68
N. Hoepffner et al.
Taking advantage of the high spatial and temporal resolution of thermal sensors,
the detection and monitoring of thermal fronts from composite SST fields can contribute to develop forecasting capabilities of fish population and their movements
(Agenbag et al. 2003), and subsequently, improve the harvest of the stocks in an effective and sustainable way. Temperature is indeed an important factor determining
the distribution of fishes, as many of them tend to migrate along preferred temperature ranges. Lan et al. (2011) observed maximum aggregation of yellowfin tuna in
equatorial Atlantic waters with temperature above 24–25
◦ C. According to Zainuddin
et al. (2008), the distribution of albacore tuna in the northwestern Pacific is narrowly
associated with a combination of environmental parameters, which can be described
from thermal imagery, ocean colour, and altimetry. Specific isopleths in the sea surface temperature coincide with highest catch per unit efforts, underlining the benefit
to monitor these temperature gradients to generate maps of potential fishing ground
and predict spatial patterns of albacore habitats.
Also frontal structures associated with meanders and eddies are potential sites for
fish aggregation due to increasing productivity at lower trophic levels (Bakun 2006).
Consequently, TIR images are often used to identify so-called Potential Fishing
Zones (PFZs) through the detection of SST gradients as generated by these oceanic
features. The maps are then disseminated to fishermen in real time to help in reducing
search time for fishing grounds, in saving on fuel and, thus, in reducing operational
costs (Dwivedi et al. 2005). Moreover, the system could improve the quality of the
catch and the sustainability of the stocks, targeting on adults populations rather than
juvenile and nursery grounds, otherwise endangered by a blind and unsupervised
harvesting process. This operational process to support fisheries is not yet very much
used in Africa when compared to Asian countries where the benefit-to-cost ratio of
fishing activity largely improves when using satellite data, combining thermal and
visible imagery.
As part of the AMESD programme, a Thematic Action related to ‘Coastal and
Marine Management’ was recently implemented through the Mauritius Oceanography Institute (MOI), thus acting as AMESD regional Implementation Centre. The
main objective of this Action is to support the governments and institutions of the
Indian Ocean Commission (IOC) and eastern African countries to make better use of
Earth Observation data in their marine and coastal policies. Accordingly, following
an agreement with EUMETSAT, MOI is regularly receiving daily chlorophyll and
SST data at 1 km resolution to provide IOC users with oceanographic charts for the
detection of Potential Fishing Zones. Figure 3.6 is an extract of such operational
service showing sequential daily maps of MODIS SST in the Mozambique Channel.
The data were further analysed to identify frontal structures favourable to aggregations of important commercial fishes. Using TIR data and other satellite sensors, Tew
Kai and Marsac (2010) underlined the importance of eddy boundaries to monitor the
distribution of top predators in this region.
N. Hoepffner et al.
Taking advantage of the high spatial and temporal resolution of thermal sensors,
the detection and monitoring of thermal fronts from composite SST fields can contribute to develop forecasting capabilities of fish population and their movements
(Agenbag et al. 2003), and subsequently, improve the harvest of the stocks in an effective and sustainable way. Temperature is indeed an important factor determining
the distribution of fishes, as many of them tend to migrate along preferred temperature ranges. Lan et al. (2011) observed maximum aggregation of yellowfin tuna in
equatorial Atlantic waters with temperature above 24–25
◦ C. According to Zainuddin
et al. (2008), the distribution of albacore tuna in the northwestern Pacific is narrowly
associated with a combination of environmental parameters, which can be described
from thermal imagery, ocean colour, and altimetry. Specific isopleths in the sea surface temperature coincide with highest catch per unit efforts, underlining the benefit
to monitor these temperature gradients to generate maps of potential fishing ground
and predict spatial patterns of albacore habitats.
Also frontal structures associated with meanders and eddies are potential sites for
fish aggregation due to increasing productivity at lower trophic levels (Bakun 2006).
Consequently, TIR images are often used to identify so-called Potential Fishing
Zones (PFZs) through the detection of SST gradients as generated by these oceanic
features. The maps are then disseminated to fishermen in real time to help in reducing
search time for fishing grounds, in saving on fuel and, thus, in reducing operational
costs (Dwivedi et al. 2005). Moreover, the system could improve the quality of the
catch and the sustainability of the stocks, targeting on adults populations rather than
juvenile and nursery grounds, otherwise endangered by a blind and unsupervised
harvesting process. This operational process to support fisheries is not yet very much
used in Africa when compared to Asian countries where the benefit-to-cost ratio of
fishing activity largely improves when using satellite data, combining thermal and
visible imagery.
As part of the AMESD programme, a Thematic Action related to ‘Coastal and
Marine Management’ was recently implemented through the Mauritius Oceanography Institute (MOI), thus acting as AMESD regional Implementation Centre. The
main objective of this Action is to support the governments and institutions of the
Indian Ocean Commission (IOC) and eastern African countries to make better use of
Earth Observation data in their marine and coastal policies. Accordingly, following
an agreement with EUMETSAT, MOI is regularly receiving daily chlorophyll and
SST data at 1 km resolution to provide IOC users with oceanographic charts for the
detection of Potential Fishing Zones. Figure 3.6 is an extract of such operational
service showing sequential daily maps of MODIS SST in the Mozambique Channel.
The data were further analysed to identify frontal structures favourable to aggregations of important commercial fishes. Using TIR data and other satellite sensors, Tew
Kai and Marsac (2010) underlined the importance of eddy boundaries to monitor the
distribution of top predators in this region.