developed
on a specific site.
The framework for spatial multi-criteria decision analysis used in this study began
with a recognition and definition of the decision problem. Subsequently, 31
production functions (factors and constraints) were identified, defined and
subdivided into 8 sub-models. These sub-models were then integrated into a GIS
database in the form of thematic layers and later scored for standardization. At this
stage, the database was verified by field sampling to establish the quality of data
used. The decision maker’s preferences were incorporated into the decision model
by assigning weights of relative importance to the evaluation under consideration.
These, together with the thematic layers, were integrated by using Multi-criteria
Evaluation (MCE) and simple overlays to provide an overall assessment of
possible alternatives. Finally, sensitivity analysis was performed to determine the
model robustness. The integration, manipulations and presentation of the results
by means of GIS-based models in this sequential and logical flow of steps proved
to be very effective for helping the decision-making process of site selection in
study. On the whole, this study revealed the usefulness of GIS as an aquaculture
planning and management tool.
Cage systems that can withstand harsh environments were found to be suitable
for use over a broader area of Tenerife’s coastline. Thus, the more robust self-tensioned
cage (SeaStation速) could be used over a greater area than the weaker
gravity cages (Corelsa速). From the 228 km2 of available area for siting cages in the
coastal regions with depth of 50 m, the suitable area (sum of scores 6, 7 and 8) for
siting SeaStation速 cages was 61 km2, while the suitable area for SeaStation速 and
Corelsa速 cages was 49 and 37 km2 respectively. Most of the variation between
these three cage systems was found among the intermediate suitability scores. It
was concluded that the biggest differences in suitable area among cage systems
are between Corelsa速 and SeaStation速 systems, followed by differences between
Corelsa速 and OceanSpar速 cages, and OceanSpar速 and SeaStation速 respectively.
This variability was mostly located on the N and NNW of the island, where waves,
both long and short-term, are higher.