If you have not already read last two week's posts, What's the Neighborhood Like? The Importance of Connectivity in Stream Networks and Sources, Sinks, and Population Regulation: Neighborhoods, part II, I suggest starting there. Those posts are the ecological background that informs the applications that I will talk about in this post possible. They were also some fun strolls down memory lane (for me at least...). This post will apply lessons from those posts and bring us back to the future.
What I enjoy so much about this topic is that it is a great example of how basic science (ecology) informs management decisions (application). As we started to better understand the science behind why connectivity matters, through theory but also through field studies; we are better able to determine how to use that basic science to help inform our management decisions - and have confidence that the resources will be effectively used. The bit of ecology that really fueled the role of dispersal and connectivity was the equilibrium theory of island biogeography.
Island Biogeography and Habitat Fragmentation
MacArthur and Wilson's theory is that the number of species is dependent upon the island size (probability of extinction) and the distance from a mainland (the ability / likelihood of dispersal). And as science does, it ran with this idea and applied it to patches in a heterogeneous landscape and to populations that occur in different patches and furthered the science of patch dynamics. And from this science came much of the applications of conservation biology.
Figure from Islandbiogeography.org, the relationship between distance from a mainland and the size of the island. For a much more detailed view of the idea, visit that website.
Habitat fragmentation, to carve large, intact habitats into smaller, more dispersed island-like patches is one of the greatest conservation biology challenges we face as it is so pervasive on the landscape. We see habitat fragmentation all around us - our once vast forests, prairies, and savannas into remnant forests, prairies and savannas. And we see globally important places - like the Amazon rainforest - becoming increasingly fragmented. As island biogeography predicts, the creation of smaller patches ("islands") results in a loss of some species. Many specialist species - Giant Pandas, Koalas, and Ivory-Billed Woodpeckers, to name a few - have evolved over huge time frames to require these large intact and as we fragmented their habitats, they became less common or were driven to extinction. And species that thrive in smaller patches and along the ecotones (edges between different habitat types) - White-tailed Deer, Raccoons, and many of our most common species today - have been become much more common compared to their pre-European settlement populations.
Streams - being linear habitats - and fishes requiring water; makes the fragmentation of streams particularly impactful. Fish dispersal and their ability to access spawning, refugia, and foraging habitats are critical for their long-term success. We have done a lot to disrupt fishes' ability to disperse through their environment by building dams, poorly designed bridges and culverts, and other infrastructure. Additionally, as we degrade streams through pollution, things that simplify channels (channelization, removal of large woody debris), and other things (pollution, water withdrawals) that make parts of the travel corridor less hospitable for fishes. For example, a stream that has a long channelized section may deter fish movement and effectively fragment the stream despite there being no physical barrier to dispersal. Or as I looked at in my dissertation, acid mine drainage fragmented streams by making some stream reaches inhospitable to some or all fishes.
Reconnecting Streams
Reconnecting streams has received a ton of attention, rightfully so as it is one of the largest "bang for the buck" conservation tools we have to restore streams and fish populations. Wisconsin has been a leader in dam removal, having removed over 900 dams, many of which have outlived their original purpose and became unsafe. But many have been removed primarily for ecological reasons. And the results have been quite staggering. Warmwater rivers such as the Baraboo and Milwaukee rivers have seen great increases in fish diversity and improved IBI scores from dam. In coldwater streams, dam removal has the additional benefit of reducing water temperatures.
And it is not just dams that fragment streams but a number of other barriers, most of them man-made that have similar effects. It is estimated that there are over 6.6 million road/stream crossings in the United States (USGS) and they range from those that present no fish passage issues to complete barriers that allow no passage and fragment the stream. It is probably important to note that many of these barriers are seasonal and/or selective barriers (some fishes get through, others do not). As I had written about in part 2, it is amazing how fishes will spawn in some unbelievably small streams. And as I had written about in part 1, overwintering refugia often occurs in "non-trout streams" (e.g. Meyers et al. 1992). Reconnecting streams opens up both of these habitats - and many others - to fishes.
