Growth Increments Research Articles

Contribution of revenue enhancement plans to fiscal performance: A study of Local Government Authorities in Tanzania

This study investigates the effects of revenue enhancement plans (REPs) on revenue collection performance in Tanzanian local government authorities (LGAs), focusing on Mwanza City Council, Manyara Urban Council, and Mbeya City Council. The research adopts a mixed approach, collecting data from 400 respondents using a multistage sampling technique. The data were analyzed using a multivariate ordered probit model. The results reveal that reducing revenue leakage and improving revenue forecasting accuracy significantly enhance revenue collection performance. Specifically, the coefficient for revenue leakage was -1.221 for effectiveness (p<0.01) and -1.59 for increment (p<0.01), indicating a strong negative impact on performance. In contrast, accurate revenue forecasting positively impacted effectiveness (1.390, p<0.01) and increment (0.516, p<0.01). The model also showed that high implementation costs negatively impacted revenue growth (increment: -1.634, p<0.05). Compliance was found to positively influence reliability (1.533, p<0.01) and efficiency (1.029, p<0.01), underlining the importance of adherence to regulations. The results also highlighted the need for cost management strategies, as implementation costs and leakages hinder revenue growth and efficiency. The study recommends policy measures such as adopting digital solutions to reduce revenue leakages, investing in forecasting tools, and strengthening compliance mechanisms to optimize revenue collection and improve financial sustainability.

Efficient production, structural characterization and bioactivity of an extracellular polysaccharide from Grifola frondosa endophytic Burkholderia sp.

Efficient production, structural characterization and bioactivity of an extracellular polysaccharide from Grifola frondosa endophytic Burkholderia sp.

Lianas reduce tree height with negative consequences for carbon storage and growth estimates

Abstract Current evidence suggests that liana (woody vine) competition with trees could be threatening the carbon sink by reducing carbon uptake and storage in tropical forests. Previous studies investigating forest demography in liana removal experiments have, however, assumed similar allometries for trees, regardless of the amount of lianas they support. Yet, recent observations suggest that liana load may alter tree shape and structure, including height, which could result in an underestimation of the liana effects on forest carbon stocks and tree growth. In this study, we used terrestrial laser scanning (TLS) in a liana removal experiment in Gigante Peninsula, Panama, collected 11 years after removal to quantify the liana effect on tree height allometry. Furthermore, we assessed how the liana impact on tree allometry affects the estimates of carbon storage and sequestration. We fitted multiple tree height–diameter allometric relationships with a hierarchical Bayesian approach and combined the best resulting allometric model with inventories to estimate plot‐level biomass stocks and their changes over time. For the same diameter at breast height, we found the trees to be 1.8 m shorter on average in the control plots compared to those in the removal plots, indicating a substantial liana effect on tree height. Converting these height differences through the use of allometric models and inventory data led to a reduction in tree biomass stock estimates in the control plots of 1.8 Mg C ha,−1 while they increased by 2.5 Mg C ha−1 in removal plots 10 years after removal. TLS‐derived allometries led to estimates of tree biomass growth and tree biomass increment, respectively, 27.1% and 21.8% higher than when treatment‐specific height allometries were not accounted for. Synthesis. The use of TLS in a unique experiment site provides strong experimental evidence that lianas change tree allometry, which has repercussions for estimating the capacity of forests to store and accumulate carbon. Our findings highlight the importance of accounting for liana‐induced effects on tree shape and structure when using allometric equations to accurately estimate the impact of lianas on forest carbon dynamics.

