Anchovy Larvae Research Articles

Growth–feeding linkage in small pelagic fish larvae in the Kii Channel, Japan

AbstractThe linkage between growth rate and feeding success has been shown to strengthen the effects of early growth rate on later growth rate in the early life history of fish. However, the growth–feeding linkage largely remains to be tested at the individual level within the same populations/cohorts. We examined the growth–feeding linkage for multiple populations/cohorts in Japanese anchovy Engraulis japonicus larvae and Pacific round herring Etrumeus micropus larvae, through otolith microstructure analysis, based on samples collected from the commercial fishery for larval fish in the Kii Channel, Japan. The three growth–feeding mechanisms, which are based on the respective potential advantages of larger somatic size, higher growth rate, and earlier morphological development for achieving feeding success, were tested to understand how growth rate relates to feeding success. The “somatic size” mechanism was supported for all of six samples for anchovy larvae and three of four samples for round herring larvae. The “growth rate” mechanism was supported for two of six samples for anchovy larvae and three of four samples for round herring larvae. The “morphological development” mechanism was supported for three of four samples for anchovy larvae and all of three samples for round herring larvae. Overall, the present analysis supported the growth–feeding linkage but revealed the dynamics of the growth–feeding mechanisms. All the mechanisms were shown to operate at least for certain populations/cohorts, but none of them were universally effective over all populations/cohorts across the two species. Understanding the dynamics of the growth–feeding mechanisms would provide precious hints for considering strategies of predicting recruitment dynamics.

Seasonal variability in the otolith and somatic size relationship of Japanese anchovy larvae: Counter effects of somatic growth and temperature

Otolith microstructure analysis has played an essential role in understanding the recruitment mechanisms of fish. Despite the fundamental assumption of a close correlation between otolith size and somatic size in growth back-calculations, numerous studies have shown that somatic growth and temperature have negative and positive effects on otolith size at the same somatic size, respectively. However, few studies have investigated the effects of somatic growth and temperature on otolith and somatic size relationships at intra- and inter-cohort levels in the same study framework. The present study investigated the effects of somatic growth and temperature on the seasonal variability in the otolith and somatic size relationship in Japanese anchovy Engraulis japonicus larvae collected from multiple seasonal cohorts throughout the year in the Kii Channel, Japan. The otolith and somatic size relationships were strong within each seasonal cohort sample (R2 = 0.771–0.949), but the relationship became weaker when all the seasonal data were pooled (R2 = 0.571). Relative otolith size at a given somatic size (ROS) was negatively related to somatic growth rates within each seasonal cohort sample (i.e., at the intra-cohort level), but the relationship became weak when all the data were pooled. On the contrary, sea temperature had positive effects on ROS, which would explain the seasonal variability in the otolith and somatic size relationship. The multiple regression analysis showed that temperature influenced ROS almost six times more than somatic growth. Overall, the present study demonstrated that an uncoupling in the otolith size–somatic size relationship was generated by the counter effects of somatic growth and temperature. The observed counter effects should be taken into account in estimating past larval growth for larvae obtained from different environmental conditions.

РАСПРЕДЕЛЕНИЕ И ДИНАМИКА ЧИСЛЕННОСТИ ИХТИОПЛАНКТОНА И РАННЕЙ МОЛОДИ ТЮЛЬКИ И ХАМСЫ В АЗОВСКОМ МОРЕ В 1993–2023 ГГ.