And those reading this certainly care about the fish crossing part of the equation but probably just as importantly as restoring fish populations by allowing fishes to access more of the watershed, is allowing the passage of floods, organic debris (trees!), and sediments to pass. Bridges and culverts are the most expensive features of most roads so they tend to be build as inexpensively as possible which means they are often undersized. This means that they are less effective at passing floods and sediments which has increased in importance as climate change has increased the number and severity of large storm events and floods. While we all care about the fishes, it may surprise you not everyone does...but they care about money and having roads that are not closed due to bridges being out. Most of today's post will highlight work in northern Wisconsin but a more local example of this is that the bridge over Reads Creek on county highway JJ recently opened after being closed for nearly two years after a flood damaged it and twice in the less than four years has the bridge at Bloomingdale on West Fork of the Kickapoo had o have had its approaches blown out by floods.
Trout Unlimited Fish Passage Program in Wisconsin
Trout Unlimited in Wisconsin has partnered with a number of non-profit and governmental agencies to restore trout through fish (and flood and sediment) passage projects. Recently, I had a chance to do a Zoom call with Chris Collier, Great Lakes Stream Restoration Manager, and talk about the work he and TU are doing in the Great Lakes. Above, I did not include a lot of specific details about the effects of passage so let's do so here. Since 2017, there have been 38 passage projects that have reconnected over 135 miles of streams in the Lake Michigan and Lake Superior watersheds. Chris estimates that there are tens of thousands of road crossings in the Wisconsin part of the Great Lakes watershed and 25% to 40% present some sort of passage issue. In other words, there are projects for years.
The results have been impressive - improved fisheries, better size structure, and all the other fish-based measure we all care about. But what I found most interesting is that when the Forest Service looked at the effects of a large flood in the area, nearly all of the improved crossings held up through the flood whereas nearly all of the unimproved crossings they surveyed had been greatly damaged by the same flood event. Simply put, it is not just fish passage but flood passage and it not only improves fisheries and recreational opportunities but it is an opportunity to save a significant amount of spending on infrastructure. Our infrastructure is generally in a pretty awful state of repair so projects like this - using "infrastructure dollars" and leveraging them with funds from other sources are an incredible "bang for the buck" strategy that all fits into the TU conservation strategy.
Like most management strategies, there is a lot of learning by doing and by assessing as you go. For example, PIT tags (passive integrated transponders) have been one method to assess how effective fish passage projects have been. PIT tags are individual marks and with PIT tag readers in place, researchers can assess the direction of movement. And PIT tags allow for rather simple before and after studies - tag fish before the project, give them time to move, complete the project, and compare the before and after upstream and downstream passages. Assessment is one of the keys to continuing to be able to fund projects - it shows they are working! Improved fish passage has resulted in more and larger trout by opening access to spawning and foraging habitats.
And the data are great but sometimes the anecdotes and stories are just as valuable. Experiences with deer, turtles, amphibians, and other animals using these improved passage corridors abound. Fish passage is always full of stories. Fishes - or at least some of them - often find a way, particularly in natural systems. I know in West Virginia, I was often quite amazed at the obstacles that fishes were able to traverse. Cascades that seemed impassible were often quite passable, as we saw from our visible implant elastomer (VIE) tagged fishes. Man-made barriers are often a different story in terms of passage. Chris shared an interesting story of one particular culvert that was highly corrugated and almost created a fish ladder - but only for trout that were large enough to swim through the current but small enough to fit between the corrugations. And that is often the story of barriers, they are "semi-permeable", some species and individuals may pass but others may not or there is passage downstream but not upstream. But again, it is not just about fish passage and the passage of floods and what they carry is just as important (maybe not to the angler - but they are).
Fish passage is not just fish passage - it helps pass floods and what they move as well. With climate change, our floods are getting larger and more frequent and eliminating barriers is not just good for the fishes but for our infrastructure and pocketbooks as well.
Links and Further Reading
Many thanks to Chris Collier for sharing his experiences and for the photographs.
Updated Jan. 18, 2023 to add the recent video by Trout Unlimited.