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vol.30 número1  suppl.SympResponses of Zooplankton Populations to the 1997/98 El Niño in the Coastal Upwelling Zone off Northern Chile: Is El Niño that bad?Effects of the 1997-98 El Niño on the Oceanographic Conditions and Zooplankton Community Structure in the Coastal Upwelling System Off Northern Chile índice de autoresíndice de materiabúsqueda de artículos
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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/S0717-71782002030100025 

Shelf Fish Larval Abundance Along the
West Coast of Baja California During a
Period with two El Niño Events
1983-1987

René Funes R., Alejandro Hinojosa M.,
Gerardo Aceves M.,
Sylvia P. A. Jiménez R., M. Hernández R.,
Ricardo Saldierna M.

CICIMAR-IPN. PO. BOX. 592. La Paz, Baja
California Sur, Méx. C. P. 23069,
E-mail: rfunes@ipn.mx

Introduction

The southern region of the California Current is characterized by a marked yearly cycle of cooling and heating, and is also influenced interannually by El Niño- Southern Oscillation (ENSO) warming events. Environmental changes related to El Niño reduce the biological productivity of surface waters, and produce important changes in plankton and nekton distributions that are associated with intensification of normal seasonal poleward flow.

The main source of seasonal variation is related to the coastal circulation pattern, with the equatorward California Current as the dominant flow during the spring and summer, the inshore countercurrent during fall and winter, and the California undercurrent with subsuperficial flow throughout the year. The major interannual variation associated with El Niño occurs as warm water impinges on the South American coast, causing a rise in sea level, and a depression of the thermocline along the American Pacific coast as a coast-confined wave that progresses poleward, as it occured during the 1982-1983 and 1987-1988 events. El Niño events are irregular in terms of frequency, duration and amplitude; the 1982-1983 El Niño was one of the most intense the past century.

The study area was the Pacific coast of Baja California, from Punta Eugenia at its northernmost end to Punta Márquez at the south (23¥N - 28¥N, from 5 to 80 n. mi. offshore). A wide continental shelf characterizes the coastal region between Punta Abreojos and Cabo San Lázaro (45 mi.); however, it narrows off Bahía Magdalena and Punta Eugenia, where depths of more than 200m are found very close to the shore.

During 1982-1987 sixteen oceanographic cruises were carried out in the west coast of Baja California. Plankton samples were obtained with Bongo nets fitted with a calibrated flowmeter, and obliquely towed through the water column between the surface and 200m. Multivariate analysis was performed to describe temporal patterns in the fish larvae data.

The objectives were to determine the temporal patterns of shelf larval fish, and examine the environmental relationships in the community structure.

Results

Representatives of 113 taxa of shelf fish larvae were collected between 1982 and 1988. Engraulis mordax larvae ranked first in abundance among shelf fish larvae (30014 larvae per 10 m2; 41%), followed by Sardinops caeruleus and Scomber japonicus ranked second and third in abundance with similar densities (8192 and 7967 larvae per 10 m2) (Table 1). The following taxa composed around the 75% of total abundance: Engraulis mordax, Sardinops caeruleus, Scomber japonicus, Opisthonema spp. Chloroscombrus orqueta, Etrumeus teres, Synodus lucioceps, Prionotus ruscarius, and Auxis spp. Faunal associations of the shelf fish larvae were principally from tropical and subtropical affinities, accounting for about 80%. However, species belonging to subarctic and transition affinities were less diverse.

Fish larvae abundance reached maximum values during the winter months (February 1983, January 1984), dominated by temperate species affinity related to the California Current (Engraulis mordax and Sardinops caeruleus). Tropical fish larval abundance peaked in August 1982, September 1983, August 1985, and October 1987 (³ 5500 larvae). An important feature was that fish larval abundance showed lower abundance prior to the 1983 and 1987 El Niño events. Lower monthly values were found during spring months, but also in July 1982, August and November 1986 and July 1987 (<3000 larvae per 10 m2).

Two principal month groups (I, II), separated by a distance of about 0.65 of similarity were identified from the temporal dendrogram. Warm months appeared in group I (summer and autumn), while Group II comprised the cold period (spring-early summer).

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