The basic method to calculate the standard error is by:
$$se = \sqrt(\frac{1}{n-3})$$
For the Spearman correlation coefficients se_method "fieller"
is calculated as:
$$se = \sqrt(\frac{1.06}{n-3})$$
For the Kendall correlation coefficients se_method "fieller"
is calculated as:
$$se = \sqrt(\frac{0.437}{n-4})$$