Sand flathead was once the most abundant fish species in PPB. Between 2000 and 2010, sand flathead stocks in PPB declined by 90% and continue to decline at a rate of 15% of the remaining stock per year.
The environmental factors that triggered the decline in sand flathead abundance are not known. The decline in PPB has coincided with:
- Prolonged drought conditions (1998–2009)
- The introduction, and subsequent expansion, of the Northern Pacific Starfish (1997–present)
- A significant decline (>30%) in nutrient inputs in PPB from the Western Treatment Plant (the major nutrient source to PPB).
Prior to 1994, sand flathead populations in PPB were typified by episodic recruitment events that were important in sustaining population levels; since 2000 there has been minimal recruitment.