Search

In the Eastern Tropical North Pacific Oxygen Minimum Zone (ETNP‐OMZ), fish larvae undergo development amidst highly variable dissolved oxygen environments. As OMZs expand, understanding the implications of low‐oxygen environments on fish development becomes increasingly relevant for fisheries management and ecosystem modeling. Using horizontal zooplankton tows to track five oxygen levels (oxic [200 μmol/kg], hypoxic [100 μmol/kg] suboxic [10 μmol/kg], anoxic [<1 μmol/kg], and deep [10 μmol/kg at ~ 1000 m depth]), this study analyzed the three‐dimensional distribution of fish larvae and adults across the ETNP‐OMZ. Results revealed a wide midwater anoxic core, extending from Costa Rica to Baja California, that was almost devoid of fish larvae (< 1 larvae/1000 m3). Early larval stages primarily inhabited the oxic and hypoxic levels above the core, while postflexion and transformation stages occurred across a wider oxygen gradient, including the deep level below the anoxic core. Epipelagic species (e.g., Auxis sp.) were predominantly found in the surface oxic level, whereas coastal‐demersal species (e.g., Bregmaceros bathymaster, Ophidion spp.) were prevalent in the hypoxic level above the core. Meso‐bathypelagic species (e.g., Diogenichthys laternatus, Cyclothone spp.) were present throughout the study area, including below the anoxic core as transformation larvae and juveniles. These findings indicate that a vertical expansion of anoxic waters in OMZs could further constrain the habitat of epipelagic species, while also affecting the ontogenic vertical movements of meso‐bathypelagic species. [ABSTRACT FROM AUTHOR]

This paper aims to identify the perception of preschool teachers regarding the devaluation of their profession, in their family, society and the State, as a sign of emotional precariousness. Based on a qualitative methodology, 20 private preschool teachers were interviewed from the society of Querétaro, Mexico. Conclusions: the devaluation that teachers perceive regarding their work in State institutions, in the family, and in society, considering that this type of work derives from their status as women and that it constitutes an extension of the domestic one, generates emotional suffering and naturalization of certain roles, and invisibility. [ABSTRACT FROM AUTHOR]

This research study obtained the first morphological description of the Colorado snapper (Lutjanus colorado) larvae assisted by DNA barcoding as a molecular identification tool. Sixteen Lutjanidae larvae were separated from zooplankton samples and selected for this study. A fragment of the mitochondrial gene cytochrome oxidase subunit I (COI) of 658 bp was used in the analyses of intra‐ and interspecific genetic divergences; a neighbour‐joining tree (NJ) of K2P distances was performed with reference sequences of 15 Lutjanidae species from the Northeastern Tropical Pacific. Genetic divergences and the NJ tree identified 16 larvae as L. colorado. Morphological investigations of larvae at different developmental stages were performed; similarities and differences are discussed in comparison to four species described previously for the Northeastern Pacific. Pigmentation patterns were the best diagnostic features, particularly the caudal melanophores, at least up to 12.4 mm body length. [ABSTRACT FROM AUTHOR]

According to the typical thermal structure of the ocean, the water column can be divided into three layers: the mixed layer, the thermocline and the deep layer. In this study, we provide a new methodology, based on a function adjustment to the temperature profile, to locate the minimum and maximum depths of the strongest thermocline. We first validated our methodology by comparing the mixed layer depth obtained with the method proposed here with three other methods from previous studies. Since we found a very good agreement between the four methods we used the function adjustment to compute the monthly climatologies of the maximum thermocline depth and the thermocline thickness and strength in the global ocean. We also provide an assessment of the regions of the ocean where our adjustment is valid, i.e., where the thermal structure of the ocean follows the three-layer structure. However, there are ocean regions where the water column cannot be separated into three layers due to the dynamic processes that alter it. This assessment highlights the limitations of the existing methods to accurately determine the mixed layer depth and the thermocline depth in oceanic regions that are particularly turbulent such as the Southern Ocean and the northern North Atlantic, among others. The method proposed here has shown to be robust and easy to apply. [ABSTRACT FROM AUTHOR]