Effect of daily thinning on biweekly increment of growth and yield of maize (Zea mays L.) in mountainous agroecosystem

Maize (Zea mays L.) growth and yield are severely affected due to intraspecific competition and agroclimatic conditions when cultivated with high plant densities. Field trials comprising four daily thinning patterns (0, 0.5, 1.0, &1.5% till silking) carried out in three consecutive years (2019–2021) using RCBD experimental design consisting of three replicates. Growth variables, dry matter allocation and growth rates in maize were examined during five biweekly periods starting from the emergence (15, 30, 45, 60 and 75 days after emergence, DAE) till silking whereas yield parameters i.e., biological yield, economic yield, and sustainability yield index (SYI) were recorded. Biweekly increase in growth variables, dry matter partitioning and growth rates of maize differed significantly due to the influence of daily thinning computed for the periods from 31 to 45, 46 to 60 and 61 to 75 DAE but the same parameters didn’t differ significantly during the first two biweekly periods (1–15 & 16–30 DAE). Increase in growth variables, dry matter distribution, absolute growth rate (AGR), yield and SYI was the greatest where maize was established with 1% daily thinning. This increase in growth and dry matter partition observed highly associated to economic yield and biological yield. Current research highlighted that 3, 4th, and 5th biweekly periods are the most critical stages and daily thinning of 1% is suggested for higher and sustainable economic and biological returns from high density broadcasted maize.

Age and growth of Todaropsis eblanae (Ommastrephidae) through comparison of statoliths, beaks and eye lenses

The age composition of Todaropsis eblanae from the Sardinian waters (western Mediterranean Sea) was studied for the first time through the analysis of growth increments and the comparison of three structures: statoliths, beaks and eye lenses. The analysis was performed on 270 wild specimens of both sexes at different sizes (45-200 mm of mantle length; 6.98-443 g of total weight) and maturity stages (immature, maturing and mature) caught from July to September by trawl net. Significant differences in growth and length-weight relationship were observed between sexes, due to females reach a larger size than males. All the three structures had dimensions positively correlated with the size of the animals and showed clearly readable growth increments. Low values of IAPE, CV and PA confirmed the accuracy and good reproducibility of age readings. Eye lenses showed a very high number of growth increments (106-640), and a daily deposition was excluded. In contrast, beaks and statoliths showed NI values (70-316 and 73-310, respectively) always consistent with the size and maturity of the specimens, then a daily deposition has been suggested and their value compared. Moreover, the Mann-Whitney W-test confirmed a highly significant relationship between the number of growth increments in beaks and statoliths, suggesting that the beak can be considered a valid alternative to statoliths for age estimation in T. eblanae. The absolute growth rates confirm that females grow faster than males. Both sexes showed a higher initial growth rate, which gradually decreases, with the highest values at the age of 101-151 days, before reaching sexual maturity. According to a semelparous cycle, the estimated ages for the largest mature female (310-316 days) and male (288-292 days) suggest a lifespan of less than one year. Overall, the age and growth results reported, although referred to a specific area and a short sampling, could represent useful knowledge for a correct evaluation and management of this important commercial species in the future.

Dealing With Two Stresses: Impact of a Damaging Spring Frost Followed by a Summer Drought on Saplings of Four Temperate Tree Species.

Global warming increases the likelihood that temperate tree species will face damaging late spring frost (LSF) and severe summer drought during the same growing season. However, the interactive effects of these two stresses are barely explored. We investigated the physiological and growth responses of Acer campestre, Fagus sylvatica, Quercus robur and Quercus petraea saplings to artificially induced LSF and drought, focusing on stomatal gas exchange, carbon partitioning, nonstructural carbohydrates (NSCs), phenology and tree growth. LSF depleted NSCs and changed carbon allocation patterns 1 month after the event. Additionally, LSF decreased diameter increment and root growth of A. campestre and F. sylvatica in the current year. Drought affected gas exchange of all species, decreased NSCs of A. campestre, reduced biomass of Q. robur, and exacerbated the detrimental LSF effect on Q. robur's NSCs. Our findings indicate that saplings prioritized canopy restoration immediately after LSF, and favored reserve replenishment before growth until the end of the growing season. Furthermore, we highlight the risk that LSF and drought in the same year could push tree species beyond their physiological limits and we emphasize the importance of studying multiple stressors' interactions to better understand threshold effects that could profoundly alter forest ecosystems.

