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The population structure of the jumbo squid (Dosidicus gigas) is complex, containing several cohorts and three groups defined by their size (small, medium, and large) and by differences in maturation, growth, and life span. Several authors have indicated the possibility of such groups representing discrete genetic units even at level subspecies or species in statu nascendi. Genetic divergence was tested in samples from the Gulf of California (Mexico) and Peruvian Sea by estimation of population divergence statistics, an exact test of homogeneity of allele frequencies, analysis of molecular variance, and genealogical trees applied to data obtained with two molecular markers: RAPDs and mtDNA sequences identified by SSCPs. Neither significant values of θ (FST) nor significant heterogeneity in allele frequencies were detected. Lack of evidence does not imply complete lack of differentiation among the groups but supports the fact that a geographically spread population can have different size groups without relevant genetic differentiation, implying that the hypothetical genetically differentiated groups can occur in different ecological niches.

A regular seasonal pattern of periodicity was detected in monthly catch data for Dosidicus gigas during the most recent period of high abundance of the species off Chile. Monthly catch data covering from 2002 to 2005 were grouped into three large zones, and the trend of the time series was removed by using loess smoother. The residuals between the original and the loess trend curve were computed and analyzed using autocorrelation and cross-correlation at different lags, and a trigonometric model was fitted to detect seasonal oscillation. A coherent pattern in the short-term monthly residuals was observed in the three time series, revealing a similar underlying process in the catch data, with a six-month cycle. We postulate that the seasonal and interannual fluctuations observed in the catch records could be related to the reproductive success of the species through the average occurrence of two reproductive cycles per year, and hence the generation of two cohorts per year.

The oocyte structure of jumbo squid (Dosidicus gigas) female gonads was analyzed to validate morphochromatic sexual maturation stages based on a six-phase scale. Samples were obtained fortnightly from the Santa Rosalía area, Baja California Sur, from June 2001 to November 2002. Histological preparations were obtained from each gonad to count the number of oocytes at each level of development. The frequency of oocytes at each level was then used to estimate a maturity index (MI) to assess the correspondence between morphochromatic maturation stages and the oocyte structure in the gonad tissue. The histological analysis showed that morphochromatic stages I, II and III were ruled by oocytes in developmental level 2 or less (i.e., secondary growth has not yet begun), and thus correspond to sexually immature juveniles. Stages IV, V and VI were ruled by oocytes in more advanced developmental levels and correspond to mature or maturing adults. According to the analysis of variance, the morphochromatic maturity scale allowed sexually immature individuals to be readily and reliably distinguished from mature ones. A detailed analysis of MI confidence intervals showed that each morphochromatic maturity stage had a specific oocyte structure, except for stages II and III, which presented morphological differences.

The population structure of the jumbo squid (Dosidicus gigas) is complex, containing several cohorts and three groups defined by their size (small, medium, and large) and by differences in maturation, growth, and life span. Several authors have indicated the possibility of such groups representing discrete genetic units even at level subspecies or species in statu nascendi. Genetic divergence was tested in samples from the Gulf of California (Mexico) and Peruvian Sea by estimation of population divergence statistics, an exact test of homogeneity of allele frequencies, analysis of molecular variance, and genealogical trees applied to data obtained with two molecular markers: RAPDs and mtDNA sequences identified by SSCPs. Neither significant values of θ (FST) nor significant heterogeneity in allele frequencies were detected. Lack of evidence does not imply complete lack of differentiation among the groups but supports the fact that a geographically spread population can have different size groups without relevant genetic differentiation, implying that the hypothetical genetically differentiated groups can occur in different ecological niches. [ABSTRACT FROM AUTHOR]

