Upper Gulf Of California Research Articles

Mercury and Arsenic in Muscle and Liver of the Golden Cownose Ray, Rhinoptera steindachneri, Evermann and Jenkins, 1891, from the Upper Gulf of California, México

Mercury and arsenic levels in muscle and liver of Rhinoptera steindachneri were determined in organisms collected in 2006. Element concentrations in both tissues were directly related to size. Maxima mean concentrations of Hg and As (0.41 and 59.9 microg g(-1) dry wt, respectively) were found in adults muscle. Mercury concentrations were significantly different between juveniles and adults in muscle and liver. For As concentrations, differences between juveniles and adults were found only in muscle. Mercury concentrations were higher in muscle of juveniles and adults. Arsenic concentrations were higher in liver of juveniles, and in muscle of adults. Maximum Hg concentration in muscle (0.65 microg g(-1) dry wt) was below the safe limit established by Mexican regulations for seafood.

Direct nematode predation in the marine nematode Synonchiella spiculora (Selachinematidae: Nematoda)

This study documents direct evidence of nematode predation in the free living marine nematode Synonchiella spiculora recorded in the intertidal of Santa Clara beach in the Upper Gulf of California, Mexico. The heavily armoured buccal cavity that allows S. spiculora to break larger particles and ingest other organisms is characteristic of nematodes categorized as predators and omnivores. The inferred feeding behaviour of S. spiculora and other Selachinematidae suggests that engulfing whole and relatively large prey items may be common in this group. Synonchiella spiculora could be classified in the guild of ‘predators’ sensu Jensen (1987) and Moens & Vincx (1997). Nevertheless, more direct observations are required to ‘ground truth’ inferences based on their morphological variation and to better understand their feeding ecology.

Isolation by distance among California sea lion populations in Mexico: redefining management stocks

Understanding the spatial structure of a population is critical for effective assessment and management. However, direct observation of spatial dynamics is generally difficult, particularly for marine mammals. California sea lions (Zalophus californianus) are polygynous pinnipeds distributed along the Pacific coast of North America. The species' range has been subdivided into three management stocks based on differences in mitochondrial DNA, but to date no studies have considered nuclear genetic variation, and thus we lack a comprehensive understanding of gene flow patterns among sea lion colonies. In light of recent population declines in the Gulf of California, Mexico, it is important to understand spatial structure to determine if declining sea lion colonies are genetically isolated from others. To define population subdivision and identify sex biases in gene flow, we analysed a 355-bp sequence of the mitochondrial DNA control region and 10 polymorphic microsatellite loci from 355 tissue samples collected from six colonies distributed along Mexican waters. Using a novel approach to estimate sex biases in gene flow, we found that male sea lions disperse on average 6.75 times more frequently than females. Analyses of population subdivision strongly suggest a pattern of isolation by distance among colonies and challenge current stock definitions. Based on these results, we propose an alternative classification that identifies three Mexican management units: Upper Gulf of California, Southern Baja Peninsula, and Upper Pacific Coast of Baja. This revised classification should be considered in future assessment and management of California sea lion populations in Mexican waters.

Geometry of the Wagner basin, upper Gulf of California based on seismic reflections