Growing Waves in Semiconductors with Two Energy Minima of the GaAs Type

In two-valley semiconductors of the GaAs type, under the influence of external electric E0 and magnetic fields H0 at certain orientations and , a current oscillation with a specific frequency and growth rate was obtained. The orientation of the electric E0 and magnetic fields H0 plays a significant role in the excitation of growing waves in semiconductors of the GaAs type. The frequencies and growth increments are determined when exciting current oscillations in a circuit. The dimensions of the crystal are determined by Lz >> Lx, Ly, Lx = Ly. If the dimensions of the sample differ from the condition Lz >> Lx, Ly, Lx = Ly, the growing waves can fade or grow. And in this case, the frequencies of the oscillation growth and the value of the electric E0 and magnetic H0 fields will be different. The values of the magnetic field in the valley “a” are strong, i.e. μaH0 >> c, and in the valley “b” are weak μbH0 >> c. If the magnetic field values in the valleys “a” and “b” are strong, then electromagnetic waves with other frequencies will also be excited. The theory for other values of the magnetic, electric field and, of course, for other values of the crystal dimensions will show other values for the frequency and growth increment. When preparing semiconductor devices (generators, amplifiers, etc.), the dimensions of the sample play a significant role. In this work, analytical expressions for the electric and magnetic fields for certain sample sizes Lx, Ly, Lz were obtained.

A shift in circadian stem increment patterns in a Pyrenean alpine treeline precedes spring growth after snow melting

Abstract. Changing snow regimes and warmer growing seasons are some climate factors influencing the productivity and growth of high-elevation forests and alpine treelines. In low-latitude mountain regions with seasonal snow and drought regimes such as the Pyrenees, these climate factors could negatively impact forest productivity. To address this issue, we assessed the relationships between climate, snow, and inter- and intra-annual radial growth and stem increment data in an alpine Pinus uncinata treeline ecotone located in the central Spanish Pyrenees. First, we developed tree-ring-width chronologies of the study site to quantify climate–growth relationships. Second, radial growth, tree water deficit, and shrinking–swelling cycles were quantified and identified at monthly to daily scales using fine-resolution dendrometer data. These variables were extracted for three climatically different years, including one of the hottest summers on record in Spain (2022), and they were related to soil water content, soil and air temperature, and the dates of snow duration across the treeline ecotone. Warmer February and May temperatures enhanced tree radial growth, probably because of an earlier snow meltout, the start of the growing season, and the higher growth rates in spring, respectively. The characteristic circadian cycle of stem increment, defined by night swelling and day shrinking, was detected in summer and fall. However, this pattern was inverted during the snow season from November through April, suggesting a transition phase characterized by wet soils and swollen stems preceding the spring onset of growth. Air temperature, soil temperature and moisture, and the presence of snow are strong indicators of how much and for how long mountain trees can grow. Shifts in daily stem increment patterns reveal changes in early growth phenology linked to snow melting.