Background. Natural and anthropogenic factors have a major influence on the fish population status. In the Azov Sea, for the last 30 years, substantial changes in the environment have been observed and new exotic species of aquatic living organisms have been introduced, which affected reproduction of fish species. Relevance. To identify the driving forces behind the present dynamics of population abundance of European anchovy and Black and Caspian Sea sprat (tyulka), it is crucial to summarize the data collected during the annual ichthyoplankton surveys of the Azov Sea. This work is aimed at the assessment of the distribution of the ichthyoplankton and early juveniles of Black and Caspian Sea sprat (tyulka) and European anchovy in the Azov Sea area over time with regard to various environmental factors. Methods. Ichthyoplankton surveys are customarily conducted over the entirety of the Azov Sea in the middle of June, when eggs and larvae of Black and Caspian Sea sprat (tyulka) and European anchovy are caught at the highest quantities. Results. The dynamics of distribution and abundance variations for the early developmental stages of Black and Caspian Sea sprat (tyulka) and European anchovy under the influence of environmental factors, including ctenophores and scyphozoan jellyfishes, has been identified; a decrease in the survival rates of their jellyfishes juveniles in the present period of the Azov Sea salinization has been observed. Conclusion. In the context of increasing salinity of the Azov Sea waters, the main factors contributing to the reduced survival rates of the Black and Caspian Sea sprat (tyulka) larvae and fingerlings are the decrease in spawning ground area and competition for food resources with scyphozoan jellyfishes and ctenophores. In the case of the European anchovy larvae and fingerlings, the main factor affecting their abundance is a small number of breeders; food competition and predation of the scyphozoan jellyfishes and ctenophores are of secondary importance.

Anchovy boom and bust linked to trophic shifts in larval diet

Although massive biomass fluctuations of coastal-pelagic fishes are an iconic example of the impacts of climate variability on marine ecosystems, the mechanisms governing these dynamics are often elusive. We construct a 45-year record of nitrogen stable isotopes measured in larvae of Northern Anchovy (Engraulis mordax) in the California Current Ecosystem to assess patterns in food chain length. Larval trophic efficiency associated with a shortened food chain increased larval survival and produced boom periods of high adult biomass. In contrast, when larval food chain length increased, and energy transfer efficiency decreased, the population crashed. We propose the Trophic Efficiency in Early Life (TEEL) hypothesis, which states that larval fishes must consume prey that confer sufficient energy for survival, to help explain natural boom-bust dynamics of coastal pelagic fishes. Our findings illustrate a potential for trophic indicators to generally inform larval survival and adult population dynamics of coastal-pelagic fishes.

Temperature and prey density drive growth and otolith formation of the world's most valuable fish stock

Peruvian anchovy (Engraulis ringens) represents the largest single-species fishery worldwide. Knowledge on how temperature and prey availability influences growth and age estimation during marine fish early life stages is critical for predicting bottom-up processes impacting stock productivity under changing environmental conditions. We reared Peruvian anchovy larvae at two temperatures (14.5 and 18.5 °C) and prey concentrations [high (HF), and low (LF)] from 6 to 30 days post-hatch (dph) to measure growth rate and examine daily deposition of otolith increments. Peruvian anchovy larvae grew faster at 18.5 °C compared to 14.5 °C. Larvae reared at low prey concentration (18.5-LF) and low temperature (14.5-HF) grew 61 and 35% slower, respectively, than those at high prey and warm temperature (18.5-HF). Age and growth rates of larvae were well depicted in the otolith microstructure of well-fed larvae at 18.5 °C. However, larvae reared at 18.5-LF or 14.5-HF, had only 55 and 49% of the expected number of daily otolith increments. Our results suggest caution when attempting to explore how ocean processes regulate small pelagic stocks, the productivity of which are largely driven by changes in the survival and growth of young larvae.

Potential impact of predation by larval Spanish mackerel on larval anchovy in the central Seto Inland Sea, Japan

Japanese anchovy is used as an essential dried fish material from the larval to adult stages. In the central Seto Inland Sea, Japan, the catch of larval anchovy has markedly decreased to <3.9% of the maximum recorded in 2002 since 2013; however, the reason causing this reduction has not been well understood. The abundance of recruit fish, including larvae and early juveniles, has decreased in the last decade, despite abundant eggs, suggesting that the majority of larvae do not survive before recruitment. In contrast, the stock of Japanese Spanish mackerel, whose larvae are the major predator of larval anchovy, has increased in the Seto Inland Sea. It is hypothesized that an increase in the density of Spanish mackerel may have a top-down control on the decrease in anchovy recruitment by an increase in predation opportunities. In this study, we investigated the abundance of Spanish mackerel and anchovy larvae using a bongo net in the field in 2018 and 2019. The average densities of larvae in late May were 1.5–3.3 individuals (inds)/100 m3 and 1058–1346 inds/100 m3 for the Spanish mackerel and the anchovy, respectively; both were higher than those in 2002–2005. We constructed a Stella model, simulating the growth and survival of larval anchovy until they reached the commercial sizes by taking into account consumption by larval Spanish mackerel. The model suggested that the consumption of larval anchovy by larval Spanish mackerel accounted for <4% of the initial abundance of anchovy in 2018, which was not greater than that in 2005. In contrast, the reduction in the growth rates of larval anchovy due to reduced maternal conditions can adversely affect their survival. Thus, the results did not fully support the hypothesis mentioned above.

