Non-stationary responses in anchovy (Engraulis encrasicolus) recruitment to coastal upwelling in the Southern Benguela

Sleen, Peter van der; Rykaczewski, Ryan R.; Turley, Brendan D.; Sydeman, William J.; García‐Reyes, Marisol; Bograd, Steven J.; Lingen, Carl D. van der; Coetzee, Janet C.; Lamont, Tarron; Black, Bryan A.

doi:10.3354/meps12567

Cited by 19 publications

(8 citation statements)

References 31 publications

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“…Therefore, upwelling has different degrees of effect on retention/transport success for the west coast and the south coast, with it being an important driver in the west coast system. The opposite effect was reported by van der Sleen et al (), who found that cumulative December–March upwelling was significantly and positively related to anchovy recruitment on the west coast. This highlights the importance of investigating intraannual relationships in addition to yearly indices.…”

Section: Discussionmentioning

confidence: 53%

“…By not including the success of particles released inshore of the central Agulhas Bank in the calculation of P 0 , the value decreases to 13.5%. However, little difference was observed to the overall frequency distributions of transport success when seasonality of spawning was taken into account (van der Lingen & McGrath, 2017). The introduction of biological realism is the logical next step.…”

Section: Discussionmentioning

confidence: 99%

“…Distributed along almost the entire coast of South Africa and with extended temporal spawning periods, the species has a complex population structure, with varied spawning strategies and recruitment mechanisms. The South African sardine population is hypothesized to consist of three spatially separate stocks, on the west, south and east coasts, with some degree of mixing between them (Butterworth et al, 2016;van der Lingen, Weston, Ssempa, & Reed, 2015;de Moor, Butterworth, & Lingen, 2017). The western and southern stocks are targeted by the commercial purse-seine fishery and are managed together under a single operational management procedure (OMP); therefore, these two stocks are the focus of this study.…”

Section: Introductionmentioning

confidence: 99%

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Investigating connectivity between two sardine stocks off South Africa using a high‐resolution IBM: Retention and transport success of sardine eggs

McGrath

Hermes

Moloney

et al. 2020

Fisheries Oceanography

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This study applied a previously used Lagrangian individual-based model (IBM) for sardine in the Southern Benguela to an improved and more robust hydrodynamic model to investigate whether a more representative spatial coverage, greater horizontal and vertical resolution, more realistic winds and improved representation of mesoscale features such as eddies and filaments would give different results for transport and retention of early life stages. Despite major differences between the old and new hydrodynamic models, overall the IBM results were quite similar to the previous southern Benguela sardine IBM study. This surprising result indicates that it is the macroscale circulation features resolved by the two hydrodynamic models that are controlling transport and retention of sardine early life stages. The contribution of transient mesoscale features such as eddies and filaments appears to be less important when transport patterns are averaged over the 21-year-long experiment.Another aim of this study was to better estimate the contribution of south coast spawning to west coast sardine recruitment. This was possible because of an eastward extension of the geographical domain of the new hydrodynamic model which provided a more realistic representation of the south coast spawning ground. Three main spawning and nursery area systems, similar to those identified in the previous sardine IBM, were identified: west coast and west coast (WC-WC), south coast and west coast (SC-WC), and south coast and south coast (SC-SC). Spawning area proved to be an important determinant of modelled retention and transport success, with spawning depth also playing an important role on the west coast. The main difference observed from the previous study was an increase in the average percentage of particles released on the south coast and transported to the west coast (P 0 , 17.4%). This indicates more connectivity between the southern and western sardine stocks than previously thought and is therefore important for fishery management.Standardized anomalies from the modelled retention/transport were compared with recruitment estimates from stock assessment models but there was no correlation between the two sets of anomalies. However, a significant correlation was observed between the modelled retention/transport anomalies for the west coast and total cumulative upwelling anomalies for the Southern Benguela (r = −0.67, p < .001).

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Section: Discussionmentioning

confidence: 53%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigating connectivity between two sardine stocks off South Africa using a high‐resolution IBM: Retention and transport success of sardine eggs

McGrath

Hermes

Moloney

et al. 2020

Fisheries Oceanography

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“…While nonstationarity has not been frequently considered in the scientific literature, when it has been investigated, results are similar to ours in that changes in organismal-environmental relationships are widespread. In studies comparing whether fish and invertebrate density, biomass, recruitment, and catch can be best modeled with stationary or non-stationary models, there is a pattern where the best fit model is usually non-stationary (Ciannelli et al, 2007;Lindegren and Eero, 2013;Beggs et al, 2014;Litzow et al, 2018;van der Sleen et al, 2018;Puerta et al, 2019). Similar results have been seen among non-marine taxa.…”

Section: Non-stationary Fish-environment Relationshipsmentioning

confidence: 71%

Assessing the reliability of species distribution models in the face of climate and ecosystem regime shifts: Small pelagic fishes in the California Current System

Asch

Sobolewska²,

Chan³

2022

Front. Mar. Sci.

