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Patterns
of catch |
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Resources |
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New
Zealand fish catch histories and quota levels to 1991 |
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Marine
fisheries research |
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Fishing
methods |
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History
of fishing in New Zealand |
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Background
Information |
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There
are four broad patterns of population stability and two
further patterns resulting directly from fishing. Some
species fall midway between two patterns, and species
may, over time, and particularly with heavy fishing pressure,
move from one pattern to another. The patterns are: |
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Steady
state
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Steady state catch pattern graph.
Click for larger image
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The population size and catch remain within about 25 percent
of the long-term average, or the catch increases steadily
with moderately increasing fishing pressure. These fish
are usually fairly long-lived. If they are short-lived,
there are usually only minor variations in recruitment.
Examples are butterfish, groper, stargazer, tarakihi and
John dory. Sharks would qualify if they were less heavily
fished. |
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Regular
cycles
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Regular cycles catch pattern graph.
Click for larger image
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The arrow squid with an annual life cycle is the most
obvious example. Annual catches vary, but monthly catches
are seasonal, reflecting each year's growth and mortality. |
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Irregular
cycles
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Irregular cycles catch pattern graph.
Click for larger image
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This is the most common pattern. It covers species with
short life cycles and either highly variable recruitment
or strong predator/prey relationships. These species are
often heavily fished. Examples are red cod, snapper and
soles. |
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Intermittent
cycles
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Intermittent cycle catch pattern.
Click for larger image
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Periods of high abundance are followed by collapse. These
are often short-lived species. Populations of long-lived
species can be fished almost to extinction. Examples are
scallops in some areas and Chatham Islands rock lobsters;
there is some risk that orange roughy might come into
this category if it continues to be overfished. |
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A
developing fishery
In
a developing fishery there is a period of low catches
followed by a rapid rise. Then the fishery shifts into
one of the four natural patterns or into a declining state.
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A
declining fishery
A declining fishery results from overfishing a fish
stock, which would otherwise show a natural pattern.
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top
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Activities |
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a |
Look
at the tables of historical fish catch data in Fish Catch
Histories and Quota Levels to 1991. Graph six species
which most clearly illustrate the six patterns of catch. |
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b |
What
species have been the most commonly caught from the 1930s
or 1940s onwards? Find out about regional differences
in the abundance and popularity of any of these species? |
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c |
By
looking at the tables can you see how the first quotas
for some deepwater species were reached? |
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d |
The
Quota Management System, which covered most of the common
inshore species, plus the main deepwater species, was
introduced in 1986. The quota for some species was considerably
less than recent catches. Find some examples and consider
why these reductions were made. |
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e |
What
other information do you think you would need to determine
reliable quotas? |
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f |
There
are more detailed (ie, monthly) catches for snapper, school
shark and squid (they do not cover the whole fisheries).
Graph the data over a period of several years. Describe
the patterns on the graphs. Can you match these to any
of the patterns given (steady state, regular, irregular
or intermittent)? |
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g |
Snapper
and squid |
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1 |
What
is the seasonal pattern of snapper catches? |
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2 |
What
are the similarities and differences between the patterns
for squid and snapper? |
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