Contrasting distributional patterns of two co-occurring ctenophores in relation to ichthyoplankton and environmental features in the Southwestern Atlantic Ocean

Assessing the ecological role of ctenophores is crucial to understanding ecosystem functioning, including the recruitment of fish stocks. During austral summer in the North Patagonia Ecosystem (NPE) (41-48°S), the ctenophores Mnemiopsis leidyi and Pleurobrachia pileus co-occur with the peak of ichthyoplankton abundance of 2 important fishing resources: the Argentine anchovy Engraulis anchoita and the Argentine hake Merluccius hubbsi, in association with a highly productive tidal front system. We analyzed 367 plankton samples collected in the NPE over 13 yr (2005-2018) to determine the abundance and spatial distribution of M. leidyi and P. pileus, their spatial overlap with ichthyoplankton (eggs and larvae of hake and anchovy), and their relationship with environmental features. Both ctenophore species displayed contrasting distributional patterns, associated with different physical environments, particularly temperature. M. leidyi showed a higher spatial overlap with ichthyoplankton compared to P. pileus. In addition, we found a significant negative correlation between the biomass of M. leidyi and the abundance of both fish larvae, suggesting a potential negative impact (via predation and competition) on the survival and recruitment of these 2 fisheries resources.

Spatiotemporal and Environmental Dynamics of Abundances and Diversity of Larval Fish in Artificial Reef Edge Habitats of Kitros, Pieria (Northern Aegean Sea, Eastern Mediterranean)

Spatiotemporal and physiochemical influences on the abundances and diversity of ichthyoplankton were assessed in the Thermaikos Gulf and edge habitats surrounding the Pieria (Northern Greece) artificial reef complex. The collection of data was performed in edge habitats in the marine protected area near the artificial reef offshore of Kitros. Sampling trips occurred in each season of the spring, summer, and autumn in each year from 2015–2017. This artificial reef complex lies at a distance offshore of 11.5 km from Kitros and the delta of River Aliakmonas. A bongo net sampler was used to sample ichthyoplankton over a network of 16 sampling stations. Seventy species of larval fish were identified. The greatest measures of ichthyoplankton diversity were found during warmer seasons. Non-metric multidimensional scaling showed that seasons play a significant role in species assemblages, as months during the spring, summer, and autumn from different years clustered together. Ten groups of larvae were identified to the family or genus level, such as Arnoglossus spp., Callionymus spp., Crenilabrus spp., Gobius spp., Liza spp., Scorpaena spp., Solea spp., and Spicara spp. Overall, the species with the greatest abundance was the larvae of the European anchovy (Engraulis encrasicolus). The second genera (in order of highest abundance) were Gobius spp. followed by relatively abundant (but lesser numbers of) larvae representing the families Callionymidae, Centracanthidae, and Bothidae. The largest total abundances were found in July 2015 and September 2016. The biodiversity index indicated that measures of diversity were greater in July 2015, which was the only sampling performed in the middle of the summer, and indicated higher diversity in autumn 2015. The aim of this study was to present the assemblages of fish larvae in the marine protected area surrounding the artificial reef of Kitros Pierias as the result of a 3-year sampling program (2015–2017). The novelty of this study is that it is the only study of Ichthyoplankton ever performed in Greece with seasonal repetitions and densely located stations around a coastal marine protected area.