The totoaba (Totoaba macdonaldi) is a sciaenid (croaker) fish endemic to the Gulf of California with high commercial importance. Because it was considered at risk of extinction (since 2021 it was reclassified as vulnerable by the IUCN), and aquaculture procedures were developed for restocking and commercial purposes. The present study was conducted with the hypothesis that the early stages of totoaba present depensatory individual growth and an observed variance-at-age modelling approach is the best way to parametrize growth. Ten models were tested including asymptotic, non-asymptotic, exponential-like, and power-like curves including a new one that represents a modification of Schnute's model. The model that best described the growth trajectory of larval and early juveniles of T. macdonaldi in a controlled environment is a sigmoid curve with two inflexions, related to changes in the feeding regime. [ABSTRACT FROM AUTHOR]

According to the typical thermal structure of the ocean, the water column can be divided into three layers: the mixing layer, the thermocline and the deep layer. In this study, we provide a new methodology, based on a function adjustment on the temperature profile, to locate the minimum and maximum depths of the thermocline, and therefore its thickness, to separate the water column into layers. We first validated our methodology by comparing the mixed layer depth obtained with the method proposed here with that of 5 two previous studies. Since we found a very good agreement between the three methods we used the function adjustment to compute the monthly climatologies of the mixed layer depth, the maximum depth of the thermocline and the thermocline thickness, throughout the ocean. We also provide an assessment of the regions of the ocean where our adjustment is valid, and consequently the regions where the thermal structure of the ocean follows the three-layer structure. However, there are ocean regions where the water column cannot be separated into three layers due to the dynamic processes that alter it and the major contribution of salinity to stratification. This assessment highlights the limitations of the existing methods to accurately determine the mixed layer depth and the thermocline in oceanic regions that are particularly turbulent as the Southern Ocean and the northern North Atlantic, among others. The method proposed here has shown to be robust and easy to apply, and it can be used in both local and global studies. [ABSTRACT FROM AUTHOR]

Obtaining the best possible estimates of individual growth parameters is essential in studies of physiology, fisheries management, and conservation of natural resources since growth is a key component of population dynamics. In the present work, we use data of an endangered fish species to demonstrate the importance of selecting the right data error structure when fitting growth models in multimodel inference. The totoaba (Totoaba macdonaldi) is a fish species endemic to the Gulf of California increasingly studied in recent times due to a perceived threat of extinction. Previous works estimated individual growth using the von Bertalanffy model assuming a constant variance of length-at-age. Here, we reanalyze the same data under five different variance assumptions to fit the von Bertalanffy and Gompertz models. We found consistent significant differences between the constant and nonconstant error structure scenarios and provide an example of the consequences using the growth performance index -0 to show how using the wrong error structure can produce growth parameter values that can lead to biased conclusions. Based on these results, for totoaba and other related species, we recommend using the observed error structure to obtain the individual growth parameters. [ABSTRACT FROM AUTHOR]

Copyright of Dilemas Contemporáneos: Educación, Política y Valores is the property of Dilemas Contemporaneos: Educacion, Politica y Valores and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study investigated the relationship between phytoplankton biomass and taxonomic composition and hydrographic variables in the Northeastern Tropical Pacific for June 2015, March 2016, and September 2016. Hydrographic data were measured between surface and 100 m; samples were collected at the surface and the deep chlorophyll maximum (DCM) along one or two transects. Pigments were quantified by high-performance liquid chromatography; the CHEMTAX software was used to determine the relative contribution to chlorophyll a of the main taxonomic groups. Our results show that the studied region is characterized by a stable vertical distribution of phytoplankton biomass regardless of the season (winter, spring or summer). A subsurface maximum (DCM) is always observed close to the bottom of the mixed layer where there is a higher abundance of larger groups (diatoms and Prymnesiophytes) while at the surface community, composition was generally dominated by picoplankton (Cyanobacteria and Prochlorococcus), and occasionally Prymnesiophytes. However, during the spring cruise (June 2015), affected by the 2015–2016 El Niño, phytoplankton biomass at the DCM markedly decreased along with an increase in the abundance of Chlorophytes. On the other hand, in September 2016, there was an unexpected increase in phytoplankton biomass at the DCM, although stratification was strong, and Prymnesiophytes comprised 60% of the community at the surface. The evaluation of nutrient and light will be necessary in future studies to determine their role in this temporal variability. Finally, chemotaxonomy (HPLC/CHEMTAX) proved to be a valuable tool for describing phytoplankton distribution at group level in this region and its relationship with physical processes. [ABSTRACT FROM AUTHOR]

