Potential Fishing Zone

Somashekara S.R.^#, Harshavardhan D. Joshi^#, K.K. Ramteke^* and Kishor K.T.^#

^#KAFSU, College of Fisheries, Manglore, Karnataka, India

^*Central Institute of Fisheries Education, Seven Bunglows, Versova, Andheri (w.),

Mumbai-400061, Maharashtra, India

The seas surrounding the Indian subcontinent including the island territories of Lakshadweep, Andaman and Nicobar have a rich diversity of marine life. There are nearly 1570 species of finfishes and around 1000 species of shellfishes known from the seas surrounding our subcontinent. It is well known that adaptation of fish surrounding marine environment is controlled by important physical, chemical and biological factors. Many pelagic species are known to concentrate at current boundaries especially in areas with sharp horizontal temperature gradients. Monitoring the physical, chemical and biological parameters in space and time is time consuming and prohibitively expensive. Indirect method of monitoring selected parameters such as sea surface temperature and phytoplankton pigments (chlorophyll a) at sea surface from satellites is found very ideal as it provides high repetivity and large spatial coverage making available a real-time picture of any one of these parameters or a combination of more than one parameter.

In India potential fishing zone forecasts began in the late eighties at NRSA using NOAA-AVHRR derived sea surface temperature data. In the beginning, SST imageries were utilized by Dr. Nath at NRSA to estimate the fish catches in the Arabian Sea. In India, use of remote sensing for marine fisheries applications started in 1989 by involving various national agencies. Initially NOAA AVHRR data for Sea Surface Temperature (SST) was utilized for finding out thermal fronts. The thermal fronts were projected as Potential Fishing Zone or PFZ areas. For comparison of data during validation, PFZ charts were prepared and the information was disseminated through FAX, Telephone, Radio, TV, Newspaper and Fisheries societies etc. within shortest possible time. Fishing data collected from the PFZ and non-PFZ locations were compared. The program had the ambitious objective of PFZ prediction based on the hypothesis that fish stocks are likely to gather in those thermal fronts that are rich areas with algal food.

An integrated approach was developed by Dr. Solanki at SAC using IRS-P4-OCM derived chlorophyll concentrations and AVHRR-derived SST for locating PFZ. Dr. Shylesh Nayak and group from SAC attempted to understand the impact of PFZ on the fishermen community along the Gujarat coast. Subsequently analysis of satellite derived chlorophyll and SST features by Dr. Solanki indicated close coupling between biological and physical parameters. Way back in 1996,Dr. Pillai and group at CMFRI established the usefulness of PFZ advisories for locating pelagic fish concentrations based on validation along the Kerala coast. The PFZ forecasting technique was transferred to INCOIS, Hyderabad in the year 2000 under the leadership of Dr. Radhakrishnan who continued as Director of INCOIS till 2006. Dr. Shylesh Nayak took over as Director of INCOIS since then. On the basis of response received from fishermen societies/associations, individual fishermen, and qualitative discussions with institutions and communities, an effective assessment of PFZ penetration status and feedback has been attempted by INCOIS in the year 2001 and recommendations for new directions were implemented in stages. The PFZ validation program received a boost with the OCM (ocean color monitor)as satellite remote sensing techniques were found capable of obtaining information on water quality parameters like turbidity, suspended sediments,

chlorophyll concentration and presence of algal blooms and large sized aquatic weeds. Advantage of large swath area (1420 km) and better repeativity (once in two days) gave better chance to conduct validation exercise. The PFZ areas could now be charted with more accuracy and an integrated exercise started by involving more active participation from stakeholders.

Validation of PFZ advisories among user communities based on feedback received from different types of vessels and fishing operations aiming at a quantitative estimation of advantages derived in terms of increase in fish catches as well as saving on valuable fuel oil/ human effort through reduction in searching

time for shoaling fishes has been achieved through the commissioning of research project under the leadership of eminent marine biologist/marine fishery experts in the maritime states of Gujarat, Maharashtra, Goa, Karnataka, Kerala, Tamil Nadu, Andhra Pradesh and Orissa. Studies undertaken by Project Leaders in the different maritime states revealed the following:

1. PFZ advisories generated from satellite retrieved SST and chlorophyll were found to be good indicators of the availability as well as abundance of pelagic fishes such as sardines, mackerel, anchovies, tunas, carangids etc.

2. They are found more beneficial to artisanal, motorized and small mechanized sector fishermen engaged in pelagic fishing activities such as purseseining, ringseining, gillnetting etc who could generally locate fishable concentrations of highly migratory pelagic species there by reducing fuel costs and in turn the overall cost of operations.

3. PFZ advisories derived form satellite retrieved chlorophyll data were found more advantageous for locating sardine shoals, which are herbivorous in nature with feeding preference for phytoplankton.

4. PFZ advisories derived from satellite retrieved SST data were found more advantageous for locating mackerel, tuna, carangid and anchovy shoals which exhibit feeding preference for zooplankton including small sized fin fishes and shell fishes. SST based imageries were also found useful for locating concentration of juvenile yellow fin tuna (popularly known as "Kera"). The large sized adult fish is oceanic in habitat, but the juveniles migrate to shallow coastal waters in search of preferred food, which is seasonal.

5. There are instances when mature mackerel gets caught in bottom trawling gear during daytime in summer when they exhibit diurnal vertical migration. On similar occasions PFZ advisories based on satellite retrieved SST data are good indicators of the availability of mackerel at surface levels during nighttime and bottom levels during daytime at the same locality.

References

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