  We report the first direct measurement of isotope shifts of the barium 6s$^2$
$^1$S$_0$ - 5d6p $^3$D$^\text{o}_1$ 413nm electric quadrupole transition, which
is utilized for efficient barium ion trapping via photoionization using a
single coherent light source. The measured isotope shifts relative to
$^{138}$Ba are $392.5\pm0.6$ MHz, $177.8\pm0.4$ MHz, $400.6\pm1.0$ MHz, and
$125.9\pm1.4$ MHz for isotopes with atomic number 137, 136, 135 and 134,
respectively. We verified the measured isotopes with King plot analysis and
compared the result with the formerly known shifts inferred from previous
studies on neighboring transitions. The results could be used for efficient
isotope selective loading of low-abundant barium ions, while careful
suppression of line broadening is required for successful isotopic selectivity.
