Soil erosionl



Climate variability and spawning in capture fisheries

Data collected (primary and secondary) over a timeline (1977-2012) on the availability of spawning fishes along the Chennai coast indicated that there is a gradual shift in the spawning season of oil sardine from January-March during 1977-78 to June-July in 2011-12. The same feature was noticed in threadfin breams also. SST between 27.5 - 28.0oC is the optimum for thread fin breams and when SST exceeds 28.0oC, the fish shift the spawning activity to seasons when the temperature is around the preferred optima. Spawning season has shifted from September – October during 1990-99 decade to November –December during 2002-10.

Abiotic factors and fish catch:

Step-wise multiple regression was carried out between total pelagic fish catch (sardine, mackerel, tuna) and environmental parameters to find the specific abiotic factor affecting the catch. Chlorophyll and rainfall were found to be the two principal environmental factors determining catch of pelagic fish along Gujarat coast. Colored dissolved organic matter (CDOM) was found to be the most significant factor in determining the catch of demersal fishes like threadfin breams and pomfrets.

Impact of temperature and salinity on mariculture:

Cobia embryonic development and larviculture showed that highest hatching percentage was obtained at 31°C, while the lowest hatching percentage was in 34oC. Larval deformity was noticed in Cobia when temperature exceeded 32°C. 79% of fertilized cobia eggs hatched at 31ppt salinity and very poor percentage hatching of 15% in 24ppt. Ambient temperature was 29-30.5oC. Experiments conducted to ascertain growth of cobia larva indicated that faster growth of 6.47 mm was noticed in larva maintained at 32oC at 40 dph whereas at 34oC all larvae showed retarded growth.



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