The present state of deoxygenation in the northern limits of the shallow oxygen minimum zone off Mexico is examined in order to detect its effects on larval fish habitats and consider the sensitivity of fish larvae to decreased dissolved oxygen. A series of cruises between 2000 and 2017 indicated a significant vertical expansion of low oxygen waters. The upper limit of suboxic conditions (<4.4 μmol/kg) has risen ~100 m at 19.5°N off Cabo Corrientes and ~50 m at 25°N in the mouth of the Gulf of California. The larval habitat distribution was related to the geographic variability of dissolved oxygen and water masses between these two latitudes. One recurrent larval habitat, with Bregmaceros bathymaster larvae as the indicator species, extended throughout the water column off Cabo Corrientes from Subtropical Subsurface Water (suboxic conditions) to the surface (220 μmol/kg). The second recurrent habitat was located between the oxycline (>44 μmol/kg) and the surface in association with the Gulf of California Water, with Benthosema panamense as the indicator species. During the warm El Niño event of 2015–2016, a tropical larval fish habitat (Auxis spp.) associated with Tropical Surface Water appeared to change the larval habitat distributions. These results indicate that some species are resilient to changes of dissolved oxygen and temperature generated by El Niño events and by continuing deoxygenation, although other species with more limited environmental windows could be affected by deoxygenation, probably leading to a change of the pelagic ecosystem over time. Plain Language Summary: Dissolved oxygen in the ocean is crucial for the biological cycles of all organisms. There are vast zones in the ocean where the oxygen has dropped to levels that only a few, very well adapted, organisms can live. Dissolved oxygen measurements in the past two decades in the Mexican Pacific have shown that the concentrations have decreased, and water layers with nearly no oxygen are now closer to the surface, potentially impacting larval fish species that are not adapted to extremely low oxygen concentrations. Nevertheless, there is a set of fish larvae that is well adapted to low dissolved oxygen concentrations, principally small forage fish, which have a permanent presence in the poorly oxygenated waters, while some larvae of species with fisheries interest, like small tunids, only live in the well‐oxygenated surface layer and are more abundant in warm years. The loss of oxygen in the Mexican Pacific has not had an effect on the small forage fish larvae but can affect those larvae of fish of commercial interest, with less adaptation to low oxygen concentrations. Key Points: Deoxygenation processes occur in the northern limit of OMZ off MexicoThinning of the hypoxic layer affects its inhabitants in different waysFish larvae of some species show resilience to changes of dissolved oxygen [ABSTRACT FROM AUTHOR]

In this study, we explored the changes in the vertical distribution and abundance of copepod nauplii and ichthyoplankton every hour in three different depth strata during a period of strong internal tides, which have been shown to accumulate and transport plankters. In the deeper stratum, the abundance of copepod nauplii was significantly greater, significantly increased during the cold phase of the internal tide, and was significantly correlated with both total and baroclinic current flows in the direction of internal tide propagation. On the other hand, ichthyoplankton abundance was generally low, with no stratification in vertical distribution, no significant changes across the two phases of the internal tide, and no correlation at any depth with any current flows. The cold phases of the internal tide were characterized by a shallow thermocline, a cooler water column, and a significant increase in the abundance of copepod nauplii in the bottom stratum. On the other hand, the warm phases of the internal tide were characterized by abrupt warming in surface waters, a depression of the thermocline, and a significant decrease of copepod nauplii in the bottom stratum. The depth distribution and buoyancy of the different groups of larvae may be responsible for the differences found. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Biologia Marina y Oceanografía (RBMO) is the property of Universidad de Valparaiso, Facultad de Ciencias del Mar and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: A simplified analytical model was used to solve the salinity balance equation and study the relative contributions of freshwater flux and salt advection to the salinity tendency between the Gulf of Tehuantepec and Cabo Corrientes (14–22 °N). The model used climatological mixed‐layer salinity, satellite‐derived geostrophic velocity and evaporation minus precipitation data in a four‐domain scheme. The mean circulation derived from the model largely coincides with previous reports and suggests that, in the steady state, the Mexican Coastal Current is decoupled from the Tehuantepec region. The analysis of the time‐dependent variability showed that the salt advection can be largely explained by the annual variations of the alongshore velocity (corresponding with the Mexican Coastal Current) and an average salinity. At the seasonal scale, the salt advection and the freshwater flux have similar contributions to the resulting salinity tendency. Near Tehuantepec, due to a local salinity regime, the analytical model does not represent well the observations, while in Manzanillo and Zihuatanejo the agreement between the model and the observations is good in both amplitude and phase. The accuracy of the model in representing the observations is improved in the first third of the year by inclusion of the semiannual scale and the nonlinear processes in the equation of salt advection. [ABSTRACT FROM AUTHOR]

