Feeding habits variability of Lutjanus synagris and Lutjanus griseus in the littoral of Campeche, Mexico: an approach of food web trophic interactions between two snapper species

The study of the feeding habits variability (spatial and temporal scales) allows us to evaluate the trophic interactions between species, thus, the short and long-term effects of the removal of different species by the presence of different phenomena. In this study, we carried out stable isotope (δ13C and δ15N) and stomach content analyses to infer the trophic linkages between two snapper species (Lutjanus synagris and Lutjanus griseus) captured in the littoral of Campeche, Mexico. In total, 781 specimens were collected (528 L. synagris and 253 L. griseus) and based on relative importance index [%PSIRI] both snapper species consumed based on the prey-specific index of relative importance (PSIRI), Penaeidae family (PSIRI = 23.41%) was the most important species in the diet of Lutjanus synagris, while Callinectes sapidus (PSIRI = 21.45%) was the primary prey of Lutjanus griseus. The isotopic analyses indicated that both snapper species feed in the coastal-marine (δ15N: 10.6 to 12.1‰ and δ13C: -15.7 to -12.7‰); however, according to PERMANOVA, low diet similarity was found between snapper species (R = 0.07, P < 0.01), also, significant differences was detected in the δ15N and δ13C values between L. synagris, and L. griseus. Therefore, despite both snapper species presents similar trophic positions (L. synagris: 4.2 ± 0.2; L. griseus: 3.9 ± 0.1) and feeding behavior (according to SIBER = opportunistic predators), a low trophic overlap was observed, probably associated with the differential use of habitat in the coastal zone; where L. synagris is ecologically fed in areas of seagrass, while L. griseus is probably intermittent between pasture and mangrove areas, therefore, the role of each species is crucial in the dynamics of coastal-marine ecosystems as predators and potential structuring of the populations of their prey.

INFLUENCES OF UPPER FLORIDAN AQUIFER WATERS ON RADIOCARBON IN THE OTOLITHS OF GRAY SNAPPER (Lutjanus griseus) IN THE GULF OF MEXICO

ABSTRACTThe otoliths (ear stones) of fishes are commonly used to describe the age and growth of marine and freshwater fishes. These non-skeletal structures are fortuitous in their utility by being composed of mostly inorganic carbonate that is inert through the life of the fish. This conserved record functions like an environmental chronometer and bomb-produced radiocarbon (14C)—a 14C signal created by atmospheric testing of thermonuclear devices—can be used as a time-specific marker in validating fish age. However, complications from the hydrogeology of nearshore marine environments can complicate 14C levels, as was the case with gray snapper (Lutjanus griseus) along the Gulf of Mexico coast of Florida. Radiocarbon of these nearshore waters is influenced by freshwater input from the karst topography of the Upper Floridan Aquifer—estuarine waters that are 14C-depleted from surface and groundwater inputs. Some gray snapper likely recruited to this kind of environment where 14C levels were depleted in the earliest otolith growth, although age was validated for individuals that were not exposed to 14C-depleted waters to an age of at least 25 years with support for a 30-year lifespan.

Gene flow between subpopulations of gray snapper (Lutjanus griseus) from the Caribbean and Gulf of Mexico

Background The gray snapper (Lutjanus griseus) has a tropical and subtropical distribution. In much of its range this species represents one of the most important fishery resources because of its high quality meat and market value. Due to this, this species is vulnerable to overfishing, and population declines have been observed in parts of its range. In recent decades, it has been established that knowing the level of genetic connectivity is useful for establishing appropriate management and conservation strategies given that genetic isolation can drive towards genetic loss. Presently the level of genetic connectivity between subpopulations of L. griseus of the southern region of the Gulf of Mexico and the Caribbean Sea remains unknown. Methods In the present study we analyze genetic structure and diversity for seven subpopulations in the southern Gulf of Mexico and the Mexican Caribbean Sea. Eight microsatellite primers of phylogenetically closely related species to L. griseus were selected. Results Total heterozygosity was 0.628 and 0.647 in the southern Gulf of Mexico and the Mexican Caribbean Sea, however, results obtained from AMOVA and RST indicated a lack of genetic difference between the major basins. We also found no association between genetic difference and geographic distance, and moderately high migration rates (Nm = > 4.1) suggesting ongoing gene flow among the subpopulations. Gene flow within the southern Gulf of Mexico appears to be stronger going from east-to-west. Conclusions Migration rates tended to be higher between subpopulations within the same basin compared to those across basins indicating some regionalization. High levels of genetic diversity and genetic flow suggest that the population is quite large; apparently, the fishing pressure has not caused a bottleneck effect.

POPULATION ANALYSIS OF SNAPPER LUTJANUS GRISEUS, THROUGH THE ARTISANAL FISHERY ON THE COAST OF TAMIAHUA, VERACRUZ

Artisanal fishery in the Gulf of Mexico is mainly undertaken for subsistence and is, thus, of great socioeconomic importance, with Lutjanidae one of the most important families caught in the region. However, there is scarce fisheries knowledge in the Gulf of Mexico and, in light of pressure from the fishing community, research into the population dynamics of these species is of vital importance for the management or conservation of coastal resources. This study aims to contribute information for the analysis of the population of Lutjanus griseus (Linnaeus, 1758), a common species on the Tamiahua coast, in the state of Veracruz. Samples and biometric data (weight, sex, total length and maturity) were recorded by the fishing community on this coast. The monthly population structure was constructed using fish size. Data from 987 individuals, the size of which oscillated from 15 to 80 cm, were registered over the course of a year. The sex ratio was 1:1, while the maximum calculated age was 10 years. Von Bertalanffy and Gompertz growth models reported a maximum age and growth of L∞=182.46 K= 0.05 and to = -1.71. The best fit was achieved by means of the Gompertz model, as based on the Akaike criteria and the biological interpretation of the parameters. Reported data and the models used in this study suggest that the minimum catch size should be 40 cm and that the fishery should either cease activities in the months of the reproductive peak or that quotas should be among the fishing cooperatives on the coast of Tamiahua.