RNA/DNA and derived condition indices for anchovy and hake larvae as relevant information for comprehensive fisheries management

The nutritional condition of anchovy and Argentine hake larvae in the Northern Patagonian Frontal System (NPFS) area was studied in the austral spring of 2018. We hypothesized that this area provides adequate features for larval growth and survival. The RNA/DNA index (RD) and its derived index of growth performance were employed. A critical RD value for starvation was calculated. The percentage of individuals under starvation and in optimal growth conditions was calculated. Because the period of study was the beginning of the hake spawning period, a limited number of larvae of this species were collected. The RD index showed a significant increase throughout larval ontogeny for anchovy larvae, being 1.84±1.39 (N=739) and 2.77±1.50 (N=220) in the pre-flexion and flexion stages respectively. These values were significantly higher at stations close to the NPFS and at the upper level of the water column. No differences were observed throughout the day. The area inside the NPFS showed a lower proportion of starved anchovy and a higher proportion of individuals in optimal growth, standing as a favourable nursing area. For hake larvae, the average RD was 1.64±0.55 (N=15). The great sensitivity of the RD index makes it a powerful tool for assessing the probability of larval survival and posterior recruitment into fisheries and allowing the identification of favourable rearing areas for these important species for fisheries.

Overlap between suitable nursery grounds for Japanese anchovy (Engraulis japonicus) and Japanese sardine (Sardinops melanostictus) larvae

AbstractSome areas of the spawning and nursery grounds of Japanese anchovy (Engraulis japonicus) and Japanese sardine (Sardinops melanostictus) overlap both spatially and temporally. The sardine's spawning ground overlap ratio is greater than that of the anchovy. Many sardine larvae inevitably share their habitat with anchovy larvae. However, the interspecific interaction is found only from sardine to anchovy. The focus was on overlapping suitable nursery grounds to explain this unidirectional interspecific interaction. Suitable nursery grounds are defined as the areas where larvae grow faster. If an area with both anchovy and sardine has a specific environmental condition suitable only for sardine growth, sardine will survive there more easily than the anchovy. Suitable conditions based on growth rates were obtained from a combination of otolith analyses and backward particle tracking experiments were estimated. The sizes of suitable areas for each species and both species were estimated considering the ideal conditions for both species. The overlap ratio for suitable anchovy nursery grounds was higher than for sardine during the overlapping spawning period. Based on these results, the following hypotheses were proposed. Although anchovy and sardine larvae occur in the same area, the area is often suitable only for sardine larvae growth. Rapid growth works advantageously regarding interspecific competition as long as food resources are limited. This hypothesis can explain the one‐way interspecific interaction from sardine to anchovy.

Acoustic evidences of the beginning of anchovy (Engraulis encrasicolus) schooling in the Northern Alboran Sea (Mediterranean Sea)

During the MEDiterranean International Acoustic Survey (MEDIAS) carried out in 2016 and 2017 in the Northern Alboran Sea in July, a benthic scattering layer located mainly in Malaga Bay was acoustically detected at multiple frequencies and biologically identified using different sampling devices (plankton net and pelagic trawl). This layer mainly corresponded to an anchovy larvae aggregation ranged 2 and 40 mm standard length. Our results pointed out that anchovy larvae massively migrate from the surface to the bottom near the coast, until the 70 m isobath, forming large aggregations acoustically detected as a scattering benthic layer, in which small schools form and emerge.This work has highlighted the potential of acoustic surveys such as MEDIAS to generate anchovy recruitment success indicators complementary and simultaneously to the traditional ones (biomass of the reproductive stock) and their great utility as a fisheries management tool in areas such as the Alboran Sea where the fishing resource is scarce.