A regular seasonal pattern of periodicity was detected in monthly catch data for Dosidicus gigas during the most recent period of high abundance of the species off Chile. Monthly catch data covering from 2002 to 2005 were grouped into three large zones, and the trend of the time series was removed by using loess smoother. The residuals between the original and the loess trend curve were computed and analyzed using autocorrelation and cross-correlation at different lags, and a trigonometric model was fitted to detect seasonal oscillation. A coherent pattern in the short-term monthly residuals was observed in the three time series, revealing a similar underlying process in the catch data, with a six-month cycle. We postulate that the seasonal and interannual fluctuations observed in the catch records could be related to the reproductive success of the species through the average occurrence of two reproductive cycles per year, and hence the generation of two cohorts per year. [ABSTRACT FROM AUTHOR]

This study describes the population structure of jumbo squid (Dosidicus gigas) in the area of Santa Rosalía (central Gulf of California) during the years 2003 and 2004, and analyzes the interannual variability in the size structure over a wider time period, 1996–2004 (except 2000–2002). The results revealed clear differences in the size structure and sexual maturity of males and females between 2003 and 2004. The jumbo squid population observed during the 2003 fishing season showed a high proportion of large and sexually mature individuals, whereas most specimens sampled during 2004 were smaller and immature. Expanding our time period, we observed a strong interannual variability in the size structure of jumbo squid within the Gulf of California, which was also reflected in the size at maturity. These changes in the population structure seem to be related to the occurrence and intensity of El Niño events. We recommend taking this variability into account at the beginning of each fishing season when the authorities establish the management strategy for the jumbo squid fishery in the Gulf of California. [ABSTRACT FROM AUTHOR]

The oocyte structure of jumbo squid (Dosidicus gigas) female gonads was analyzed to validate morphochromatic sexual maturation stages based on a six-phase scale. Samples were obtained fortnightly from the Santa Rosalia area, Baja California Sur, from June 2001 to November 2002. Histological preparations were obtained from each gonad to count the number of oocytes at each level of development. The frequency of oocytes at each level was then used to estimate a maturity index (MI) to assess the correspondence between morphochromatic maturation stages and the oocyte structure in the gonad tissue. The histological analysis showed that morphochromatic stages I, II and III were ruled by oocytes in developmental level 2 or less (i.e., secondary growth has not yet begun), and thus correspond to sexually immature juveniles. Stages IV, V and VI were ruled by oocytes in more advanced developmental levels and correspond to mature or maturing adults. According to the analysis of variance, the morphochromatic maturity scale allowed sexually immature individuals to be readily and reliably distinguished from mature ones. A detailed analysis of MI confidence intervals showed that each morphochromatic maturity stage had a specific oocyte structure, except for stages II and III, which presented morphological differences. [ABSTRACT FROM AUTHOR]

The fishery of the giant squid (Dosidicus gigas D'Orbigny, 1835) is an unstable resource that has shown wide variations in its abundance and availability in the last 20 years, which were tried to be explained by a hypothesis that related the effects of El Niño and the sea temperature on the fishery. Recently, with data obtained in research surveys, the hypothesis that water temperature is a factor that affects the displacement of the squid has been considered again, in such a way that catches can be related to the average temperature in the fishing zones, validating the hypothesis with relative abundance data (AR), obtained in a research survey, which are known to be highly skewed. In this way, the accuracy in the catch-environment relationship of the giant squid is determined by two factors: (a) the correct estimation of the resource's AR index, which must be corrected with an unbiased estimator of minimum variance, under a lognormal distribution, what allows working data series without discarding information; and (b) the functional relationship of AR with temperature and therefore, recognizing that the relationship between temperature and squid catches is not direct (linear), thus understanding that the effect of the sea temperature on the squid's AR index is random, since in the AR there is an observation error that must be evaluated.

The relation between water temperature and the capture of giant squid in the Gulf of California was analyzed. Data were collected in May and June 1996 at 60 stations. Each fishing session lasted 30 minutes, and an average of 100 organisms per 0.5º · 0.5º square were caught. The hypothesis was that if water temperature is a factor affecting squid movement, we can infer that the catch of squid is successful in an optimum temperature range. With both exploratory and correlation analyses, the conclusion was that the hypothesis was true.