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SEAFDEC Warning System Cages Threat of Fish Farms

by Ellen Hardy
06 October 2008, at 1:00am

PHILIPPINES - SEAFDEC are in the process of developing an early warning system to guard against the negative impacts of fish cages to mariculture parks.

The Southeast Asian Fisheries Development Center (SEAFDEC) Aquaculture chief Dr. Joebert Toledo said the early warning system is a simple technique, wherein mariculture park managers have only to collect samples of the sediments or the soil under the cages.

The sample's colour is then compared to a reference colour chart which will let them know how far off or how near they are from the ideal condition.

This colour comparison method is basically the same technique used by rice farmers to see if their rice needs additional leaf fertilizer.

Toledo said the SEFADEC is developing a very detailed sediment colour chart for this purpose.

According to SEAFDEC the Department of Agriculture-Bureau of Fisheries and Aquatic Resources, the government has so far put up 34 mariculture parks around the country.

The DA's emphasis on mariculture parks to boost fish production has been noted in President Arroyo's recent SONA, where a sea cage measuring 10x10x6 meters in the park can produce as much fish as a 10-hectare fishpond in one cropping cycle of five months.

In developing the system, SEAFDEC first monitored a non-fish cage and a fish cage site in its Igang Marine Station in Nueva Valencia, Guimaras.

SEAFDEC researcher Sheila Mae Santander said she compared the nutrients, the presence or absence of infauna and sulfides in the sediments collected using a core sampler, where she found out the sediment colour mirroring the degree of sediment deterioration.

This finding is the basis of a very detailed colour chart being developed by SEAFDEC.

Santander said pollution in sea cages comes from the feeds given to the fish to sustain the large stocking densities and feeds that are not eaten or digested properly, plus the other waste products go to the water, some eventually settling down onto the sediment bottom, leading to higher sedimentation rates in the area.

Santander said that sedimentation rates, ammonia and phosphate concentration were higher in cage sites compared to non-cage sites, while dissolved oxygen was found to be lower in the cage sites, reason that no polychaetes were found in these areas.

Should mariculture park operators or BFAR find out that the parks sediment is getting bad, SEAFDEC suggests that a "fallow period" be implemented. The fish cages may be moved into another area of the mariculture park, which will allow the sediments and infauna of the threatened area to recover.

SEAFDEC also said that park locators should check their feeding regimes so as not to do overfeeding because proper feeding management will help reduce wastes.

Further, park locators should follow the advice of BFAR and SEAFDEC once the early pollution alert is issued.

Ellen Hardy