Efecto del dragado de un canal de comunicación al mar (estero) sobre la asociación de peces en la Laguna Larga, Cayo Coco, Cuba

En este trabajo se caracterizaron el hábitat y la comunidad de peces en el canal de comunicación al mar de Laguna Larga, antes y después de un proceso de dragado realizado en el año 2012. Para ello el canal se dividió en cuatro secciones, dos iniciales cercanas al mar y dos finales cercanas a la laguna. Se realizaron 112 censos visuales mediante buceo libre. Para caracterizar el hábitat se midieron el área de refugio, sombra, temperatura del agua, salinidad, profundidad y velocidad de la corriente. Se determinaron la distribución espacio-temporal de los peces, riqueza de especies, densidad y frecuencia relativa en cada sección y se relacionaron con las características del hábitat. Se registraron 22 especies de peces distribuidas en 14 familias. Las especies Abudefduf saxatilis, Halichoeres bivittatus, Stegastes leucostictus y Lutjanus griseus fueron dominantes. Se encontró que las densidades y riquezas de peces en el inicio del canal eran más altas que en el extremo, particularmente la especie Lutjanus griseus, la cual cambió sus preferencias de nichos, desde el final del canal hacia el inicio. Se encontró que las comunidades de peces variaron espacial y temporalmente. El proceso de restauración produjo una disminución en la disponibilidad de refugios y, en consecuencia determinó la disminución de la densidad y riqueza de especies solo en el canal de entrada a la laguna. Los cambios más drásticos en el patrón espacial y temporal de los peces estuvieron asociados a las secciones finales del canal, las cuales sufrieron las mayores alteraciones de hábitat.

Feeding ecology of juvenile marine fish in a shallow coastal lagoon of southeastern Mexico

Many species of marine fish use coastal lagoons during early stages of their life cycles due to the protection provided by their turbid waters and complex structure of the environment, such as mangroves and mudflats, and the availability of food derived from the high productivity of these sites. In this study, we analyzed the diet of six species of juvenile marine fishes that use a karstic lagoon system in the northwest portion of the Yucatan Peninsula, Mexico. Through stomach contents analysis we determined the trophic differences among Caranx latus, Oligoplites saurus, Trachinotus falcatus, Synodus foetens, Lutjanus griseus, and Strongylura notata. C. latus, O. saurus, S. foetens, and S. notate, which are ichthyophagous species (>80% by number). L. griseus feeds mainly on crustaceans (>55%) and fish (35%), while T. falcatusfeeds on mollusks (>50% bivalves, >35% gastropods). The analysis of similarities (ANOSIM) showed differences in the diet of all species. Cluster analysis, based on the Bray-Curtis similarity matrix revealed three groups; one characterized by the ichthyophagous guild (S. notata, S. foetens, C. latus, and O. saurus), other group formed by the crustacean consumers (L. griseus), and the third, composed by the mollusk feeder (T. falcatus). Species of the ichthyophagous guild showed overlap in their diets, which under conditions of low prey abundance may trigger competition, hence affecting juvenile stages of these marine species that use coastal lagoons to feed and grow.

Crecimiento en cautiverio de lotes de reproductores dos especies de lutjánidos

La explotación petrolera en el Golfo de México ha reducido las áreas de pesca costera, por lo que la acuicultura puede ser una alternativa laboral. Para evaluar la susceptibilidad de su cultivo, se utilizaron ejemplares silvestres de Lutjanus griseus y L. analis, procedentes de una zona costera de Paraíso, Tabasco. En la Estación de Acuicultura Marina (EAM) de la División Académica de Ciencias Biológicas (DACBiol) de la Universidad Juárez Autónoma de Tabasco (UJAT), se conformaron lotes de ambas especies. Los peces se distribuyeron por especie en tanques de 12.6 m3 de capacidad (4 m Ø). Para determinar el crecimiento de los organismos de cada lote, se realizaron ocho biometrías mensuales, registrándose el peso y la longitud total de todos los peces. A lo largo del estudio, los peces fueron alimentados a saciedad aparente, cuatro veces al día empleándose mayoritariamente alimento para peces marinos marca Skretting® y ocasionalmente alimento para trucha marca el Pedregal®. Se realizaron recambios totales de agua tres veces por semana para mantener la calidad del agua. Diariamente se registró el pH, la salinidad y el oxígeno disuelto; los nitratos, nitritos y amonio se midieron una vez por semana. De octubre de 2015 a mayo de 2016, L. griseus tuvo una ganancia promedio por organismo de 7,54 cm y 108,4 g, mientras que L. analis ganó en promedio 14,86 cm y 221,04 g. El contraste de pendientes para la asociación de peso y longitud indica que ambas especies presentaron un patrón de crecimiento estadísticamente similar (p=0.09). La elección de la especie más adecuada dependerá de otros parámetros como la sobrevivencia, ya que aunque L. analis obtuvo mejor crecimiento promedio, su sobrevivencia fue de 37.5% mientras que L. griseus alcanzó 66.67 %.