ВОЗМОЖНОСТЬ ВЫРАЩИВАНИЯ СЕВЕРОАМЕРИКАНСКИХ ПРЕДСТАВИТЕЛЕЙ РОДА CARYA В УСЛОВИЯХ МОСКОВСКОГО РЕГИОНА

The aim of this study is to determine whether it is possible to cultivate the North American species of the genus Carya in the Moscow region. The study was conducted on 4 species: Carya laciniosa, C. illinoensis, C. cordiformis and C. ovata, that grow in the arboretum and in the nursery of the Main Botanical Garden of Russian Academy of Sciences. There were 15 samples comprising 55 specimens. During 3 years, most of the studied Carya plants were documented to increase by the value ranging from 30 to 80 cm, whereas most central leaders grow annually by 5-45 cm. Maximum annual growth of C. laciniosa is 78 cm, C. illinoensis – 50 cm, C. cordiformis – 58 cm, C. ovata – 76 cm. The maximum central leader growth is observed for C. laciniosa, the minimum one – for C. cordiformis. Largest annual growth increment is characteristic of C. lacinosa, and the smallest one is for C. ovata, C. cordiformis and also C. lacinosa. Plant growth has no features in common and it varies within both species and specimens. With high rainfall during the year, a minimum sum of active temperatures above 15℃ and relatively cold April, most plants showed reduction in growth of leader shoots. There are no clear connections between growth of species or samples and temperature, the sum of active temperatures and annual precipitation. Generally, the climate of the Moscow region has an insignificant influence on the growth of different Carya species.

Field Evaluation of Biochar Application on the Early Growth of Falcataria moluccana: Effects of Pyrolysis Temperatures and Biochar Application Rates

Faltacaria moluccana at its early plantation, is devastated by heat and water stress due to current global climate change. Production forests in Indonesia suggested to use biochar to enhance the durability of early growth F. moluccana in the field. Empty fruit bunches (EFB), a gigantic abundant waste material in Indonesia, pose its potential as biochar feedstock. This study aims to evaluate the effects of EFB biochar on the growth of F. moluccana for one year in a field setting. The experiment used two biochar application rates (25 and 50 tons/ha) and biochar produced at two pyrolysis temperatures (400°C and 600°C). Climatic factors (rainfall and average temperature) were monitored to assess how biochar interacted with field conditions to influence the growth of F. moluccana. EFB biochar increased height and diameter increment by up to 25% and 42%, respectively, compared to control after one year. While pyrolysis temperatures show no impact on growth, biochar application rates of 25 and 50 tons/ha significantly boost diameter increments by 36% and 42%, respectively, compared to controls, without affecting height. Biochar also improves monthly growth increments under water and heat stress. EFB biochar optimizes growth under current climate conditions in Indonesia and mitigates the negative effects of extreme temperature fluctuations. Keywords: biochar, early plant growth, empty fruit bunch, Faltacaria moluccana, field experiment

Sclerochronology and oxygen isotope variations in modern Conomurex luhuanus shells: An archive for reconstructing palaeotemperature and shellfish gathering on the Great Barrier Reef, Australia

Sclerochronology and oxygen isotope variations in modern Conomurex luhuanus shells: An archive for reconstructing palaeotemperature and shellfish gathering on the Great Barrier Reef, Australia

Making sense of variation in sclerochronological stable isotope profiles of mollusks and fish otoliths from the early Eocene southern North Sea Basin

Making sense of variation in sclerochronological stable isotope profiles of mollusks and fish otoliths from the early Eocene southern North Sea Basin

Long-Term Growth Trends of 18 Native and Non-Native Tree Species Based on Data from Experimental Plots Since 1878 in Brandenburg, Germany

The rapid environmental changes associated with climate change increase the need for adaptation strategies in forest management based on profound knowledge about tree species, particularly in the context of assisted migration. For research purposes, selected native and non-native tree species were planted in Brandenburg, Germany more than 120 years ago. Today, these sites provide an opportunity to gather insights about their performance and growth-response throughout the past century. We analyzed the height growth increment of 18 tree species on 1765 long-term experimental plots, the earliest of which have been monitored since 1878. We additionally investigated the stand-level volume increments on 60 unmanaged plots for two of these species. Our results show increasing trends in forest stand growth for Scots pine (Pinus sylvestris L.) and Sessile oak (Quercus petraea (Matt.) Liebl.). However, long-term height increment showed positive, negative, and indifferent growth trends in reaction to changing environmental conditions. Remarkably, 16 out of 18 species showed a growth decline between the years 2000 and 2020, likely attributable to increasing frequencies of single and consecutive drought events. We found non-native species to perform comparably to native tree species. Forest management should reconsider the role of native and non-native species in climate-adapted forests. We recommend focusing on provenance and local site adaptability in assisted migration efforts and argue that maintenance of long-term experiments can provide us with valuable insights on species performance in the near future.

