1United Graduate School of Agricultural Sciences, Ehime University, Tarumi, Matsuyama, Ehime 790-0905, Japan, 2Graduate School of Kuroshio Science, Kochi University, Nankoku, Kochi 783-8502, Japan
We observed the territory of juvenile red sea bream Pagrus major to detect the relationships between density and territory size at Morode Cove in Ehime Prefecture from January 2001 to October 2003 using SCUBA. The density of juveniles showed the highest value in 2001 (0.201 individuals/m2), the lowest one in 2002 (0.051 individuals/m2) and the intermediate one in 2003 (0.096 individuals/m2). The growth in 2001 was slower than that in both 2002 and 2003. We confirmed 131 territories of individually identified fish during the 3 years, and some territories were maintained for a long period. At the time of high density in 2001, the mean value of the territory sizes in each size class increased up to 8 cm size class, but did not show any clear increase thereafter and became nearly constant at c. 6.4 m2. At the time of intermediate density found in 2003, that value increased up to 9 cm size class, but became nearly constant thereafter at the level of c. 15 m2. At the time of low density found in 2002, that value increased with growth and became c. 50 m2 at the stage of 14 cm size class. These results suggest that the territory size of juvenile red sea bream is clearly correlated with the individual density, and the size became smaller at the time of high density and vice versa.