Do Not Pass Go: The Failed Promise of Fish Ladders

Lori Pottinger
Tuesday, March 19, 2013

New research reveals that fish-passage facilities at US Atlantic Coast mainstem dams don't work at maintaining healthy runs of migrating species. We asked the lead scientist, Jed Brown, about his team's findings.

WRR: Your research found that the actual numbers of fish who make it to their spawning grounds above dams with fish passages is a small fraction of targeted goals of these facilities. What has been the impact on fisheries for the rivers you studied?

a complex fish ladder is intended to lead anadromous fish up the John Day Dam on the Columbia River in the US Northwest. The fish that do make it up the ladder face deadly conditions in the reservoir.
A complex fish ladder is intended to lead anadromous fish up the John Day Dam on the Columbia River in the US Northwest. The fish that do make it up the ladder face deadly conditions in the reservoir.
Photo by USACE

JB: In the river systems we examined, very few of the fish species that migrate from the sea to rivers to spawn (anadromous fish species) that are targeted for restoration actually make it to their historical spawning grounds. For example, for American shad – an important species for commercial and recreational fisheries that sustained generations on the East coast of the US – on average about only 3% percent of the fish that pass the first fishway make it past the last dam with a fishway in these rivers. Another example is that species such as Atlantic sturgeon cannot pass fish ladders—so for certain species, fishways do not work at all. Thus, in these systems, effective up and down stream passage is not being provided for anadromous fish. The result is that these species are getting listed as endangered or threatened one by one.

Limiting the ability of fish to reach their spawning grounds (and also to return back downriver) means that many fish won’t be able to spawn in high quality habitat, which can result in lower numbers of juvenile fish. Loss of entire populations resulted from the original large dams constructed in the 1800s, and since then there has only been very limited success in maintaining the few runs that have persisted. Atlantic salmon on the Connecticut River are a clear example, where a few remained in 1808 and none by 1820. Since the late 1960s a hatchery program has attempted to restore them to the Connecticut, but the program was halted this past year. The lost species represent links between freshwater and marine systems, and have historically been economically important.

The rivers in our analysis exemplify the coast-wide problem of declining anadromous fish populations. Unfortunately, goals set by federal agencies for the number of fish passing each dam are not being approached. There does not appear to be much consequence for these failures, where a private industry is responsible for harming a public resource. We wish there was better oversight, enforcement and expectations placed on hydropower companies. There may be some changes here as federal agencies such as the US Fish and Wildlife Service move toward a policy on fish passages based on actual fish passage results rather than fishway design. In other words, dam owners may be required to demonstrate that they passed X number of fish, rather than just complying with a requirement that they build a fishway.

WRR: You looked at mainstem dams on three major river systems in the US Northeast. Has other research elsewhere found similar results? How widespread is the problem in your estimation?

JB: In the US, the mainstem of the Delaware River is undammed, but some of the major tributaries which are dammed also have problems passing shad through fishways. Research out of Brazil has found that there are a lot of problems with fish ladders on large dammed rivers in Brazil. They have been called ecological traps by Brazilian researchers, because fish ladders transport fish in one direction in the river and this had led to local declines in other areas of these rivers. In Europe as well, low passage efficiency through fishways is common. In Sweden, this is now considered a critical issue in the survival of native Atlantic salmon.

WRR: Your study states: “It may be time to admit failure of fish passage and hatchery-based restoration programs and acknowledge that ecologically and economically significant diadromous species restoration is not possible without dam removals.” Can you elaborate on this a bit?

JB: Dams cause dramatic change to rivers and fisheries. At best they slow down migrations to spawning grounds, even where fishways work to some degree. They create still water behind dams that confuses migrating fish and these standing waters increase water temperatures, which may be unsuitable for juvenile fish. They also prohibit or reduce movements of other fish and invertebrates, altering a river’s normal ecology. Ecologists call it a loss of “connectivity.” In the case of migratory fishes, dams have resulted in a loss of connectivity between inland and marine chains of ecological production. It appears that adding fishways and hatchery programs is not sufficient to restore anadromous fish populations to pre-dam levels. Because a wide variety of other factors are impacting river fisheries –including climate change, overfishing, and habitat degradation – we cannot guarantee that dam removal will fully restore these migrating fish populations. That said, we do not believe that meaningful anadromous fish restoration will occur with the dams in place.  

Our study focused on the large mainstem dams. In small coastal rivers and tributaries, in cases where dam owners or communities are not willing to remove a dam, there is some evidence that fish ladders may benefit alewife (a species of river herring). However, even past success with a species does not guarantee the effectiveness of a new fishway project.

WRR: What are key lessons learned from your research that would be relevant for other dam-building nations with significant migrating fish populations?

JB: Don’t be lulled into thinking you can build dams and still sustain anywhere near normal-sized runs of migratory fish. Don’t assume you can remediate the impact of the dam with fish ladders and hatcheries to produce fish – it may not work, and even if some fish pass the dams, their numbers may be far below targeted levels (and targeted levels often are well below original estimated numbers). Once you go down the path of dam building, it may not be possible to go back to pre-dam fish population levels.

WRR: Why should people care about this issue? Why are migrating fish something we should be worried about?

JB: Migrating fish are an integral part of the natural ecology and the culture of many of the world’s rivers. In the Northeastern US, rivers once “ran silver” with the bodies of these fish, providing both abundant food and a remarkable natural spectacle. A lot of public money has gone into these restoration programs for staff, hatcheries, etc., with poor results. Smaller anadromous fish such as river herring are a prey source for important recreational fish species like striped bass and commercial species like cod.

We hope that one day these rivers will once again “run silver” with fish and that humans will once again make a cultural connection with this resource. However, this may not happen without dam removal.