Comparative Study on Growth Characteristics and Early Selection Efficiency of Hybrid Offspring of Populus deltoides 'DD-109' and P. maximowiczii in Liaoning, China.

Poplar is an important tree species for timber supply and ecological protection in northern China. Cultivating and selecting high-quality varieties and germplasm resources suitable for cultivation are key factors in enhancing the quality and productivity of poplar plantations in the arid and semi-arid northern regions with shorter growing seasons. This study conducted a field cultivation experiment on 10 progeny clones from the direct cross (D × M) of imported Populus deltoides 'DD-109' with Populus maximowiczii and 7 progeny clones from the reciprocal cross (M × D) using one-year-old rooted cuttings planted at a 4 m × 8 m spacing. Based on 17 years of annual growth observations, the study systematically compared growth characteristics, age of quantitative maturity, path relationships between traits, and early selection efficiency in the hybrid offspring. The results indicated that the D × M population had superior diameter at breast height (DBH), tree height (H), and volume (V) compared to the M × D population, while the height-to-diameter ratio (HDR) was lower. The growth rate of the 17 clones peaked from 10 to 14 years, with annual volume growth increments (PAIs) higher than mean annual volume increments (MAIs) during the early growth stages; the quantitative maturity age ranged between 12 and 16 years. The D × M population generally reached quantitative maturity earlier than the M × D population, with the fastest clone maturing in 12 years. Four clones (DM-9-17, DM-9-18, DM-9-14, and MD-61) showed values for V, DBH, H, and HDR above the hybrid group average. Path analysis demonstrated that DBH had the most significant direct and indirect effects on V, suggesting it as the best predictor for V. Using DBH as a reference, correlation and early selection efficiency analysis showed a strong relationship between growth characteristics at planting years 4-5 and later-stage performance, indicating this as the optimal period for early selection. These findings contribute to evaluating the production potential of P. deltoides 'DD-109' and P. maximowiczii germplasm in northern China and provide valuable guidance for selecting poplar clones suitable for local cultivation, accelerating breeding processes, and informing management planning for poplar plantations.

Impact of climatic and water quality parameters on Tilapia (Oreochromis niloticus) broodfish growth: Integrating ARIMA and ARIMAX for precise modeling and forecasting.

This study aims to assess the impact of climatic factors and water quality parameters on the growth of tilapia broodfish and develop time series growth models using ARIMA and ARIMAX. Three years longitudinal data on tilapia growth, including length and weight were collected monthly from February 2021 to January 2024. Climatic data were obtained from the Bangladesh Meteorological Department, while water quality parameters in the broodfish pond were measured daily on-site. Key variables such as air temperature, humidity, rainfall, solar intensity, water temperature, dissolved oxygen (DO), pH, and ammonia, showed fluctuation in the ponds. The highest growth rate (5.93%) occurred in April, and the lowest (0.023%) in December. Overall, tilapia growth in weight followed an exponential trend, while the percent growth rate exhibited a seasonal pattern. Pearson correlation analysis indicated a significant association between growth increments and water quality parameters. The ARIMA (3,0,3) model predicted a consistent upward trend in tilapia weight from February 2024 to January 2027. If the pattern continues, the estimated weight of tilapia will reach 803.58 g by the end of January 2027, a 17.05% increase from January 2024, indicating a positive outlook for broodfish health and production. However, the ARIMAX (1,1,1) model for percent weight gain revealed seasonal fluctuations that were strongly influenced by water temperature and solar intensity. Over the three-year period, forecasts indicated a downward trend in percent weight gain during the first year, followed by an upward trend in the second and third years. This indicates the influence of seasonal changes on percent weight gain. The simulation behaviors were consistent with the forecasted trend. These findings have important implications for planning and managing tilapia broodfish production, highlighting the need to consider environmental factors in future aquaculture management.