The Wagner basin occupies the northernmost spreading centre in the Gulf of California, located along the Pacific‐North America plate boundary. It is filled with sediments from the Colorado River that obscure its bathymetric expression; therefore it is not as well defined as other basins in the central and southern Gulf of California. To define the geometry and extension of the Wagner basin, a 2D multi‐channel seismic reflection database was used. Data were collected by Petroleos Mexicanos (PEMEX) in 1979–1980. The most important regional structural features identified are the Consag and Wagner normal faults and the Cerro Prieto strike‐slip fault. These structures play an important role in the development of the basin. The Consag fault, described for the first time in this paper, marks the western side of the basin. The eastern and northwest limits are bound by the Cerro Prieto and Wagner faults respectively. The Wagner fault intersects the Cerro Prieto fault at an angle of 130°, bending the depocentre in a NW direction, adjacent to the Cerro Prieto fault zone. The northernmost segment of the Consag fault bends 25° in a NE direction and joins the Cerro Prieto fault at an angle of 110°. Greater subsidence (up to 300 m) takes place along the northern trace of the Cerro Prieto fault, with a downthrown displacement of 400 m. The Consag and Wagner breaks obliquely intersect the Cerro Prieto fault, and, inasmuch as both are normal faults, they have small horizontal slip components which generated oblique displacement. This structural pattern is different relative to the pattern of basins located south of Wagner basin, such as the Upper and Lower Delfin basins. The orientations of the normal faults are perpendicular to the master fault (Ballenas transform fault). The relationship between normal and transform faults in the Wagner basin and the observed ‘S’ shape are typical of a basin that has not yet reached maturity. As a result of this study, the previously uncertain area (∼1330 km2) and perimeter (158 km) of the Wagner basin were defined.

Establishing a Baseline for Management of the Rock Scallop, Spondylus calcifer (Carpenter 1857): Growth and Reproduction in the Upper Gulf of California, Mexico

Abstract The rock scallop (also known as “donkey thorny oyster,” “spiny oyster,” and “thorny oyster”), Spondylus calcifer, is the largest member of any Panamic Province Spondylus and has played important economic, political, and cultural roles in coastal communities of the Eastern Tropical Pacific for thousands of years. Despite its importance, knowledge of its biology is scant. We assessed seasonal variations in shell and adductor muscle growth, longevity, reproductive age and period, and population sex ratios in the upper Gulf of California, Mexico, the northernmost area within the geographic distribution of this species. Information on shell growth and age was obtained via the use of stable oxygen isotope profiles of shell aragonite cross-referenced with mark recapture data. Spondylus calcifer forms white growth bands during winter and spring months. Shell growth accelerates during warmer months and diminishes during colder months. Likewise, the adductor muscle increases in size and weight during colde...

Larval fish assemblages, environment and circulation in a semienclosed sea (Gulf of California, Mexico)

Fish larvae and hydrographic data collected in the Gulf of California (GC) in December 2002 are used to describe larval fish assemblages (LFAs) and to explore their relationships with environmental variables (temperature, salinity, dissolved oxygen, fluorescence maximum, ϕ and superficial chlorophyll a). The Bray–Curtis dissimilarity index defined three LFAs, distributed in areas with distinctly different environmental conditions. The affinity of most of the species with the environmental characteristics of their areas of distribution could be interpreted as an indication that spawning occurred inside those areas. Particle tracking in current fields from a 3D numerical model and connectivity matrices are used to assess larval retention in the LFA areas. The technique is well suited for seas like the GC that have well-defined circulation patterns. On time scales around 30 days, retention (from 56% to 73% of the particles) occurred (1) for the North LFA in the Upper GC, (2) for the Channel-Center LFA in the anticyclone over the Northern GC and in Ballenas Channel, and (3) for the South LFA in the eddy over San Pedro Mártir basin and in the shallow zone off the peninsula. Therefore, the Lagrangian analysis revealed that the observed LFAs have a permanency long enough to allow fish larvae to remain in a favorable environment until they develop motility. The main particle export path (less than 26% of the particles) was from the North to the South LFA, following the anticyclonic main flow and coinciding with the gradient in species number and larval abundance.

Shifting environmental and cognitive baselines in the upper Gulf of California

Local fishers' knowledge (LFK) obtained from 49 fishers in the upper Gulf of California indicates that fishery resources have declined by at least 60% over the past 50 years, most likely due to overfishing and environmental changes associated with upstream damming of the Colorado River. LFK can provide supporting evidence of trends and changes. In marine ecosystems, for example, relative abundances obtained from LFK for several commercial and non-target species are closely correlated with stock assessment biomass, fishing effort, and landings reported by the Mexican Government. Rapid shifts in perception of the degree of degradation of this ecosystem, as well as greatly reduced nutrients and river flows (over just a few decades), should act as a red flag to the Mexican Government and management agencies. It is crucial for the restoration of this ecosystem that young fishers and the Mexican public are able to visualize previous states of their local ecosystems.

