River Ecology

River Ecology

River Ecology

Rivers and riverbanks support a range of wildlife. Let’s look at the ecology of rivers more closely.

Atlantic salmon

The wild Atlantic salmon is an extraordinary and mysterious fish. It is able to survive in both fresh and salt water and navigate thousands of miles to feeding grounds in the northern oceans before returning to the riverit was born to spawn and reproduce.

Its presence, or absence, is a vital indicator of the health of our rivers and seas. Worryingly over the past 30 years numbers of wild Atlantic salmon returning from the sea have fallen by more than half. The survival of the Atlantic salmon as a species can no longer be taken for granted.

Salmon appear to be under threat in both their freshwater and marine phrases. In rivers, changing land use and pollution and at sea poor survival rates. Climate change may be affecting salmon through changes in sea surface temperatures which in turn reduces the amount of available food around Greenland and the Faroes. The number of fish farms on the west of Scotland has rapidly increased since the 1970s, and disease and parasites (sea lice) can be passed from farmed salmon to wild, causing infection and reduced mortality. Some parts of the coast still operate net fisheries, where large numbers of salmon are caught and sold for human consumption.

Activity 1 – Atlantic salmon life cycle

a)Investigate the different stages of the Atlantic salmon life cycle. Investigate what challenges salmon face and threats to their survival.

b)Create a display for your classroom or individual mobiles using fish of differing sizes and wire coat hangers.

Online Resources:

  1. Atlantic Salmon Trust Learning Zone Interactive Map
  2. Video on River Dee Trust website. INSERT LINK

Activity 2–Maths Challenge - how many salmon will survive?

Can you work out how many Atlantic salmon return to the river to spawn?This can be done individually or as a class. Or you could use it as a basis to create a game to play outdoors.

Online Resources:

  1. Atlantic Salmon Trust worksheet

Activity 3 – Freshwater Pearl Mussels

Freshwater pearl mussels are related to many other more familiar marine mussel species such as common mussels and scallops. They have a complex life cycle and can live for over 100 years.

Freshwater pearl mussels are rare and endangered and over half of the world’s breeding mussels live in Scotland, so Scotland is globally important for their survival. In fact over 1 million mussels live in the River Dee.

Famously and as their name suggests some produce pearls, used in jewellery. Freshwater pearls were once highly prized. In the 16thCentury all valuable pearls had to be kept for the King. There are freshwater pearls on the Scottish Crown jewels, including the biggest pearl ever found, on the KellyBurn on the River Ythan.

a)Investigate why the life cycle of freshwater pearl mussels is complex and what other river animals it depends on to survive. Find out why freshwater pearl mussels need a river with good number of trout and salmon.

b)Make a list of all the factors that threaten the survival of freshwater pearl mussels. As a class or smaller groups, decide which factors threaten their survival most and which factors have least affect.

Online Resources:

  1. Pearls in the Classroom education sheets
  2. Maggie the Mussel story book -
  3. River Runners by Scottish Natural Heritage

Activity 4 – River Food Chain

Rivers that are clean and healthy will support a wide variety of plants and animals. These are linked together in a food chain which begins with green plants, which get their energy from the sun. In a river, the smallest plants at the bottom of the food chain are microscopic algae. These plants provide food for tiny animals such as shrimps and snails which are then eaten by larger animals such as small fish. Small fish are eaten by larger fish or birds, mammals or people in some rivers, as we eat large fish like trout.

a)Create river food chains and webs in your classroom by making one person the sun, one person leaf litter, a shrimp, a salmon and an otter. Ask them to arrange themselves in a line based on who eats who, creating a river food chain.

b)Add other animals such as mayfly, mallard duck, eel, water vole, mink, trout, kingfisher, osprey and heron. Ask the group to arrange themselves showing who eats who. Once complete, ask each person to link to the animals they eat and are eaten by using pieces of string or wool. This will create a river food web. Certain creatures (salmon and trout) will be eaten by more than one predator.

c)Discuss who is at the bottom and at the top of the food chain. Ask the group what would happen if parts of the food web (sun, leaf litter, shrimp) were removed or their numbers reduced. Ask if there are any animals who do not get eaten by any other animal. What do we call these animals?