Permafrost Degradation and Vegetation Growth Beyond the Polar Circle in Siberia

Permafrost thawing is potentially a crucial but poorly investigated factor that influences vegetation dynamics in the Arctic. We studied the permafrost thaw rate beyond the Polar Circle in Siberia. We analyzed its influence on the larch (Larix spp.) growth and Arctic vegetation (sparse larch forests, tundra, and forest–tundra communities) productivity (NPP). We checked the following hypotheses: (1) satellite gravimetry is valid for permafrost thawing analysis; (2) meltwater runoff stimulated trees’ growth and NPP. We used satellite (GRACE, Terra/MODIS) and field data, and larch tree radial growth index measurements. We found a continuous negative trend in the terrestrial water content (r2 = 0.67) caused by permafrost thawing beyond the Polar Circle. Runoff is maximal in West and Mid Siberia (9.7 ± 2.9 kg/m2/y) and decreases in the eastward direction with minimal values in the Chukotka Peninsula sector (−2.9 ± 3.2 kg/m2/y). We found that the growth increment of larch trees positively correlated with meltwater runoff (0.5…0.6), whereas the correlation with soil water content was negative (−0.55…−0.85). Permafrost thawing leads to an increase in the Arctic vegetation productivity. We found a positive trend in NPP throughout the Siberian Arctic (r2 = 0.30). NPP negatively correlated with soil water content (r = −0.55) and positively with meltwater runoff (West Siberia, r = 0.7). An increase in VPD (vapor pressure deficit) and air and soil temperatures stimulated the larch growth and vegetation NPP (r = 0.5…0.9 and r = 0.6…0.9, respectively). Generally, permafrost degradation leads to improved hydrothermal conditions for trees and vegetation growth and contributes to the preservation of the Arctic as a carbon sink despite the increase in burning rate.

Carbon storage potentiality in successional and secondary old growth forests

As the capacity of old-growth forests to store carbon until very old ages has been proved, their conservation has become a mitigation strategy to reduce net CO2 emissions and moderate climate warming. We investigated the effect of tree age, competition and climate on aboveground standing biomass and C stocks over a 50-years period in two Spanish forest stands (successional Pinus pinea forests with old-growth attributes, OGFA and secondary Pinus nigra old-growth Forest, SOGF), combining dendroecological methods with forest inventory data, using semiparametric modeling. P. nigra SOGF stored 69.9 t C ha−1 in standing volume, while P. pinea OGFA stored 58.2 t C ha−1. Carbon stored during the last 50 years increased in both forests, with a steeper increase in P. pinea OGFA. The fraction of annual C stored by the oldest trees was 20–25% in P. nigra SOGF and 17–23% in P. pinea OGFA. The different patterns of biomass growth increment in the two forests were explained by different biophysical environments, climate and history effects. The response to contrasted climate events was forest-specific. Results for P.nigra showed a similar response to climate irrespective of tree age, while biomass growth in P. pinea increased in humid periods compared to dry periods in trees older than 100-years. The negative effect of drought is evidenced in P. pinea trees over 100-years old, while P. nigra showed a cumulative negative effect of drought for all ages. A lower effect of competition was recorded in the oldest trees in both forests. The interaction of competition with climate and tree age showed attenuated climate-mediated differences when competition was high.

Age Determination and Growth of Frigate Tuna (Auxis thazard, Lacepede, 1800) in the Celebes Sea

