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Investigaciones marinas

versión On-line ISSN 0717-7178

Investig. mar. v.30 n.1 supl.Symp Valparaíso ago. 2002

http://dx.doi.org/10.4067/S0717-71782002030100042 

Impacts of El Niño and La Niña Events
on the Populations of Clam (Mesodesma
donacium
, Lamarck 1818) along the
Southern Peruvian Coast

Edward Barriga R., Marco Quiroy R.

Laboratorio Costero de Ilo - Instituto del Mar del Perú,
P.O. Box 22, Callao, Peru,
E-mail: ebarriga@imarpe.gob.pe,
mquiroz@imarpe.gob.pe

Introduction & Objectives

Mesodesma donacium, Lamarck 1818, is a bivalve of economic importance that is distributed from Sechura (05° 50' S, Perú) to Isla Chiloé (42° S, Chile). It typically inhabits the meso- and infralittoral zones of sandy beaches that are exposed to strong waves. In southern Perú, this species forms large natural banks, which support an intense extraction activity, involving hundreds of families. Our objectives are:

1. To assess the impact of the 1997-98 El Niño on the populations of Mesodesma donacium of the main natural banks of the southern Peruvian littoral.

2. To determine the negative influence of the 1999-2000 La Niña event on the natural re-colonization of M. donacium in the southern Peruvian coast.

3. To describe the consequences of the disappearance of the fishery activity of M. donacium on the main artisanal communities of southern Peru.

Results & Discussion

During the 1997-1998 El Niño event, Mesodesma donacium was one of the species of nearshore sandy bottoms of the southern Peruvian coast most affected, since bio-oceanographic disturbances resulted in massive mortalities and the collapse of natural banks. Abundant dead organisms were detected in beaches several times from December 1997 to February 1998 (Barriga & Quiroz, 1998). In Playa Tacna, a biomass of 747 Tons during November 1997 was estimated, while only 0.98 Tons were estimated for March 1998. In Pozo Lisas no stock was detected in March 1998 (Table 1, Fig. 1).

Table 1 Changes in biomass of clams (Tons) in natural banks
of Moquegua and Tacna (1996-1998)

Pozo de Lizas

Date

May-June 96

Jan-97

Nov-97

Mar-98

 

Total

226.16

119.35

178.21

0.00

Playa Tacna

Date

0

Oct-Nov 96

Oct-Nov 97

Mar-98

 

Total

0

3595.06

747.25

0.98


Fig. 1 Biomass changes of Mesodesma donacium in natural banks (1996-1998)

Artisanal clam extractors were deprived of their main economic activity. Therefore important migrations were recorded. For example, the population size of clam extractors diminished from 800 in summer 1997 to 250 in 1999 (Table 2). Currently a small population (less than 30 families) lives in the location of Santa Rosa, where the few residents combine agricultural activities with nearshore artisanal fishery, using fish-hooks, trawl lines and eventually dragnets.

Table 2 Number of registered clam extractors of the main natural
banks of southern Perú in 1997 and after the 1997-98 El Niño (1999)

Natural

Lomas

Camaná

Quilca

Mollendo

Ilo

Tacna

TOTAL

bank

0
0
0
0
0
0

(tons)

1997

600

1200

0
0

200

800

2800

1999

138

198

46

30

50

250

712

The IMARPE's coastal laboratory at Ilo leads a monitoring program for the assessment of natural banks. This program yields periodic reports about the status of population recovery of M. donacium in the main natural banks. It was determined that cold anomalies related to the 1999-2000 La Niña prevented a natural re-colonization of this species, resulting in low levels of abundance. At the beginning of 2001, several important settlements were detected in the littoral of Islay (Arequipa), with a size structure characterized by a significant relative abundance of recently recruited animals, and smaller numbers of juveniles and adults, suggesting a population recovery process. Nevertheless, currently the population levels are still lower than before the 1997-98 El Niño. A significant increase in abundance and distribution of clams in the natural banks of Islay (up to 22 ind/m2) was observed in summer 2002, coinciding with normal environmental conditions that, in the short term, will allow the recovery of the exploitation activity and local development.

In conclusion, the populations of Mesodesma donacium, Lamarck 1818, and its fishery activity are highly sensitive to bio-oceanographic changes associated with El Niño and La Niña events.

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