AnchovetaEngraulis ringensalong the Chilean coast: Management units, demographic units and water masses: Insights from multiple otolith‐based approaches

Abstract

Three management units (MUs) are used for stock assessment and fishery regulations of anchoveta Engraulis ringens in Chilean waters (>65% of E. ringens latitudinal range): MU‐I [18–25)°S, MU‐II [25–32)°S and MU‐III [32–42)°S. To evaluate whether these three MUs correspond to separate demographic units (DUs), as well as to estimate mixing rates and spatial distribution of these DUs, we combined three types of otolith natural markers: isotopic signatures (δ13C and δ18O), elemental compositions (Na, Mg, Mn, Sr and Ba) and microstructural indexes. All otolith markers were determined in nuclear and marginal regions of juveniles and adults from cohorts 2012 and 2015. Differences in core region markers indicated spatial segregation between three environmentally distinct nursery areas, probably related to Subtropical Water (MU‐I), Subantarctic Water (MU‐III) and the Subtropical Convergence (MU‐II). Comparison of core and marginal regions, from juvenile and/or adult fish, suggested that adult fish remained nearby nursery areas, separated from fish nursed in other MUs. Nonetheless, ontogenetic migrations from warmer (offshore) nursery habitats to cooler (deeper/more coastal) feeding habitats occurred within MUs. In summary, our results support the consideration of the three MUs as three separate DUs. Estimated mixing rates indicated MU‐II received contributions of 31% from MU‐I and 3% from MU‐III, while complete segregation existed between MU‐I and MU‐III. Such mixing rates between MU‐I and MU‐III seem large enough to justify its further consideration by stock assessment models and management procedures.

Intraspecific variation and energy channel coupling within a Chilean kelp forest

“…With the exception of anchoveta, all fish samples were collected at each site via spearfishing, or double fyke‐net fished overnight (Doppelreuse Typ 3, Engel‐Netze GmbH & Co. Kg, KG, Bremerhaven, Germany). Anchoveta were found stranded alive on the coast by local fisherman; we assume these individuals were feeding locally, as previous research suggests there is limited immigration of non‐local anchoveta into the northern Chile stock (Garcés et al 2019). All producers and consumer samples were kept on ice for 2–8 h immediately post collection, and then either processed and lyophilized, or stored frozen at −20°C until analysis.…”

Endogenous, Climate, and Fishing Influences on the Population Dynamics of Small Pelagic Fish in the Southern Humboldt Current Ecosystem

“…They are the dominant species in terms of biomass in the pelagic communities of the southern Humboldt Current ecosystem and vital species in the transfer of energy from plankton to higher trophic levels (Neira, 2008). In addition, these species aggregate into a small number of populations (Cubillos et al, 2007;Garcés et al, 2019). Several factors have been reported to influence the dynamics of SPF in the Humboldt Current system, such as ocean temperature, zooplankton, oxygen, plankton size structure, cannibalism, and fishing (Alheit, 1987;Chavez et al, 2003;Ayón et al, 2008;Bertrand et al, 2011;Essington et al, 2015;Canales et al, 2016).…”

Spatiotemporal analysis of the daily growth traits of the prerecruits of a small pelagic fish in response to environmental drivers

“…In the current study, clear differences in early growth rates of E. Ringens prerecruits were found between the northern and southern Chilean stocks of this species, which inhabit different water masses (Garcés et al., 2019), which exhibit large differences in temperature, productivity and other environmental drivers. Empirical evidence about the influence of environmental drivers upon growth of early juveniles is very scarce (Bacha & Amara, 2012), but suggest growth is strongly influenced by prey availability, prey quality, and temperature, as found in larval stages of several teleosts (Takasuka & Aoki, 2006; Payne et al., 2013; Costalago, Potter, Pattrick, & Strydom, 2017; Itoh et al., 2011; Seljeset, Vollset, Folkvord, & Geffen, 2010).…”

“…In this area, intense fishery activity has caused anchoveta landings to reach the highest levels in recent decades, with 4.3 and 3.1 million tons landed by Peru and Chile, respectively, between 2015 and 2016 (Pikitch et al., 2012). Recent studies have addressed the population structure of this species along the Chilean coast with the use of otolith‐based ecological markers (i.e., Cerna, Saavedra‐Nievas, Plaza, Niklitschek, & Morales‐Nin, 2019; Garcés et al., 2019), revealing the existence of three different demographic units (“stocks”) in a northern zone (18º21'S and 24º00'S), a central‐northern zone (24º00'S and 32º10'S), and a central‐southern zone (32º10'S and 41º00'S), which suggest high heterogeneity in the population structure of this species.…”