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Brain-machine interfaces (BMIs) can restore motor function to people with paralysis but are currently limited by the accuracy of real-time decoding algorithms. Recurrent neural networks (RNNs) using modern training techniques have shown promise in accurately predicting movements from neural signals but have yet to be rigorously evaluated against other decoding algorithms in a closed-loop setting. Here we compared RNNs to other neural network architectures in real-time, continuous decoding of finger movements using intracortical signals from nonhuman primates. Across one and two finger online tasks, LSTMs (a type of RNN) outperformed convolutional and transformer-based neural networks, averaging 18% higher throughput than the convolution network. On simplified tasks with a reduced movement set, RNN decoders were allowed to memorize movement patterns and matched able-bodied control. Performance gradually dropped as the number of distinct movements increased but did not go below fully continuous decoder performance. Finally, in a two-finger task where one degree-of-freedom had poor input signals, we recovered functional control using RNNs trained to act both like a movement classifier and continuous decoder. Our results suggest that RNNs can enable functional real-time BMI control by learning and generating accurate movement patterns.

Background Functional resistance training is frequently applied to rehabilitate individuals with neuromusculoskeletal injuries. It is performed by applying resistance in conjunction with a task-specific training, such as walking. However, the benefits of this training may be limited by motor slacking, a phenomenon in which the human body attempts to reduce muscle activation levels or movement excursions to minimize metabolic- or movement-related costs. While kinematic feedback could reduce one's tendency to minimize effort during training, this has not been verified experimentally. Research Question Does functional resistance training during walking lead to motor slacking, and can techniques such as visual feedback be used to reduce these effects? Methods Fourteen able-bodied individuals participated in this experiment. Participants were trained by walking on a treadmill while a bidirectional resistance was applied to the knee using a robotic knee exoskeleton. During training, participants were either instructed to walk in a manner that felt natural or were provided real-time visual feedback of their kinematics. Electromyography and knee kinematics were measured to determine if adding resistance to the limb induced slacking and if feedback could reduce slacking behavior. Kinematic aftereffects were measured after training bouts to gauge adaptation. Results Functional resistance training without feedback significantly reduced knee flexion when compared to baseline walking, indicating that participants were slacking. This reduction in knee flexion did not improve with continued training. Providing visual feedback of knee joint kinematics during training significantly increased knee muscle activation and kinematic aftereffects. Significance The findings indicate that individuals are susceptible to motor slacking during functional resistance training, which could affect outcomes of this training. However, motor slacking can be reduced if training is provided in conjunction with a feedback paradigm. This finding underscores the importance of using additional methods that externally motivate motor adaptation when the body is not intrinsically motivated to do so.

The dusky finless skate Gurgesiella furvescens appears sporadically as part of the bycatch in the trawl fishery targeting demersal crustaceans on the continental shelf and upper slope of the north-central area of Chile (26ºS-33ºS). Demersal crustaceans could be forage for deep-water predators such as G. furvescens, and sizes and shapes of prey eaten could be restricted by mouth size. The diet composition of G. furvescens was determined based on specimens collected from the bycatch of trawls targeting demersal crustaceans in 2013. Stomach contents revealed nylon shrimp Heterocarpus reedi (32.8% by weight), deep-water shrimp Haliporoides diomedeae (7.2% by weight), and indeterminate crustaceans (9.0% by weight). The diet composition was similar between sexes, body length, or depth strata. Prey size was a linear function of Gurgesiella furvescens mouth width, and prey mass positively related with G. furvescens individual mass. Although squat-lobsters Pleuroncodes monodon and Cervimunida johni were abundant in the study area, the nylon shrimp and deep-water shrimp in the diet of G. furvescens may be due to the preference or selection of this kind of prey in deep waters.

Increasing attention is paid to the interdependence between the ecological and human dimensions to improve the management of natural resources. Understanding how artisanal fishers see and use the common-pool resources in a co-management system may hold the clue to establishing effective coastal fisheries policies or strengthening existing ones. A more comprehensive planning of the system will also have a bearing on how to reduce conflicts and strengthen social networks. We surveyed artisanal fishers and decision-makers to determine their perceptions about the Management and Exploitation Areas of Benthic Resources (known as MEABR) in Chile’s Biobio region. We performed a field study from November 2018 to August 2019, applying a set of questionnaires to determine the ecological and human attributes that contribute to MEABR outcomes, and then constructed composite scores for those attributes according to a multidimensional scaling technique (“Rapfish”). We find that fishers have different perspectives: surprisingly, women highlighted that the institutional dimension was the most influential on MEABR performance, whereas men highlighted the ecological and economic outcomes. The decision-makers’ role in the MEABR system was considered adequate, but communication and socialization of regulations were irregular. Results also showed that fishers expressed dissatisfaction with illegal fishing practices (poaching), productivity, profits, and conflicts inside and outside the MEABRs. Our study allowed us to better understand how the MEABR has developed in the region. We recommend strengthening local management strategies with particular attention paid to networking among stakeholders, including gender inclusive relationships.

A key factor in population models, the temporal scale, should both reflect intra-annual biological processes and avoid over-parameterization. We applied the separability assumption to model recruitment process error as additive effects of random annual deviates and quarterly fixed effects (QFEM) to improve our understanding of intra-annual recruitment patterns and, at the same time, minimize the impact of over-parameterization. We formulated a length-based model with a quarter-year temporal resolution and applied it to the anchovy (Engraulis ringens) fishery off northern Chile and southern Peru, using data from 1984 to 2015. Model performance was compared to that of a larger model in which the process error is treated as an interaction of quarter-year effects (QYIM). QFEM proved to be most adequate only when the variability of population processes and the fishery are determined by a clear seasonal pattern. In those cases, QFEM characterized recruitment seasonality as well as inter-annual trends. Under these conditions, the separability hypothesis of recruitment process error substantially reduced the number of parameters in the stock assessment model, the bias of estimated population variables, and uncertainty when the most recent data were incomplete or non-informative. QFEM provides an alternative way to improve assessments and fishery management for fast-growing and short-lived species such as small pelagic fish.

Common sardine, Strangomera bentincki, support an important artisanal fishery along the Chilean coast; however, there is lack of knowledge of the early life history traits of this species. Using satellite-derived environmental conditions (sea surface temperature, SST, and chlorophyll-a), and otolith microstructure analysis of larval stages collected in coastal waters of central Chile, larval age, growth rates, and back-calculated yolk-sac absorption date patterns were analyzed for 2010–2013. SST varied from 11 to 20 °C and showed the highest values during austral summer 2013, whereas Chl-a varied between 0.2 and 66 mg m−3. The abundance of larval S. bentincki was similar during 2010 and 2011, decreased in 2012 but increased again in 2013 to similar densities of 2010 to 2011. Similarly, larvae collected during 2012 had the largest otoliths (radius, perimeter, area). Larval growth rates did not vary significantly among years and ranged between 0.32 and 0.42 mm day−1. From 2010 to 2011, a significant decrease occurred in the size-at-age of larval S. bentincki, and then, size-at-age was maintained until 2013. Back-calculated yolk-sac absorption dates differed among years and were delayed from winter to spring during 2012. The latter occurred in a period with significantly warmer waters. Additionally, SST and Chl-a concentration were not linearly related to the mean growth rates of larval S. bentincki.