Temporal variation in the abundance of postlarval and juvenile blue shrimp (Litopenaeus stylirostris) and brown shrimp (Farfantepenaeus californiensis) in the Colorado River estuary

The temporal variation in the abundance and species composition of penaeid shrimp postlarvae and juveniles was studied in a tidal channel of the Colorado River estuary. Biweekly sampling during flood and ebb tide was conducted from March through November 2000. Postlarvae of the blue shrimp, Litopenaeus stylirostris, were observed beginning in May, with highest densities in early June during flood tide. A much smaller peak in densities occurred in late September, with few postlarvae found in October and November. Juvenile L. stylirostris were present in highest densities during ebb tide in mid-June, with smaller peaks in mid-July and late September. Densities of postlarval and juvenile brown shrimp, Farfantepenaeus californiensis, were much lower than those of L. stylirostris and without clearly defined peaks. The growth rate of juvenile L. stylirostris appeared similar to rates (30–60 mm month–1) reported for penaeid shrimp from the Pacific Ocean, Gulf of Mexico, and Australia. Management decisions affecting the Upper Gulf of California and Colorado River Delta Biosphere Reserve need to be cognizant of the importance of May and June as critical months in the use of the estuarine tidal channels by these commercially important species.

Sound and Fury Signifying Nothing: Using Geoinformatics to Inform Resource Policy in the Gulf of California, Mexico

In this issue of Environmental Management, Glenn and others posit that a previous study had analytical and interpretive errors in analysis of shrimp fishing in the Upper Gulf of California, Mexico. Unfortunately, much of their evidence is too indirect and of insufficient scale to address the central question of salinity in the Upper Gulf. Also, many of their suppositions did not include direct interviews with local officials or a robust understanding of remote sensing literature. This response to their rebuttal presents a set of figures and analysis demonstrating that the Colorado River flows into a closed evaporative basin known as the Laguna Salada and thus cannot flow into the Gulf of California. Readers are asked to examine the images and interpret their meaning for themselves.

Colorado River Floods, Droughts, and Shrimp Fishing in the Upper Gulf of California, Mexico

Accurate procedures that measure hydrologic variability would have great value for evaluating ecosystem impacts of upstream water use in the Colorado River Basin. Many local extractive income-based stakeholders rely directly or indirectly on ecosystem health and are adversely affected when the river does not flow. This study focuses on the impact of little or no Colorado River flow on the Mexican shrimp industry. Although there have been complaints that U.S. diversions of Colorado River flow have greatly impaired the shrimp fishery, this research demonstrates that freshwater rarely reaches the Gulf even during times of flooding, and that other factors such as overfishing may influence the instability of shrimp populations. Advanced very-high-resolution radiometer (AVHRR) satellite imagery was used to assess water volumes diverted away from the channel of the Colorado River and ultimately the Gulf of California during flooding periods. Analysis of data demonstrated that little freshwater actually reaches the Gulf even during floods because of its diversion into a large dry lake bed basin known as Laguna Salada. Fuller use of the Colorado River throughout its entire course to the sea is possible and could benefit a large cohort of users without catastrophic habitat destruction in delta ecosystems. Reconstruction of a natural earthen berm, as proposed by Ducks Unlimited, would maximize the use of floodwaters for ecosystem benefits. These findings have profound implications for local economic activities dependent on hydrologic resources in the Colorado River Delta and Upper Gulf.

