Enrique Morales-Bojórquez

Review of stock assessment and fishery biology of Dosidicus gigas in the Gulf of California, Mexico

Two periods in the Dosidicus gigas fishery in the Gulf of California, Mexico, have been examined. The first was in the early 1980s, when there was a single stock with multiple cohorts and recruitment to the principal fishing grounds was in May. Management schemes were difficult to establish because of the variation in the annual abundance of the cohorts. During 1983, the fishery collapsed; an effect of El Nino was an acceptable hypothesis. The second period began in 1994. Landings increased from 1994 to 1996. During this time there was only one annual cohort in the fishery with recruitment in May. A management strategy was proposed adopting the stock assessment used for Illex argentinus in the Falkland Islands; assuming an annual recruitment, an estimate of the proportional escapement and modelling the catch-per-unit-effort data of the three commercial fleets. Using this approach, the landings in 1997 were 120 000 t. However, in 1998 a decrease in landings occurred, a possible cause could have been the 1998 El Nino. Some aspects of these two periods are discussed, principally showing the differences in the management approach.

Biomass and distribution of the jumbo squid (Dosidicus gigas; d’Orbigny, 1835) in the Gulf of California, Mexico

Abstract The objective of this study was to estimate the total biomass and distribution of the population of jumbo squid Dosidicus gigas in the Gulf of California and its relation to sea temperature. Data were collected on the R/V BIP XI during a 20-day cruise (16 May to 3 June 1996). The cruise covered a grid of 59 stations within 25°10′–28°50′N and 109°30′–112°45′W. At each station, fishing was done by using attraction of light and jigs with six rings of barbless hooks. Biomass was estimated by stratified random sampling, and swept area by strata. The first method yielded an estimate of 85xa0513 metric tons (t), 95% interval of 79xa0613–93xa0413xa0t, and the second method 118xa0170xa0t (95% interval of 113xa0243–123xa0097xa0t). Squid were found in almost all the area covered by the cruise. There was a north to south gradient in catch, with the highest catch between 28° and 28°30′N and lower catch along the coast of Sonora, south of 27°N. There was no relationship between biomass, distribution, and water temperature from surface to 70xa0m depth.

Interannual variability in mantle length structure, recruitment, and sex ratio of jumbo squid, Dosidicus gigas, in the Central Gulf of California, Mexico

ABSTRACT Changes in the number and abundance of the cohorts of jumbo squid are a demographic response associated with high variability in recruitment, and have implications for availability and accessibility to the fishing fleets. In this study, we analyzed the interannual changes in the size structure, recruitment, and sex ratio of jumbo squid Dosidicus gigas in the central Gulf of California, Mexico. Data were analyzed for the 2000 to 2009 fishing seasons (from March to November). The biological data were collected biweekly at the port of Santa Rosalía, Baja California Sur, during each fishing season. We recorded mantle length and mantle weight, and sex (male or female) was identified from morphochromatic properties of fresh gonads. We concluded that the mantle length structure of jumbo squid changed between 1 cohort and 3 cohorts from 2000 to 2009. In the study zone, the presence of 2 cohorts is common. The species shows positive allometric growth, and the females are more abundant than the males in the region. The comparison between the most important fishing grounds in the central Gulf of California (Santa Rosalia and Guaymas) showed similar patterns, such as the number of cohorts, sex ratios, growth pattern, and migration pattern identified between both coasts. We believe that this could be evidence of one population that is widely distributed in the central Gulf of California.

Geoduck Panopea generosa Growth at Its Southern Distribution Limit in North America using a Multimodel Inference Approach

ABSTRACT n The Pacific geoduck Panopea generosa is distributed throughout the North Pacific temperate zone from Alaska to Baja California and is described as a species that reaches large sizes, has prolonged longevity, and exhibits slow growth. This study assessed the individual growth and population structure of the P. generosa population located at its southernmost geographic distribution limit. Shell length and total weight data were obtained from a commercial fishery established on Punta Canoas, Baja California. Individual age was determined by counting growth lines for 243 organisms. The results revealed the following averages: shell length (SL), 113.5 mm; total weight, 511.8 g; age, 12.5 y. The relationship of SL to total weight showed negative allometric growth (b = 2.16). Size-at-age data were adjusted to von Bertalanffy, Gompertz, logistic, Johnson, and Schnute growth models according to the multimodel inference (MMI) approach. The best candidate growth model was selected based on the Akaike information criterion (AIC) and the Schwartz—Bayesian criterion (SBC). The AIC indicated that the Schnute growth model was the best candidate growth model, whereas the SBC showed the Johnson growth model was best. These growth models indicate that between 7 y and 8 y of age, organisms reach 75% of their estimated asymptotic length (SL, ∼103 mm), and although the growth rate decreases subsequently, growth continues up to 25 y (maximum age observed). The MMI approach applied to the analysis of growth in Panopea species identified particular population attributes that are not observable via the von Bertalanffy model. The population of P. generosa from Punta Canoas exhibited smaller mean SL, lower mean weight, an age structure with fewer age classes, and slower growth when compared with northern populations in Washington state and British Columbia, Canada.