Frigate tuna (Auxis thazard, Lacepede, 1800) is a commercially valuable food fish thriving in tropical marine waters. In the Philippines, despite its abundance, information on its estimated age and growth patterns is lacking. This study reported the relationship between the size (fork length, FL) and age (otolith growth increment) of frigate tuna using the sagittal otoliths. Sampling was conducted in the Celebes Sea, including the inner bay and gulfs within it (e.g., Moro Gulf, Sarangani Bay, and Davao Gulf) from November 2020 to September 2022. A total of 1,046 frigate tuna samples with sizes ranging from 14.5 cmFL to 44.7 cmFL, caught using ring nets, hand lines, and purse seine nets, were examined. Results of the aggregated fish lengthweight relationship (R2 = 0.9819; a = 0.0068; b = 3.2632) indicated a strong positive allometric growth pattern. Similarly, a strong positive correlation (R2 = 0.7130) between the otolith length (n = 344) and fork length relationship indicates that the otolith increases in length as the fish grows. However, for the successfully aged otolith sections, only individuals collected in the western Celebes Sea (n = 113) demonstrated a good result covering ages ranging from one to four years old. From this information on the age-growth relationship, the von Bertalanffy growth function model generated the following values for L∞ at 62.1 cmFL and K at 1.0016/yr. The latter growth parameter estimates from otolith microstructure is the first record for frigate tuna derived from the age-length data.

The Core Story: Intertwined Maternal and Progeny Signatures Enclosed in the Otolith

Analytical imaging via synchrotron analysis was used to study sagittal otoliths of four freshwater pipefish species exhibiting amphidromous or freshwater resident lifestyles. We undertook a hyperfine elemental scanning of a 25 μm diameter length area centred on the core, namely the pre-hatch zone, corresponding to the sagitta formed during embryogenesis. We analysed calcium (Ca), strontium (Sr), manganese (Mn), chromium (Cr), cobalt (Co), nickel (Ni) and sulphur (S), with the latter serving to count growth increments. Whatever the species, a Ca pit consistently marked the core; the amphidromous species exhibited Mn enrichment at the core and the sagitta formed a week before hatching. These results illustrate common otolith formation mechanistic processes. Sr and heavy metals’ signals in the pre-hatch zone were compared to their signal in the edge of the otolith, an area encompassing the adult freshwater (adFW) environmental signature. We found that Co and Ni otolith signals had no relation to environmental conditions, but it is worth looking into Cr as a marker of early-life environment. While we caution against the use of a Sr:Ca ratio for life history interpretations at the core because of the Ca pit, the Sr signal analysis uncovered possible variations in the parental behaviour that potentially trigger newly-hatched juvenile migration to sea or residency. Finally, our results demonstrate that the microchemistry of otolith formation during early development is a melting of maternal signal during egg yolk elaboration, of the environmental signal during egg incubation, and of individual physiology during early growth.

Unveiling Ecosystem Shifts in the Southern Benguela Through Otolith Biochronologies of Sardine (Sardinops sagax)

ABSTRACTSardine (Sardinops sagax) in the southern Benguela has shown substantial changes in population size over the past 70 years. Heavy fishing pressure in the 1950s to early 1970s caused the collapse of sardine stocks in South Africa. A fishery collapse happens because of significant alterations in the marine community, hindering the recovery of valuable commercial species and leading to cascading effects across multiple trophic levels in marine food webs. In this study, a robust 58‐year biochronology (1962–2019) was developed using archived sardine otoliths from the West of Cape Agulhas in South Africa. Sequential t‐test analysis of regime shifts (STARS) performed on the biochronology of fish growth indicated four regimes with three alteration points in 1986, 2006 and 2015 that correspond with periods of low, high, average and low biomass, respectively; that is, high growth rates occurred during the high biomass period and vice versa. A series of mixed effects models was developed to determine increment width response to selected environmental, prey availability and sardine biomass factors based on the assumption that otolith increment growth is a proxy for somatic growth. Predicted sardine growth positively correlated with sardine biomass, sea surface temperature and copepod abundance estimates. This observation suggests that sardine population dynamics exhibit a depensation mechanism, potentially destabilizing populations after the fishery collapse. Sea surface temperature and copepod abundance have been primary factors influencing sardine growth, partly because of depensatory population dynamics. Furthermore, the study improves understanding of how different factors have affected sardine growth following the collapse of the sardine fishery.