Marine biota are redistributing at a rapid pace in response to climate change and shifting seascapes. While changes in fish populations and community structure threaten the sustainability of fisheries, our capacity to adapt by tracking and projecting marine species remains a challenge due to data discontinuities in biological observations, lack of data availability, and mismatch between data and real species distributions. To assess the extent of this challenge, we review the global status and accessibility of ongoing scientific bottom trawl surveys. In total, we gathered metadata for 283,925 samples from 95 surveys conducted regularly from 2001 to 2019. We identified that 59% of the metadata collected are not publicly available, highlighting that the availability of data is the most important challenge to assess species redistributions under global climate change. Given that the primary purpose of surveys is to provide independent data to inform stock assessment of commercially important populations, we further highlight that single surveys do not cover the full range of the main commercial demersal fish species. An average of 18 surveys is needed to cover at least 50% of species ranges, demonstrating the importance of combining multiple surveys to evaluate species range shifts. We assess the potential for combining surveys to track transboundary species redistributions and show that differences in sampling schemes and inconsistency in sampling can be overcome with spatio‐temporal modeling to follow species density redistributions. In light of our global assessment, we establish a framework for improving the management and conservation of transboundary and migrating marine demersal species. We provide directions to improve data availability and encourage countries to share survey data, to assess species vulnerabilities, and to support management adaptation in a time of climate‐driven ocean changes., While many species are changing their spatial distributions rapidly with climate change, the global capacity to track these changes and then adapt management and policy has been limited. To build this capacity for demersal fishes, we compiled the largest worldwide collection of bottom trawl survey metadata and demonstrate how surveys can be combined to follow species across national and survey boundaries. Open data and transparent scientific assessment can be a key step towards improved management of redistributing transboundary species and stocks.

The Inland Sea of Chiloe is a semi-enclosed sea of northern Patagonia characterized by freshwater inputs from a fjord in the north and high influence of offshore waters in its southern sub-basin. The zone has been referred to as an important fish nursery ground. In order to assess its relevance as a spawning ground and the strategies for temporal coexistence of larvae of fish species from diverse origins in these inshore waters, we investigated both the horizontal and vertical distributions, and the feeding habits of early stages of fish during the period of highest productivity (austral spring). Ichthyoplankton richness and abundance were higher in the northern sub-basin, dominated by the offshore midwater lightfish Maurolicus parvipinnis, and the shelf-break and demersal hake Merluccius gayi. The larvae of the coastal rockfish Sebastes oculatus and the clupeid Strangomera bentincki were more abundant in surface waters, while the larvae of Merluccius australis, M. gayi, and M. parvipinnis reached deeper waters. The co-occurring inshore larvae of M. gayi, M. parvipinnis, and S. oculatus preyed actively at day and night times on a wide spectrum of zooplankton sizes, with the small calanoid copepods being the most commonly consumed food items in the largest larvae of M. parvipinnis and M. gayi. Nauplii were frequent food items for smaller larvae of M. parvipinnis, S. oculatus, and S. bentincki. The high spring productivity and the large abundances of potential zooplanktonic prey, along with larval spatial segregation, are visualized as the main factors enabling species with different origins to co-inhabit and grow at inshore waters in northern Patagonia.

The management of small pelagic fisheries is a complex task due to its large variability of both environmental and biological processes. This high variability can impact the reliability of stock assessment models and fishery management recommendations. When this occurs, management decisions should explore alternative control rules based on empirical abundance indices or pragmatic management procedures. In this paper, we examined the performance of a harvest control rule (HCR) for the Chilean fleet in the shared Chile-Peru anchovy (Engraulis ringens) fishery (16°S–24°S), which is one of the most important stocks in the Humboldt marine ecosystem in the Southeast Pacific. The HCR uses the annual changes in spawning biomass estimated by Daily Egg Production Method (DEPM) surveys in the waters off northern Chile. Analyzes are carried out through operating models simulating population regime shifts under different uncertainty sources. The results show that despite the latent risk of overfishing caused both by recruitment variability and the lack of fisheries management coordination between two jurisdictions, the control of one of the parties' fishing mortality can enable the sustainability of the entire stock, provided the fishing effort of the other jurisdiction be remained at similar levels as in the last decade. The use of an HCR would avoid increases in fishing mortality and would facilitate BMSY-based management goals. This research determined conditions under which the shared Chile-Peru anchovy fishery can be sustainable considering different sources of uncertainty of the biological-fishing system.

The Territorial Use Rights for Fisheries (TURF) system are a kind of marine property where user rights are assiged to collective entities of artisanal fishers’ organizations. But their effectivity continues to be limited, which demands a comprehensive evaluation of their social, economic, and ecological performance. Consequently, the practical integration and application of these aspects continue to be a significant challenge for their management. The “RAPFISH” multidimensional scaling technique was applied to assess the sustainability status of 19 TURFs of the Biobio Region (Chile), using 51 transdisciplinary attributes relating to ecological, economic, social, among other dimensions. The results obtained in the two-dimensional arrangement presented a sustainability gradient, due to the marked variations among the different TURFs, and only four cases had very weak sustainability scores. Broadly speaking, this study determined that the social dimension (score: 61.37%) had a “high” influence on the best performance of the TURF system, while the ecological, ethical, and institutional dimensions were rated from ‘regular’ to ‘bad’. Overall, results indicate an average performance in the “medium” sustainability range (score: 54.68%), and these results generated questions about the TURFs’ viability, mainly in those that have not reached their sustainability objectives. Therefore, more local studies are needed on the social dimension of this system, in order to define the effective participatory tools and social management plans in TURFs, which will contribute to improve their performance.

