Sylvia P. A. Jiménez-Rosenberg

Vertical Distribution of Fish Larvae and Its Relation to Water Column Structure in the Southwestern Gulf of California

ABSTRACT The seasonal evolution of vertical distribution of fish larvae and its relationship with seasonal stratification, as measured by a quantitative stability parameter, were analyzed for a region off Bahía de La Paz in the southwestern Gulf of California. Samples were obtained with an opening-closing net (505 μm) in 50-m depth strata from surface to 200-m depth in May, July, and October 2001 and February 2002. Significant differences in total larval abundance and in dominant species (mesopelagic and epipelagic) were found among strata from May to October. More larvae were found in maximum-stability strata (from 16 ±5 to 48 ±17 m depth) than below the pycnocline (from 100- to 150-m depth). In February, the 100-m-deep surface mixed layer had a weak pycnocline at its base, and no significant difference was found. Results show that vertical distribution of fish larvae in this area depends mainly on the seasonal evolution of the water column structure, with most fish larvae in the pycnocline, at the most stable stratum of the water column.

Influences of El Niño on assemblages of mesopelagic fish larvae along the Pacific coast of Baja California Sur

Abstract Seasonal assemblages of mesopelagic fish larvae and changes related with environmental factors (plankton biomass, sea surface temperature anomaly, upwelling, and the multivariate El Niño index) were investigated. From 1982 to 1987, 16 oceanographic cruises were carried out along the Pacific coast of Baja California Sur, Mexico. Larvae of 42 mesopelagic fish taxa were collected. Larval abundance was highly variable during the studied period, but summer months coincided with higher abundance (>200 larvae under 10 m2). Larval assemblages were dominated by three of the most common species of tropical (Vinciguerria lucetia, Diogenichthys laternatus) and subtropical affinity (Triphoturus mexicanus). A group of species of tropical affinity (Diplophos proximus, Diaphus pacificus, Benthosema panamense) was useful for distinguishing the 1982–84 El Niño event, and an assemblage of larvae of temperate affinity (Symbolophorus californiensis, Melamphaes lugubris, Bathylagus ochotensis, Leuroglossus stilbius, Protomyctophum crockeri) characterized ‘normal’ years (mid‐1984 to mid‐1987).

Molecular identification and morphological description of Micropogonias megalops, Cynoscion othonopterus, C. reticulatus and Menticirrhus nasus larvae, collected in the upper Gulf of California during Summer 2012

Abstract 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.

Morphological description of genetically identified Cortez bonefish (Albula gilberti, Pfeiler and van der Heiden 2011) leptocephali from the southern Gulf of California

Abstract 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.

Larval distribution and connectivity of the endemic Sciaenidae species in the Upper Gulf of California

Because the endemic Sciaenidae species (commonly known as drum or croakers) are important to the fishing industry in the Upper Gulf of California, their larval distribution and connectivity was analyzed in relation to hydrographic conditions during spawning periods (March, June and September). Totoaba macdonaldi, Micropogonias megalops, Menticirrhus nasus and Cynoscion othonopterus larvae were morphologically and genetically identified. Genetic analysis reveals for the first time the presence of Isopisthus remifer, which had not previously been morphologically identified. The most relevant hydrographic structure in the region was the permanent stratification front (Φ = 10 J/m) originated by the convergence of mixed water of the Northern Gulf (~20 m depth) and stratified water coming from the adjacent oceanic water (~200 m). Whereas T. macdonaldi larvae were only collected in the shallowest area in March, the other species were found mostly along the front in June and September. Connectivity matrixes showed high particle retention along the front (>80%) coinciding with the larval distribution. Results indicate that the stratification front might favor larval survival and prevent their advection toward the ocean. This type of retention likely enhances endemism, not only of these species but also of others coastal demersal species.