A new record of Huttonella bicolor (Hutton, 1834) (Mollusca, Gastropoda, Streptaxidae) in Mexico

A specimen of Huttonella bicolor = Gulella bicolor (Hutton, 1834) was collected from clayey-sandy soil in Tabasco, Mexico, which constitutes its second record in the state and the third in Mexico. This small gastropod is a predator that has mainly spread through tropical and island regions as an exotic species. Its introduction to Asian and Caribbean Islands is noteworthy. Its pupiform shell and the lamella or tooth complex were compared against previous descriptions. In Mexico, this species has been found in northern Veracruz and Tabasco, which confirms that it is spreading along the Gulf of Mexico from the United States towards Brazil. The features of this streptaxid as a potential hazard through its preferred prey are discussed.Un ejemplar de Huttonella bicolor = Gulella bicolor (Hutton, 1834) fue capturado en suelo limo-arenoso en Tabasco, México; el cual constituye el segundo registro para el estado y el tercero para México. Este pequeño gasterópodo es un depredador que se ha extendido como especie exótica en regiones preferentemente tropicales e insulares; destaca su introducción en islas de Asia y del Caribe. La concha tiene forma de pupa con lamelas o dientes en la abertura. Se comparó con la descripción de la especie. La distribución de la especie en México se extiende a los estados de Veracruz y en Tabasco, lo cual confirma el avance en su distribución a lo largo de la costa del Golfo de México de los Estados Unidos hasta Brasil. Las características de este estreptaxcido en cuanto al riesgo a través del tipo de presa preferida son discutidas

The Effect of Hydrological Connectivity on Fish Assemblages in a Floodplain System From the South-East Gulf of California, Mexico

The effect of hydrological connectivity of the fish assemblages was assessed on a floodplain in the SE Gulf of California, Mexico using a before–after control-impact (BACI) design. Community structure attributes of species abundance, biomass, richness, diversity, and differences in the structure of fish assemblages were compared between two periods (January to June in 2011 and 2015) and two flood plains, one designated as the control zone which was divided by a road, and another one designated as the treatment zone which from January to June 2011 was divided by a road, and then sampled from January to June 2015, as the site was rehabilitated by removing the road in the year 2012. Fish were sampled at monthly intervals using a seine net at different stations in both floodplains. A total of 7024 organisms, comprising of 14 species belonging to 11 families, were analyzed. In the control zone during both periods and in the treatment zone before removal of the road Poecilia butleri was the most abundant species and two exotic species (Tilapia) accounted for more than 95% of the total biomass. After the removal of the road in the treatment zone Poeciliopsis latidens was the most abundant species and the relative biomass of both species of tilapia decreased to 85%, but was still the most important in terms of biomass. However, richness and diversity were higher and the structure of the fish assemblages was different in the treatment zone after the road was removed, due to the presence of species with estuarine and marine affinity in this zone and period. Our results indicate that hydrological connectivity proved to be a key factor influencing the fish composition and abundance in the floodplain system in the region. Hence, a better hydrological connectivity implied higher abundance and diversity, likely related to an increase in the habitat complexity. The priority in the management of the ecological functioning of the floodplain system should be set on minimizing the modifications of the natural flow and thus avoiding the changes on the fish biota

Age and growth of the scalloped hammerhead shark, Sphyrna lewini (Griffith & Smith, 1834) from the Southern coast of Sinaloa, México

Age and growth for the scalloped hammerhead shark (Sphyrna lewini) were determined from opaque bands (OBs) on postcephalic vertebrae from 109 organisms (44 females, 52 cm to 276 cm total length (TL) and 65 males, 47 cm to 245 cm TL) obtained bimonthly from commercial fisheries off the southern coast of Sinaloa state (23º45´25´´N and 106º05´15´´W to 21º52´N and 105º54´W) from January 2003 to February 2005. The Bowker test of symmetry and the Index of Average Percent Error, suggest that this ageing method represents an unbiased and precise age assessment. Results show that immediately after birth (in summer), the first OB was formed and in the next winter showed the second OB. Later it was observed that two OBs were formed each year, one during summer and the other during winter, influenced by the sea surface temperature (SST). Based on the comparison of five back-calculation methods, the best methods were FraserLee. The parameters of the von Bertalanffy growth function were, for females: L? = 376 cm, K = 0.1 year-1, t0 = -1.16 years, b = 3 and W? = 222 kg; for males: L? = 364 cm, K = 0.123 year-1, t0 = 1.18 years, b = 3 and W? = 193 kg. The standard index growth (?´) was 4.2 (s = 0.1). According to these results the largest sharks observed, a female of 280 cm TL would be 12.5 years old and a male of 281cm TL would be 11 years old

Spatiotemporal Variability in Fish Assemblages in a Coastal and Estuarine System in the Tropical Eastern Pacific during the Anthropause

Differences in fish assemblages’ composition and their relationship with the environmental variables were analyzed in the Urías estuarine system, Mexican North Pacific. Environmental variables and fish catches were recorded bimonthly between June 2018 and November 2021, including a period before and during the COVID-19 pandemic. Multivariate analyses were performed in the studied area to define zones based on their environmental, biotic, and abiotic characteristics and the effect of these on the fish assemblages. Two zones were identified, an estuarine with mangrove forest and a surf zone in the coastal area outside the estuarine system. Fish composition, biomass, and diversity (α and β) were evaluated among the factors of the period (before–during COVID-19), climatic seasons, and zones. A total of 5947 fish individuals of 41 species were collected using beach seines as fishing gear. The structure of the fish assemblages was different between zones and periods. Abiotic (temperature, salinity, and total matter suspended), biotic (mangrove area), and temporal (season and period before–during COVID-19) variables had an effect on fish biomass and α diversity, while the results of the β diversity only indicate changes in the nestedness component before–during the lockdown. These results indicate a change in fish assemblages’ structure and composition between periods, which might be a consequence of the limitation of human activities derived from the pandemic, climatic changes, or a combination of both effects. Our results show that fish assemblages in the estuarine systems of the Tropical Eastern Pacific are unique, and there is a need to establish local management strategies for these ecosystems