Anne Murray: From snakes to spawn, wildlife congregations show richness of local habitat

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      It is not uncommon to see eagles, seals, and salmon around the Lower Mainland, but some kinds of wildlife sightings can be more unusual. Often a species is virtually invisible in the wild until a surprising congregation occurs. This spring has seen two fascinating events on the shores of Boundary Bay in South Delta: an amazing gathering of garter snakes within the dyke, and a massive spawn of herring just offshore. Such phenomena illustrate the importance of the Fraser delta for a wide range of animals, and remind us that even if we do not commonly see them, many different species depend on these habitats.

      The 500 hibernating garter snakes were found when workers began shoring up the Boundary Bay dyke at Beach Grove in late February. Although the work crew had no idea the snakes were there until they started digging, the local schoolchildren knew of the den (hibernaculum) and raised the alarm. The snakes began to wake up once the rocks were moved, so they were taken by the bucketful to Burnaby’s Wildlife Rescue Association (WRA). The large number of snakes took everyone by surprise. It took a few days, but they were eventually all settled into cool, dark buckets lined with damp sawdust; some were tagged for later study. A month later, still in a state of hibernation and with the dyke work completed, they were released back to Boundary Bay on March 22. It is hoped that once the weather becomes warmer, they will wake up and disperse through the marsh habitat as normal. It is unfortunate that they were disturbed, and moving them was a risky strategy, but hopefully no lasting harm was caused.

      Garter snakes are an important small predator in the ecosystem. It is not uncommon to see one basking on the dyke in summer or moving secretively through the marsh grasses, but large congregations are unusual in the Lower Mainland. The ones in the hibernaculum were western terrestrial garter snakes (Thamnophis elegans), also known as western garter snakes, a species widely distributed in Western Canada. They were identified by a herpetologist, Professor Patrick Gregory of the University of Victoria, and he explained to me that garter snakes are very variable in colour and size, so they can be confusing for even experienced naturalists to identify. Typically, the western garter is greyish-brown with three paler-coloured stripes down its back. The stripes are broken by two rows of alternating, dark-coloured blotches, the top row of which invades the mid-dorsal stripe, giving it a variably wavy appearance. Yolanda Brooks at WRA mentioned that the snakes were different sizes. This is to be expected as females are larger than males, and snakes keep growing throughout their lives, with the rate of growth slowing with age.

      Western garter snakes are common in Fraser marshes, where they readily enter water, despite their “terrestrial” name. They consume a varied diet of slugs, earthworms, fish, frogs, nestling birds, and small mammals, and have a primitive constricting ability, sometimes coiling their bodies around mammal prey while biting them. Their saliva may be mildly poisonous. Live young are born between July and September and in fall the snakes cool and lower their metabolic rate, before entering a hibernaculum for the winter. According to Gregory, the Boundary Bay hibernaculum is much larger than average for our region, but in other areas of North America, winter dens of hundreds or thousands of garter snakes have been found.

      From snakes to spawn: nature’s congregations are often spectacular. The waters around the Tsawwassen-Point Roberts peninsula recently turned milky-white, as Pacific herring spawned in the eelgrass beds. Herring numbers are influenced by fishing levels and water conditions (e.g. temperature) and have fluctuated quite dramatically since the 1940s. Many people remember wonderful herring spawns along the west side of Boundary Bay from 1960 through to the late 1970s, which attracted thousands of birds into local waters every March. By the late 1980s, the spawning event had moved to other locations further north in the Strait of Georgia. The year by year changes in location and size of the annual spawn were very well-documented on the B.C. coast from 1930 onwards by the Department of Fisheries and Oceans, and there is a time-lapse map on their website. Recent years have seen more favourable environmental conditions in the water for herring and more controlled levels of fishing, though there is now also a lucrative roe (egg) fishery. As a consequence, herring populations seem to be on the rebound, and returned to spawn once again in Boundary Bay, attracting diving ducks, loons, grebes, and other birds. The spawning activity also spread to Roberts Bank eelgrass beds, on the west side of the Tsawwassen peninsula near the ferry terminal.

      As the fish deposit their roe on the fronds of native and Japanese eelgrass growing in the water, seals, sea lions, and hundreds of scoters and other waterbirds congregate around them, lured by the easy pickings. Shorelines are covered with the jelly-like roe, picked over by gulls and other birds, before they slowly dry out. Nature’s abundance is more than enough to feed the flocks, yet it is amazing that any eggs survive to adulthood.

      These two contrasting congregations, of snakes and herring roe, illustrate the wealth of our local habitats, on land and sea. Such sights are often marvelled over by local residents but can go unrecognized by wide-scale planners and developers, who too frequently consider the Fraser delta as a wasteland waiting to be urbanized. Yet for those with an interest, there is always something fascinating to observe down by the water.