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Species distribution models (SDMs) are a commonly used tool, which when combined with earth system models (ESMs), can project changes in organismal occurrence, abundance, and phenology under climate change. An often untested assumption of SDMs is that relationships between organisms and the environment are stationary. To evaluate this assumption, we examined whether patterns of distribution among larvae of four small pelagic fishes (Pacific sardine Sardinops sagax, northern anchovy Engraulis mordax, jack mackerel Trachurus symmetricus, chub mackerel Scomber japonicus) in the California Current remained steady across time periods defined by climate regimes, changes in secondary productivity, and breakpoints in time series of spawning stock biomass (SSB). Generalized additive models (GAMs) were constructed separately for each period using temperature, salinity, dissolved oxygen (DO), and mesozooplankton volume as predictors of larval occurrence. We assessed non-stationarity based on changes in six metrics: 1) variables included in SDMs; 2) whether a variable exhibited a linear or non-linear form; 3) rank order of deviance explained by variables; 4) response curve shape; 5) degree of responsiveness of fishes to a variable; 6) range of environmental variables associated with maximum larval occurrence. Across all species and time periods, non-stationarity was ubiquitous, affecting at least one of the six indicators. Rank order of environmental variables, response curve shape, and oceanic conditions associated with peak larval occurrence were the indicators most subject to change. Non-stationarity was most common among regimes defined by changes in fish SSB. The relationships between larvae and DO were somewhat more likely to change across periods, whereas the relationships between fishes and temperature were more stable. Respectively, S. sagax, T. symmetricus, S. japonicus, and E. mordax exhibited non-stationarity across 89%, 67%, 50%, and 50% of indicators. For all species except E. mordax, inter-model variability had a larger impact on projected habitat suitability for larval fishes than differences between two climate change scenarios (SSP1-2.6 and SSP5-8.5), implying that subtle differences in model formulation could have amplified future effects. These results suggest that the widespread non-stationarity in how fishes utilize their environment could hamper our ability to reliably project how species will respond to climatic change.

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“…Testing for significance: One issue with high levels of autocorrelation is that statistical assumptions of serial independence are violated, complicating efforts to establish the significance of correlations or regressions 58 . To address this problem, we apply an alternative significance test based on data simulations 59 . For the grey gurnard case study, we created 100,000 random (i.e., artificial) “environmental” time series with the same length, mean, standard deviation, and autocorrelation as the environmental data (spring SST).…”

Section: Methodsmentioning

confidence: 99%

Interannual temperature variability is a principal driver of low-frequency fluctuations in marine fish populations

et al. 2022

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Marine fish populations commonly exhibit low-frequency fluctuations in biomass that can cause catch volatility and thus endanger the food and economic security of dependent coastal societies. Such variability has been linked to fishing intensity, demographic processes and environmental variability, but our understanding of the underlying drivers remains poor for most fish stocks. Our study departs from previous findings showing that sea surface temperature (SST) is a significant driver of fish somatic growth variability and that life-history characteristics mediate population-level responses to environmental variability. We use autoregressive models to simulate how fish populations integrate SST variability over multiple years depending on fish life span and trophic position. We find that simulated SST-driven population dynamics can explain a significant portion of observed low-frequency variability in independent observations of fisheries landings around the globe. Predictive skill, however, decreases with increasing fishing pressure, likely due to demographic truncation. Using our modelling approach, we also show that increases in the mean and variance of SST could amplify biomass volatility and lessen its predictability in the future. Overall, biological integration of high-frequency SST variability represents a null hypothesis with which to explore the drivers of low-frequency population change across upper-trophic marine species.

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Non-stationary responses in anchovy (Engraulis encrasicolus) recruitment to coastal upwelling in the Southern Benguela

Cited by 19 publications

References 31 publications

Investigating connectivity between two sardine stocks off South Africa using a high‐resolution IBM: Retention and transport success of sardine eggs

Investigating connectivity between two sardine stocks off South Africa using a high‐resolution IBM: Retention and transport success of sardine eggs

Assessing the reliability of species distribution models in the face of climate and ecosystem regime shifts: Small pelagic fishes in the California Current System

Interannual temperature variability is a principal driver of low-frequency fluctuations in marine fish populations

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