Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

In this paper a depletion model with two different approaches (stochastic and deterministic) was analyzed, in order to compare the observation error hypothesis in the catch-per-unit effort (CPUE) data, and the process error in the model, as well as its effect on the recruitment and catchability estimates in the jumbo squid fishery from the Gulf of California, Mexico. Results showed an underestimation of the catchability (q) when the deterministic aproach was used. The observation error showed a bias in q (+31%) higher than in recruitment (+8%), while a Monte Carlo simulation estimated a negative bias for q, and a positive bias in recruitment. The computation of the expected value of catchability ( E(ˆqCPUE/Ci)) was 2.8 × 10–4, while the confidence intervals with the deterministic model were 3.3 × 10–4 < q < 4.1 × 10–4, showing that the estimate of E(ˆqCPUE/Ci) was not within these confidence intervals.  E(ˆqCPUE/Ci) fitted the model to the data, describing the trend of the CPUE index in time, and its implications in the management of the jumbo squid fishery.

 A common practice for inducing metamorphosis in larvae of marine invertebrates is the use of a wide variety of artificial inducers. Excess K+ and Cs+ in seawater have proved to be very effective for this purpose, but not universally effective to induce metamorphosis in different phyla of marine invertebrates. In the present study we tested the response of three species of sea urchins to excess K+ in seawater as an artificial inducer. Excess K+ in seawater was presented to the larvae as continuous (24 h) or pulse exposure in concentrations ranging from 0.01 to 100 mM. Results showed that excess K+ in the form of KCl added to seawater was an effective metamorphic inducer of the three species of sea urchins tested; the purple sea urchin Strongylocentrotus purpuratus, the red sea urchin S. franciscanus and the white sea urchin Lytechinus pictus. The response was dependent on concentration and time of exposure. Continuous exposure (24 h or more) to excess K+ (100 mM) resulted lethal to the larvae of the three species. Excess K+ (100 mM) for 15 min resulted the most effective pulse-period to induce metamorphosis in the three species. This method of induction allows us to produce synchronous metamorphosed postlarvae useful for aquaculture and studies of signal transduction mechanisms during metamorphosis of sea urchins.

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.

 Stomach contents analysis was used to describe quantitatively the feeding habits of Lutjanus guttatus. A total of 239 organisms with fork lengths between 12 and 55 cm were collected monthly from February 1993 to January 1995 in the coast of Guerrero. This species consumed a wide variety of prey organisms, mainly small fishes (index of relative importance, IIR = 67.46%) of the families Engraulidae, Clupeidae and Bregmacerotidae. Crustaceans, represented by Reptantia, Natantia and Stomatopoda, were consumed less (IIR = 30.94%). The composition of the diet varied as a function of the fish size. Seasonal and sexual differences in the diet were not significant.

The equilibrium profile concept is a useful tool for the knowledge and management of the coastline. This concept is based on several assumptions that rarely are satisfied in nature. One of these considers that the geologic setting has no influence in the profile morphology. The Victoria beach is a good example that questions this hypothesis. Muñoz-Pérez (1996) and Muñoz-Pérez et al. (1999) proposed an analytical expression of equilibrium beach profile for reefprotected beaches. In this work, data measured at Victoria beach are used to confirm the goodness of this model. The results obtained show that the occurrence of a horizontal rocky platform in subtidal zone modifies the beach slope and the seasonal evolution of the profile.

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The differential sensitivity of five chlorophyll c-containing marine microalgae to different components of solar radiation, e.g. photosynthetic active radiation (PAR), ultraviolet-A (UV-A) and ultraviolet-B (UV-B), was investigated in an exclusion experiment involving exposure to PAR, PAR+UV-A and PAR+UV-A+UV-B (P-, PA- and PAB-treatment, respectively) for 20 min and subsequent recovery for up to 24 h in dim light. The decrease in the variable to maximal chlorophyll fluorescence ratio (Fv/Fm) was used as indicator of photoinhibition. Changes in photosynthetic oxygen production, cell densities and pigment contents were also ascertained. The ratio Fv/Fm decreased in all the algae after exposure, but differences were found between the algae and the treatments. In relation to the inhibition extent, Chaetoceros sp. was the least affected alga in each treatment, while Phaeodactylum tricornutum was the most sensitive. Data of Fv/Fm during recovery fitted well to a sigmoid exponential function, and calculated constants were used to quantify the particular recovery rate of each alga. In general, recovery time did not show a direct relationship with the extent of inhibition. The highest recovery rate was shown by P. tricornutum cells exposed to only PAR, and the lowest by Isochrysis galbana cells exposed to PAB. There were no losses of cell density at the end of the recovery period in relation to the initial cell density in any of the algae. Photosynthetic oxygen production dropped in the five algae in all treatments and showed a similar evolution pattern to Fv/Fm during recovery, except for P. tricornutum and Amphidinium sp. Results of this study point out that capacity for photosynthesis inhibition is specific for each alga and, consequently, it should be taken into consideration for a reliable assessment of differential sensitivity to ultraviolet radiation among diverse marine phytoplanktonic species.