In habitats impacted by bottom trawling that influences the resilience of few and widely distributed abundant species, it is relevant to analyze how populations are structured according to their niche and niche overlap, and hence contributing to the ecosystem-based management approach. We evaluated and compared the isotopic niche width and determined the isotopic niche overlap for target and bycatch species of crustaceans and demersal fish caught with bottom trawling on the continental shelf and upper slope of the central-southern zone of Chile. Stable isotope analysis relied on carbon and nitrogen isotopes (13C and 15N) and Bayesian statistics of niche size and community metrics. Crustaceans and fish species are structured in three clusters according to the stable isotope values and the Chilean hake Merluccius gayi, which was probably clustered isolated due to its pelagic stable isotope values due to diel vertical migrations associated with feeding on euphausiids in the water column. The first group was constituted by demersal fish, that showed higher δ15N (19‰) and narrower δ13C (−16‰). The two other groups constituted a mix of crustaceans and fish, with access to different carbon sources. There were degrees of specialization for most species within the groups and overlap in the isotopic niche between populations. The benthic and demersal macrofauna species are structured by sharing resources in the habitat, probably on available sources supported by the productive pelagic system.

Climate variability and predation influence the fluctuations in the recruitment of exploited marine populations. This study analyses the dynamics of the recruitment of the nylon shrimp (Heterocarpus reedi Bahamonde 1955) over the period 1968 and 2015, considering the influence of climate variability and the biomass of hake (Merluccius gayi), as a proxy for predation in its distribution area. We collected the Humboldt Current Index (HCI) and Southern Oscillation Index (SOI) time series as climate variables and estimates of recruitment and spawning biomass of nylon shrimp, as well as biomass of hake. Annual deviations in nylon shrimp recruitment showed increased sensitivity to climate variability and hake biomass, expressed through a significant cumulative correlation over time. The recruitment drives the spawning biomass, implying an environmentally driven shrimp recruitment dynamic. Generalized Linear Models showed that hake biomass and climate indices affect negative and positively the shrimp recruitment during the recruitment year, respectively. A path diagram with Structural Equation Models showed that SOI impacted HCI, negatively impacting the hake stock. Hake negatively affected the shrimp stock biomass and recruitment, and SOI either directly or indirectly, through its effect on the hake. The hake impact on the shrimp's spawning stock and recruitment is due to predation under concurrent climate variability on longer-term periods.

Three dominant recruitment patterns were identified across 30 stocks from Australia, New Zealand, Chile, South Africa, and the Falkland Islands using data from 1980 to 2010. Cluster and dynamic factor analysis provided similar groupings. Stocks exhibited a detectable degree of synchrony among species, in particular the hakes and lings from Australia, New Zealand, Chile, and South Africa. We tested three climate indices, the Interdecadal Pacific Oscillation (IPO), Southern Annular Mode (SAM), and Southern Oscillation Index (SOI), to explore their relationship with fish stock recruitment patterns. The time series of IPO and SOI showed the strongest correlation with New Zealand hoki (blue grenadier, Macruronus novaezelandiae) and Australian jackass morwong (Nemadactylus macropterus) (r = 0.50 and r = –0.50), and SAM was positively related to Australian Macquarie Island Patagonian toothfish (Dissostichus eleginoides) (r = 0.49). Potential linkages in recruitment patterns at sub-basin, basin, and multibasin scales and regional and global climate indices do account for some of the variation, playing an important role for several key Southern Hemisphere species.

In age-structured fisheries stock assessments, ageing errors within age composition data can lead to biased mortality rate and year-class strength estimates. These errors may be further compounded where fishery-dependent age composition data are influenced by temporal changes in fishery selectivity and selectivity misspecification. In this study, we investigated how ageing error within age composition data interacts with time-varying fishery selectivity and selectivity misspecification to affect estimates derived from a statistical catch-at-age (SCA) model that used fishery-dependent data. We tested three key model parameters: average unfished recruitment (R0), spawning stock depletion (Dfinal), and fishing mortality in the terminal year (Fterminal). The Patagonian toothfish (Dissostichus eleginoides) fishery in southern Chile was used as a case study. Age composition data used to assess this fishery were split into two sets based on scale (1989–2006) and otolith (2007–2012) readings, where the scale readings show clear age-truncation effects. We used a simulation-estimation approach to examine the bias and precision of parameter estimates under various combinations of ageing error, selectivity type (asymptotic or dome-shaped), selectivity misspecification, and variation in selectivity over time. Generally, ageing error led to overly optimistic perceptions of current fishery status relative to historical reference points. Ageing error generated imprecise and positively biased estimates of R0 (range 10 to >200%), Dfinal (range −20 to >100%), and Fterminal (range −15 to >150%). The bias in Dfinal and R0 was more severe when selectivity was dome-shaped. Time-varying selectivity (both asymptotic and dome-shaped) increased the bias in Dfinal and Fterminal, but decreased the bias in R0. The effect of ageing error was more severe, or was masked, with selectivity misspecification. Correcting the ageing error inside the SCA reduced bias and improved precision of estimated parameters .

The upwelling ecosystem of central southern Chile sustains the pelagic common sardine and anchovy fisheries, which are managed by setting a global quota allocated to small-scale (artisanal) and industrial fishers. A prearranged spatial allocation of quotas for small-scale fishers is based on historical landings rather than the current spatial distribution of the target species. Artisanal fishers can only fish in their original Spatial Administrative Units (SAUs) according to fishing rights. Marked environmental variability, such as that caused by ENSO events, trigger changes in the local availability of resources. Thereafter, artisanal and industrial fishers compensate for low yields by transferring their fishing quota to quota holders (artisanal-artisanal, industrial-artisanal, artisanal-industrial) from other SAUs. The legal procedure for transferring quotas among users is efficient to harvest the total allowable catch. This procedure favors the quota holders but is detrimental to the crew of vessels that transfer quotas to other fishers. A mechanism is recommended to distribute the profits obtained by quota transfers between ship owners and crews to avoid this negative effect.

The daily egg mortality (Z) of small pelagic fish can be modulated by environmental variables as well as by population derived factors such as egg production and/or dispersion and aggregation processes. The anchovy daily egg mortality rate was compared across spawning areas distributed in the North (18 ∘ 25’S-26o03’S), Central (34o30’S-37o10’S), and South (38 ∘ S-41 ∘ 20’S) zones along the Chilean coast. Daily egg production ( P 0 ) and Z were estimated through a generalized linear model (binomial negative) from egg count data obtained in yearly Daily Egg Production Method applications (2002–2014). Co-variables included P 0 , the spawning area (SA), sea surface temperature (SST), phytoplankton biomass (Chl-a), alongshore wind (V) and an index of the El Nino-Southern Oscillation (ENSO) during the spawning period (August–September).Egg mortality was significantly higher in the North zone, influencing spatial differences rather than yearly effects. Egg mortality was not associated with ENSO, but correlated positively with P 0 , SA, SST, and V, and negatively with Chl-a. The best model explained 42.3% (P P 0 and V, which was interpreted as density-dependent effects and winds driving egg concentration processes rather than dispersion. The Lloyd’s patchiness index was computed as an index of egg aggregation by embryonic development stages (Group A: early development, Group B: middle development, and Group C: close to hatching). The spawning area was negatively correlated with the patchiness index of Groups A and B in the North zone. Overall results suggested that anchovy eggs survival would be dependent on dispersion in the North zone but concentration and retention in the South spawning area and thereafter coincident with reproductive tactics of adults in the North and South areas, respectively.

