Spatial, Seasonal, and Diel Variation in Abundance of the Bay Anchovy, Anchoa mitchilli (Teleostei: Engraulidae), in a Tropical Coastal Lagoon of Mexico

Abstract

The abundance of the bay anchovy, Anchoa mitchilli, was studied at a series of stations in Pueblo Viejo Lagoon, Veracruz, Mexico, during 1988 to 1990. We collected 27,359 individuals with a total weight of 22,900 g in monthly and 24-h samples (a total of 216 sample collections). Anchoa mitchilli was the dominant species and formed 55% of the total number of fish caught. Their abundance did not show a significant correlation with any of the measured environmental factors (salinity, temperature, dissolved oxygen, and transparency) of the lagoon. The abundance of bay anchovy did not show a well-defined spatial pattern, but we observed greater abundances near the lagoon inlet. Peaks of abundance occurred during September and October with a general increase in the rainy season. Seasonal fluctuations in abundance were linked to preceding fluctuations in local rainfall. Thus, rain and its associated influence on availability of food within the lagoon basin had a significant delayed effect on bay anchovy abundance. The bay anchovy was collected in significantly greater abundances during night hours. This nocturnal activity pattern might be related to predator avoidance. RESUMEN-La abundancia de la anchoa Anchoa mitchilli fue estudiada en una serie de localidades en la Laguna de Pueblo Viejo, Veracruz, Mexico, desde 1988 a 1990. Se colectaron 27,359 individuos con un peso total de 22,900 g en muestreos mensuales y ciclos de 24 horas (lo que representa un total de 216 muestras). Anchoa mitchilli fue la especie dominante y comprendi6 el 55% del nuimero total de peces capturados. La abundancia no mostr6 correlaci6n significativa con ningun parametro ambiental (salinidad, temperatura, oxigeno disuelto, transparencia) de la laguna. La abundancia de la especie no mostr6 un patr6n espacial bien definido, pero en general los mayores valores se registraron en las zonas cercanas a la boca. Se presentaron pulsos de abundancia en numero y peso durante septiembre y octubre, con un aumento general en la 6poca lluviosa. Las fluctuaciones estacionales de la abundancia estuvieron precedidas por las fluctuaciones de las lluvias. Asi, la lluvia y su influencia asociada con la disponibilidad de alimento dentro de la laguna, tenia un efecto retrasado significativo sobre la abundancia de esta especie. La abundancia fue significativamente mayor durante la noche y probablemente esto represente una estrategia de la especie para evitar depredaci6n. The bay anchovy, Anchoa mitchilli, is a common species found from Casco Bay in Maine, United States, south to the Florida Keys, and around the coast of the Gulf of Mexico, south to Yucatan, Mexico (Hildebrand, 1943; Whitehead et al., 1988). It is a marine species, occurring in shore waters, but more commonly in shallow tidal areas with muddy bottoms and brackish waters. It tolerates a wide range of salinities from virtually fresh to even hypersaline waters (Whitehead et al., 1988). Due to its great abundance, this species has considerable importance. The bay anchovy is canned whole or used in the production of anchovy paste; it is also widely used as bait. But, its value as forage for commercially and recreationally valuable fish species, exceeds its direct value to man. Because it usually occurs in schools a d is a rather sluggish swimmer, it is easy prey for many predators (Hildebrand and Cable, 1930; Hildebrand, 1964; Vouglitois et al., 1987). Despite its apparent role as a critical link in estuarine and nearshore oceanic food webs, the life history and population dynamics of this species are poorly understood (Vouglitois et al., 1987). The primary goals of our study were to deThis content downloaded from 207.46.13.169 on Sat, 01 Oct 2016 06:20:40 UTC All use subject to http://about.jstor.org/terms 264 The Southwestern Naturalist vol. 39, no. 3