Using a larval growth index to detect the environment-recruitment relationships and its linkage with basin-scale climate variability: A case study for Japanese anchovy (Engraulis japonicus) in the Yellow Sea

Increasing evidence has suggested that climate variability has a vital impact on the stock fluctuation of many small pelagic fishes by regulating their recruitment. However, most recruitment-related studies have focused on large spawning/nursing grounds at annual or seasonal scales, while few have considered the impact of short-term environmental variations during the vulnerable passive-transport period. In this study, a larval growth index based on a Lagrangian particle-tracking model coupled with a hydrodynamic model that focused on the early growth and passive transport of the SPF was developed to identify the key spawning/nursing period and grounds accommodating fish recruitment. Taking Japanese anchovy (Engraulis japonicus) in the Yellow Sea as an example, the key spawning grounds and time for its recruitment was identified and the impact of sea-surface temperature (SST) and climate variability on its recruitment was then investigated and discussed. Significant positive (negative) correlations were identified between the recruitment index and the mean growth index (mean water temperature) along the tracking path of eggs or larvae released in the Bohai Sea and the southwestern Yellow Sea during July (1987–2004), implying that these were the key spawning grounds and period for recruitment success. The multi-year tracking path of released particles indicated that both the southwestern Yellow Sea and the central Bohai Sea may be the key nursing grounds. Meanwhile, the SST in July was found to be associated with basin-scale atmosphere–ocean interactions. A potential “atmosphere–ocean-recruitment” influence pattern for Japanese anchovy in the Yellow and Bohai Seas was thus proposed, in which higher (lower) temperature during the key spawning/nursing period induced by atmospheric variation might diminish (promote) recruitment success by limiting the growth and survival of anchovy larvae. The larval growth index developed in this study can be widely applied to other small pelagic fishes in other waters and provide implications for climate-induced recruitment studies.

Potential environmental drivers of Japanese anchovy (Engraulis japonicus) recruitment in the Yellow Sea

Water temperature and food availability are two environmental factors that are widely considered to be likely determinants of recruitment success of fish stocks. However, marine environmental data are commonly of limited availability. Moreover, the mechanisms by which environmental variations may act to regulate fish recruitment remain incompletely understood, especially from the point of view of prey availability. Here we report a test of the feasibility of using simulated long-term hindcast of marine environmental data based on a physical and lower-trophic-level ecosystem data-assimilative model to investigate the impacts of water temperature and prey availability on recruitment fluctuations of the Japanese anchovy (Engraulis japonicus) in the Yellow Sea. Although observational data available for model validation were limited, the model reasonably reproduced inter-annual fluctuations of phytoplankton abundance. The model results for a 15-year period (1987–2001) indicated Japanese anchovy recruitment to have been negatively correlated with July sea surface temperature in the traditional spawning ground south of the Shandong Peninsula, while being positively correlated with near-surface biomass of small zooplankton (the predominant prey for anchovy larvae) in the central Yellow Sea during the summer period. These findings imply that the Japanese anchovy recruitment in the Yellow Sea is likely regulated during its early life stages by both water temperature and food availability. The negative temperature-recruitment relationship could be explained by the “spawning temperature optima” and “optimal growth temperature” hypotheses. Furthermore, model results indicated that inter-annual variation in the near-surface biomass of small zooplankton in the central Yellow Sea during summer is mainly regulated by nutrient supply, to which both vertical stratification and horizontal advection may make contributions.

Growth and nutritional condition of anchovy larvae on the west and southeast coasts of South Africa

Cape anchovy Engraulis encrasicolus is an ecologically and economically important pelagic fish species occurring along the coast of South Africa. A recent eastward shift in Cape anchovy distribution indicates that environmental conditions are becoming more favorable for the species on the east coast. This shift is particularly important in the sheltered Algoa Bay region, a nursery area for fish larvae. However, the relatively low productivity of the Agulhas Current Large Marine Ecosystem on the eastern coast of South Africa may result in an anchovy population in poorer nutritional condition and with slower growth rates than the west coast population. Using otolith and nucleic acid analyses, the growth rates of anchovy larvae from the western and southeastern coasts of South Africa were compared. The otolith analysis results indicated that, at any given age, individual growth rates for anchovy larvae were higher on the southeast coast than on the west coast. The RNA:DNA values also indicated that instantaneous growth rates of anchovy larvae were higher in Algoa Bay than on the west coast. At the time of sampling, chlorophyll and zooplankton productivity were higher at sampling sites in Algoa Bay than sites on the west coast, potentially due to favorable oceanographic features in the bay. As such, the results suggest that Algoa Bay is a suitable and potentially favorable nursery area for the early stages of anchovy, highlighting the importance of separate management of the southeast coast region in a changing world.