Selection of Models to Predict Panopea globosa Growth: Application of a Mixture Probability Distribution Function

ABSTRACT Geoduck (Panopea globosa and Panopea generosa) fisheries regulations in the Gulf of California and Baja California Peninsula, Mexico, are based on a minimum legal size (shell length, 130 mm), limited bed harvests with densities greater than 0.4 geoduck/m2, maximum allowable catch, and restrictions on fishing activity on identified beds. Data on age structure and growth rate for geoducks could greatly improve fisheries management in the region; however, variability in size-at-age data for geoducks has made it difficult to develop a sound management strategy, and the presence of outliers in the data have influenced parameter estimates significantly. Different probability density functions can be applied as fat-tail distributions in mixture probability distributions. In the current study, outlier effects on candidate growth models in P. globosa were analyzed, as well as model performance when parameters were estimated using a two-component mixture probability distribution function. The best candidate growth model was selected based on the Akaike information criterion (AIC) and the Bayesian information criterion (BIC). Results suggest that growth models analyzed yielded an estimated asymptotic length larger than 160 mm in shell length. The logistic growth model was selected following the AIC, whereas the von Bertalanffy growth model was based on the BIC. A lack of congruence between the two statistics indicated insufficient evidence in P. globosa size-at-age data to support a best candidate growth model. It is suggested that growth compensation (when cohort size-at-age variability decreases with time or age) was operating in the population evaluated. Consequently, the size-at-age data were more scattered for younger individuals compared with older ones.

Population Dynamics of Jumbo Squid Dosidicus gigas in Pacific Ecuadorian Waters

ABSTRACT Population dynamic studies of Dosidicus gigas have not been reported in Ecuadorian waters. The number of cohorts in the population and reproductive features such as sex ratio, seasonal changes in maturity stages, and size at first maturity are unknown. This knowledge is crucial in the study area, because it can provide fishery management support to Ecuadorian stakeholders. Biological data from 2013 (March–December) and 2014 (January–December) in Ecuadorian waters were analyzed. Biological sampling per month was carried out during every year in different coastal waters off of Ecuador. The biological findings indicated the presence of three size groups in the Ecuadorian squid stock, which estimated to be individuals less than 50 cm mantle length (ML). The monthly size groups changed between one and three size groups in 2013 and 2014. The ML at first maturity for females of jumbo squid estimated in 2013 was L50% = 32.4 cm ML, and L50% = 35.5 cm ML in 2014. For both fishing seasons, the ML-mantle weight relationship estimated for jumbo squid presented isometric growth, and the sex ratio for D. gigas showed that females were more abundant than males. This study found that the ML structure of jumbo squid, the number of size groups, and ML at first maturity are different from that previously estimated in traditional fishing areas of D. gigas in the eastern Pacific Ocean.

ESTIMATING BIOMASS, RECRUITMENT, AND HARVEST RATE FOR THE PACIFIC YELLOWLEG SHRIMP FARFANTEPENAEUS CALIFORNIENSIS FROM A SIZE-BASED MODEL

ABSTRACT n Catch-at-size data were analyzed for Farfantepenaeus californiensis from fishing seasons 1978/1979 to 1994/1995. The catch-at-size model could be fitted to the catch-at-size data for the different fishing seasons. It was observed that the recruitment to the fishery changed suddenly during the study period, and the recruitment to the fishery may occur over a range of length classes. The recruits were defined as size classes less than 93.5mmin abdominal length. Recruitment varied from 200–3,800 million recruits. In contrast, the size classes were larger than 93.5 mm in terms of abdominal length, and the number of adults varied from 3,500,000–50,000,000. In the study zone, it was not common to find remnant biomass of adults. Consequently, the most abundant size intervals of abdominal length were 62.4 mm, 67 mm, and 72.2 mm. The results of the harvest rate-at-size showed that the size interval from 65–80mmin abdominal length was less than 0.05. The highest levels of harvest rate-at-size were estimated to be 85–125mm in abdominal length, with an estimated variation of 0.6–0.9. It was observed that individuals less than 93.5 mm in abdominal length are in the range of length classes in which recruitment to the fishery occurs. These recruits support the fishing pressure and the yield of the fishery; in contrast, the presence of adults is scarce. Therefore, this fishery in the region is strongly recruitment dependent.