Determining the relative influence of biotic and abiotic factors on genetic connectivity among populations remains a major challenge in evolutionary biology and in the management and conservation of species. North Pacific hake (Merluccius productus) inhabits upwelling regions in the California Current ecosystem from the Gulf of California to the Gulf of Alaska. In this study, we examined mitochondrial DNA (mtDNA) and microsatellite variation to estimate levels of genetic differentiation of M. productus in relation to the role of oceanographic features as potential barriers to gene flow. Samples were obtained from nine sites spanning a large part of the geographic range of the species, from Puget Sound, Washington to Costa Rica. The microsatellite results revealed three genetically discrete populations: one spanning the eastern Pacific coast, and two apparently resident populations circumscribed to the Puget Sound and the northern Gulf of California (FST = 0.032, p = 0.036). Cytochrome b sequence data indicated that isolation between the Puget Sound and northern Gulf of California populations from the coastal Pacific were recent phenomena (18.5 kyr for Puget Sound and 40 kyr for the northern Gulf of California). Oceanographic data obtained from the Gulf of California support the hypothesis that permanent fronts within the region, and strong gradients at the entrance to the Gulf of California act as barriers to gene flow. A seascape genetics approach found significant genetic–environment associations, where the daytime sea surface temperature and chlorophyll concentrations were the best predictive variables for the observed genetic differentiation. Considering the potential causes of genetic isolation among the three populations, e.g. spawning areas in different latitudes associated with upwelling processes, oceanographic barriers, asymmetric migration and specialized diet, oceanographic barriers appear to be a likely mechanism restricting gene flow. [ABSTRACT FROM AUTHOR]

A priority issue in ecology and biogeography is understanding the patterns in species diversity and the causal factors of their distribution, which allows the generation of information for conservation strategies. The longitudinal distribution of fishes and their relationships with environmental variables were studied in the Guayalejo-Río Tamesí system (northeastern Mexico) from February 2000 to July 2001. A total of 5918 fish were caught in 27 collections along an altitudinal gradient in the main river course, from high mountain (1500 masl) to coastal plain near Tampico. Forty-three native and five exotic species, belonging to 35 genera in 23 families, were identified. Cluster analyses identified four major fish habitats in the river system. A distinctive euryhaline marine fish habitat (1) occurs near the mouth with native and two exotic species. Two other habitats consist essentially of freshwater fish species that are distributed along the longitudinal gradient. One of these habitats (habitat 4) shows greater diversity, as per the Shannon index value, and also includes amphidromous fish, in addition to two exotic freshwater fish; the other (habitat 2) includes freshwater, euryhaline and three exotic species. The changes in the frequency of occurrence and the abundance of Gambusia vittata, Astyanax mexicanus, and Xiphophorus variatus contribute to explaining differences between these habitats. Another habitat (3) is represented by two sampling sites located near the mouth and consist of freshwater and euryhaline fish and three exotic cyprinids with broad salinity tolerance. The low abundance and richness of exotic species suggest little impact on native fish fauna in this river. The fish assemblage of the Guayalejo-Tamesí river system species changes along a longitudinal gradient with the addition, replacement and presence of indicator species. Upstream fish fauna is mostly composed of freshwater species, some of them generalists that inhabit the entire longitudinal gradient, others that are restricted to certain sites, and the remainder of species is an assemblage composed of a mixture of euryhaline freshwater and marine species near the mouth. [ABSTRACT FROM AUTHOR]

Within the Sciaenidae family, the genusMicropogoniasis composed of three recognized species along the Pacific coast of Mexico:Micropogonias altipinnis,M. ectenes, andM. megalops. These species exhibit overlapping diagnostic characters, which make species identification difficult. This study ties morphological differences (meristic, morphometry of body, and otolith) with DNA sequences (CO1 and 16S fractions of mtDNA and 28S of nDNA) amongMicropogoniasspecies in the Pacific. Meristic analysis showed a latitudinal variation among the three species in the number of rays, the number of gill rakers, and length of the longest spine of the dorsal fin. Discriminant analysis of morphometric characters (body and otolith) showed three morphological entities (p < 0.001). However, the mean genetic divergences among the three species with partial sequences of mtDNA (CO1and16S), and nuclear (28S) were lower than those reported at the interspecific level (>2%). Genetic results suggest that the three species are one species and that the differences in meristics and morphometry could be the result of phenotypic plasticity or incipient speciation. In this sense,M. ectenesandM. megalopsare proposed as junior synonyms ofM. altipinnis. [ABSTRACT FROM PUBLISHER]

