{"id":495,"date":"2016-06-14T05:37:38","date_gmt":"2016-06-14T05:37:38","guid":{"rendered":"http:\/\/habitat.fisheries.org\/?p=495"},"modified":"2016-06-14T05:37:38","modified_gmt":"2016-06-14T05:37:38","slug":"intentional-river-fragmentation-can-it-be-a-good-thing-for-fish","status":"publish","type":"post","link":"https:\/\/units.fisheries.org\/habitat\/intentional-river-fragmentation-can-it-be-a-good-thing-for-fish\/","title":{"rendered":"Intentional River Fragmentation: Can It Be a Good Thing for Fish?"},"content":{"rendered":"

\u201cWe\u2019ve spent years convincing the public of the need to maintain connectivity in aquatic systems.\u00a0 Now the challenge is to explain why there are exceptions to that paradigm.\u201d<\/em>\u00a0 – F. Rahel<\/p>\n

This quote reflects a unique but relevant perspective in fisheries management, as dam removal has been increasingly championed in recent years as a necessary approach for helping migratory fish populations.\u00a0 Dam removal can be crucial for these populations by increasing connectivity to river habitat for spawning and rearing, habitat that was historically available before humans arrived on the scene.\u00a0 Accordingly, large-scale dam removals in the United States have been accelerating; the San Clemente Dam (California), Elwha and Glines Canyon Dams (Washington), and Veazie Dam (Maine) were removed just within the last five years.\u00a0 Encouragingly, migratory fish populations have shown quick responses in migrating upstream and utilizing previously unavailable habitat once these barriers are removed.<\/p>\n

While there\u2019s no doubt that restoring river connectivity can be hugely beneficial for migratory native species, can there also be cases where keeping dams is actually better for ecological systems?\u00a0 A recent publication by Rahel (2013) says yes, and argues that intentional fragmentation (the purposeful act of disrupting aquatic connectivity) can serve as a conservation tool in its own right.<\/p>\n

Rahel suggests there are four potential advantages to maintaining some degree of fragmentation in aquatic systems: (1) preventing the expansion of invasive species, (2) limiting the spread of disease, (3) maintaining the genetic purity of native fish populations, and (4) restricting fish from entering human-made ecological traps (e.g. irrigation channels).<\/p>\n

\"101.011_HR\"<\/a>
Spawning Great Lakes Sea Lamprey (T. Lawrence, GLFC)<\/figcaption><\/figure>\n

Focusing on the threat of invasive species, one characteristic common to these species is their rapid spread to new habitats and resulting disruption of existing biological communities.\u00a0 Intentional fragmentation, according to Rahel, can stop invasive species from ever reaching these new habitats in the first place.\u00a0 He notes that barriers have successfully blocked regionally-invasive Lake Trout, Common Carp, and Smallmouth Bass from accessing habitat occupied by vulnerable native species in states like Montana, Tennessee, and Arizona.<\/p>\n

Now, let\u2019s apply these small-scale examples to a practical case study of fisheries management on a regional scale: increasing connectivity in the Great Lakes\u2019 watersheds and the spread of Sea Lamprey and Asian carp (Bighead Carp and Silver Carp specifically).\u00a0 There is increasing pressure for dam removals in this region, in order to improve public safety, increase connectivity for migratory species, and restore natural river flow.\u00a0 However, the Sea Lamprey is a significant Great lakes invasive species that relies on these same streams for both spawning and larval habitat.\u00a0 Dams serve a crucial role in blocking upstream migrating lamprey spawners from accessing potential habitat, and are important enough to warrant a dedicated task force within the Great Lakes Fishery Commission\u2019s (GLFC) Sea Lamprey Control program.<\/p>\n

\"108.006_HR\"<\/a>
A Great Lakes dam designed to block upstream sea lamprey migration (M. Siefkes, GLFC)<\/figcaption><\/figure>\n

Asian carps are additional invasive species in the region; an electrical barrier in the Chicago Sanitary and Ship Canal is all that stands in the way of their Great Lakes invasion.\u00a0 If they do bypass this barrier, there\u2019s widespread concern that the fish species could dramatically disrupt the Lakes\u2019 food webs due to their high growth and\u00a0feeding rates. In this instance, dams on Great Lakes\u2019 rivers may end up becoming even more important in blocking both Asian carps and Sea Lamprey from accessing upstream habitat.<\/p>\n

In essence, dam removal decisions for the Great Lakes, or in any other region of the world, are all about evaluating trade-offs.\u00a0 In addition to the always pressing social and economic concerns, Rahel argues for explicit consideration of the biological costs and benefits in barrier removals, in which managers carefully consider ecological trade-offs, identify an optimal level of connectivity, and select management actions accordingly (see diagram below).<\/p>\n

\"Balancing<\/a>
Summary of trade-offs in making dam removal decisions (Adapted from Rahel 2013)<\/figcaption><\/figure>\n

Or, to put it more formally, \u201cthe relative value of the connectivity versus the fragmentation of aquatic habitats needs to be evaluated on a case-by-case basis, through which the beneficial effects\u2026are weighed against the potential detrimental effects on the movement patterns of native species\u201d.<\/p>\n

Reference<\/em><\/p>\n

Rahel, F.J. 2013. Intentional fragmentation as a management strategy in aquatic systems. BioScience<\/em> 63: 362-372.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

\u201cWe\u2019ve spent years convincing the public of the need to maintain connectivity in aquatic systems.\u00a0 Now the challenge is to explain why there are exceptions to that paradigm.\u201d\u00a0 – F. […]<\/p>\n","protected":false},"author":2,"featured_media":498,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[76],"tags":[],"class_list":["post-495","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research-brief"],"acf":[],"_links":{"self":[{"href":"https:\/\/units.fisheries.org\/habitat\/wp-json\/wp\/v2\/posts\/495","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/units.fisheries.org\/habitat\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/units.fisheries.org\/habitat\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/units.fisheries.org\/habitat\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/units.fisheries.org\/habitat\/wp-json\/wp\/v2\/comments?post=495"}],"version-history":[{"count":0,"href":"https:\/\/units.fisheries.org\/habitat\/wp-json\/wp\/v2\/posts\/495\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/units.fisheries.org\/habitat\/wp-json\/wp\/v2\/media\/498"}],"wp:attachment":[{"href":"https:\/\/units.fisheries.org\/habitat\/wp-json\/wp\/v2\/media?parent=495"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/units.fisheries.org\/habitat\/wp-json\/wp\/v2\/categories?post=495"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/units.fisheries.org\/habitat\/wp-json\/wp\/v2\/tags?post=495"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}