The importance of Colorado River flow to nursery habitats of the Gulf corvina (Cynoscion othonopterus)

We test the hypothesis that Colorado River flow is important in providing nursery habitat for the Gulf corvina (Cynoscion othonopterus), a commercially valuable and endemic fish in the upper Gulf of California. We use oxygen isotopes in otoliths to determine when these fish inhabit isotopically different bodies of water (Gulf of California versus the Colorado Estuary). The δ18O values in the natal otoliths of C. othonopterus, significantly more negative than can be predicted by temperature alone, provide evidence that this species uses the brackish habitats created by flow of the Colorado River. A significant log-linear relationship between the natal δ18O values and the cumulative flow of the Colorado River during natal development confirms use of brackish habitat in years that the Colorado River water reached the Gulf. Natal δ18O values indicate that C. othonopterus seek out estuarine habitats with salinities between 26‰ and 38‰. Reduction in Colorado River flow since the construction of upstream dams has reduced the size of nursery habitat for C. othonopterus. Our results support the hypothesis that declines in commercial landings can be at least partially attributed to reduced river flow. Increased flow would increase nursery habitat and likely benefit recruitment.

Hydrography and circulation in the Northern Gulf of California during winter of 1994–1995

Hydrographic and current measurements in the Northern Gulf of California from December 1994 through March 1995 show conditions that are markedly different from those accepted as typical for winter. A rapid subsurface warm water intrusion (∼0.5 °C warmer) was observed, which reduced the stratification and stopped, and eventually reversed the typical anticyclonic winter circulation. An empirical orthogonal function analysis of the mean vertical structure of temperature and salinity of historical hydrographic data reveals that similar conditions occurred during March 1973 (warm water intrusion and weakening of stratification). In this study, it is proposed that these anomalous conditions are due to a combination of local and remote forcings: extensive water-mass formation in the Upper Gulf of California and the arrival of an intraseasonal downwelling coastally trapped wave to the Northern Gulf of California.

Short-term Observations of Suspended Particulate Matter in a Macro-tidal Inverse Estuary: The Upper Gulf of California

Studies on suspended matter in inverse estuaries are relatively scarce compared with similar studies in classic estuaries. The longitudinal circulation pattern in such estuaries is opposite to that observed in classic estuaries and may significantly affect the transport of suspended sediments. The Upper Gulf of California is a macrotidal inverse estuary having negligible river input but sustaining a high concentration of suspended matter, mainly derived from erosion of bed sediments. The amount of suspended particulate matter in the water column is controlled by tidal resuspension. On the western side of the Upper Gulf, horizontal fluxes of suspended particulate matter integrated between 1 m and 5 m above the bed were influenced by near-bed density-driven flow during neap tides. Maximum neap tide fluxes during ebb tide were − 21.5 g·m−1·s−1 to −24.9 g·m−1·s−1 while peak fluxes during flood tide were one order of magnitude smaller. The loss of suspended sediment to deeper water was controlled by gravity currents, which are typical of the near-bed circulation of inverse estuaries. Similar outflow from the Upper Gulf was not observed on the eastern side.

Phenotypic variation among populations of Atherinops affinis(Atherinopsidae) with insights from a geometric morphometric analysis

Morphological character variation was examined in Atherinops affinis, a temperate marine silverside with a broad geographic range and presumed limited powers of dispersal. Populations of this species were sampled from three California mainland sites, one Channel Island site and one site in the upper Gulf of California. A geometric morphometric analysis yielded higher resolution in the assessment of phenotypic divergence among the four Pacific coast populations than either body measurement or meristic analysis, and it showed that most of the shape variation among these populations occurs in the head region and body depth of the fish. All three analyses supported the hypothesis that populations of A. affinis from central and southern California coastal waters and from Santa Catalina Island are morphologically distinct from each other; the Santa Catalina Island population was found to be the most divergent. On the basis of meristic characters alone, the population of A. affinis from the upper Gulf of California was different from A. affinis populations along the Pacific coast of California. The analyses revealed variation in several morphological characters, e.g. body depth and meristics, known to vary in association with environmental conditions. Given that A. affinis appears to have low among‐population genetic variation, this species may be phenotypically plastic in response to the environmental conditions of the habitat of each population.

