Wednesday, May 8, 2019

Fish Scales and American Shad

american shad It’s tempting to simply view fish scales as armor, but there’s more to them than that. They provide camouflage; they also play a role in locomotion. For scientists working on the recovery of American Shad in the Connecticut River, scales provide a record of a fish’s life history and a way to measure the success of restoration efforts.

American shad is our largest river herring. The males, called bucks, run up to six pounds. The females, or row shad, up to four. Like their cousins alewife and blue-backed herring, shad are anadromous, spending most of the year in the ocean, then running up fresh water rivers like the Connecticut in spring to spawn.

Shad have large silver scales – all the river herring do. The silver reflects the surrounding environment and allows the schooling fish to become nearly invisible to predators, sort of like that invisible car in the James Bond film. A quick shift in direction becomes a game of “Now you see us, now you don’t.”

For migratory fish like the river herring, the less obvious but no less important role of scales is their function as part of a fish’s lateral line system. A fish is a delicate sensing device, like a swimming antenna. The lateral line is a system of sensors and channels that run across the fishes’ head and body, controlled by the arrangement of the scales and the microscopic hairs between them that respond to flow, turning mechanical motion into electric signals. Fish are said to be able to detect earthquakes before the most sensitive of human inventions. It’s the lateral line that shapes fish behavior, whether that fish is an ambush predator like northern pike or a fish like American shad that has to navigate fishways, falls, changeable flows from dams, and hot water plumes from nuclear power plants to spawn.

Shad seem made for long distance travel. The 18- to 22-inch body is ovoid in profile, a small head with an expansive back and wide sides that slim down to a narrow, deeply forked tail. Shad: one big muscle with just enough room for the stores of fat needed to make the spawning journey.

There’s beauty in that economy. Scale patterns have been described as fractals: objects of “expanding symmetry.” Shad scale patterns bring to mind the art of the ancient Chinese, say from the Ming Dynasty, or a classic Zen fish you might see in an art store window. Functional beauty. You can see them migrating past the window at the Vernon Dam fish ladder, powering like pale green ghosts through the roil and bubbles on their way upstream to Bellows Falls.

Unfortunately, river herring populations across their northeastern range have been severely reduced. Dams, power plants, and habitat loss are all factors. Only about 5-10 percent of the shad that make it as far Holyoke, Massachusetts (measured in the hundreds of thousands, but down from three to five million historically) make it to Vernon. But there’s hope. With some changes to the fishways and flows on the Connecticut, we could see huge increases in river herring in the Connecticut River over the coming decades.

I spoke last summer with Ken Sprangle, a fisheries biologist with US Fish and Wildlife Service who’s in charge of protecting and restoring migratory fishes in the Connecticut River Watershed. Sprangle described analyzing about 1,300 shad in the lab annually. He records fish age by looking at otoliths – ear bones. He also looks at scales. Scale analysis shows the number of times a fish has spawned. Shad typically return to the river to spawn after only one year in salt water, Sprangle said. Since shad can live up to ten years and spawn as many times, improving return rates and expanding upstream habitat by reducing the stress of migration and mortality, in both upstream and downstream trips, could have a profoundly positive effect on shad populations.

The challenges are great for shad, particularly at Turner’s Falls, Sprangle said. Here, the fish deal with both low-flow conditions and massive surges of water when the Northfield regenerating station discharges water. Three separate fish ladders divert shad from the stream’s natural channel into a mile-long canal, which is as far as many of them get.

An agreement could be negotiated in the course of the dam’s relicensing process that would replace the faulty fishway at Turners Falls. Meanwhile, we’re left to imagine what a half a million shad at Bellows Falls might look like.

Tim Traver writes about fish and wildlife issues from his home in Taftsville, Vermont. The illustration for this column was drawn by Adelaide Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation.

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One Response

  1. Bill Waterhouse says:

    Thanks for the article Tim. I lived in Turners Falls and have visited the fish ladder many times, and can tell you may have never been to this funky little village. I’ve explored the area in and around the dam/falls numerous times. I’m a bit confused by the mention of three fish ladders – I’ve only seen one at TF, and it allowed mostly shad and lampreys to navigate from the natural channel below the dam to above the dam, circumnavigating the power canal. When the ladder is running, it is quite an interesting engineering feat. Unless I’m totally missing something, this ladder allows aquatic fish to continue upstream, not into the canal. Maybe the three ladders you’re referring to include all fish ladders/bucket lifts on the Connecticut (Holyoke/Turners/Vernon?)?

    I’m not sure of the number of tributaries between Holyoke and Vernon, but one major river that intersects with the Connecticut is the Deerfield river. I have canoed up the Deerfield during migration, and the Deerfield is full of shad and lamprey. Another tributary is at French King Bridge. Would be interesting to find out what percentage of shad go to tributaries before Vernon.

    The Northfield Mountain regeneration plant actually causes the Connecticut to REVERSE during night time hours, as it sucks river water up to the mountaintop reservoir. Of all the concerns I’ve heard about the migratory fish and Turners Dam/Power Canal/Northfield Mountain, this is the one that is constantly discussed. The fish get confused, as upstream is now downstream. If you travel the Connecticut above the dam, you see logs set in the banks all the way to Northfield MA. The erosion from reversing the flow has a detrimental effect on this slow moving part of the Connecticut. What should be a nice rest for the fish must turn into a confusing nightmare at night. I can’t comment on the pump filters, if they are sucking up fish along with the water, something to explore. The discharge of water occurs during the day when electricity demand is highest. The fish ladder is open every day during migration, and the fish have no issues with the flow because the dam regulates how much goes over the Falls and power canal. The fish ladder flow is greatly increased after a rainstorm, and the water is muddied enough that the viewing station is hardly worth a visit. The daily release from Northfield is minute compared to a good rainstorm near Turners or from up your way in Vermont.

    I can understand the low-flow issue, although the article’s description can be confusing for someone who has never seen the power canal, dam and fish ladder. If the Connecticut hasn’t had rain to keep flow going over the dam, all water is diverted to the power canal. (This doesn’t happen often, as most days one or more of the dam’s “locks” are down and allowing water to flow over the dam). Remember, this is downstream flow. Shad and other fish are coming up the natural channel, which now has little to no flow because of the complete diversion to the power canal. And who knows what happens at night during low flow and Northfield Mountain sucking even more out above the dam. Thank you for this, as I hadn’t thought about how this may have affected migration. And again, the fish are always in the natural channel, unless of course they take a wrong turn after the fish ladder and end up in the power canal.

    I would suggest a trip to Turners Falls to see how this all works. The fish ladder opens soon, and is a beautiful facility. Walk across a bridge that looks like it’s about to fall into the canal (right by the Great Falls Discovery Center) over to where the fish ladder comes up from just below the falls. You’ll see the fish do not go into the power canal. Bring along a canoe or kayak and paddle both upstream from the dam (launch just off Rt. 2 past the Wagon Wheel) and downstream from the power canal (drop in where the Deerfield and Connecticut converge). Here you’ll see how the fish could be affected by flow. And if you paddle far enough up from the dam, you’ll see the intake gates for Northfield Mountain, and all the ugly erosion logs, just before a really neat leanto.

    I am with you on your last sentence, and hope we both live long enough to see that many shad in another funky cool town, Bellows Falls.

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