Biodiversity and biomass patterns of megafaunal assemblages were assessed from the yellow (Cervimunida johni) and red (Pleuroncodes monodon) squat lobster fishing grounds in the Southeastern Pacific Ocean during four years. Bottom trawls were conducted applying the swept-area method in a stratified sampling design, obtaining global and specific catch per unit area (CPUA). We recorded two target and 47 by-catch species, with a total CPUA of 80.000 t/km2 (cumulative from 2005 to 2008) Fishes and crustaceans dominated over other taxonomic groups. Classes Actinopterygii and Malacostraca attained the highest specific richness; the presence of a few dominant and many rare species in terms of CPUA and frequency, was characteristic of the studied assemblages, hence, the general CPUA pattern parallels that of the most abundant species in the bathymetric and latitudinal gradients. The three most conspicuous non-target species, Heterocarpus reedi, Merluccius gayi gayi and Hippoglossina macrops accounted for 91% of the by-catch CPUA, whereas Class Malacostraca also represented 91% of the total CPUA. The highest average specific richness occurred at intermediate depths (300–400 m) and the lowest in shallow waters (50–100m); the highest overall CPUA occurred at 100–200m and the lowest at both 400–600m and 50–100m. Depth was the most significant factor in the variability of our assemblages. However, particular features of the Humboldt Current System might act as drivers of important effects across the latitudinal gradient on the high productivity and dynamism of the squat lobster fishery, despite the homogeneous composition of the community. This study shows the importance of considering the whole biodiversity within appropriate management actions, in order to achieve ecological benefits (e.g. resilience, functional diversity, water quality, primary productivity) in communities subjected to fishing pressure.

Conocer los parámetros de historia de vida de las especies de condrictios es uno de los principales requisitos para evaluar el estado de sus poblaciones y vulnerabilidad a la explotación pesquera. En este estudio se estimó el crecimiento en longitud, la talla de madurez (LM50%), la longevidad (Emax) y la tasa de mortalidad natural (M) del pez gallo, Callorhinchus callorynchus, en el Golfo San Matías, Argentina. En los muestreos de las capturas comerciales se obtuvo un rango de tallas de 22 a 58 cm para machos y de 25 a 76 cm para las hembras, mientras que en las campañas de investigación fue de 13 a 59 cm para los machos y de 14 a 69 cm para las hembras. La proporción de sexos estuvo sesgada hacia los machos. El modelo de crecimiento de Gompertz L0 fijo fue el más adecuado según el criterio biológico de selección. Los parámetros fueron: i) hembras: L∞= 70,75 cm y K= 0,17 año-1; ii) machos: L∞= 56,11 cm y K= 0,257 año-1. Para machos se obtuvo un LM50%= 43,39 cm, una Emax= 13,7 años y una Mmedia= 0,35 año-1 y para hembras se obtuvo un LM50%= 47,48 cm, una Emax= 21,4 años y una Mmedia= 0,23 año-1. Los resultados de este estudio indican que existe dimorfismo sexual en la especie, siendo las hembras las que alcanzan mayor talla, maduran más tarde, crecen más lento y son más longevas que los machos.

The Puyuhuapi Fjord is an atypical fjord, with two mouths, located in northern Patagonia (44.7° S). One mouth lies to the south, close to the Pacific Ocean, whilst the second connects with the Jacaf Channel to the north where a shallow sill inhibits deep water ventilation contributing to the hypoxic conditions below ~ 100 m depth. Acoustic Doppler Current Profiler moorings, scientific echo sounder transects, and in-situ abundance measurements were used to study zooplankton assemblages and migration patterns along Puyuhuapi Fjord and Jacaf Channel. The acoustic records and in-situ zooplankton data revealed diel vertical migrations of siphonophores, euphausiids and copepods. A dense layer of zooplankton was observed along Puyuhuapi Fjord between the surface and the top of the hypoxic layer (~ 100 m), which acted as a physic-chemical barrier to the distribution and migration of the zooplankton. Aggregations of zooplankton and fishes were generally more abundant around the sill in Jacaf Channel than anywhere within Puyuhuapi Fjord. In particular, zooplanktons were distributed throughout the entire water column to ~ 200 m depth, with no evidence of a hypoxic boundary. Turbulence measurements taken near the sill in the Jacaf Channel indicated high turbulent kinetic energy dissipation rates (ε ~ 10−4 W kg−1) and vertical diapycnal eddy diffusivity (Kρ ~ 10−2 m2 s−1) values. These elevated vertical mixing ensures that the water column well oxygenated and promotes zooplanktons aggregation. The sill region represents a major topographic contrast between the two fjords, and we suggest that this is an feature for future research on carbon export and fluxes in these fjords.

The procedures used to estimate the daily spawning fraction of northern Chile anchovy (Engraulis ringens) have been revised based on information from 17 Daily Egg Production Method (DEPM) survey estimates of the anchovy spawning biomass. The most commonly used spawning marker is postovulatory follicles (POFs). POFs are transitory remnants of the ovulated follicles that remain within the ovary after spawning, until they are fully resorbed. As the process of Postovulatory Follicles (POF) degeneration is continuous, the assignment of POF stages to daily cohorts of spawners can be imprecise. Therefore, the main objective of this paper is to review the criteria used to assign females to daily spawning cohorts in anchovy (Engraulis ringens) located off northern Chile. For our first step, we review the peak spawning time using recently fertilized eggs. To study the POF duration, we divided the POF degenerative process into seven stages and then fitted a gamma probability distribution to the hourly POF stage fractions in a daily cycle. This approach is a quantitative, objective way to define the range of time during which the POF stages are present in the samples, as well as the overlap between daily cycles. The hourly distribution of recently fertilized eggs (Stage 1) indicated a strong daily spawning time synchrony that peaked at 4:00 GMT (00:00 local time). We found that the class Day1 cohort (females that spawn on the night before their capture) belongs primarily to POF Stages 1 to 3, with some proportions belonging to POF Stages 4 and 5 according to the capture time. The migratory nucleus (MN) and hydrated (H) phases correspond to the cohort that spawns on the night of capture. The daily spawning fraction estimates the based on the POF or MN and H phases did not show significant differences. Our results indicated an average spawning frequency of four days (S = 0.27 day−1). The prevalence of POFs according to female size follow an asymptotic model of the von Bertalanffy type, indicating an asymptote around 0.27 day−1. The POF presence was higher during cold periods, probably due to a longer period of decay. A general linear model analysis showed that body weight, time of catch and mean temperature significantly influenced the spawning fraction.

