Fish larvae assemblages in the Gulf of California

Abstract

The distributional diversity and assemblages of fish larvae in the Gulf of California indicated two main seasonal stages and two transitional periods: in winter, the tropical water mass is confined to the south-east portion of the mouth of the Gulf and larval fish assemblages are dominated by subtropical and temperate-subarctic species; in summer; tropical water invades the Gulf and assemblages are dominated by tropical species. Both seasonal stages are separated by transitional periods coinciding with strong latitudinal temperature gradients. During the autumn and spring transitional periods, the Gulf of California splits into three regions: a northern region where temperate and subarctic species spawn from autumn to spring, a southern region dominated by tropical and subtropical species year round and a central region where tropical and temperate assemblages merge. Seasonal changes in the location of the regions, as well as the borders between them, show expansion and contraction of the northern and southern faunas related to the general oceanic circulation patterns during the year. # 2004 The Fisheries Society of the British Isles

A study of the population structure of the Pacific sardine Sardinops sagax (Jenyns, 1842) in Mexico based on morphometric and genetic analyses

“…No evidence was found of movement toward the north of individuals tagged in Bahia Magdalena (Clark, 1945). Studies carried out on the seasonal and geographic distributions of larvae show that the principal spawning areas are centered in three areas (Marr, 1960): off Central California in April (Lynn, 2003); near Bahia Magdalena, Baja California Sur, in summer; and in the Gulf of California in fall and winter (Aceves- Medina et al, 2004). This supports the existence of three stocks (Smith, 2005).…”

Regionalization in the distribution of larval fish assemblages during winter and autumn in the Gulf of California

“…The area between the 18 and 21°C SST isotherms likely represents a transition zone in the central region of the GC in which both larval fish species complexes coexist during the spring and autumn. These three zoogeographic regions were proposed by Aceves-Medina et al (2004) and roughly match the adult ichthyofaunal bioregionalization pattern (Walker, 1960). The geographic limits among regions change seasonally, influenced by climate and sea current patterns that modify the surface isotherms positions throughout the year.…”

“…The larval fish assemblage north of the 21°C isotherm was significantly different from that in the southern region. Because the SST range in Nov-Dec 2005 was >19.4°C, it was not possible to test the hypothesis that the 18°C isotherm was the northern limit of the southern larval fish assemblages, as suggested by Aceves-Medina et al (2004). The southern species group (WG2) was present throughout the studied area, overlapping distribution with the northern assemblage.…”

“…The geographic limits among regions change seasonally, influenced by climate and sea current patterns that modify the surface isotherms positions throughout the year. The original conceptual ichthyoplankton zoogeography scheme proposed by Aceves-Medina et al (2004) only included samples from the area north of 27°N during the winter (late December to March), leaving out much of the central and southern region of the GC during that period. This model seems to work well in absence of coastal upwelling events, since Avalos-García et al (2003) detected similar latitudinal patterns of the larval fish species assemblages in the spring but not during the autumn, when strong wind-forced upwelling events are coupled with mesoscale eddies (Pegau et al, 2002).…”

“…To provide additional observational evidence about latitudinal zoogeographic patterns, particularly in the southern region during the winter, to fill the previous knowledge gap, the present study has three goals: 1) to compare larval fish assemblages, in February-March (winter) vs November-December (autumn) of 2005, in a large portion of the GC; 2) to test if the regionalization of the Gulf of California, as previously proposed (Aceves-Medina et al, 2004), is seasonally valid, by comparing two cruises carried out in 2005; and 3) to analyze the effect of jets and eddies, coupled with upwelling processes, on the larval fish assemblages observed during November-December 2005.…”