Let the number of male participants at the start be \( 3x \), and the number of female participants at the start be \( x \).
After the tea break, 16 participants left, and 6 more females registered, so the number of male participants becomes \( 3x - m \) and the number of female participants becomes \( x - f + 6 \), where \( m \) and \( f \) are the number of males and females who left.
The ratio of males to females after the tea break is given as 2:1, so:
\[
\frac{3x - m}{x - f + 6} = 2
\]
But we do not have enough information about \( m \) and \( f \), so the data is insufficient to calculate the total number of participants at the start.
Thus, the answer is Data Insufficient.