The recruitment rate of anchovy in the Peru–Chile upwelling system was studied by testing sensitive to environmental variability when the spawning stock is low in abundance. Times series of sea surface temperature, salinity, depth of the 15 °C isotherm, the upper limit of the oxygen minimum zone, upwelling indices, the Southern Oscillation Index, and indices El Nino 1+2 and El Nino 3.4 were summarized trough Principal Component Analysis (PCA). The first PCA (PC-I) explained 57% of variance and was related to interannual variability driven by the El Nino-Southern Oscillation. The second Principal Component explained 15% of variance and was linked to upwelling indices. Anchovy recruitment rate anomalies were correlated with PC-I scores on the basis of a 6-year-moving-window and accumulated correlation as time progressed. Significant correlation coefficients were found when the spawning stock biomass was low in abundance before 1990. Once sufficient spawning biomass was accumulated (after 1990), the stock was less sensitive to environmental variability. Thus, sensitivity to environmental changes in anchovy, and probably in other small pelagic fishes, is stock-size dependent. This is a key aspect to be considered in the management of transboundary fish stock shared between Chile and Peru, upon current efforts to develop an ecosystem approach to fisheries management.

espanolSe evaluaron cambios interanuales en la talla de madurez (Lm) de sardina comun, Strangomera bentincki, para el periodo 2007-2012 en la zona centro-sur de Chile. Los datos consistieron en estados de madurez microscopicos de los ovarios de las hembras que fueron colectadas durante la epoca de maxima actividad reproductiva en cada ano. Se identificaron las hembras maduras de las inmaduras, y se ajusto el modelo logistico de madurez utilizando modelos lineales generalizados (MLG) asumiendo independencia entre anos, y modelos lineales generalizados de efectos mixtos (MLGM) asumiendo efectos aleatorios asociados a los anos. El mejor modelo se caracterizo por tener intercepto y pendiente variable, revelando cambios interanuales significativos en la talla de madurez. Aunque en los anos mas recientes se observo una tendencia leve a disminuir en la talla media de la fraccion inmadura, la talla de madurez fluctuo aleatoriamente entre 8,4 y 12,7 cm, y alrededor de Lm= 10,7 cm de longitud total. De esta manera, se concluye que el MLGM es mas adecuado para representar cambios interanuales aleatorios en la talla de madurez de la sardina comun, ya que no hubo una tendencia a la disminucion que pudo ser atribuible a la intensidad de pesca bajo la hipotesis de truncamiento de la estructura de tallas/edad. Mas bien, en la expresion de los cambios aleatorios en la talla de madurez pueden ser consecuencia de factores asociados ya sea al muestreo, al crecimiento o a los retrasos en la madurez debido a la asincronia espacio-temporal del proceso reproductivo. EnglishInterannual changes in size-at-maturity (Lm) of common sardine, Strangomera bentincki, were evaluated for the period 2007-2012 in the south-central area of Chile. Data consisted of microscopic maturity stages of female ovaries, which were collected during the reproductive peak each year. Immature females were identified from mature females and a logistic model was fitted to data through generalized linear model (GLM) and generalized linear mixed model (GLMM). The best model was characterized by having both variable slope and intercept, revealing significant interannual variations in size-at-maturity. Although the average length of the immature fraction showed a tendency to decline over time, interannual changes in size-at-maturity varied at random between 8.4 and 12.7 cm, and around Lm= 10.7 cm total length. It is concluded that GLMM technique was suited to representing interannual random changes in size-at-maturity of common sardine. There was no trend to diminish according to the hypothesis of truncation of size/age due to fishing intensity. Rather, the random expression in size-at-maturity could be a consequence of factors associated with sampling, growth or delayed response in maturity due to spatio-temporal asynchrony in the reproductive process.

Size and shape of fish otoliths are species-specific, but some species also display intraspecific variations. The common sardine, Strangomera bentincki, is a small pelagic fish inhabiting a seasonal upwelling ecosystem off central-southern Chile, having two discrete spawning sites along its latitudinal distribution. Otoliths of specimens were collected from commercial catches in Talcahuano and Corral, representing the central and south spawning zones. On the basis of otolith images, size-based shape descriptors were used to detect ontogenetic variation, and morphometric variables (length, breadth, area, perimeter and weight) were used to detect geographical differences in size and shape of otoliths. Outline analysis was studied on the basis of elliptic Fourier descriptors through multivariate statistical procedures. Size-based shape descriptors showed that otolith shape starts to be stable for fish larger than 12 cm total length, which keep an elliptical form. Morphometric variables for fish larger than 12 cm revealed intraspecific variation between central and south zones, which were associated with otolith weight and breadth. Outline analysis did not reveal significant spatial differences, but extreme intraspecific variation was due to the antirostrum, excisure, and posterior part of otoliths. Intraspecific variation in otolith size could be linked to differences in each spawning habitat and related to geographical origin, whose differences are not clearly identified. It is concluded that intraspecific variability in morphometric variables of sardine otoliths revealed geographic differences in size that are not attributable to allometric effects, and that otolith shape was similar between specimens from different geographic origin. El tamaño y la forma de los otolitos de los peces son específicos, pero algunas especies también muestran variaciones intraespecíficas. La sardina común, Strangomera bentincki, es un pez pelágico pequeño que habita en un ecosistema de afloramiento estacional en la zona centro-sur de Chile, y tiene dos áreas discretas de desove a lo largo de su distribución latitudinal. Se obtuvieron otolitos a partir de las capturas comerciales en Talcahuano y Corral, que representan las zonas de desove del centro y sur. Sobre la base de imágenes de otolitos, los descriptores de la forma basados en el tamaño fueron usados para detectar variación ontogenética, y las variables morfométricas (longitud, ancho, área, perímetro, y peso) se utilizaron para detectar diferencias geográficas en el tamaño y la forma de los otolitos. El análisis de contorno fue estudiado sobre la base de los descriptores elípticos de Fourier a través de procedimientos estadísticos multivariados. Los descriptores de forma mostraron que la forma del otolito comienza a ser estable en peces mayores de 12 cm de longitud total, manteniendo la forma elíptica. Las variables morfométricas de los peces mayores de12 cm reveló variación intraespecífica significativa entre las zonas centro y sur, las que se asociaron con el peso y amplitud del otolito. El análisis de contorno no reveló diferencias espaciales significativas, pero la variación extrema intraespecífica se debió al antirostrum, excisura, y la parte posterior de los otolitos. La variación intraespecífica en el tamaño del otolito podría estar relacionado con diferencias en cada hábitat de desove y en relación con el origen geográfico, cuyas diferencias no están claramente identificadas. Se concluye que la variabilidad intraespecífica en las variables morfométricas de los otolitos de sardina reveló diferencias geográficas en el tamaño que no son atribuibles a efectos alométricos, y que la forma del otolito fue similar entre especímenes de diferente origen geográfico.

