Forage fish matters

This material is taken from an article written by Connie Haist that originally appeared in the summer 2016 newsletter of the Lasqueti Island Nature Conservancy (LINC). We are grateful to LINC for their permission to use this material on our website.

Small is beautiful and essential for life

Sunlight streaming into ocean waters is soaked up by phytoplankton, the living solar collectors of the sea. They use solar energy to convert carbon dioxide and water, through photosynthesis, into food that zooplankton graze upon. Phytoplankton and zooplankton (the smallest of marine animals) are tiny organisms that drift in huge numbers in the middle to upper levels of the ocean. Together, both kinds of plankton become a nutritious energy-rich superfood that fuels the whole web of marine life. Yet this food is unavailable to most marine mammals, seabirds, and large fish. So how is it transformed for their use?

An important group of small fish called “forage fish” have evolved to thrive on a diet of plankton. Forage fish form massive schools which are measured in metric tonnes. These dense schools of small fish are concentrated sources of fuel for larger marine predators: through their immense numbers, forage fish make the captured solar energy stored in plankton available to their predators. Uniquely, these forage fish are the energetic link between that vast nutritious biomass of plankton and fish eating seabirds, marine mammals, and the larger fish that we humans rely on for food.

Collectively, forage fish are also known as cornerstone species because they are the critical link between energy-rich plankton and the very survival of the hundreds of larger marine predators which forage on them.

Surf smelt and Pacific sand lance

Example forage fish species are: Surf smelt (Hypomesus pretiosus) and Pacific sand lance (Ammodytes hexapterus). They are drawn back year after year to spawn on coarse sand and gravel beaches around the Salish Sea. Thanks to marine biologist, Ramona de Graaf, and hundreds of volunteers, many spawning beaches are now being documented, but life cycle and biology of Surf smelt and Pacific sand lance is still largely unknown.

At maturity, both species of fish are about 20 cm. (8”) long. Surf smelt have olive green backs and silvery bellies while Pacific sand lance have reflective blue top sides and silver bottoms—the perfect camouflage from predators, both from above and below. Surf smelt have a typical fish shape while Pacific sand lance, also known as needlefish, have thin, elongated bodies. Our beach spawners have relatively short lives: up to 5 years for Surf smelt and 7 years for Pacific sand lance. Those that survive the hazards of life as a small fish will return every year to spawn.

Pacific sand lance are somewhat unique in their behaviour pattern, schooling and feeding in open water during the day. At night, they burrow into well-oxygenated, sub-tidal, sandy bottoms to avoid predation. During the winter, these little fish will lie dormant, hibernating in their burrows for long periods of time. Burrowing habitats are usually close to their feeding ground, and perhaps also their spawning grounds.

Scientists believe that Surf smelt in the open Pacific and those in Puget Sound are two separate stocks which evolved from the same ancestors living along the outer Pacific coast of North America. Around 13,000 years ago, as the thick ice of the Fraser Glaciation began to melt, ocean waters flooded into the Puget Sound area, bringing with it the sea life of the Pacific, including Surf smelt. Then, glacial events created conditions that restricted further influx of Surf smelt from the Pacific, cutting off the Puget Sound smelt. These two populations evolved so differently that now they do not mix. We do not know how our local Surf smelt are related to these two distinct populations in Washington State.

Spawning on the beaches

During the winter spawning season, from early November until late March, winter Surf smelt stocks arrive in the upper inter-tidal area. Individual female Surf smelt separate from the school and are followed by several males into the shallows to spawn, releasing eggs and milt and leaving small patches of fertilized eggs on the beach. It is likely that female Surf smelt will spawn several times in one season, laying thousands of eggs.

Pacific sand lance use a slightly different spawning strategy. Once a year, in the late fall and winter, when their biological alarm clock goes off, the whole school arrives in the shallow water over a spawning beach and together they churn up spawning pits. Here, the females all lay their thousands of eggs and the males release their milt. Otter Be Good Productions has made an interesting video with live footage of this phenomenon from a beach in Powell River.

The fertilized embryos of Pacific sand lance are just 0.5 mm in size, while Surf smelt embryos are a whopping 1.0 mm in diameter. Both are easily overlooked on the beach. Surf smelt eggs come equipped with a suction cup which allows them to tightly adhere to beach pebbles. Pacific sand lance eggs are sticky and sand quickly coats the eggs making them invisible and heavy. Anchored to beach substrates, wave action helps to cover the fertilized embryos with a protective layer of sand and gravel. While some drift is inevitable, embryos of both species are usually found buried just below the surface in the substrate, between 2 and 4 metres below the high tide line. Here, they stay moist and ride out our winter storms for their 4 weeks or more of incubation. Embryo survival is improved by the presence of overhanging shade on the beach and the lack of human disturbance.

Newly hatched larval Surf smelt and Pacific sand lance, pulled by the tides, currents and storms, drift and feed in the rich, plankton-laden surface waters throughout the Salish Sea. As juveniles, young fish rear in protected bays, inlets and estuaries. Pacific sand lance adults form vast schools feeding throughout the water column while adult Surf smelt tend to stay closer to shoreline or benthic habitats, feeding at depths of no more than 30-50 metres.

Forage fish are important!

What we know about the populations of BC’s Surf smelt and Pacific sand lance: in 1904, at the peak of the commercial harvest, 230 metric tonnes of Surf smelt were caught in B.C. The commercial harvest reported for 2002 was a mere 710 kg. No reporting is required for recreational harvesting, although it may exceed the commercial fishery and is perhaps the reason for the local Burrard Inlet stock being driven to perilous low numbers. Because there has been an unlimited and unreported catch for many years, and no recent stock assessments have been done, no one knows how many Surf smelt live in BC waters. No stock assessments have ever been done for Pacific sand lance in BC, and there is no commercial fishery in Canada at this time. However, this species is a common by-catch during commercial trawling. Numerous fish, seabird, and marine mammal populations are in precipitous decline in BC and scientists have started to look at the link between forage fish biomass reduction and these declining populations.

While we know little about the dietary needs of most marine animals, we do know that Pacific sand lance make up 35% of juvenile salmon diets, a critically important food for these young fish. With all of the human resources we have invested in restoring salmon habitat in the watersheds of the Salish Sea, we also need to be mindful that our coastal beaches are important to salmon survival, because our beach spawning forage fish provide that critical link between energy rich plankton and energy hungry salmon, sea mammals, sea birds and people.

These little, unassuming forage fish are the most important fish in our ocean waters. Their spawning beaches scattered around the Salish Sea are particularly sensitive, and we should strive to leave them undisturbed and pollution free.