Bonefish leptocephali of the genus Albula are difficult to identify to the species level due to morphological similarities between two different species present in the Northeastern Pacific Ocean, A. esuncula and A. gilberti. In this study, 22 bonefish leptocephali (premetamorphic and early metamorphic), collected from two locations in the southern Gulf of California were identified as Albula gilberti by comparing 459 bp of their mitochondrial cytochrome b gene sequences to those of four other species of bonefish. The characteristics of these A. gilberti leptocephali were compared to those of previously described bonefish leptocephali in the region. No distinctive morphological characteristics (meristic and pigmentation) were found that differentiate premetamorphic leptocephali of A. gilberti from those of other Albula species, making species identification by molecular-genetics a necessity. In early metamorphic leptocephali some differences in horizontal eye diameter-head length ratio, number of rays of pelvic and anal fins and myomere of pelvic-fin origin may help to differentiate A. gilberti from A. esuncula. [ABSTRACT FROM AUTHOR]

The analysis of primary productivity (PP) is essential for understanding the dynamics of marine ecosystems such as the Gulf of California Large Marine Ecosystem (GC-LME). This ecosystem is highly productive and supports an intense fishing activity (deep-sea, artisanal and sport fishing). The main objective of this investigation was to describe the spatial and temporal variability of phytoplankton primary productivity within the GC-LME based on 14 regions. A primary productivity database was built using 524 surface 14 C productivity measurements from 1960 to 2016. This information was supplemented with productivity calculations from satellite models. The analysis of the statistical descriptors of in-situ measurements revealed that primary productivity spatial distribution displayed a latitudinal gradient with increasing values to the north. In the warm season, the highest with 363.90 mgC m −3 D −1 ), Archipelago Region (Region VII 181.74 mgC m −3 D −1 ) and Canal de Ballenas (Region V 152.99 mgC m −3 D −1 ). The lowest surface values were reported in the southern regions (IX, XI and XIII), with average values of 19.42, 29.22 and 18.15 mgC m −3 d −1 . This is the deepest portion of the GC-LME that has been described as a complex area with a thermohaline structure related to the confluence of three different currents — North Equatorial Current, California Current and GC-LME water — that produce local fronts, eddies and intrusions, that affect productivity. In general, the temporal comparison showed that surface PP averages were higher in the warm season than in the cold season. In the GC-LME nutrient availability is high all year round, so these higher PP values are explained because in the warm season phytoplankton has more day-light hours. [ABSTRACT FROM AUTHOR]

Sciaenidae fish larvae were collected from the upper Gulf of California during September 2012 using a conical net (505 μm) through surface tows. These were pre-classified into four larval morphotypes, based on external characteristics (mainly meristic and pigmentation). Partial sequences of cytochrome c oxidase, subunit 1 and 16S rRNA (16S) genes of mitochondrial DNA, were used in molecular genetic identification from each larval morphotype. Genetic results indicated the identification of four larval morphotypes as Micropogonias megalops, Cynoscion othonopterus, C. reticulatus and Menticirrhus nasus. Pigmentation patterns of larvae described after molecular genetic identification made it possible to distinguish between M. megalops, M. nasus and C. othonopterus (postflexion). However, pigmentation was not reliable for differentiating between preflexion larvae of C. othonopterus and C. reticulatus. From these results, both morphological and genetic approaches were proposed as complementary tools in taxonomic studies of ichthyoplankton, particularly in early fish larvae identification of congeneric species with similar morphological characteristics. [ABSTRACT FROM AUTHOR]

