Alejandro Hinojosa-Medina

Influences of El Niño on assemblages of mesopelagic fish larvae along the Pacific coast of Baja California Sur

Abstract Seasonal assemblages of mesopelagic fish larvae and changes related with environmental factors (plankton biomass, sea surface temperature anomaly, upwelling, and the multivariate El Niño index) were investigated. From 1982 to 1987, 16 oceanographic cruises were carried out along the Pacific coast of Baja California Sur, Mexico. Larvae of 42 mesopelagic fish taxa were collected. Larval abundance was highly variable during the studied period, but summer months coincided with higher abundance (>200 larvae under 10 m2). Larval assemblages were dominated by three of the most common species of tropical (Vinciguerria lucetia, Diogenichthys laternatus) and subtropical affinity (Triphoturus mexicanus). A group of species of tropical affinity (Diplophos proximus, Diaphus pacificus, Benthosema panamense) was useful for distinguishing the 1982–84 El Niño event, and an assemblage of larvae of temperate affinity (Symbolophorus californiensis, Melamphaes lugubris, Bathylagus ochotensis, Leuroglossus stilbius, Protomyctophum crockeri) characterized ‘normal’ years (mid‐1984 to mid‐1987).

Interannual distribution of Pacific hake Merluccius productus larvae in the southern part of the California Current

The interannual distribution of early life stages of Pacific hake Merluccius productus, within the southern part of the California Current (32-23 degrees N) from 1951 to 2001, was examined to describe the relationship between spawning habitat and environmental conditions. Mean annual abundance was affected by different factors along the west coast of the Baja California Peninsula. In the northern areas (Ensenada and Punta Baja), reduced abundance of larvae coincided with the El Niño and a North Pacific Ocean climatic regime shift, but in the southern areas (San Ignacio to Bahía Magdalena), the drastic reductions suggested a fishery effect for large adults of the coastal migratory population, starting in 1966. Two spawning stocks, coastal and dwarf, were evident in comparisons of latitudinal differences in occurrence of early stages and differences in temperature preferences that seemed to break at Punta Eugenia.

Identificación de zonas propicias para el desarrollo larval de la macarela del Pacífico(Scomber japonicus) en la porción sur de la Corriente de California

espanolEl tamano larval es una variable importante para entender los cambios en el desarrollo y la identificacion de un entorno adecuado para el crecimiento y la supervivencia larval. Las larvas de la macarela del Pacifico (Scomber japonicus) presentan un lento crecimiento durante las primeras fases del desarrollo (6-8 mm de LE); posteriormente, la velocidad de crecimiento aumenta, pero el desarrollo depende principalmente de la temperatura y del alimento. El objetivo del presente trabajo fue identificar las zonas y temporadas propicias para el desarrollo larval de S. japonicus, en relacion a la temperatura superficial del mar y la biomasa del zooplancton, frente a la costa occidental de la Peninsula de Baja California (~25-32°N) del 2006 al 2010. Las larvas de la macarela del Pacifico mostraron la mayor amplitud en su distribucion espacial en primavera, pero con mayor abundancia restringida frente a Punta Eugenia (~28°N) durante el verano. Los cambios en su distribucion, estuvieron bajo la influencia del flujo geostrofico y la variabilidad termica. El analisis de regresion lineal permitio identificar zonas propicias para el desarrollo de larvas, con un menor desarrollo en primavera, relacionado con un intervalo estrecho de temperaturas y niveles de biomasas del zooplancton comparativamente bajos. En contraste, durante el verano el mayor incremento en la altura del cuerpo (s) fue relacionado con un amplio intervalo de temperaturas, mientras que su baja variabilidad (error estandar) coincidio con altos niveles de biomasa del zooplancton. Se considera que las condiciones termicas y de disponibilidad de alimento favorecen un optimo desarrollo larval particularmente en la epoca de verano. EnglishLarval size is considered as an important variable to understand the changes in larval development and identification of a suitable environment for larval growth and survivor. Larvae of the Pacific mackerel (Scomber japonicus) have a slow growth during the early stages of development (6-8 mm SL); subsequently, the growth rate increases, but the development depends mainly on the temperature and food. The aim of this study was to identify the areas and seasons favorable for larval development of S. japonicus, in relation to the sea surface temperature and the zooplankton biomass, off the west coast of the Baja California Peninsula (~25°-32°N) from 2006 to 2010. Larvae of the Pacific mackerel showed the greatest amplitude in their spatial distribution during spring, but with greater restricted abundance compared to Punta Eugenia (~28°N) during summer. Changes in its distribution were influenced by geostrophic flow and thermal variability. Linear regression analysis allowed to identify areas favorable for larvae development, with a lower development in spring, related to a narrow range of temperatures and levels of comparatively low zooplankton biomass. In contrast, during summer the largest increase in body height (s) was related to a wide range of temperatures, while its low variability (standard error) coincided with high levels of zooplankton biomass. It is considered that thermal conditions and food availability, favor an optimum larval development, particularly during the summer season.