Week 2 - Overfishing

Question 1

What is recruitment overfishing

Answer 1

“recruitment overfishing” – taking such a high proportion of the breeding stock that there
is no longer enough juvenile recruitment to sustain the fishery or allow it to recover.

E.g Peruvian anchovy

Question 2

What is ecosystem overfishing?

Answer 2

The ecosystem effects of taking so many fish out of the water are only beginning to be
appreciated. These include the effects of removing predators on prey
populations or trophic cascades that can alter the structure of the marine habitats

Another ecosystem effect is known as “Fishing down the food web” or the progressive shift
to smaller species or from predators to herbivores – leading to shorter food chains.

What can seem natural to us now is often the result of the effects of overfishing fishing for
over many generations. Shifting baseline is a term used to describe the way significant
changes to a system are measured against previous baselines, which themselves may
represent significant changes from the original state of the system (Pauly 1995).

Question 3

How have we somehow mitigated fisheries collapse?

Answer 3

Given that there has been successive collapses of most of the major fisheries over this
period, it is clear that high total catch is only being maintained by expanding fishing effort,
which continues to accelerate (Fig. 4). We are using better and better fishing gear, and are
progressively shifting to species that are further offshore, deeper in the oceans, harder to
catch.

Question 3

What is peak fish?

Answer 3

The point in time when the amount of fish that is caught will reach its maximum rate, after which the amounts of fish will gradually decline.

It is believed this was reached in the 1980’s

Question 4

What is happening with Aquaculture?

Answer 4

Aquaculture can fill the gaps to some extent. However, it is not a solution on its own.

Question 5

Progressive collapse of the world fisheries

Answer 5

Over 365 collapsed marine fisheries have been documented (1 in every 4 fisheries approx). Defined as reduction 10% to maximum catch
Almost all commercial fisheries have bee a succession of discovery, exploitation and depletion
Overfishing of the Antarctic Baleen Whales. Collapsed due to low stocks, life history, value and open access. Commercial whaling was banned by IWC in 1986. Collapses then goes up pattern

Question 6

What are the five main contributing

Answer 6

Factors contributing to the collapse included:
1. the overexploitation of low stocks;

2. poor replacement capacity due to long life, slow growth and low reproduction;
3. high value;
4. the open-access nature of the fishery,
5. the fact that there was essentially NO management. Quotas were actually set during the 50’s and 60’s, but the quotas were set at or above current catch levels, which equates to no management at all (Fig. 15).