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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/S0717-71782002030100082 

The Jumbo Squid (Dosidicus gigas)
Fishery of the Gulf of California and its
Relation to Environmental Variability

Manuel O. Nevárez Martínez1,2,
G.I. Rivera Parra1, E. Morales
Bojórquez1, J. López Martínez2,
D.B. Lluch-Cota3, E. Miranda Mier1,
C. Cervantes Valle1

1 Centro Regional de Investigación Pesquera Guaymas,
Instituto Nacional de la Pesca. Calle 20 Sur 605
Col. La Cantera, Guaymas, Sonora, 85400, México.
E-mail: nevarez@gys.megared.net.mx
2Centro de Investigaciones Biológicas del Noroeste,
S.C. Apdo. Postal 349 Guaymas, Sonora.
C.P. 85454, México.
3Centro de Investigaciones Biológicas del Noroeste,
S.C. Apdo. Postal 128 La Paz, B.C.S.
C.P. 23000, México.

The cephalopod fishery, specifically of the jumbo squid Dosidicus gigas, is relatively recent in Mexico, and has developed in the Gulf of California and occasionally in the western coast of the peninsula of Baja California. The great abundance of squid present in the region during 1994 motivated the development of the fishery, which has characteristically high interannual variability in the catch. It has been suggested that the squid emigrate from the Gulf of California when environmental conditions are not favourable, for example during El Niño events. The squid fishery in the area would be a function of environmental variations that could influence the abundance and availability of the resource for the fishing fleet. Due to scant information from the first studies of the resource, (before 1995), it had not been possible to associate interannual variation of the catch with changes in availability or in squid abundance which would allow in turn exploration of the relationships with environmental changes or with the effect of the activity of the fishing fleet.

In this work we propose that fluctuations in the catch of jumbo squid are not due to overfishing problems, but to changes in environmental characteristics which modify the habitat of the squid, causing in turn modifications in their distribution and abundance - factors that affect the availability of the resource.

Six cruises were made during the period of May 1996 to May 1999, which show significant variations in biomass estimations, with values of 94,000 t in May 1996, increasing to a maximum of 171,000 t during October of 1996 and diminishing to 36,000 t in November 1997. The biomass showed a consistent decrease until reaching the minimum value of 3,000 t in December 1998. The population then showed a recovery of biomass, with an estimated 30,000 t for May 1999.

The results of the cruises showed that, during El Niño 1997-1998, the area of distribution of the squid was modified, since, during the cruise of May 1996, the squid occupied the area between 25 °N and 28 °N, while during May 1998 they were in a more narrow area, from 27.5 °N to 28.5°N. In later cruises, it was observed that the squid distribution widened again.

The correlation analyses indicated that, among the estimates of squid biomass and the catch of this resource arriving in Guaymas, Sonora, Mexico, there was a correlation of 58%; between the estimate of biomass and the catch of small pelagic fishes (their main food source) in the area, the correlation was 78%, while between the estimates of squid biomass and the anomalies of sea surface temperature, the correlation was of -27%.

If we consider the results of the prospecting cruises as an appropriate indicator of biomass (and of the distribution) of jumbo squid in the Gulf of California, then we could say that a decrease in squid abundance occurred between 1996 and 1998, probably due to: vertical movements of the resource in the area or emigration of organisms from the Gulf of California, since significant catches of jumbo squid were landed in Magdalena Bay, B.C.S. (12,000 tons), and/or that the jumbo squid population decreased due to increments in natural mortality, caused by changes in the biotic and abiotic characteristics of the habitat. The decrease in abundance coincided with the decrease in the distribution area from May 1996 to November 1998. The increase in the distribution area for June 1999 also coincided with the increase in abundance for that period. Similar results have been found for small pelagic fishes by other authors, who found that the variations in geographical distribution are dependent on the variations in the size of the stock, and that these variations are smaller or bigger depending on the variability of the temperature of the seawater.

At the beginning of the 80's, diverse authors outlined the possibility of a potential impact of the squid on the small pelagic fishes fishery in the Gulf of California. The results presented here indicate that it is possible that the distribution of the squid is a function of the distribution of the small pelagic fishes, which are well-known for their association with temperate waters and are therefore vulnerable to positive temperature anomalies .

The results of the correlation between squid and sardine presented here allow us to outline a relationship between squid and sardine abundance, coinciding with that outlined previously, which would imply that one of the most probable causes of decreases in the squid population in the Gulf in 1997-98 was a consequence of changes in the population of sardine of the Gulf of California in that period, owing to the presence of El Niño conditions in 1997-1998, which modified the habitat of these species. According to this, the distribution and abundance of jumbo squid inside the Gulf of California and their variation on interannual scales may be a consequence of the distribution of their food, more than of thermal characteristics.

This explanation is more probable than that which relates the abundance of jumbo squid directly to the thermal characteristics of the Gulf, since, in the period analyzed, we found that the squid were present over a very wide temperature range, indicating a high tolerance of the organism to this physical variable. This way, variations in temperature would directly influence the potential food of the squid, causing migratory movements of the preys or changes in their abundance, and increased natural mortality of the squid. According to this model, the prey responds first to changes in temperature, and later, lagged in time, the jumbo squid respond.

Even in the most adverse conditions caused by El Niño 1997-1998, during the period analyzed, squid were present in the area of the Gulf between 27.5 N and 28 N, indicating that a permanently resident population exists in the Gulf of California, although with a small populational level and small sizes.

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