Transcript SOCIAL AND ECONOMIC IMPACT OF GLOBAL CHANGE ON

SOCIAL AND ECONOMIC
IMPACT OF GLOBAL CHANGE
ON SOME TROPICAL
FISHERIES
Ernesto A. Chávez & José Luis Castro-Ortiz
CICIMAR, Instituto Politécnico Nacional. La Paz, MEXICO
[email protected]
One of the main problems in fisheries
management is linked to accurate
assessment of exploited stocks and in the
provision of realistic advice.
The main constrain in this task is the
strong influence of environment upon
recruitment of new generations,
imposing high uncertainty to the
estimations of stock size
Clear discrimination of changes in
stock size caused by the fishing
intensity from those caused by climatic
change is a task difficult to
accomplish, especially in those
fisheries based on highly variable
short-lived stocks strongly linked to
annual variability
Only the El Niño Southern
Oscillation (ENSO), with a
period of to five-to-seven year
oscillations, has been recognized
for several decades, to have a
significant impact on many
fisheries of West America
Many species repond to climate
shifts. However, the response to
climatic change is not the same in
all cases, some species respond
with different sign and intensity
to regime shifts
Influence of environment has been
perceived intuitively in short-lived
species like sardines, and anchovy,
rather difficult to assess by traditional
models applied to fisheries, because
their sudden changes in recruitment
rate and natural mortality, strongly
influenced by the environment, are
difficult to evaluate
Abrupt climatic shifts have been
recently discovered
These abrupt shifts have had strong
influence in ecosystems worldwide
There is an implicit thought that the
relative stability of tropical
environments are not quite
susceptible to show the effects of
climatic change
GOAL
To examine the response of main
fisheries of West Mexico in the
context of several indices of
climate change, identifying their
response against climate shifts
THE INDICES OF CLIMATE OCEAN
Some indicators of climatic processes
describing the major climate and ocean
systems are a good evidence of the impact of
climate change on biological systems
Fisheries may be the best source of
information available to understand the nature
and intensity of these impacts on exploited
stocks
The main oceanic climate indices
(After several sources. Y axis is the Cumulative Summation of anomalies)
10
5
0
-5
-10
-15
-20
LOTI
-25
1950
CTI
1960
ALPI
1970
PDO
1980
SOI
1990
NAOI
2000
THE IMPACT OF CLIMATE CHANGE
ON FISHERIES
Sixteen fisheries of West Mexico
were selected
Their overall biomass landed
accounts for nearly 570,000 metric
tonnes (mean for 1995-1999)
representing 78% of total landings of
West Mexico
CLIMATE CHANGE AND FISHERIES
YIELD t, WEST MEXICO (Mean 1995-99)
California pilchard
Penaeus shrimps
Brown seaweeds
Skipjack tuna
Californian anchovy
Mullets
Snappers, jobfishes
Abalones
0.E+00 1.E+05 2.E+05 3.E+05 4.E+05
Landing data were analyzed as
normalized departures from fiveyear moving mean values each year.
This way, decadal patterns of high or
low recruitment are shown and shifts
expressed as response of stocks to
climate change are displayed
CLIMATE SHIFTS
AND THE FISHERIES
The most striking characteristic
of the indices of climate change
described above, is the shift
occurring by the middle of the
70’s
Three main patterns of impact of the
climate change are identified on the
fisheries:
1. A response to the shift in middle 70,s.
2. A shift in 1989, approximately
3. Species that apparently respond to El
Niño-La Niña events
1. Impact of the
shift of the middle seventies
on:
Abalone
California pilchard
Sharks
Jacks
Skipjack tuna
Red and brown seaweeds
Normal Dev. from mean Catch
IMPACT OF THE SHIFT
OF THE MIDDLE SEVENTIES
2.0
Skipjack tuna
CA Pilchard
1.5
Abalone
1.0
0.5
Red seaweeds
0.0
-0.5
-1.0
-1.5
-2.0
Jacks
Sharks
-2.5
1950
1960
1970
1980
1990
2. The shift of the Middle 80´s
Characterized by a moderate
negative response before the
middle 80’s, then an abrupt
response leading to spectacular
increases in catches afterwards:
Crabs
Groupers
Giant squid
Chub mackerel
Normal Dev. from mean Catch
The shift of the Middle 80´s
3.0
2.5
Crabs
2.0
Giant squid
1.5
1.0
0.5
Chub mackerel--------->
0.0
-0.5
Groupers
-1.0
1950
1960
1970
1980
1990
3. Response to El Nino events
Is well known as warm above
normal temperatures followed by
cold periods occurring every five to
seven years
Fisheries impacted :
Shrimp
Snappers
Spiny lobster
Mullets
Response to El Niño Events
Normal Dev. from mean Catch
3.0
2.0
1.0
Shrimp
Snappers---
0.0
-1.0
-2.0
Mullets
-3.0
Brown seaweeds--o--
-4.0
-5.0
Spiny lobster
-6.0
1950
1960
1970
1980
1990
Normal Dev. from mean Catch
A clear pattern of response to climate
change, although not identified, is
observed in the anchovy
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
1950
1960
1970
1980
THE HUMAN DIMENSION AND
THE GLOBAL CHANGE
Climate regime and shifts impose
drastic effects on marine ecosystems
Its knowledge opens a new perspective
regarding our understanding of
environmental processes ruling the
dynamics of exploited species
A clear discrimination between
changes in stock size caused by
the fishing intensity and those
caused by climatic change makes
it a task rather difficult to
accomplish
Impact of climate change in the
long term may be one of the main
factors constraining the
possibility of accurate estimation
of the stock biomass when
planning fishing activities for the
next season is required
Its knowledge will allow to
understand the sources of noise
specially related to estimates of
recruitment rates of exploited
stocks, but it may not be a good
help trying to input this
knowledge directly into the
issues of fisheries management in
the short term
Adaptive management is a process by
which a continuous stock assessment is
carried on year by year, to reorient the
exploitation policies for the next season
Hence, there would be no place for long
term considerations of climate change
effects beyond those related to long term
planning
Under a climate regime imposing low
recruitment and biomass levels to a fishery, it
is not likely to restore the stock to levels
similar to those when yields were very high
This is the case of abalone, whose yields
were two orders of magnitude higher four
decades ago
The best management strategy applied
nowadays, would not be able to restore the
stock size to those high levels in the short
term
The case of the California pilchard
is analogous, but with opposite sign
According to the positive effect of
climate change that it displays, it is
suspected that it might be difficult to
expect a significant impact by the
fishing intensity
CONCLUSION
Within the framework of climate change
the human impact as the responsible one
for the depletion or restoration of
exploited stocks is perceived as the most
likely effect in short term
Overexploitation may play an important
role depleting the stocks, but in the long
term, the main role is played by the
climate