 Very little information is available with respect to dynamic aspects of oocyte development and to yolk composition of tuna species. Since histological approaches can offer considerable information about the ovarian development of fish, and because different cytochemical/immunohistochemical tests are suitable tools for proving the presence of different macromolecules in several organs/tissues/cells, they can be good biomarkers of the reproductive mechanism in fish. The present study investigates the presence and distribution of carbohydrates, proteins, glycoconjugates, lipids, calcium, iron and vitellogenin in the bluefin tuna, Thunnus thynnus oocytes during the synthesis of yolk (globules and granules) in the vitellogenic phase. During the initial vitellogenic phase, oocytes (diameter: 249 ± 21.87 mm) contain oil globules (or vacuoles) which consist exclusively of neutral lipids. During this phase very small yolk granules appear around the cytoplasm. Glycolipids, phospholipids, glycoproteins (Nacetyl- D-galactosamine –GalNAc– sugar residues), calcium, proteins rich in tyrosine, tryptophan, lysine, arginine, cysteine and cystine, as well as vitellogenin are the main constituents of the yolk granules and the follicular envelope of these real vitellogenic oocytes (diameter: 386 ± 79.04 mm). The intergranular cytoplasm of the vitellogenic oocytes also contain glycogen and glycoconjugates with Mannose –Man– and/or Glucose –Glc–; N-acetyl-D-galactosamine –GalNAc–; L-Fucose –Fuc– and Nacetyl- D-glucosamine –GlcNAc– and/or sialic acid –NANA– sugar residues. The zona radiata is mainly composed of proteins; in this cellular layer, scarce neutral glycoproteins and lipids (phospholipids/glycolipids) are also present.

 The costal zone of the Northeastern Mediterranean (Catalan Sea) was divided along (North, Center and South) and across (Coastal, Middle and Far fields) to see the influence of the continental water runoff over the stoichiometric ratios Dissolved Inorganic Nitrogen (DIN):P:Si. The ratios N:P show that nitrogen acts in a great percentage as a potential limiting nutrient, pattern which is clearer in the middle field with more than 60% of the cases. In contrast, in the coastal field P could act as the potential limiting nutrient (40% approximately). A two-way ANOVA showed significant differences between effects 1 and 2 and their interaction, which means that along and across the study area the concentrations and the stoichiometric ratios were different among each other. When the three nutrients (N, P and Si) were considered, silicate acts as the potential limiting nutrient with more than 50% of the cases in most fields and zones, with percentages as high as 75% in the case of the central middle field. Assuming that the phosphate concentration is the unique source of P for the phytoplankton, we estimated that the "potential" primary productivity of the surface waters in the study zone is 32.6 µg Chla L–1 for the coastal field, 4.3 µg Chla L–1 for the middle field and 2.2 µg Chla L–1 for the far field, differences due to coastal eutrophication. We suggest that the nutrient runoff along the continental waters and/or the significant changes in the nutrient ratios induced by anthropogenic activities could favor the seasonal incidence of noxious algal blooms along the Catalan Coast.

 The effects of different incident irradiances on growth, photosynthesis, pigment content and nutrient uptake were studied in dense cultures of the cryptophyte Rhodomonas salina (Wislouch) Hill y Wetherbee. Cells were grown for ten days at different incident irradiances: 11, 33, 75, 260 and 320 µmol photon m-2s-1. The average pigment content (phycoerythrin and chlorophyll a) was lower when cells were grown at high irradiances (260 and 320 µmol photon m-2s-1) compared with cells grown under low irradiances (11, 33 and 75 µmol photon m-2s-1).The maximum photosynthetic rate (Pmax) was maximal at 75 µmol photon m-2s-1 , decreasing considerably at the highest irradiance in which apparent photosynthetic efficiency per cell and per chlorophyll a unit (αcell and αchla) also decreased. Results showed that dense cultures of R. salina grew optimally in a range between 75 and 260 µmol photon m-2s-1 with optimal photosynthetic performance at 75 µmol photon m-2s-1. Nitrogen and phosphorus depletion occurred as a consequence of the exponential growth, except under the lowest and the highest irradiances (11 and 320 µmol photon m-2s-1, respectively). Associated to N-limitation, phycoerythrin (PE) and chlorophyll a decreased considerably. It is suggested that R.salina responds to nitrogen-depleted conditions by mobilizing nitrogen from PE, this behaviour being modelled by a relationship between external nitrogen availability and PE mobilization.