Colorado River Delta and Upper Gulf of California: Focus of Binational Research

Colorado River Delta and Upper Gulf of California: Focus of Binational Research

Effects of the 1997-1998 El Niño and 1998-1999 La Niña events on breeding waterbirds and sea lions in the Upper Gulf of California, México

En 1998 y 1999 revisé las colonias de aves acuáticas que anidan en Isla San Jorge, La Purinera e Isla Montague, en el norte del Golfo de California, al igual que la de lobos marinos de la Isla San Jorge. Encontré que El Niño coincidió con que los bobos cafés de San Jorge dejaran de anidar y se ausentaran de la isla, al tiempo que llegaban varios miles de bobos de patas azules. Las condiciones de El Niño coincidieron con un incremento en el número de individuos anidantes de gallitos menor, elegante y máximo y de rayadores, en Montague. Ni los patos buzo orejones en San Jorge, ni los gallitos menores en La Purinera, ni las garzas níveas, perros de agua , gaviotas risueñas, ni gallitos picogrueso, en Montague, parecen haber sido afectados. Los lobos marinos en San Jorge duplicaron aproximadamente su población, sin que esto repercutiera sobre la producción de crías. La Niña coincidió con un regreso de las poblaciones de las especies anteriores a las condiciones previas a El Niño. Además, durante 1999 en San Jorge anidaron gaviotas plomas y patos buzo de Brandt. Esa gaviota había dejado de anidar hacía mucho tiempo en San Jorge, y el pato buzo nunca se había registrado anidando ahí. Es prematuro concluir si estos registros fueron resultado de La Niña o de fenómenos en otra escala.doi: sin doi

Influence of oceanographic processes on the early life stages of the blue shrimp ( Litopenaeus stylirostris) in the Upper Gulf of California

The possible relationship between circulation patterns and the recruitment of early stages of penaeid shrimp in the Upper Gulf of California was explored by collecting postlarvae (mesh size 0.505 mm) simultaneously in two locations, one off the coast of Sonora (Golfo de Santa Clara: 31°44′49ʺN–114°33′12ʺW) and the other off the Baja California peninsula (San Felipe: 31°11′8.3ʺ N–114°53′13.9ʺW) during two complete fortnightly cycles (July 12–27, 1995 and June 30–July 16, 1996). Individuals with cephalothoracic length from 0.8 to 3.91 mm without a clear size-increasing pattern were found throughout the sampling period, suggesting continuous recruitment to the area. The circulation in the study area was simulated with a three-dimensional baroclinic model forced with tides and climatological hydrography at the mouth of the Gulf of California, and winds and heat and freshwater fluxes at the sea–air interface. Spawning stock surveys have shown that maximum concentration of mature females is near the coast of Sonora (mainland Mexico). The model predicts surface currents of about 8 cm s −1 and suggests that postlarvae found off the coast of the peninsula may come from a different reproductive unit than those found off the mainland coast. This may explain why postlarvae found in Golfo de Santa Clara (mainland) are larger (and, presumably, older) than those found in San Felipe (Baja California). Possible relationships among circulation patterns, lunar cycle, former Colorado River runoffs and time of spawning are discussed.

Spatial and vertical distributions of elements in sediments of the Colorado River delta and Upper Gulf of California

