May 21st is World Fish Migration day! It is a one-day global initiative to educate people about the importance of global fish migrations. The first ever World Fish Migration Day (WFMD) was held in 2014 and was largely successful. This year, we continue to reach out to the public to share the marvel of fish migrations and demonstrate the value of this behavior. As an ecologist studying a fish migration, I think they are a big deal. But humans have been taking advantage of these annual migrations since the dawn of civilization.
The Types of Migration
There are two main modes of annual fish migrations: fish that migrate from the ocean to freshwater, and fish that migrate from freshwater to the ocean. The general term that applies to all fish that migrate through rivers to spawn is diadromous fishes (to be clear, many species of fish migrate on a regular basis from one area of ocean to another. However, these migrations are not the focus of WFMD or this post because these migrations are not profoundly impacted by humans the way fish that migrate from oceans to rivers and vice versa are).
Most diadromous fish would fall into the category of anadromous, or fish that spend most of their adult life in the ocean, but come into freshwater to spawn. Salmon are the most famous example of anadromous fish with herring, striped bass, and sturgeon joining their ranks. The flip side of this strategy is catadromous fish which spend the majority of their life in freshwater but migrate into the ocean to spawn. Eels are the primary example of catadromous fish. Thanks to their highly predictable natural spawning migrations, anadromous fish like salmon or herring leave the large ocean where they are very difficult to catch and come right to our backyard in highly concentrated numbers. Because anadromous fish have proven extremely easy to catch relative to many other fish species, they have been a staple to human diets for centuries.
The Peril of Migratory Fish
It should come as no surprise that any fish that was harvested literally by the boat-load (Figure 1) eventually had population problems. The problem of overfishing is all-too-familiar for so many fish species. But migratory fish in particular have another major issue to be concerned about – dams. Any obstacles built on the river, such as a large dam, prevents the fish from reaching their spawning grounds upstream and ultimately from reproducing (Figure 2). The combination of harvesting adults and preventing reproduction is a recipe for disaster that has resulted in severely depleted stocks of most diadromous fishes around the world.
Fig, 1 Fishermen unloading salmon from a lighter, Nushagak, Alaska, 1917. University of Washington Libraries, Special Collections, Cobb 4148, http://www.bristolbaysockeye.org/historic-photos/
Fig, 2 An example of a fish ladder – engineers’ attempt to allow diadromous fish to pass dams – on the Columbia river. Photo by USACE, Public Domain.
The Role of Migratory Fish
These migratory fish species are more than a convenient (and admittedly delicious) meal. They serve an incredibly important ecological role. After rain storms, soil, leaves, and many other bits of matter and nutrients wash into streams and rivers and are subsequently swept out to sea. Therefore, there is constant delivery of material and nutrients to the ocean. Anadromous fish are one of the only mechanisms to return energy and nutrients back to freshwater and terrestrial systems. After spending years feeding in the ocean, anadromous fish carry all those ocean-based nutrients accumulated in their tissues with them into rivers where bears, eagles, osprey, raccoons, otters, turtles, and so much more can receive energy inputs from the ocean.
What You Can Do
Interested in participating in WFMD? There’s a few things you can do. You’ve already done the first step by reading this post! Next, feel free share this post with others to spread the word about WFMD. Then, go to the World Fish Migration Day website or their Facebook page to learn more about the mission and what is being done. You can search for local events that may be taking place near you using this interactive map. If you are in Western Massachusetts, but not near one of the sponsored events listed on the site, consider visiting the Holyoke Dam fish lift which has a public viewing window to watch anadromous fish continue their journey past the dam (Figure 3). Or, if you live near a river that has a herring run, you may be able to volunteer to assist in estimations of river herring population trends by conducting visual counts. The most important thing you can do is help to educate yourself and others about the value of these species and our impacts on them.
Fig. 3 Salmon passing the viewing window at Ballard/Chittenden locks fishway in Seattle, WA (similar to the Holyoke Dam viewing window). Photo by Joe Mabel, Wikipedia commons.
Herring volunteer count opportunities
Video count option
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