The influence of oceanographic processes on jack mackerel (Trachurus murphyi) larval distribution and population structure in the southeastern Pacific Ocean

Abstract

Vásquez, S., Correa-Ramírez, M., Parada, C., and Sepúlveda, A. 2013. The influence of oceanographic processes on jack mackerel (Trachurus murphyi) larval distribution and population structure in the southeastern Pacific Ocean. – ICES Journal of Marine Science, 70: 1097–1107. The distribution of jack mackerel larvae in the main oceanic spawning area of the southeastern Pacific Ocean was investigated through three consecutive spring bio-oceanographic surveys (2003–2005). In this study, otolith microstructure analysis revealed a spatial age gradient with the smallest/youngest larvae specimens found primarily in the offshore area and the largest/oldest found in the coastal area, implying offshore-inshore larval drift. This suggests a connection between the oceanic spawning area and the historical coastal nursery ground (north of 30°S). In order to understand the oceanographic processes that drive this larval transport, we inferred circulation patterns from two data sources: mesoscale eddy trajectories identified by applying the Okubo-Weiss parameter to satellite geostrophic currents, and 20 years of satellite tracking data of drifters. Our results showed that eddy trajectories lead to net northwestward offshore transport (the opposite direction of larval connectivity). In addition, mean circulation associated with the subtropical anticyclonic gyre and recurrent energetic meandering structures seem to be the major mechanisms driving the spatial dynamics of the early jack mackerel life history, determining a net transport to nursery grounds. These mechanisms could play a key role in recruitment, which supports the continuity of the jack mackerel population.

The first report of liver coccidian Goussia cruciata in jack mackerel, Trachurus murphyi, from the South Pacific and its relationship with host variables

“…T. murphyi is a highly migratory fish species supporting important fisheries along South Pacific coasts. Molecular studies (Cárdenas et al 2009) and larval distribution (Vásquez et al 2013) support the hypothesis that T. murphyi is only one population across the South Pacific Ocean. The 100 % prevalence of G. cruciata found in T. murphyi could be concordant with the above studies.…”

Genetic structure analysis of Girella laevifrons populations in central Chile

“…Because it is a coastal species, larvae are produced in areas near the coast. From here, mesoscale eddies, superficial circulation and Ekman transport could generate off‐shore larval transport towards the north, which could eventually combine with the net flow toward the north generated by the HCS (Vásquez, Correa‐Ramírez, Parada, & Sepúlveda, ). If larvae are considered passive particles, and if they were to enter the HCS, they would be transported for approximately 69 days (i.e., PLD) (Mansur et al, ) towards the north at an average speed of 0.2 m/s.…”

Modelling South Pacific jack mackerel spatial population dynamics and fisheries

“…Data paucity can also lead the model outputs to be mostly driven by habitat suitability and to the underestimation of migration speed by which one school of fish can be targeted over time by different vessels in different areas. Previous studies highlighted the strong heterogeneity of JM distributions in areas of high mesoscale activity (Nunez et al., 2004; Vasquez et al., ). Namely, JM is known to aggregate on the edge of eddies (SPRFMO, ).…”

“…A large feeding ground is known in the central‐south zone off Chile (30–40°S), where the recruitment of 2–3 year‐old individuals occurs. The oceanic spawning area located off central Chile extends up to 1,800 km offshore during spring (Vasquez et al., ). A single stock structure is currently used within the SPRFMO assessment studies.…”

“…At its maximal expansion, the species was distributed continuously from the Chilean and Peruvian coasts to the coast of New Zealand (Ashford, Serra, Saavedra, & Letelier, 2011;C ardenas et al, 2009). Despite this large transoceanic habitat range, previous studies described the JM population structure as including a panmictic single stock for the whole South Pacific (C ardenas et al, 2009;Vasquez, Correa-Ramirez, Parada, & Sepulveda, 2013).…”