Intertidal: Celebrating fish migration - Portland Press Herald - pressherald.com

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This is supposed to be a column about the intertidal – the area where the water meets the land and where we humans are able to explore when the tide is out. But, it is also about the connectivity between parts of the ecosystem and what we can learn from it. One of those connections is between freshwater and salt, and that often takes us further into the connection between land and water since many of the rivers and streams meander from inland areas out towards salty bays.

There are many things – natural and unnatural that determine the extent of connectivity between these bodies of water. In a recent geography game I tackled with my daughters on a remote learning day, I was reminded of the definitions of several natural features that describe these bodies of water and the areas around them – deltas, isthmuses, straits, and peninsulas, for example. I needed a reminder that an isthmus is basically the opposite of a strait – the first is a narrow strip of land that connects two larger pieces of land and has water on either side, and the second is a narrow “strip” of water that separates two pieces of land. These two features, in particular, can either isolate or connect bodies of water together.

Then, there are the man-made features along the water that can also determine this connectivity – features like bridges, dams, and culvert. There are myriad designs for each of these, some of which provide more exchange of water than others. But, each of them has an impact on what water mixes with what. And, that determines what happens to all the living and non-living stuff that is in that water. Perhaps the best-known example of living things in the water not being able to travel from one body of water to another is that of migratory fish.

There are plenty of fish that need to travel around because of what is called their “life history.” Life history simply refers to what a plant or animal does at a particular time in their life. Where do they live? What are they doing at that point in their life? For migratory fish, the biggest factor in question is when and where they reproduce. Some do this entirely in saltwater and some do this entirely in freshwater – but often they travel from one area to another. Others may live part of their life in freshwater and then reproduce in saltwater or vice versa. Regardless of the specifics of their pattern, migratory fish species have to be able to move around. And, their movements are of great interest to scientists and citizens interested in making sure there are plenty of these fish in the future.

As such, last week many people around the world celebrated World Fish Migration Day. While it is a worldwide event, several local organizations have become deeply involved in related efforts. Restored runs of local species like alewives and salmon are being celebrated by organizations like The Nature Conservancy and the Atlantic Salmon Federation, the offices of both which are located on the Androscoggin River, the site of a fish ladder designed to aid the passage of migratory fish up and over the dam.

World Fish Migration Day usually takes place in the spring, but due to the pandemic, it is being held this fall. Always looking for an opportunity to link seasonal events to a learning opportunity, I am particularly grateful that it is happening in the fall when schooling is typically in full swing, but this year much of it is quite independent. There are some neat resources for anyone interested in learning more, even if you missed some of the live held events last week. NOAA Fisheries has a site full of links (https://ift.tt/37JTTdM) and you can also find plenty of resources on the World Fish Migration Day page (https://ift.tt/2F6kMX8). There’s nothing like watching a fish struggle to make it upstream and succeed to bring a little whimsical and positive energy to your day.

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