Off southern-central Chile, the impact of spring upwelling variability on common sardine (Strangomera bentincki) recruitment was examined by analyzing satellite and coastal station winds, satellite chlorophyll, and common sardine recruitment from a stock assess- ment model. In austral spring, the intensity of wind- driven upwelling is related to sea surface temperature (SST) from the Nino 3.4 region, being weak during warm periods (El Nino) and strong during cold periods (La Nina). Interannual changes in both spring upwell- ing intensity and SST from the Nino 3.4 region are related to changes in remotely sensed chlorophyll over the continental shelf. In turn, year-to-year changes in coastal chlorophyll are tightly coupled to common sar- dine recruitment. We propose that, in the period 1991- 2004, interannual changes in the intensity of spring upwelling affected the abundance and availability of planktonic food for common sardine, and consequently determined pre-recruit survival and recruitment strength. However, the importance of density-depen- dent factors on the reproductive dynamic cannot be neglected, as a negative association exists between spawning biomass and recruitment-per-spawning biomass. Coastal chlorophyll, upwelling intensity, and SST anomalies from the Nino 3.4 region could poten- tially help to predict common sardine recruitment scenarios under strong spring upwelling and El Nino Southern Oscillation (ENSO)-related anomalies.

The bigheaded shrimp, Heterocarpus vicarius, is a commercially important species fished by bottom-trawling fleets in the Colombian Pacific. However, the life-history parameters necessary for a proper analysis of the population dynamics of this species remain unknown. This paper studies the growth, maturity, and size-at-age variations, of Heterocarpus vicarious, as well as observations on recruitment patterns. The Von Bertalanffy growth parameters were estimated by sex through modal progression analysis, which consisted of grouping cohorts into age classes. Growth parameters were similar for males and females, without significant differences (F = 3.23, p > 0 . 05 ). The growth of both sexes is described by the following parameters: L ∞ = 15 . 26 ± 1 . 93 cm total length (TL), K = 0 . 594 ± 0 . 24 yr − 1 , and t 0 = − 0 . 66 ± 0 . 31 yr . Size-at-age variability was due mainly to processes occurring before larval settlement, since the mean length of same-age individuals born during different reproductive events (intercohort) varied more than that of individuals born during the same reproductive event (intracohort). Length at 50% maturity was estimated at 11.72 cm TL for females, with 95% confidence intervals between 10.57 and 13.71 cm TL. The growth curve and the relatively advanced age at maturity estimated for H. vicarius in the study area suggest the species is very vulnerable to fishing exploitation.

Anchovy Engraulis ringens and common sardine Strangomera bentincki are two small pelagic fish that co-occur in the same reproductive habitat off central and southern Chile and have a similar reproductive strategy. Interannual and spatial changes in the batch fecundity of both fish were analyzed with the purpose of detecting variability in the parameters and inferring different reproductive tactics that could affect the reproductive potential. Samples were obtained from adult surveys carried out to estimate spawning biomass by the Daily Egg Production Method, from 2002 to 2007, off Chile. The study area was divided into two zones: central and south. The batch fecundity was linearly related to ovary-free female body weight for each year. For anchovy, the slope was not different across years and zones, while for sardine, changes in intercept and slopes varied significantly among years, but not between zones. The average weight of mature females tended to be higher in the south zone for both species, and average batch fecundity ranged from 4,283 to 8,903 eggs per mature female anchovy, and from 5,901 to 10,414 eggs per mature female sardine. Although the anchovy and sardine reproductive strategy is similar, differences in batch fecundity seemed to be the main distinction between the species in the central and southern spawning sites off Chile, with implications for the reproductive potential. La anchoveta Engraulis ringens y la sardina comun Strangomera benticki son dos peces pelagicos menores que concurren en el mismo habitat reproductivo frente a las costas del centro y sur de Chile, con una estrategia reproductiva similar. Se analizaron los cambios interanuales y espaciales en la fecundidad parcial de ambas especies con el fin de detectar la variabilidad en sus parametros e inferir diferentes tacticas reproductivas que pudieran afectar su potencial de reproduccion. Se obtuvieron muestras de ejemplares adultos para estimar la biomasa desovante mediante el Metodo de Produccion Diaria de Huevos, de 2002 a 2007, frente a la costa de Chile. El area de estudio fue dividida en dos zonas, central y sur. La fecundidad parcial estuvo linealmente relacionada cada ano con el peso corporal (sin los ovarios) de las hembras. Para la anchoveta la pendiente no mostro diferencias interanuales, ni entre zonas, mientras para la sardina la ordenada al origen y las pendientes tuvieron cambios interanuales significativos, pero no entre zonas. El promedio de peso de las hembras maduras de ambas especies tendio a ser mayor en la zona sur, y el promedio de fecundidad parcial vario entre 4,283 y 8,903 huevos por hembra madura de anchoveta, y entre 5,901 y 10,414 de sardina. A pesar de la similitud entre las estrategias reproductivas de las especies estudiadas, las diferencias encontradas en su fecundidad parcial perecen constituir una diferencia primordial entre sardina y anchoveta en su zona de desove frente a Chile, lo cual puede tener implicaciones en su potencial reproductivo.

During the late Pleistocene-Holocene, the Humboldt Current System (HCS, Peru-Chile) was subject to important oceanographic variations that may have affected the abundance and distri- bution of marine populations, as well as their genetic structure and diversity. The fast growth and short life span of jumbo squid Dosidicus gigas make this squid a valuable model organism for evalu- ating how environmental fluctuations affect the genetic diversity of marine populations. We sequenced a 657 bp fragment of the mtDNA cytochrome c oxidase I (COI) gene of 169 jumbo squids from 6 locations in the HCS. We measured and compared genetic diversity among localities and per- formed neutrality tests to detect deviation from mutation-drift equilibrium. We inferred the demo- graphic history of jumbo squids using Bayesian skyline analyses to estimate effective population size through time. A total of 23 haplotypes were found among the sequences. Haplotype and nucleotide diversity were low in all locations. D. gigas was characterized by an absence of population genetic structure and a star-like haplotype network. Neutrality test values were negative and statistically sig- nificant, and therefore consistent with a past population expansion. Similarly, Bayesian skyline analyses indicated a recent demographic expansion after the last glacial maximum. Our results suggest that D. gigas consists of a single, large population in the HCS, that may have experienced a dramatic demographic popu lation expansion consistent with the oceanographic changes associated with the last glacial- interglacial transition.

