In 1997, HMCS Saskatchewan was sunk off Nanaimo; 448 days later divers recorded 46 taxa, including 9 molluscs and 7 echinoderms

HMCS Saskatchewan, which belonged to the Mackenzie class of destroyer escorts, was sunk near Nanaimo in British Columbia, Canada, on June 14, 1997, to form an artificial reef. Divers investigating the artificial reef during the first 448 days after the sinking found 46 different types of flora and fauna, including 9 molluscs and 7 echinoderms, which marks one of the earliest records of colonization by marine life of this man-made reef. In this case, the speed of colonization is similar to other projects of the Artificial Reef Society of British Columbia (ARSBC): for example, in the case of G.B. Church, the first of the ARSBC's artificial reefs, sunk in 1991, surveys carried out within two and a half years of sinking recorded 96 species (62 invertebrates, 20 fish, and 14 algae) and in the case of HMCS Annapolis, which sank in 2015, almost twenty years after HMCS Saskatchewan, citizen-science surveys monitored recruitment over the course of a five-year investigation.

The Saskatchewan was part of the Royal Canadian Navy service for approximately thirty years and was decommissioned in 1994. After it was purchased by ARSBC, it was made non-hazardous, its hatches and doors opened for diving purposes, and it was sunk using the process that, according to the 1997 conference paper 'Artificial Reefs in British Columbia, Canada' by Jones and Welsford presented at OCEANS '97 MTS/IEEE in Halifax, NS, takes at least seven months, corresponding to approximately 75 person-months of volunteer time. Currently, the Saskatchewan rests upright at depths of 24 to 40 meters, becoming one of the most popular dive spots in British Columbia, according to local dive companies like Nanaimo Dive Outfitters.

Why sunken ships attract marine life


The logic behind reefing a ship is straightforward: bare steel placed on an otherwise soft or featureless seabed gives marine organisms a hard, stable surface to settle on, something the Strait of Georgia's silty bottom rarely offers on its own. Over time, filter feeders, anemones, sponges and mobile species such as rockfish and lingcod move in, layer by layer, until the wreck functions as a self-sustaining habitat rather than a static piece of scrap metal. That basic premise, though, doesn't mean an artificial reef behaves exactly like a natural one. This is where more rigorous, quantitative research becomes useful.

What regional research shows about artificial versus natural reefs

The following peer-reviewed study conducted in BC is titled ‘Differences in fish communities on natural versus artificial temperate reefs, groundfish conservation applications in British Columbia’. It was written by Bulger, Volpe and Fisher and published in Marine Environmental Research in 2019. The study involved ROV and sonar surveys of 18 reef sites, 9 artificial and 9 natural, located off the south coast of BC. The authors noted significant differences in the communities' composition in the reefs and concluded that artificial reefs demonstrate much higher variability in terms of rockfish abundance than natural reefs. Namely, the number of rockfish in artificial reefs may be exceptionally large in some cases and exceptionally small in other instances, while the number of rockfish in natural reefs remains fairly moderate and predictable. In addition, the authors concluded that total diversity of groundfish is significantly higher in natural reefs than in artificial reefs. Depth and structural relief turned out to be the best predictors of the abundance and species richness for all surveyed reefs.

As stated in the same study, supplemented by an additional graduate thesis on the subject matter, another important point of consideration that needs to be added in terms of the design of marine conservation initiatives is that artificial reefs have such a diverse performance in terms of their physical structure that shipwrecks, such as the Saskatchewan, cannot simply be assumed to be ecological equivalents of a natural reef located near them, even if they have been submerged for decades, as explained in Bulger’s 2019 MSc thesis at the University of Victoria.

Reading the Saskatchewan through that lens

Considering the findings with respect to the particular case of the Saskatchewan, they provide insight into what divers see for themselves: an abundance of plumose anemones, cloud sponges and rockfish schooling on a wreck which is, however, clearly distinguished by its species and density from the natural rocky reefs in the immediate vicinity. It should be noted that, as for the depth, around 24 to 40 meters and the height of the superstructure of the wreck, they do coincide with the structural parameters described in the above-mentioned study.

The broader case for reefing programs

Since 1991, 35 years ago now, the ARSBC has used this same preparation process to sink a series of ships into BC coastal waters, including HMCS Chaudière, HMCS Mackenzie, HMCS Columbia, and HMCS Cape Breton, along with the decommissioned Boeing 737 at 27 meters depth. The project appears aimed at creating artificial marine habitat that will reduce diver pressure on natural reef ecosystems. That's a plausible rationale: there is evidence that artificial structures provide greater habitat area, though not necessarily the same community composition found on natural reefs. The Saskatchewan's second career, anchoring a long-running study of marine colonization off the coast, may prove just as significant as its three decades of service defending Canadian waters.