Wandering behaviour prevents inter and intra oceanic speciation in a coastal pelagic fish

Small pelagic fishes have the ability to disperse over long distances and may present complex evolutionary histories. Here, Old World Anchovies (OWA) were used as a model system to understand genetic patterns and connectivity of fish between the Atlantic and Pacific basins. We surveyed 16 locations worldwide using mtDNA and 8 microsatellite loci for genetic parameters, and mtDNA (cyt b; 16S) and nuclear (RAG1; RAG2) regions for dating major lineage-splitting events within Engraulidae family. The OWA genetic divergences (0-0.4%) are compatible with intra-specific divergence, showing evidence of both ancient and contemporary admixture between the Pacific and Atlantic populations, enhanced by high asymmetrical migration from the Pacific to the Atlantic. The estimated divergence between Atlantic and Pacific anchovies (0.67 [0.53-0.80] Ma) matches a severe drop of sea temperature during the Gunz glacial stage of the Pleistocene. Our results support an alternative evolutionary scenario for the OWA, suggesting a coastal migration along south Asia, Middle East and eastern Africa continental platforms, followed by the colonization of the Atlantic via the Cape of the Good Hope.Portuguese Foundation for Science & Technology (FCT) [SFRH/BD/36600/2007]; FCT [UID/MAR/04292/2013, SFRH/BPD/65830/2009]; FCT strategic plan [UID/Multi/04326/2013]info:eu-repo/semantics/publishedVersio

Oxygen: A Fundamental Property Regulating Pelagic Ecosystem Structure in the Coastal Southeastern Tropical Pacific

Background: In the southeastern tropical Pacific anchovy (Engraulis ringens) and sardine (Sardinops sagax) abundance have recently fluctuated on multidecadal scales and food and temperature have been proposed as the key parameters explaining these changes. However, ecological and paleoecological studies, and the fact that anchovies and sardines are favored differently in other regions, raise questions about the role of temperature. Here we investigate the role of oxygen in structuring fish populations in the Peruvian upwelling ecosystem that has evolved over anoxic conditions and is one of the world's most productive ecosystems in terms of forage fish. This study is particularly relevant given that the distribution of oxygen in the ocean is changing with uncertain consequences. Methodology/Principal Findings: A comprehensive data set is used to show how oxygen concentration and oxycline depth affect the abundance and distribution of pelagic fish. We show that the effects of oxygen on anchovy and sardine are opposite. Anchovy flourishes under relatively low oxygen conditions while sardine avoid periods/areas with low oxygen concentration and restricted habitat. Oxygen consumption, trophic structure and habitat compression play a fundamental role in fish dynamics in this important ecosystem. Conclusions/Significance: For the ocean off Peru we suggest that a key process, the need to breathe, has been neglected previously. Inclusion of this missing piece allows the development of a comprehensive conceptual model of pelagic fish populations and change in an ocean ecosystem impacted by low oxygen. Should current trends in oxygen in the ocean continue similar effects may be evident in other coastal upwelling ecosystems

Pelagic ecology of a northern boundary current system: effects of upwelling on the production and distribution of sardine (Sardinops sagax), anchovy (Engraulis australis) and southern bluefin tuna (Thunnus maccoyii) in the Great Australian Bight

Shelf waters of southern Australia support the world's only northern boundary current ecosystem. Although there are some indications of intense nitrate enrichment in the eastern Great Australian Bight (GAB) arising from upwelling of the Flinders Current, the biological consequences of these processes are poorly understood. We show that productivity in the eastern GAB is low during winter, but that coastal upwelling at several locations during the austral summer-autumn results in localized increases in surface chlorophyll a concentrations and downstream enhancement of zooplankton biomass. Sardine (Sardinops sagax) and anchovy (Engraulis australis) eggs and larvae are abundant and widely distributed in shelf waters of the eastern and central GAB during summer-autumn, with high densities of sardine eggs and larvae occurring in areas with high zooplankton biomass. Egg densities and distributions support previous evidence suggesting that the spawning biomass of sardine in the waters off South Australia is an order of magnitude higher than elsewhere in southern Australia. Sardine comprised >50% of the identified prey species of juvenile southern bluefin tuna (SBT, Thunnus maccoyii) collected during this study. Other studies have shown that the lipid content of sardine from the GAB is relatively high during summer and autumn. We suggest that juvenile SBT migrate into the eastern and central GAB during each summer-autumn to access the high densities of lipid-rich sardines that are available in the region during the upwelling period. Levels of primary, secondary and fish production in the eastern GAB during summer-autumn are higher than those recorded in other parts of Australia, and within the lower portion of ranges observed during upwelling events in the productive eastern boundary current systems off California, Peru and southern Africa. © 2006 Blackwell Publishing Ltd