Future distribution of early life stages of small pelagic fishes in the northwestern Mediterranean

We studied the effect of climate change on the potential spawning habitats of two marine small pelagic fishes. We examined the projected changes in the potential spawning habitat of the summer-spawning anchovy (Engraulis encrasicolus) and round sardinella (Sardinella aurita) in the northwestern Mediterranean by combining the regionalized projections of RCP scenarios with an existing species distribution model (SDM). The SDM was based on a separate generalized additive model for the eggs and larvae of the two species computed from ichthyoplankton sampling that was conducted with simultaneous readings of surface temperature, salinity and chlorophyll-a values as predictor variables. The SDM was projected for the 2010 decade, which represented the present-day conditions, with these environmental variables obtained from the regionalized POLCOMS-ERSEM biogeochemical model forced by the RCP 4.5 and RCP 8.5 scenarios. The comparison of the present-day projection results with the projections for the middle and final decades of the twenty-first century showed that the suitability of the spawning habitat as defined by the anchovy eggs model was likely to increase over time under RCP4.5 or decrease slightly under RCP8.5, but the habitat for anchovy larvae was likely to decrease in all cases. Loss of habitat was projected to be particularly important in the south of the study area on the Ebre River delta continental shelf. Conversely, the probability of round sardinella occurrence will significantly increase under both scenarios. The potential habitat of this species, which is of subtropical origin, is likely to shift northwards. The limitations of the existing models to extrapolate the current results to future scenarios are discussed regarding (i) the uncertainty in the projections of driving environmental variables (e.g., chlorophyll-a), (ii) the simplified nature of the projection models, which did not capture the dynamics of the early life stages of the fish at a small scale, and (iii) insufficient consideration of important drivers, such as larval transport or retention by mesoscale hydrographic phenomena.

A comprehensive model-based index for identification of larval retention areas: A case study for Japanese anchovy Engraulis japonicus in the Yellow Sea

Abstract Larval retention has been recognized as a key factor/process affecting the recruitment of many pelagic fish species and detection of the larval retention areas (LRAs) is thus of crucial importance for studies of both recruitment dynamics and of fisheries management. However, most studies in relation to larval retention have adopted either retention rate or time to represent retention level. In this study, a newly developed approach based on a Lagrangian particle-tracking algorithm coupled with a hydrodynamic model, thereby jointly considering both retention rate and time to quantify larvae retention level, was introduced and used to identify the prominent LRAs for Japanese anchovy Engraulis japonicus in the Yellow Sea. Four prominent LRAs were identified, two of which locating in the Southern Yellow Sea match well with the aggregation of Japanese anchovy larvae found in previous field surveys. The spatial–temporal variation of instantaneous retention rate was further analyzed and the contribution rates of spawning grounds to LRAs as well as sensitivity of pelagic larval duration to the LRAs were investigated. Meanwhile, the LRAs defined in this study can be also used to explain the aggregations of microzooplankton and green algae in the southern part of the Yellow Sea. This approach can be widely applied to other pelagic species during their planktonic stages, which may further provide implications for studies on recruitment dynamics and on marine protected areas (MPAs) in the Yellow Sea as well as in other continental shelf regions containing abundant fishery resources.

Changes in the spawning habitat of two small pelagic fish in the Northwestern Mediterranean

AbstractWe investigated the effects of three sea surface oceanographic variables (temperature, salinity, and chlorophyll a) on the abundance of eggs and larvae of two summer‐spawning species in the NW Mediterranean Sea, the anchovy Engraulis encrasicolus and the round sardinella Sardinella aurita, based on data from ichthyoplankton surveys carried out in the 1980s, 2000s, and 2010s. The environmental data showed an increase in seawater temperature and salinity along time, coupled with a decrease in chlorophyll a (proxy for primary production). These long‐term directional changes in environmental conditions helped explain the important reduction observed in the abundance of eggs and larvae of anchovy, as well as shrinking of spawning habitat in this species. At the same time, the probability of occurrence of round sardinella has increased from practically zero in the 1980s to probabilities near 1 along the coastal area of the study region in the two decades of the 21st century. Given that the trends observed in the environmental variables along the three decades of study are expected to continue during the 21st century, as a consequence of climate change, the spawning habitat of anchovy is expected to continue decreasing, while round sardinella habitat can expand. Considering that anchovy is of high commercial importance in NW Mediterranean fisheries, while round sardinella has very low commercial interest, our results show that the viability of small pelagic fisheries in the area may be compromised.

