"Tsleil-Waututh argues in part that Trans Mountain's regulatory assessment was improperly done because it did not consider the expansion's effect on marine shipping."

The expansion amounts to about 300 more transits on the Juan de Fuca Strait every year.  This will be added to the 11,000 annual seagoing transits on the strait, many of which already carry American oil to American refineries.  The increase is negligible.  

Funny though, the Tsleil-Waututh don't mention the 51 bands that have signed agreements with Kinder Morgan to allow the pipeline to proceed.  Pretending that the Tsleil-Waututh represent the mainstream in BC is just that - a pretense.