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

The first check-list of fishes from La Paz Bay, Baja California Sur (Mexico), is presented. A total of 390 species, belonging to 251 genera and 106 families, are reported. The list includes species collected in the area between 1981 and 1986, species that were sighted (and positively identified) and species reported in the literature. The specimens collected were catalogued and deposited in the ichthyological collection of CICIMAR, IPN, in La Paz, B.C.S.

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In this study we describe the spatial variability of the particulate organic matter (POM), expressed in terms of proteins, carbohydrates and chlorophylls, and the specific abundance of phytoplankton at Concepción Bay during the maximum reproductive peak of Argopecten circularis. The distribution of these variables shows two zones of high concentration of particles: one located in the first “third” of the bay and the other in the upper end. High values of chlorophyll a were due to the nannophytoplankton size class, which is the major contributor to the total phytoplankton abundance. The most abundant species of microphytoplankton were Chaetoceros curvisetus, C. lorenzianus C. teres, C. cinctus and Lithodesmiun undulatum. The phytoplanktonic-POM and non-phytoplanktonic-POM contribution estimated at the surface shows that the highest protein percentage (69.5%) was due to phytoplankton, whereas at 10 m depth it corresponded to non-phytoplankton-POM or detritus. This indicates that a high quality POM in the water column represents a potential source of food for the different development stages of A. circularis.

Surface wind data measured in San Felipe, B.C., during some months in the summer of 1984 and spring of 1987 are analyzed and described. The relative importance of the breeze system in relation to the synoptic field is established, specially during the summer. Monthly hodographic representation in the time domain permits the study of the breeze system, provides information on the average wind direction and speed for each hour of the day, and presents seasonal events. Typical days from some of the months are represented, which constitute one of the first contributions to describe the phenomenon in this region. The rotary spectra in the frequency domain permit us to state that during the 1984 period of measurement, the diurna1 band explains 57% of the total spectral energy, while during 1987, the diurna1 and synoptic bands explain 35 and 31%, respectively. The synoptic events in each period of measurement can also be observed in the filtered time series. They demonstrate that when winds stronger than 5 m/s are present and persist in direction longer than one day, the breeze system is interrupted making the land breeze disappear. The first two months of the 1987 spring period of measurement still reflect winter conditions as described by severa1 authors. This study suggests that the transition period is reduced to May and June only.

The annual pattern of distribution and abundance of tintinnids and copepods -taking them as the representatives of the major components of microzooplankton (20 to 200 µm) and mesozooplankton (200 µm to 2 mm), respectively-was studied at the Pichavaram mangroves (India). Monthly samplings were made from January to December 1989, covering three stations. For tintinnids, density varied from 60 to 44,990 org./m3. Agglomerated tintinnids were the dominant form. The maximum abundance (80,740 org./m3) of copepods was recorded in the freshwater and neritic water mixing zone (station 2) during summer and the lowest (80 org./m3) in the freshwater zone (station 1). The genera Acartia and Acrocalanus (belonging to the suborder Calanoida), Macrosetella and Euterpina (belonging to the Harpacticoida), and Oithona (belonginp to the Cyclopoida) were coincident with the maximum species abundance at station 2. Species like Acartia southwellii and Oithona brevicornis were observed during the lower abundance period. Calanoid and harpacticoid copepods were also dominant at station 3. A significant positive relationship between the abundance of tintinnids and copepods was observed. The seasonal distribution and abundance of tintinnids and copepods are discussed in relation to hydrographical parameters.

The efficiency of a Renfro beam trawl net was tested in vegetated and nonvegetated habitats of Términos Lagoon, Mexico. The white shrimp, Penaeus setiferus (87%), predominated over the brown shrimp. Penaeus uztecus (13%), in the naked substrate (Palizada Vieja), whereas the pink shrimp, Penaeus duorarum (98%), was the most abundant penaeid shrimp in the habitat with vegetation (Pájaros Island). In the substrate covered by vegetation, only the brown shrimp (2%) was present in addition to pink shrimp. Estimated penaeid shrimp density through the first sample ranged from 1.2 and 1.3 org. rn–2 in Palizada Vieja to 1.8 org. rn–2 at Pájaros Island. The efficiency of the beam trawl net was estimated at 28% in naked substrate when trawlings were done countercurrent. Net efficiency decreased to 17% when trawlings were done along the water flow. Net efficiency on vegetated substrates was estimated at 15%. Size composition of the first tow was significantly different (Χ2, P = 0.05) from the total size distribution of penaeids present in the area enclosed in both substrates, although mean sizes were similar. However, the size distribution obtained with two replicates did not show significant differences in both substrates at the same probability level.

Studies of composition, abundance and specific richness of fishes caught in Concepción Bay, B.C.S., were carried out during 1987. A total of 822 organisms from 30 families, 50 genera and 59 species were analysed. The total biomass was 440.62 kg. Nine species were dominant: Nematistius pectoralis, Kiphosus elegans, Gerres cinereus, Scomberomorus concolor, Calamus brachysomus, Scomberomorus sierra, Haemulon steindachneri, Trachinotus rhodopus and Mugil cephalus. The study area has different habitats and a great richness. A list of 212 species from Concepción Bay based on 1944-1992 bibliography is presented.

An unusually extensive and well preserved marine abrasion platform of Late Pliocene age is present 84 m above sea leve1 north of El Rosario, in Baja California. The surface extends for 6 km along the coast and is up to 3 km wide. The abrasion platform is a major disconformity that separates siltstones of the Upper Cretaceous Rosario Formation from the basal conglomerates of the Upper Pliocene Cantil Costero Formation. During its creation under transgressive conditions, the platform was kept clear of nearshore sediments and colonies of the pholadid bivalve Penitella penita (Conrad, 1837) with densities of up to 200/m2, bored into the underlying platform rocks. Tectonic uplift of the peninsula and the Sierra San Pedro Martir, starting about 2 m.y. ago, stimulated a massive progradation of land-derived clastics, which inundated the platform and locally exterminated the pholadid bivalves. This example clearly illustrates a model of transition from subtidal to intertidal conditions, in contrast to unconformities of strictly submarine origin.

Time series of temperature, salinity, dissolved oxygen and chlorophyll a were obtained during one year in La Cruz Lagoon, Sonora (Mexico), in order to know the processes that generate variability in the lagoon. Spectral analysis of these time series showed that the variability was associated to processes with periods of 3 to 15 days. These fortnightly periods are related to spring and neap tide cycles, and the three-day periods are due to wind and/or differences in the sampling hour. The flux index (intertidal volume to total volume ratio) estimated for this lagoon is high, and it can be considered that the circulation and variability of this lagoon are determined by the sequence of the spring and neap tide cycles.

The spawning period, length and age at first maturity of Scomber japonicus were determined from fish measuring 173 to 383 mm, sampled monthly from commercial purse-seinc catches in Vizcaíno Bay from 1984 to 1986. Macroscopic observations of the gonads indicate an annual spawning period from April to August with a maximum in June. Two condition factors and the monthly growth rate in weight per age varied with the spawning period. Otoliths were used to determine age. Length and age at first maturity were 293 mm standard length and 4.3 years, respectively. An important proportion of four-year-old and older mature females suggests that these ages contribute significantly to the spawning biomass.