Lesson video

Hello, my name's Mrs. Harking.

The title of today's lesson is Fish Resources.

It's taken from the unit Natural Resources: Can Earth meet our needs? Today we'll be exploring whether there actually are plenty more fish in the sea or whether there's a fish numbers problem going on.

Let's take a look.

Our outcome today is to describe different types of fishing and to explain why fish stocks are reducing.

It's a good idea to have a look at these keywords before we start the lesson as we'll be using them today.

First of all, we have commercial.

This means related to the making of money from buying or selling things.

So we'll be talking about commercial fishing today where fishers are fishing for fish in order to sell them.

Sustainable means able to continue over a long time.

You might have also heard about the environmental, economic, and social aspects to sustainability, but it's really important that we meet all of those aspects in order for something to be fully sustainable.

Exploit, to use something for personal benefit.

Depleted, used up or nearly all gone.

And lastly, habitat.

This is a natural home or environment of an animal, plant, or another organism.

If you would like to make note of any of these key terms, please pause the video now.

Today's lesson is in two parts.

First of all, types of fishing; and secondly, fish numbers in our seas and rivers.

So first of all, types of fishing.

Sofia asks, "What type of fish is this? Where does it come from and how is it caught?" So this is a typical fish found in a fish and chip shop here.

Does anybody know the answer to this? Right, so around 60% of all fish in the UK fish and chip shops is cod, and it's caught by trawling in the Northern Atlantic.

So actually, the part of the Northern Atlantic where most of our cod comes from is the North Sea, which you may not have known is actually part of the Atlantic Ocean.

So if you have a look at the map we have here, the little globe, you can see that the purple line is pointing to the North Sea, which is part of the North Atlantic Ocean.

There are many different types of commercial fishing, so remember fishing for money, including trawling, longlining and trap fishing, and aquaculture.

We are going to take a look at each of these.

We're going to look at how they work and their pros and cons.

First, we'll look at trawling.

Trawling involves a boat dragging a large net with the aim of catching large quantities of fish.

Herring, mackerel, sardines, and anchovies can be caught using a midwater trawling system, which you can see in the diagram here.

Cod, haddock, plaice, scallops, and clams are found lower in the sea, so bottom trawling is used.

And you can see here on the diagram that the net drags along the sea beds.

Trawling is widely used around the world for commercial fishing.

It is an efficient way to catch large volume of fish and it makes it profitable.

Also means that actually you can sell the fish for lower prices, meaning it's affordable for people in the shops.

However, trawling is not sustainable.

The heavy nets and equipment involved in bottom trawling, in particular, tear up the seabeds, damaging habitats such as seagrass meadows and coral reefs.

So you can see here in the diagram the fact that net is dragging along the seabed.

As it does that, it's churning up the seabed and damaging everything it knocks into.

Here are the habitats that we can see that might be on the and are very vulnerable to these nets.

Bycatch refers to marine animals that are unintentionally caught while fishing for a different species.

So we can see here there's a shark being caught.

So examples include non-target fish.

So a target fish would be the fish you're trying to catch.

A non-target fish would be something you don't want.

Turtles, dolphins, sharks as we can see here, and seabirds can all end up accidentally getting trapped in these nets.

Trawling creates a lot of bycatch.

So this is another negative of for trawling.

Around 10% of global fish captures are discarded, often dead or dying.

This threatens endangered species and disrupts ecosystems. So for example, the vaquita, which is a rare porpoise in Mexico, you could see the image here, is on the brink of extinction due to bycatch, which would mean there would be no more vaquita left.

Help Alex improve Jun's comment.

Jun has said, "Trawling destroys habitats." Jun's correct, but can we make it better? Fill in the gaps on Alex's comment to make it better.

What type of trawling destroys habitats such as? Can you give me an example? Well done, yes.

Bottom trawling destroys habitats such as, you might put coral reefs or seagrass meadows.

Either would be fine.

You might have another example.

That's absolutely fine.

Now we're going to look at longlining and traps.

Longlining uses bated hooks spaced along a single line, which can be either left adrift or anchored.

Traps left on the seabed are often used to catch shellfish; for example, crabs and lobster.

You may have heard of lobster pots, which are traps used to catch lobsters and they're one good example of the sort of traps that we're talking about here.

Both longlining and traps are more sustainable as there's significantly less bycatch than trawling, as well as the fact that habitats are not disturbed.

Longlining and traps are time-consuming though and they're really labor-intensive, which makes the fish more expensive to buy than if we are comparing it to trawling.

There's still a risk of some bycatch.

And if the equipment, for example, traps and the lines are lost at sea, they can cause something called ghost fishing.

Ghost fishing is actually a thing.

So what happens is the traps and the lines continue to fish.

But because they're lost at sea, they're not going to be brought to land so the fish won't be consumed.

The lost traps and lines also contribute to the ocean plastic.

Time to check for understanding now.

True or false? Longlining and traps do not lead to bycatch.

Well done, that is false.

There is still a risk of some bycatch, though it's a lot less than from trawling.

Now we're going to look at aquaculture.

This is a third type of fishing.

Aquaculture is the controlled breeding and harvesting of fish in enclosures; for example, tanks or sea pens.

We can see an example of this here in the photograph where there's sea pens in the sea and fish are being bred in those pens.

Here's another example of what that might look like.

Aquaculture is a growing industry that offers a reliable supply of seafood and reduces the pressure on wild fish populations.

So there's a lot of positives here.

However, poorly managed aquaculture can lead to water pollution and disease transmission to wildlife.

The fish food can also sink to the floor and impact on the nutrient balance and the ecosystem that's already there.

Time for a check for understanding.