Sinusoidal Function Modeling Applied to Age Validation of Geoducks Panopea generosa and Panopea globosa

ABSTRACT n Age validation is commonly based on the marginal increment ratio (MIR). This procedure has been used to validate the annual periodicity of growth band deposition. In this study, MIR data from geoducks Panopea globosa and Panopea generosa were analyzed using a new method for age validation based on a sinusoidal model. The model used four parameters, including the amplitude |&dgr;|, defined as half the distance between the highest and the lowest values of the function; &rgr;, which is the cycle from 0–2&pgr;; &tgr;, which is the horizontal shift; and &lgr;, which is the vertical shift, or displacement. When the parameters in the sinusoidal function were estimated, the period could be computed as . The parameters were estimated using a maximum likelihood estimator. In addition, temperature and chlorophyll a were analyzed relative to the individual growth in shells. Based on parametric and nonparametric tests of the MIR data, the analysis identified a monthly progression of growth increment formation over an annual period. The data indicated that the shell growth of the outermost band is synchronized in both species; however, analysis of variance and the Kruskal—Wallis test applied to P. generosa and P. globosa, respectively, could not describe the individual growth as an annual sinusoidal cycle. Similar results were found with the environmental variables, which suggested seasonal changes in environmental variables are associated with measurements of the MIR. The sinusoidal model proposed in this study confirmed the annual cycle of growth lines for P. generosa (Ω = 12.16 mo; CI, 11.91–12.53 mo; P<0.05) and P. globosa (Ω = 11.82 mo; CI, 11.52–12.16 mo; P<0.05). The model provides reasonable fits to the data and can be used for age validation in both species.

APPLICATION OF A GNOMONIC MODEL TO ESTIMATE THE LIFE SPAN AND NATURAL MORTALITY IN PANOPEA GLOBOSA

ABSTRACT n Natural mortality estimates are commonly computed from empirical methods or catch curve analysis, and their values are assumed constant for age or size in a population; however, estimates of natural mortality usually vary spatially, temporally, or by size and age. Several factors affect natural mortality rates, such as predation, disease, senescence, cannibalism, starvation, or environmental factors. Seven gnomonic time divisions (GTD) were used to estimate the natural mortality of Panopea globosa for specific portions of its life history: 1, egg to trochophore larvae (24 h); 2, early larvae (6.5 days); 3, late larvae (11 days); 4, early juvenile (35 days); 5, juvenile (3–9 mo); 6, late juvenile (1–2 y); and 7, preadult to adult (47 y). The statistical procedure based on gnomonic time divisions assumes units of time increase as a constant proportion of time elapsed from the end of the previous biological stage; in this manner, the method estimates a vector of natural mortality values by dividing the life cycle into specific time-based subunits. The results provided the following values of naturalmortality atGTD: 1 = 537.42/y; 2 = 230.32/y; 3 = 134.35/y; 4 = 33.58/y; 5 = 2.55/y; 6 = 2.21/y; and 7 = 0.046/y. The consistency of the estimates derived were compared with previous reports of mortality rates and yielded similar values. The gnomonic time method proved to be particularly effective in estimating natural mortality based on the specific life history and life span of the geoduck.

Modeling of Growth Depensation of Geoduck Clam Panopea globosa Based on a Multimodel Inference Approach

ABSTRACT n Growth variability has been a common feature within different Panopea species, affecting the accurate estimation of growth parameters and their theoretical trajectories. Recently, the interest in solving this problem has increased; however, the methods used for individual growth modeling of Panopea spp. have not been effective in identifying the variability within the shell length-at-age composition. In the current study, a novel approach is proposed to analyze the effect of shell length-at-age variability on the individual growth and growth parameters of Panopea globosa. The shell length-at-age data were fitted to six candidate growth models: von Bertalanffy, Gompertz, Johnson, Logistic, Generalized von Bertalanffy growth model (GVBGM), and Richards using a negative log-likelihood function. The variance for each age observed () in the population was estimated for each growth model. The best candidate growth model was selected based on corrected Akaike information criterion (AICc). The results indicated that the candidate growth models analyzed had different patterns of variance. The models that had the widest difference between L∞ estimates were von Bertalanffy and Johnson growth functions. For individual growth rate parameter, the lower value was estimated for GVBGM, whereas the higher value was computed for Johnson growth model. Estimates for t0 (age when shell length is theoretically zero) parameter only could be computed for GVBGM and Logistic growth models. The von Bertalanffy growth model showed the higher variance estimated for older individuals (), and this pattern was also observed in the variance for each age observed (), denoting growth depensation in the P. globosa population. The AICc indicated that the best candidate growth model was the Johnson growth model. This approach determined the best model for extracting more accurately the biological information in the shell length-at-age data. The applied methodology should be relevant for further geoduck clam population dynamics studies, providing a tool in aiding in sustainable development of these resourceimproving estimates such as yield per recruit, harvest rates, changes in biomass, and expected yield.