This lesson focuses on where salmon spawning occurs, the ideal habitat for spawning and its development to fry and parr. The story of a salmon was chosen because salmon live in both fresh water and salt water.

Lesson Objectives

To enable pupils to understand how salmon spawning occurs, make them aware of the factors that affect egg and fry survival and the importance of habitat conservation.

Video: Lesson 3
Presentation: Lesson 3
Teachers Guidelines

This lesson could begin by telling the story of “An Bradán Feasa” to the pupils to stimulate interest.

Salmon begin life as spawn or eggs. A female salmon returns to her natal river or river of birth to spawn. Salmon, sea trout and brown trout often use spate rivers for spawning. A fast flowing, hilly or mountain river subject to floods or high water is described as a spate river. The flood level rises quickly after heavy rain but drops just as fast. While water levels in a spate river may fluctuate very quickly, it may, at the same time, have some deep holding pools with good gravely areas for salmon to spawn.

A salmon travels upstream to the source of a river where the water is shallow and fast flowing and where the riverbed is strewn with clean, loose gravel. After selecting an area in the stream, she excavates a hole in the gravel with her tail and nose, sometimes helped by the male. The gravel is piled high, often reaching the surface of the water, and always downstream of the excavation. Then the female deposits her ova (up to 5,000 eggs) in the deepest part of the excavation. The male, who is alongside throughout, fertilises the eggs as they are deposited from the female. When spawning is complete, the hen buries the ova (fertilised eggs). Then all of the excavation is fully covered, forming a mound of approximately 40cm by 40cm, depending on the size of the fish. The mound of gravel or egg nest made by a trout or salmon in a stream is called a “redd”.

A small number of females and males (about 5%) may go back to sea a second time and return to spawn again. Salmon that return to sea after spawning are called spent fish or kelts and some even return a third time. This completes the life cycle of a salmon.

The presence of clean, loose gravel in a spawning bed is essential to ensure a free flow of oxygen-rich water through the stones for salmon eggs to develop. Field drainage, bog drainage, pollution, overgrazing, afforestation and deforestation can threaten survival of juvenile salmon. All of these can impact negatively on clean, loose gravel.

To highlight the importance of good-quality gravel in the spawning area, a simple experiment, oxygen in water, can be carried out.

The idea of habitat or home of a plant, animal, insect or fish can be a difficult concept for some pupils to grasp. Discussing the habitats of the pupils, animals, insects or birds in your area could be a good exercise to reinforce this concept.

Endangered habitats can be protected by building or erecting fences along the banks of the stream. This allows vegetation to grow and stops silt from falling into the river. Plants provide plenty of leaf litter for the local insects or invertebrates. Putting fewer sheep on mountains means more grass for the animals and less land erosion – the animals are happy and fish can thrive.

To illustrate this idea, an experiment on Land Erosion can be carried out

Too many coniferous trees planted along the banks of a stream are not good. They block light completely and prevent other vegetation from growing. The banks become bare and muddy. When it rains, silt from the bare muddy banks lodges in the gravel bed. Needles from the trees drop into the stream, producing acid which sours the water. The spawning eggs in the stream will not survive. Pupils could be asked to suggest a solution for this problem, e.g. planting trees correctly near a stream or river environment.

Much damage is also caused to streams and small and large rivers by arterial drainage, which is the drainage of a river bed and its adjoining tributaries.

To aid with the teaching of this lesson, a glossery of terms and definitions discussed in this lesson are available

Revision

Two different types of revision material accompany this lesson; activity cards and whiteboard material.
The activity card is a 3 page document that is filled out by the pupils to test their knowledge of the lesson taught. The teacher can decide if the activity card is filled out individually or in teams

The whiteboard resource tests the pupils knowledge of the lesson taught. Pupils are encouraged to actively engage in answering questions relating to salmon spawning, factors affecting egg and fry survival and habitat conservation.

At the end of the lesson, Pupils should know
How and where spawning occurs.
How landslides occur and the factors that cause stream and riverbank erosion.
That the conservation of streams is necessary to ensure that salmon eggs and fry survive.

1.  How and where spawning occurs.
2.  How landslides occur and the factors that cause stream and riverbank erosion.
3.  That the conservation of streams is necessary to ensure that salmon eggs and fry survive.