Worldwide large-scale fluctuations of sardine and anchovy populations

Decade-scale regimes of sardine #Sardinops sagax and anchovy #Engraulis spp. have been observed in the productive coastal waters of the North-Western, North-Eastern and South-Eastern Pacific and the South-Eastern Atlantic. In each of these systems, the two genera fluctuate out of phase with each other. The subdominant genus may initiate a recovery while the other species is still abundant, so population growth is not necessarily a response to a vacant niche. Rather, it appears to be triggered by formation of one or a few powerful year-classes. At high population levels, quality of sardine and their eggs decreased in Japan, leading to decreased production and survival of eggs, poor year-classes and stock collapse. Excessive fishing of strong year-classes early in the recovery stage may prevent a species from assuming dominance, so influencing the natural succession of species. This may greatly alter the structure and functioning of an ecosystem. For example, a mesopelagic forage fish may replace an epipelagic one, with severe repercussions for predators that can only feed in the upper ocean, e.g. some seabirds. Biological factors also may influence the succession of forage fish. For example, off California, peaks in abundance of predatory species such as bonita #Sarda, and chub mackerel #Scomber separate those of the planktivorous sardine and anchovy. In the Pacific Ocean, sardine distribution has changed greatly. Compared with its range when scarce, a population at a high level of biomass can extend 1 000-1 800 miles farther along the coast and 400-2 200 miles farther out to sea. In different periods of high biomass, sardine did not always have the same distribution. In the 1930s and 1940s, near simultaneous fluctuations of sardine in the North-Western and North-Eastern Pacific were in phase. In the 1980s and 1990s, sardine in the North-Western and South-Eastern Pacific were fluctuating in phase... (D'après résumé d'auteur

Woldwide large-scale fluctuations of sardine and anchovy populations

Decade-scale regimes of sardine Sardinops sagax and anchovy Engraulis spp. have been observed in the productive coastal waters of the North-Western, North-Eastern and South-Eastern Pacific and the South-Eastern Atlantic. In each of these systems, the two genera fluctuate out of phase with each other. The subdominant genus may initiate a recovery while the other species is still abundant, so population growth is not necessarily a response to a vacant niche. Rather, it appears to be triggered by formation of one or a few powerful year-classes. At high population levels, quality of sardine and their eggs decreased in Japan, leading to decreased production and survival of eggs, poor year-classes and stock collapse. Excessive fishing of strong year-classes early in the recovery stage may prevent a species from assuming dominance, so influencing the natural succession of species. This may greatly alter the structure and functioning of an ecosystem. For example, a mesopelagic forage fish may replace an epipelagic one, with severe repercussions for predators that can only feed in the upper ocean, e.g. some seabirds. Biological factors also may influence the succession of forage fish. For example, off California, peaks in abundance of predatory species such as bonita Sarda, and chub mackerel Scomber, separate those of the planktivorous sardine and anchovy. In the Pacific Ocean, sardine distribution has change greatly. Compared with its range when scarce, a population at a high level of biomass can extend 1 000-1 800 miles farther along the coast and 400-2 200 miles farther out to sea. In different periods of high biomass, sardine did not always have the same distribution. In the 1930s and 1940s, near simultaneous fluctuations of sardine in the North-Western and North-Eastern Pacific were in phase. In the 1980s and 1990s, sardine in the North-Western and South-Eastern Pacific were fluctuating in phase. However, along the west coast of North America, sardine started their most recent increase later than in other regions of the Pacific Ocean. This increase is continuing, whereas sardine populations in the North-Western and South-Eastern Pacific have decreased both in catch and geographic distribution since the late 1980s. Therefore, the North-Eastern Pacific has moved out of phase with other major Pacific sardine populations. This may be because abundance of sardine in the California Current has not yet reached a level at which density-dependent effects exert a major influence. Sardine and anchovy in the South-Eastern Atlantic have been out of phase with populations in the Pacific Ocean, especially those off Peru and Chile. Over the last 300 years, episodic fisheries for Bohuslän herring Clupea harengus in Sweden coincide with periods of high anchovy abundance off California. Near simultaneous fluctuations of fish stocks in widely separated regions support the view that they are sometimes influenced by climate operating at a global scale. Changes of the gyre-scale circulation seem to be major factors in the decadal climate. In Australia, sardine have a wide range, but the less productive waters support a much lower biomass than is found in the other four systems. Engraulis occur in some systems from which Sardinops are absent, for example, Brazil, where they and Sardinella are segregated vertically in the water column