FISH STORIES

Redside Shiners – flying fish and flood riders?

One April day as I was walking east from the Seward Park clay studio, I saw a boy splashing in the water clearly trying to grab something. I aimed my binoculars to see what he was hunting and was immediately confronted with a writhing swarm of fish all spawning in the gravel. The yellow lateral line and bright red ventral markings, especially behind and below the head seemed distinctive, and with a list of fish found in Lake Washington to narrow the choices and the aid of a field guide, they allowed me to identify the fish as redside shiners (Richardsonius balteatus).

These smallish (up to 7”) members of the carp and minnow family (cyprinids) are not considered to be game fish and consequently are not widely known. They congregate in large schools near vegetated shores of lakes, ponds, headwaters, and slow-moving parts of rivers or streams, where they feed on plankton, invertebrates, algae, eggs and even small fish. They are in turn preyed on by trout, mergansers, loons, and others. The females lay unguarded, adhesive eggs from late April through July that attach to gravel or plants and hatch in 3-7 days (at 21^◦C).

Redside shiners occur across the Pacific Northwest, notably throughout in the large Columbia-Snake River drainage that encompasses eastern Washington, most of Oregon and Idaho, and parts of British Columbia. It therefore doesn’t seem surprising that these fish should also live in Lake Washington, but how exactly did they get here? During the Pleistocene 15,000 years ago Lake Washington lay under 3000 feet of ice, and had only frozen fish, if any. Then after the ice melted some 13,000 years ago, Lake Washington was an arm of Puget Sound before the growth of the Cedar River delta separated it from the sea and allowed the salt to be flushed out.

Salmon and other anadromous fish presumably entered the newly freshwater Lake Washington from the ocean as they do today, but in an age when fish move easily around the globe with the help of humans, hatcheries and helicopters, it is easy to forget the difficulties that freshwater fish like redside shiners face in moving from one drainage to another. Indeed, the occurrence of only about 200 species of freshwater fish in the entirety of Canada (fewer species than occur in states like Kentucky or Georgia) is attributed to the slow progress of fish species in crossing drainage boundaries after the vast Laurentide ice sheet that covered most of Canada melted away over several thousand years.

How do freshwater fish ‘jump’ or ‘fly’ between drainages? In rare cases, winds in the form of tornados or waterspouts have been known to lift up live fish from one location and deposit them in another. Another form of aerial transport that is frequently invoked for dispersal of aquatic plants and invertebrates and that might also apply to fish eggs is hitchhiking on migratory waterfowl. While this seems like a plausible transport method, there is surprisingly little direct evidence for it, and as a general mechanism it is constrained by the abilities of different eggs to resist desiccation, by distances between favorable habitats, and by usage patterns of local flyways.

A different method of freshwater fish dispersal is by changes in the drainages themselves. For example, in the 19^th century, the White River merged with the Green River in Auburn and then joined the Black River flowing out of Lake Washington in Tukwila to form the Duwamish River that empties into Elliott Bay. After a flood in 1906, however, the White River was diverted away from the Green and into Stuck Creek, where it now flows into the Puyallup River and out to Commencement Bay. Any fish present in the upper White River during this switch were moved from the Duwamish drainage to the Puyallup drainage, and could spread through the Puyallup drainage while their relatives still populated the Duwamish drainage. This particular switch of the White River is thought to have occurred multiple times, and so might have served to shuttle fish species in both directions. Similar drainage changes were probably frequent as the glacial ice melted, and may have helped the spread of fish species in the wake of the retreating ice. In particular, large lakes formed from meltwater in front of the glacier and may have served to connect adjacent drainages.

As glacial ice melted, redside shiners in the Columbia-Snake River system probably spread north along the Okanagan, Columbia, Kootenai, and Flathead Rivers into Canada. Whatever the method of ‘jumping’ between drainages, they ‘jumped’ to the coastal slope drainages of Puget Sound and into the Fraser River drainage. Moving along the Fraser into central British Columbia, the redsides ‘jumped’ into the Peace River drainage and followed it into northwest Alberta, all in less than 13,000 years. The Peace River drains to the Arctic Ocean, but additional northward expansion may be limited by cold temperatures. Global warming could lead to the redsides’ further northward migration.

Redside shiners also occur as far south as southern Utah, distributed through the eastern half of the Great Basin in now separate drainages that during the Pleistocene were all part of Lake Bonneville, the enormous freshwater ancestor of the Great Salt Lake that once covered almost all of western Utah. A comparable large lake, Lake Lahontan, filled the western half of the Great Basin in Nevada. The redside shiner’s only close relative, the Lahontan redside (Richardsonius egregius), occupies drainages that once were part of Lake Lahontan. Both the Bonneville and Lahontan Basins have remained largely isolated from the Columbia-Snake and other river systems for probably six million years.

The occurrence of the two redside species in the Great Basin raises the possibility that their common ancestor also evolved in the Great Basin. In this case, one would imagine that redside shiners spread from Lake Bonneville into the Columbia-Snake system after their isolation from their Lahontan relatives. In fact, a famous drainage change that moved fish from Lake Bonneville to the Snake River occurred some 14,500 years ago when the Bonneville shoreline eroded at Red Rock Pass in Idaho, resulting in the enormous Bonneville Flood that lowered Lake Bonneville by 300 feet in a matter of weeks and left its mark along the Snake River all through southern and western Idaho. Could redside shiners have first entered the Columbia-Snake drainage by riding this massive flood alongside boulders the size of watermelons?

Alternatively, the ancestor of both species of redsides could have evolved in the Columbia-Snake system and ‘jumped’ into the Lahontan Basin long ago, perhaps in the vicinity of the Owyhee River, tributary of the Snake in southwest Idaho and northern Nevada. After divergence of the two redsides, the Columbia-Snake redside may have spread to the Bonneville Basin via the Bear River of southern Idaho and northern Utah, which switched from its ancestral drainage into the Snake to drainage into the Bonneville Basin some 50,000 years ago. The added water from the Bear River contributed an estimated one third of the water that filled Lake Bonneville. In this scenario, the Bonneville Flood would have returned redside shiners and other species that entered the Bonneville Basin from the Bear River back to their ancestral home in the Columbia-Snake drainage. These two scenarios could potentially be distinguished by testing to see whether genetic divergence, an indicator of age, is greater in the Bonneville Basin redside populations or in the Columbia-Snake populations.

The Lahontan redside has managed to ‘jump’ from the Lahontan Basin into the adjacent upper reaches of the Sacramento River drainage, probably in the Lake Tahoe or Honey Lake areas, but otherwise has remained isolated. Whatever the mechanisms of drainage jumping are, they seem to be particularly inefficient in the Great Basin. For example, isolation has led to the evolution of distinct subspecies of cutthroat trout in both the Lahontan and Bonneville Basins. Furthermore, the Great Basin states of Utah, Nevada, Idaho and Arizona each have fewer species of freshwater fish than any other state except Hawai’i, with its mere five species of locally evolved anadromous o’opu. The present aridity of the Great Basin no doubt contributes to the lack of freshwater fish dispersion by waterfowl or drainage changes, but even during the wet climate of the Pleistocene the Lahontan and Bonneville Basin remained relatively isolated from each other and adjoining basins, as evidenced by their unique fish species and subspecies.

In recent years, humans have transplanted redside shiners into the upper Colorado River system, leaving them with the potential to spread to the Gulf of California as well as to the Arctic Ocean. That’s not bad for a small fish that few have heard of, but it’s entirely in keeping with the whole cyprinid clan, the world’s largest family of fish, which has spread itself into freshwater habitats throughout Eurasia, Africa and North America.