Ichthyoplankton, euphausiids, and zooplankton biovolumes (summer-autumn 2015)

Abstract

The 1502-04 hydroacoustic research cruise for pelagic resources was conducted between February 22 and March 31, 2015. 144 zooplankton samples were collected, using Hensen net of 300 μm mesh opening, in vertical trawls with the vessel stationary up to 50 m deep. A total of 18 euphausiid species belonging to the genera Euphausia, Nematoscelis, Nematobrachion, Nyctiphanes, and Stylocheiron were determined. The calyptopis and furcilia early stages predominated with frequencies of 68% and 87%, respectively. Likewise, 63 ichthyoplankton species distributed in 35 families were determined. Engraulis ringens was the most abundant species. Eggs and larvae ranged from 3 to 4,566 eggs/m2 and 3 to 2,574 larvae/m2 distributed from Talara to San Juan de Marcona. Vinciguerria lucetia eggs and larvae fluctuated from 3 to 4,212 eggs/m2 and 3 to 1,512 larvae/m2. They were distributed mainly outside the continental shelf, with eggs being found between Punta Sal and Pimentel, off Salaverry, and between Huarmey and San Juan de Marcona, while the larvae were located between Punta Sal and Punta La Negra, Pimentel and Salaverry, Huarmey and Independencia Bay, as well as off San Juan of Marcona, with densities greater than 500 larvae/100 m2 off Punta Sal, Talara, and Independencia Bay. In terms of frequency, other important Myctophidae species were Diogenichthys laternatus, Lampanyctus parvicauda, Triphoturus oculeus, and Myctophum nitidulum, which were recorded in 35%, 11%, 8%, and 6% of the total samples collected. Zooplankton biovolumes ranged from 0.001 to 5.72 mL/m3, with a median of 0.62 mL/m3. Values below 0.26 mL/m3 were the most frequent (47%) occurring from Paita to San Juan Marcona, mainly on the continental shelf. These values were located outside the continental shelf at 80 nm offshore between Punta La Negra and Salaverry.