The yellownose skate ( Dipturus chilensis ) is one of the most important component of the commercial elasmobranch fishery off Chile with an extensive distribution range from 36°44′ S − 55°13′ S. Nevertheless, fishery management for this species does not extend beyond the central zone off Chile (36°44′ − 41°28′ S), leaving the southern zone (41°28′ S − 55°13′ S) without a proper fishing effort regulation. As a result, fishing pressure has increased dramatically in the southern zone, with unknown potential consequences for this elasmobranch population. In the absence of rigorous fishery-biological data, we used a matrix population model to assess yellownose skate demographic traits under different fishing mortality levels. A Leslie matrix model was implemented, where changes in age classes are defined in terms of of life history parameters. Uncertainty was incorporated by applying a Monte Carlo method to survival, age at maturity, and fecundity. Three scenarios were evaluated based on different assumptions about survival, fishing mortality rates, and age at 50% of vulnerability. These scenarios showed a slow growth rate for population abundance (3–15% per year) with no fishing exploitation. The population reaches equilibrium at low mortality levels (0.31 yr −1 ), which is consistent with estimates reported for other rajidae skates. The elasticity analysis indicates that juvenile survival contributes the most to variations in the population growth rate. The sustainable mortality rate has a positive, non-linear relationship with age at 50% of vulnerability. Projections using different selectivity patterns showed that the population abundance is stable only when age-dependent fishing mortality removes individuals of older ages. We concluded that yellownose skate is extremely vulnerable to fishing exploitation and it is remarkably sensitive to juvenile and early life stages survival, implying that management actions are needed to ensure a sustainable exploitation.

The growth rate, reproductive aspects, and natural mortality of chimaeras and ratfish are poorly known. In this study, life-history parameters for cockfish Callorhinchus callorhynchus (Holocephali—Callorhin- chidae) are estimated, which is an important fish resource exploited in Chile. Specimens were sampled from the artisanal fishery captures, from November 2006 to November 2007. The standard length (SL) of males fluctuated between 20 and 62 cm, and between 21 and 70 cm for females. Von Bertalanffy growth parameters were estimated through length-frequency data analysis using MULTIFAN. The length-weight relationship and von Bertalanffy growth parameters were significantly different for males and females, as well as the length at 50% maturity. For males a model with 5 age-classes was the best, with asymptotic length L∞=52 cm SL, growth coefficient K=0.473 yr −1 ,a nd age at length zero t0=−0.690 yrs. For females the best model was represented by 10 age-classes (L∞=70.3 cm SL, K=0.193 yr −1 , t0=−1.158 yrs) in the length- frequency data sets. Length at 50% maturity of males was estimated in 43.7 cm SL, and in 50.2 cm SL for females. The natural mortality rate fluctuated between 0.42 and 0.82 yr −1 for males and between 0.12 and 0.37 yr −1 for females, depending upon the method used. It is concluded that C. callorhynchus is a species with life- history parameters significantly different between males and females, and such differences should be taken into account in future population dynamics analysis.

The Chilean hake (Merluccius gayi gayi) is the predominant groundfish species inhabiting the southern Humboldt, mainly from Coquimbo (29 ◦ S) to Puerto Montt (42 ◦ S). At present there is only limited knowledge on the spatial distribution of juveniles of this species, particularly concerning its dependence on key physical characteristics. On the basis of annual surveys carried out during austral winters from 1997 to 2006, changes in the presence of juveniles were studied using Generalized Additive Model techniques. Temporal factors and spatial effects were more important than single physical variables in explaining the presence of juvenile hake (

The inter-cohort variability in the von Bertalanffy (VB) growth parameters of common sardine (Strangomera bentincki) was analyzed for the period between 1990 and 2007. Time series of monthly length–frequency data were used to study the growth of the species. The MIX software was used to separate normal components and modal progression analysis was used to identify cohorts that have recruited each year. The VB growth parameters were estimated using nonlinear mixed-effects model (NLME) by considering that the population growth parameters have a common distribution, and that cohort-specific parameters can be treated as random effects. A model that considered L∞ (asymptotic length) and K (growth coefficient) as random effects was the best in explaining inter-cohort changes in body growth. The growth rate during the first fast-growing period of sardine cohorts exhibited a significant change after 1998. Cohorts recruited between 1990 and 1997 showed higher growth rates than cohorts recruited from 1999 to 2006. This significant change is coincident with a colder period established in the area after 1998, and with a significant increment in the Ekman transport. Sea surface temperature anomalies explained 46.2% of the variability observed in the early growth rate of the cohorts. It is concluded that environmental conditions encountered by the cohorts during the spawning period could modulate the growth rate of common sardine year to year, but the possibility of further intrinsic factors affecting the growth dynamics of common sardine could be also important and deserve to be considered in future studies.

The recruitment rate of Peruvian anchoveta, Engraulis ringens, was studied to test the hypothesis that long-term environmental variation (regime shifts) had a significant impact on density-dependent processes governing the anchovy recruitment during the period 1963–2004. On the basis of previous defined regimes and turning points for the Humboldt Current System, we identified two groups of years for increased recruitment of anchoveta (1963–1971 and 1986–2004), and one unfavorable period (1972–1985). A common intercept and significantly different slopes were found when the recruitment rate was plotted as a function of the spawning stock biomass during those groups of years, suggesting that density-dependent effects on recruitment were affected during different climate regimes. The favorable (unfavorable) regime was characterized by higher (lower) zooplankton volumes, and with a higher frequency of colder (warmer) waters. Dome-shaped relationships between recruitment rate, spawning stock biomass and SST, were detected with a Generalized Additive Model for the favorable regime. Thus, recruitment could be explained by non-linear effects of environmental variables. Ultimately, climatic regimes are affecting the density-dependent effects on recruitment of anchoveta and the mechanisms involved may be associated with changes in the carrying capacity of the spawning habitat of anchoveta off Peru, which in turn are related with the effects of cold and warm regimes.

Se analizaron los cambios espacio-temporales de las capturas de merluza de cola obtenidas por la flota industrial de cerco en la zona centro-sur de Chile (34°-41°30'S), para revisar la hipótesis de migración hacia el norte de la fracción juvenil de merluza de cola en primavera. Se utilizaron datos de bitácoras de pesca del periodo 1986-2003, y a partir de éstos se calcularon centros de gravedad de las capturas y su varianza. Se postula que si la flota sigue el comportamiento migratorio de la fracción juvenil, se esperaría que los centros de gravedad de las capturas migren latitudinalmente de sur a norte conforme la estación de pesca avanza. No obstante, sólo se encontró cuatro casos en que ocurrió una migración hacia el norte de los centroides. Más bien, los centros de gravedad se presentan estacionarios, al interior de cada temporada de pesca. Se postula que existe una fracción juvenil residente que sólo incrementa su accesibilidad y vulnerabilidad en aguas superficiales en primavera debido al régimen ambiental, que se caracteriza por la dominancia de eventos de surgencia y no a una migración de sur a norte.

