The present study was designed to assess the composition and abundance of intertidal animals and seaweeds at key points along the Bowen Island shoreline; and to provide the data as a baseline for comparison with any future assessments at the same precise locations. The results were evaluated in terms of potential impacts from waves generated by Pacificat catamarans.
The south facing station on the Fairweather shoreline is a low slope rocky shore dominated by a very few species and significant cover of attached animals and seaweeds. Mobile species such as chitons, wrinkled whelks, limpets and periwinkles were absent or nearly absent. There were a few purple sea stars. Sugar kelp was present but with unusually tattered fronds. Brief observations on a rock slope bounding Arbutus Bay about 1km away indicated a very similar biotic composition.
The north facing control site at Grafton Bay was also impoverished in terms of species number, and, further, did not have significant seaweed cover. However, the shield limpet was common. The absence of the wrinkled whelk at both the south sites and the control site is likely due to an antifouling paint based on information from DFO. The Grafton Bay site was a poor control as the fjord conditions, perhaps coupled with impacts from industrial sources would be expected to result in an impoverished biota.
The absence or near absence of most mobile species, and the poor condition of a wave exposure indicator species (sugar kelp) on the south facing Fairweather and Arbutus Bay rock shores strongly suggests some unnatural impact. The waves generated by Pacificat ferries are a prime candidate as a causative agent. The mobile species occur in other areas with storm generated waves and the sugar kelp does well during the summer on other semi-exposed coasts with winter storms.
The impoverished fauna on the Arbutus Bay muddy sand beach may be related to the instability of the sediment during winter storms. This instability might be increased by catamaran ferry wakes but evidence is lacking.
Eight recommendations are made on potential follow-ups to this report.