Effects of geostrophic kinetic energy flux on the three-dimensional distribution of fish larvae of mesopelagic species (Vinciguerria lucetia, Diogenichthys laternatus, Benthosema panamense and Triphoturus mexicanus) in the southern Gulf of California during summer and fall seasons of stronger stratification were analyzed. The greatest larval abundance was found at sampling stations in geostrophic kinetic energy-poor areas (<7.5 J/m3), where the distribution of the dominant species tended to be stratified. Larvae of V. lucetia (average abundance of 318 larvae/10m2) and B. panamense (174 larvae/10m2) were mostly located in and above the pycnocline (typically ~ 40 m depth). In contrast, larvae of D. laternatus (60 larvae/10m2) were mainly located in and below the pycnocline. On the other hand, in sampling stations from geostrophic kinetic energy-rich areas (> 21 J/m3), where mesoscale eddies were present, the larvae of the dominant species had low abundance and were spread more evenly through the water column, in spite of the water column stratification. For example, in a cyclonic eddy, V. lucetia larvae (34 larvae/10m2) extended their distribution to, at least, the limit of sampling 200 m depth below the pycnocline, while D. laternatus larvae (29 larvae/10m2) were found right up to the surface, both probably as a consequence mixing and secondary circulation in the eddy. Results showed that the level of the geostrophic kinetic energy flux affects the abundance and the three-dimensional distribution of mesopelagic fish larvae during the seasons of stronger stratification, indicating that areas with low geostrophic kinetic energy may be advantageous for feeding and development of mesopelagic fish larvae because of greater water column stability. [ABSTRACT FROM AUTHOR]

The seasonal variations and the interactions of the water masses in the tropical Pacific off central Mexico (TPCM) and four surrounding areas were examined based on an extensive new hydrographic database. The regional water masses were redefined in terms of absolute salinity ( SA) and conservative temperature (Θ) according to the Thermodynamic Equation of Seawater 2010 (TEOS-10). Hydrographic data and the evaporation minus (precipitation + runoff) balance were used to investigate the origin and seasonality of two salinity minima in the area. The shallow (50-100 m) salinity minimum originates with the California Current System and becomes saltier as it extends southeastward and mixes with tropical subsurface waters while the surface salinity minimum extends farther north in the TPCM in summer and fall because of the northward advection of tropical surface waters. The interactions between water masses allow a characterization of the seasonal pattern of circulation of the Mexican Coastal Current (MCC), the tropical branch of the California Current, and the flows through the entrance of the Gulf of California. The seasonality of the MCC inferred from the distribution of the water masses largely coincides with the geostrophic circulation forced by an annual Rossby wave. [ABSTRACT FROM AUTHOR]

We examined the effect of a mesoscale cyclonic eddy on the three-dimensional distribution of Vinciguerria lucetia and Diogenichthys laternatus in southern Gulf of California during July 2010. CTD data and zooplankton samples collected with a closing-opening net (505 |Jm), were obtained on 2 transects across the eddy, and on a transect outside of the mesoscale structure. In the later the thermocline depth was at ~40 m where larvae V. lucetia dominated. Opposite to V. lucetia distribution, D. laternatus larvae was the dominant species in the deepest strata. In the area influenced by the cyclonic eddy (~350 m depth and ~60 km diameter), the thermocline was sunk from ~25 m (eddy edge) to ~50 m depth (eddy center). The isotherms below the thermocline formed a dome from ~350 m to ~100 m depth in the eddy center. This upwelling coincided with an increase of D. laternatus larvae in the water column. Compared with the transect outside of the cyclonic eddy, the shoaling of the isotherms inside the eddy produced not only an increase of D. laternatus larvae, also decreased the V. lucetia abundance. These variations in larval distribution of both mesopelagic species are closely correlated with the mesoscale cyclonic eddy. [ABSTRACT FROM AUTHOR]

We examined the effect of a tidal-mixing front on the three-dimensional distribution of larval fish habitats (LFHs) in the Midriff Archipelago Region in the Gulf of California during winter. Zooplankton and environmental variables were sampled from 0 to 200 m in 50 m strata. Four LFHs were defined in association with the front, two on the northern side and two on the southern side. The northern LFHs were: (1) the Mainland Shelf Habitat, located from the surface to 100 m depth on the north-east mainland shelf, characterized mainly by the presence of Citharichtys fragilis; and (2) the Wide Distribution Habitat, extending from north-west to south across the front from the surface to 200 m depth, dominated by the ubiquitous Engraulis mordax. The southern LFHs were: (3) the Eddy Zone Habitat, defined nearly on an anticyclonic eddy, with the highest larval abundance and richness from the surface to 100 m depth, dominated by Leuroglossus stilbius; and (4) the Southern Gulf Habitat, associated with low temperature waters from the southern Gulf of California, dominated by southern-gulf species (e.g. Scomber japonicus and Sardinops sagax). Despite the weak stratification and low thermal contrast (~1.5°C) across the south front compared to summer (~3°C), our results demonstrate that the frontal zone may influence the formation of planktonic habitats even during generally homogeneous periods, which may also be relevant in other regions of the world. [ABSTRACT FROM PUBLISHER]