The abundance of major components (Fe, Ca, K, and organic carbon) and trace elements was analyzed in surface sediments and core samples from the Colorado River delta (CRD) and the Upper Gulf of California (UGC) using instrumental neutron activation analysis . The spatial distribution patterns of the elements studied are consistent with the model of sedimentary dynamics proposed for this area [Mar. Geol. 158 (1999) 125]: intense tidal resuspension of sediments in the delta with subsequent transport of suspended particulate matter in a southerly direction, followed by sedimentation of fine-grained material in a depocenter near the southwestern margin of the UGC. Concentrations of most of the elements are higher in the surface sediments of this depocenter. The gradual mixing of terrigenous and marine biogenic materials , normally expected for the estuarine sediments , was not detected in the CRD–UGC system because of homogenization of the sediments by tides and wind. Vertical profiles of element contents in samples of the sediment core collected in the depocenter area revealed (i) almost no anthropogenic contamination of the area by environmentally important trace elements such as Cr, Co, Sb, and As; (ii) a twofold decrease of Fe, Sc, Cr, and Co in upper core sediments; and (iii) the enrichment of the sediments at 60–62 cm depth in the core, in calcium carbonate , Ca, Sr, and the Eu n /Sm n shale-normalized ratio along with a depletion in this layer of Fe, Sc, Cr, Co, light rare-earth elements (REEs), and some other elements of terrigenous origin, presumably caused by the dilution of fluvial terrigenous material by biogenic carbonates, which were probably introduced at this level in the sediments by the action of a strong episodic winter storm, followed by the advective transport of shell fragments from the coastal clam banks or as a result of strong planktonic bloom.

Factors Influencing Suspended Sediment Flux in the Upper Gulf of California

Few studies exist of sediment dynamics in inverse estuaries, which are characterized by hypersaline water bodies and associated gravity currents and arise in arid regions where little precipitation and runoff combine with a high evaporation. Observations of velocity, density and suspended sediment concentration profiles have been made using an acoustic Doppler current profiler, CTD, optical backscatter sensors and water sampling at a shallow water site in the Upper Gulf of California over a spring to neap tidal cycle. These revealed contrasting dynamic conditions in which gravity current events produced significant net near-bed suspended sediment fluxes of 2·5gm−2s−1 out of the Gulf during neap tides. Instantaneous suspended sediment fluxes exceeded 30gm−2s−1during spring tides due to tidal resuspension, but net fluxes were near zero. The baroclinic gravity current is shown to be the dominant mechanism for net flux of suspended sediment toward deeper waters, at least during quiescent summer conditions. This flux is proposed to be confined within a wide, western along-Gulf channel. This is consistent with evidence that the Colorado River delta system is exporting sediments to deeper water after becoming unstable due to switching off of river discharge since 1930.

Two new species of Acanthobothrium Beneden, 1849 (Tetraphyllidea: Onchobothriidae) from horn sharks in the Gulf of California, Mexico.

Between 1993 and 1996, 26 individuals of two species of horn sharks were collected from the upper Gulf of California and their spiral intestines examined for onchobothriid tapeworms. Heterodontus francisci was found to host Acanthobothrium puertecitense n. sp. Based on the criteria of Ghoshroy & Caira (2001), this is a Category 4 species (with >15 mm total length, >50 proglottids, >80 testes and a symmetrical ovary). It differs from the four Category 4 species previously reported from either the western Atlantic or eastern Pacific Oceans, including A. bajaense (emend.) which was described from H. francisci, in hook-shape, total length, number of proglottids, number of testes and number of columns of vitelline follicles. H. mexicanus was found to host Acanthobothrium santarosaliense n. sp., which, based on the criteria of Ghoshroy & Caira (2001) is a Category 3 species (with >15 mm total length, >50 proglottids, >80 testes and an asymmetrical ovary). A. santarosaliense differs from the five Category 3 species previously reported from either the western Atlantic or eastern Pacific Oceans in its size, euapolytic nature, lack of dark matrix from the bases of the hooks, hook-shape, and distribution and number of testes. In addition to the difference in ovarian symmetry, A. puertecitense possesses fewer testes, fewer proglottids, is a shorter worm, possesses a more anterior genital pore and vitelline follicles which extend further forward anteriorly than in A. santarosaliense. This represents the first report of onchobothriids from H. mexicanus and the first report of onchobothriids from H. francisci in the Gulf of California. The apparent host-specificity of both new species should be viewed with caution until a greater sample of host individuals of both species can be examined. The fact that both new tapeworm species are known only from the Gulf is also considered to be a preliminary result, given the small sample of host individuals examined from these regions to date. This brings the total number of species of Heterodontus known to host Acanthobothrium to four and the total number of Acanthobothrium species described from heterodontiform sharks to five.