Effects of seasonal upwelling on hydrography and mesozooplankton communities in a Pacific tropical cove off Colombia

Introduction: The effects of seasonal upwelling on the conditions of the water column and mesozooplankton communities are poorly understood in the coastal zones of the Eastern Tropical Pacific (ETP), despite the important role of upwelling events in the modulation of productivity in these zones. Objective: To evaluate the influence of seasonal upwelling over the Panama Bight on the structure of the water column and mesozooplankton communities in a tropical cove of the ETP. Methods: Hydrographic data and mesozooplankton samples were collected during four field campaigns in Ensenada de Utría (December 2011, February 2012, October 2013, and February 2013), an estuary located in the Northern Pacific coast of Colombia. Non-parametric and multivariate analyses were used to evaluate seasonal differences in the environmental and biotic variables. Results: Surface waters were warm (&gt; 25 °C) and presented low salinities (&lt; 30) throughout the study period. In contrast, subsurface waters were colder (&lt; 20 °C), saltier (&gt; 33), and presented low dissolved oxygen concentrations (&lt; 2.0 ml l-1) during the dry season (January - March), whereas the water column was homogeneous during the rainy season (April - December). Despite the seasonal changes in the environmental conditions, the expected enhancement in the productivity of the system during the dry season (i.e., higher biomass and abundance of the mesozooplankton) only occurred in February 2012. Contrary to expectations, ichthyoplankton abundance was higher during the rainy season, when the assemblage was dominated by the larvae of anchovy (Cetengraulis mysticetus) and an unidentified Gobiidae. Conclusions: The entrance of upwelled waters into Ensenada de Utría is an important factor modulating the seasonal changes observed in the water column. However, there is high interannual variability in the response of mesozooplankton communities to the upwelling events. Because upwelled waters are oxygen-depleted and more acidic, the entrance of upwelled waters into Ensenada de Utría could be causing physiological stress to the benthic and pelagic organisms inhabiting the deepest zones of the cove. This condition may worsen in the future given the predicted increase of deoxygenation and ocean acidification due to climate change.

Putting the pieces together: Recent growth, nutritional condition, and mortality of Engraulis anchoita larvae in the Southwest Atlantic

AbstractDynamics of clupeiform fish populations such as anchovy are frequently impacted by environmental variations which can affect the success of the species recruitment. Herein, we have analyzed recent otolith growth rate, RNA/DNA nutritional condition index (sRD), and mortality rate of argentine anchovy larvae Engraulis anchoita from three different nursery areas in the Southwest Atlantic. We have evaluated the relationship between the environmental variables (abundance of copepod nauplii, temperature, chlorophyll‐a concentration, and abundance of E. anchoita larvae) and larval endogenous variables (size, weight, age, and otolith radius) to sRD and recent growth rate. Fast larval growth rates were observed toward the northern sector of the studied area, characterized by higher temperature. High values of sRD were associated with higher nauplii abundance in the proximity of coastal fronts. The larvae with the lowest growths and lowest minimum values of nutritional condition coincided with the area where there was less abundance of nauplii and higher larval mortality. Larval size and nauplii abundance were positive explanatory factors for both recent growth rate and sRD index. Temperature had a positive effect on recent growth rate and a negative effect on sRD index. This condition index was poorly explained in terms of model fit in comparison with the growth model. The results herein provided could be significant to better understand the recruitment of the species, as to determining favorable areas for the growth and survival of anchovy larvae.

Autumn growth and condition of anchovy larvae in the Argentine-Uruguayan Common Fishing Zone

Autumn growth and condition of anchovy larvae in the Argentine-Uruguayan Common Fishing Zone