Will Alex Semin return to his elite goal-scoring levels?

From 2006 to 2010, Alexander Semin scored a total of 166 goals in 340 games, establishing himself as one of the elite scoring wingers in the NHL. The last three seasons, however, have seen a sharp decline in his offensive production, which resulted in only 41 goals over the course of 166 games. That represents a major downtick in goals per game, from 0.49 to 0.25.

As evidenced by the animated HERO chart below, Semin experienced quite the drop off in goal production.

What went wrong?