tuna()distributioninfishinggroundsinthetropicalIndianOceanandthermoclinecharacteristics,calculatedfrommonthlytemperatureprofiledatafromArgobuoysandthemonthlyCPUE(catchperuniteffort)frombigeyetunalonglines.Seasonalvariabilitywasobservedinthedepthoftheupperboundarytemperatureandinthelowerboundarydepth.Ouranalysissuggestedthatthedistributionofbigeyetunawasrelatedtotheseseasonalvariationsofthethermocline.TherangeoftheupperboundarydepthforhighCPUEduringthesummermonsoonwas30–50m,whichwaslowerthaninthewinter(50–70m).AhigherCPUEwasfoundfromnorthernMadagascartoSomaliawherethelowerboundarydepthwasat170–200m.Wherethelowerboundarydepthwasmorethan300m,thevalueofCPUEwaslow.TherangeofupperboundarytemperaturesinthehigherCPUEfishinggroundswas27–30mduringthewintermonsoonand24–30mthesummermonsoon.Frequencyanalysisandtheempiricalcumulativedistributionfunction(ECDF)wereusedtocomputetheoptimumrangeofthermoclinecharacteristics.Theoptimumdepthrangeoftheupperboundarytemperaturewas26–29mandtheforthelowerboundarytemperature,itwas13–15m.Theoptimumrangeoftheupperboundarydepthwas30–60mandthelowerboundarydepthwas140–170m.TheconclusionswereconfirmedusingKolmogorov-Smirnovtest.inthecentralfishinggroundofbigeyetunawerepreliminaryobtainedinthispaper.Theresultscouldpro