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An aerial view of the Fraser River Delta.

Few cities in the world can claim the kind of wild backdrop that Metro Vancouver has.

The Fraser River estuary is a globally important zone of biodiversity with 17,000 hectares of rich wetlands used annually by 1.4 million migratory birds and 2 billion juvenile salmon. The area's importance was recognized in 2012 under the Convention on Wetlands of International Importance.

The estuary, which spreads along the shorelines of Delta, Richmond and Vancouver, is a remarkable natural treasure that deserves the highest level of protection a government can provide. Unfortunately, a new study shows that the Fraser estuary is slowly being eroded by development despite a 30-year-old federal policy that has sought to protect the area from any net loss of habitat by requiring developers to replace any that are destroyed.

A paper recently published by the Community Mapping Network (CMN) looked at a large sample of the 151 habitat-compensation projects completed over nearly three decades. It found that most of the projects had failed to achieve the goals set by government.

"The findings from this study indicate that only one-third of sampled marsh habitat compensation projects created between 1983 and 2010 are acceptably compensating for habitat losses; and that several riparian habitat compensation projects from this same time period had significant deficiencies," state the authors.

The study found that replacement marshes were often over-run with invasive plants, and that other projects along the shorelines "failed to resemble natural riparian environments in their structure, function and connectivity to the aquatic environment."

In other words, for the past three decades, developers have been carving up prime wetlands and replacing them mostly with something of lesser value, while the government has been claiming no net loss of habitat.

The federal government adopted the no-net-loss policy in the mid-1980s. Under the regulations, a developer could destroy a marsh to build a dock only if it replaced that lost habitat by creating another marsh nearby.

"No net loss" has been the guiding principle of habitat management across Canada, and it is used often to mitigate the environmental impact of everything from pipelines to port developments. But the CMN researchers found that often there was no follow-through on the compensation projects.

Replacement marshes were plunked down in the estuary and then, after a few years, largely forgotten. Sometimes the marshes were promised but never built.

The study does not calculate how much habitat has been lost, largely because over the years inconsistent methods of measurement were used. Some projects were measured in linear metres, some in square meters, and sometimes those measurements were mixed up, making it uncertain just how much new habitat was involved.

What the researchers were sure of is that when they looked at the compensation habitat, they found a lot of it was inferior to the natural habitat it replaced. Seventy-four per cent of the compensation sites had fewer trees, for example, a mean of 157 per hectare compared to a reference site that had 733 trees per hectare.

And some supposedly "wild" sites were being groomed, with "large spaces of manicured lawn" and trees trimmed to maintain sight lines. "Very few sites had wide areas of vegetation resembling a natural riparian habitat," the report says.

Vital wildlife habitat in the Fraser estuary is being managed so it looks nice to people, not for the survival of wildlife.

The study, intended as a guide for habitat compensation managers, recommends a more adaptive approach and longer-term monitoring so that adjustments can be made to better ensure there really is no net loss.

But the paper warns that even with such changes "uncertainty remains as to whether the current compensation framework is effective at recreating all elements of habitat lost."

That is a sobering caution on the Fraser River delta, a globally important biodiversity hot spot, where the federal government is considering whether to approve expansion of Roberts Bank Terminal 2. The proposed new container port would encroach on mud flats used by 100,000 migrating western sandpipers. That is vital habitat, and it is hard to see how that project can go ahead when the report makes it clear that "no net loss" is largely a myth.