Select the correct statements.

Is it A, Aquaculture is when fish are reared in tanks, not fish from C? B, Aquaculture is when fish are reared in tanks or sea pens? Is it C, Sea pens allow people working in the fishing industry to write underwater? Yes, well done, it's B, Aquaculture is when fish are reared and tanks or in sea pens.

Aisha says "Trawlers should be banned." Discuss whether you agree with Aisha and pause the video now for discussion.

Well done, everyone.

Let's see what other students have said.

Lucas has said he agrees.

"I agree, fish numbers are in decline, bottom trawlers destroy seafloor habitats and lead to significant bycatch.

There are more sustainable ways to fish." Laura disagrees, she says "Trawlers are important for large-scale commercial fishing.

Buying fish and chips would be way more expensive if there was no trawlers.

Also, midwater trawling does not damage seafloor habitats." Time for task A now.

Complete the table to assess each of the fishing methods.

On the left hand side, we have our methods.

Trawling, then line fishing and traps, then finally aquaculture.

For each of these, I would like you to give some advantages and disadvantages.

What can you remember? Pause the video now to give yourself a chance to do this properly, good luck.

Well done, everyone.

Let's take a look at some answers.

Your completed table may look like this: For trawling, we've got high catch volume and efficient for commercial fishing are the advantages.

And disadvantages are damages seabed habitats and high bycatch.

For line fishing and traps, we have minimal bycatch and habitat damage are our advantages.

And labor-intensive, slower catch rate, still risks bycatch, equipment loss can cause ghost fishing, all of the many disadvantages.

Aquaculture is our last fishing method.

Advantages included reliable supply and reduces pressure on wild fish stocks.

However, the risk of disease spread and pollution are associated problems. How did you do with that? Is there anything you need to add? Well done, let's take a look at the second half of our lesson now.

Fish numbers in our seas and rivers.

In 2018, nearly 90% of the world's marine, that means sea, fish stocks were fully exploited, overexploited or depleted.

So in 2018, we can see that the blue section of the pie chart is all of the fish stocks that were not doing well.

This is not great.

Between 1970 and 2020, global populations of migratory fresh water fish like salmon have declined by around 80%.

Now migratory fish are fish which travel probably for breeding.

And migratory fresh water fish mean that they are travelling up rivers.

We can see from the graph here that the decline is really significant.

Time for a check for understanding now.

True or false? There are still plenty more fish in the sea.

False, well done.

Can you tell me why? In 2018, nearly 90% of the world's marine, or sea, fish stocks were fully exploited, overexploited or depleted.

The number of fish is decreasing due to: overfishing, habitat damage, and bycatch.

So we're gonna take each of these different causes and have a look at them in a little bit more detail.

Overfishing means that more fish are caught than can be reproduced, so the number of fish decline.

Habitat damage a little bit more complex.

It plays a really large role in reducing fish populations.

So we've talked about our first example, bottom trawling, destroying seafloor habitats, but there are other ways in which habitats can be destroyed as well.

Let's take a look.

Global warming affects river water levels and water temperature.

This also reduces oxygen levels and spawning opportunities.

So this is something that can affect fish that need to migrate up river to breed.

Pollution also affects habitats.

For example, sewage waste can directly harm fish through poisoning, which can cause disease or death.

Disruptions in their ecosystem and contamination of the food chain are really problematic consequences.

Dams block migratory routes, preventing fish like salmon from reaching upstream breeding grounds.

Here's an example of a dam, which clearly would make it extremely hard for a salmon to travel from the river below, up to now reservoir above.

Salmon actually leap up small obstacles in a river, but a large-scale dam will defeat them.

There is an invention called a fish ladder, which solves a problem of dams stopping migratory fish swimming upstream.

This was first invented in the 1800s so it's not a new idea.

The idea is that there's a series of pools that allow fish to jump up the heights of the dam gradually.

They can be really successful in allowing species to travel upstream to breed.

However, it's a very small proportion of dams that do have fish ladders integrated into them.

Bycatch reduces fish numbers by accidentally catching and often killing non-target species and endangered fish.

So bycatch is a real contributor to fish number decline as well.

Time for a check for understanding.

Which of the following does not cause declining fish populations? Is it A, overfishing; B, habitat destruction, C, bycatch; or D, aquaculture? Well done, it's D, aquaculture.

Time for our task B now.

I would like you to suggest some reasons why Egyptian fish stocks might not be within sustainable levels.

You're applying your knowledge in this question, so don't worry if you don't know the ins and outs of Egyptian fishing.

I don't expect you to know that.

You are just applying what you've learned in today's lesson to suggest what you think could be causing this problem.

Pause the video now to give yourself time to do the task, good luck.

Well done, everyone.

Let's take a look at some answers.

The answer may include: Overfishing means that more fish are caught than can be reproduced, so the number of fish decline.

Habitat damage plays a large role in reducing fish populations, for example: bottom trawling destroys seafloor habitats; global warming affects water temperature; pollution, for example, sewage waste affects water quality;; dams block migratory routes, preventing fish like salmon from reaching upstream breeding grounds.

Bycatch is another problem, which reduces fish numbers by accidentally catching and often killing non-target species and endangered fish.

How did you get on? Is there anything you'd like to add? Well done, we are onto our summary now.

So to remind you, there are three main types of commercial fishing.

These are trawling, longlining and trap fishing, and aquaculture.

In 2018, nearly 90% of the world's marine, sea, fish stocks were fully exploited, overexploited, or depleted.

Overfishing, bycatch, and marine habitat damage are some of the concerns associated with fishing.

I hope you found today's lesson interesting.

See you next time, bye.