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

O ne of the main problems in fisheries management is linked to accurate assessment of exploited stocks and in the provision of realistic advice. T he 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

C lear 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

O nly 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

M any 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

I nfluence 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

A brupt 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 S ome indicators of climatic processes describing the major climate and ocean systems are a good evidence of the impact of climate change on biological systems F isheries 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)

THE IMPACT OF CLIMATE CHANGE ON FISHERIES S ixteen fisheries of West Mexico were selected T heir overall biomass landed accounts for nearly 570,000 metric tonnes (mean for ) representing 78% of total landings of West Mexico

CLIMATE CHANGE AND FISHERIES

Landing data were analyzed as normalized departures from five- year 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

IMPACT OF THE SHIFT OF THE MIDDLE SEVENTIES

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: CrabsGiant squid GroupersChub mackerel

The shift of the Middle 80´s

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 : ShrimpSpiny lobster Snappers Mullets

Response to El Niño Events

A clear pattern of response to climate change, although not identified, is observed in the anchovy

THE HUMAN DIMENSION AND THE GLOBAL CHANGE C limate regime and shifts impose drastic effects on marine ecosystems I ts 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

A daptive 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 H ence, there would be no place for long term considerations of climate change effects beyond those related to long term planning

U nder 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 T his is the case of abalone, whose yields were two orders of magnitude higher four decades ago T he best management strategy applied nowadays, would not be able to restore the stock size to those high levels in the short term

T he case of the California pilchard is analogous, but with opposite sign A ccording 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 W ithin 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 O verexploitation may play an important role depleting the stocks, but in the long term, the main role is played by the climate