Se analizaron los cambios espacio-temporales de las capturas de merluza de cola obtenidas por la flota industrial de cerco en la zona centro-sur de Chile (34°-41°30'S), para revisar la hipótesis de migración hacia el norte de la fracción juvenil de merluza de cola en primavera. Se utilizaron datos de bitácoras de pesca del periodo 1986-2003, y a partir de éstos se calcularon centros de gravedad de las capturas y su varianza. Se postula que si la flota sigue el comportamiento migratorio de la fracción juvenil, se esperaría que los centros de gravedad de las capturas migren latitudinalmente de sur a norte conforme la estación de pesca avanza. No obstante, sólo se encontró cuatro casos en que ocurrió una migración hacia el norte de los centroides. Más bien, los centros de gravedad se presentan estacionarios, al interior de cada temporada de pesca. Se postula que existe una fracción juvenil residente que sólo incrementa su accesibilidad y vulnerabilidad en aguas superficiales en primavera debido al régimen ambiental, que se caracteriza por la dominancia de eventos de surgencia y no a una migración de sur a norte.We analyzed spatio-temporal changes in Patagonian grenadier catches by the purse-seine fleet off central-southern Chile (34°-41°30'S) in order to check the hypothesis that the juvenile fraction of the population migrates northward in spring. Log-book data from 1986 to 2003 were used to calculate the center of gravity of and variance of each catch. We proposed that, if the fleet follows the migratory behavior of the juvenile fraction, the centers of gravity of the catches will migrate from south to north as the fishing season progresses. Nevertheless, the centers of gravity migrated northward in only four cases. Unexpectedly, the centers of gravity remained stationary within each fishing season. Now we propose that, in spring, a resident juvenile fraction of Patagonian grenadier increases its accessibility and vulnerability in the surface waters due to the environmental conditions, characterized by the dominance of upwelling events, and rather than a northward migration.

A regular seasonal pattern of periodicity was detected in monthly catch data for Dosidicus gigas during the most recent period of high abundance of the species off Chile. Monthly catch data covering from 2002 to 2005 were grouped into three large zones, and the trend of the time series was removed by using loess smoother. The residuals between the original and the loess trend curve were computed and analyzed using autocorrelation and cross-correlation at different lags, and a trigonometric model was fitted to detect seasonal oscillation. A coherent pattern in the short-term monthly residuals was observed in the three time series, revealing a similar underlying process in the catch data, with a six-month cycle. We postulate that the seasonal and interannual fluctuations observed in the catch records could be related to the reproductive success of the species through the average occurrence of two reproductive cycles per year, and hence the generation of two cohorts per year.

Se implementa dos modelos de evaluación de stock indirecta para analizar los cambios de abundancia en sardina común. Un modelo utiliza una asignación año calendario (enero-diciembre del año t), y el segundo un año biológico (julio del año t a junio del año siguiente, t + 1). El modelo se contrasta con datos de captura en número a la talla, capturas totales en peso, captura por unidad de esfuerzo en el periodo 1990-2002, y biomasa acústica evaluada en enero de 2000 al 2002 en la zona centro-sur de Chile. El modelo de dinámica poblacional aplicado, se diferencia estructuralmente sólo en el tratamiento de los datos para reflejar cambios anuales, tanto bajo el enfoque año calendario como biológico. Los cambios observados en el stock de sardina común, según año calendario o biológico, indican tendencias similares a los que han sido reportadas en evaluaciones previas. Sin embargo, se observan diferencias en los estimados de ambas evaluaciones, donde la estructura año biológico, presenta índices de abundancia de menor magnitud y estrechamente ligados al reclutamiento, esto considerando la real composición en magnitud que posee la clase anual. En contraste, la evaluación año calendario incorpora la presencia de clases anuales remanentes, generando de esta manera un escenario erróneo en la fuerza de la clase anual. Ambos modelos se contrastan con un indicador que utiliza la composición de la verosimilitud, encontrándose a la evaluación año biológico el mejor modelo basado en un mayor ajuste frente a los datos y mayor grado de explicación.Two indirect stock assessment models are implemented in order to analyze changes in the common sardine abundance. One model uses a calendar-year configuration (January-December year t) and the other a biological-year configuration (July year t - June year t+1). Each model is contrasted with catch-at-length data, total catch in weight, catch per unit effort from 1990 to 2002, and biomass from acoustic surveys done every January from 2000 to 2002 off central-southern Chile. The two applied population dynamics models (calendar and biological year approaches) differ structurally only in the treatment of the data that reveal the annual changes. The changes observed in the common sardine abundance, per calendar or biological year, indícate similar trends as those reported in earlier studies. Nevertheless, differences were registered in the esti-mations for both assessments, with the biological year showing lower abundance levéis that are closely related to recruitment; this, considers the magnitude of the real composition of the annual class/cohort. On the other hand, the calendar year assessment incorporates the remaining annual classes/cohorts, thereby generating an erroneous estimation of the annual class/cohort abundance. The two models are compared with a likelihood indicator, finding that the assessment using the biological configuration was the best model, with a better fit to the data and greater degrees of explanation.

In this paper, the first daily egg production method (DEPM) parameters were estimated for anchovy and common sardine stocks distributed in the central-south area off Chile (33–40°S). The study area was stratified according to the topography, shape and orientation of the coastal line, and the survey was carried out on the continental shelf during the main spawning peak (August–September, 2002). The bulk of the spawning of both species was successfully covered, which was characterized by a coastal distribution within the first 20 nautical miles, and following the inner zone associated with the 100 m bottom depth. The coastal distribution of the spawning can be related to the oceanographic conditions occurring during the transition from winter to spring (southern Hemisphere), which are characterized by the alternation between northerly and southerly winds. Probably, these factors are interacting to produce enrichment, concentration and retention of egg in coastal zones in the study area. The daily egg production rate ( P 0 ) was estimated for two geographic strata, and was different in each region. Also, the length frequency and adult reproductive parameters were different between geographic strata, specially the daily spawning fraction. For anchovy, the P 0 was lower in comparison with available estimates for the same species in Peru and in the north area off Chile. Also, the relative fecundity of anchovy was lower, probably because anchovy in the study area have bigger eggs as compared with the anchovy in Northern Chile. The DEPM parameters estimated for common sardine in the investigated area were similar to the range of existing values for the Engraulis genus in other upwelling areas. The stratified spawning stock biomass estimate was 133,031 t (CV = 44%) for anchovy and 706,792 t (CV = 68%) for common sardine. Probably, daily egg production and adult reproductive parameters of both species are highly variables and further research is suggested for improvements future DEPM application for the species.