Sardine Stock Research Articles

Towards sustainable exploitation of European pilchard (Sardina pilchardus) stocks off West African waters

European pilchard (Sardina pilchardus), herein referred to as “sardine” or “European sardine”, is the most productive and economically important small pelagic fish in the Northwest African waters. Thus far, very little is known about its stock status in the West African region despite the rapid decadal increase in its catch production. The present study provides avenues vital to improving guidance for sustainable species management. In this region, sardine is divided administratively into three stocks (northern: stock N, central: stock A + B, and southern: stock C). Thus, the present study used two Surplus Production Models (SPM) to evaluate sardine's stock status. Sardine's catch and scientific survey biomass data obtained from FAO-CECAF's (Fishery Committee for the Eastern Central Atlantic (CECAF)) latest reports were used in this analysis to fit the SPMs and investigate the effectiveness of the available catch-per-unit-effort (CPUE) trends in setting the total allowable catch (TAC) for sustaining the different sardine stocks in the region. Results from the SPMs indicate that the sardine stock in the north is fished at optimum levels. Meanwhile, the SPMs output based on the scientific survey biomass indices indicated a healthy state for the central and southern sardine stocks. Similarly, the fishery CPUE indices for the central and southern stocks showed similar biomass trends compared to the survey biomass index, indicating healthy stock status. Therefore, in cases where survey biomass index data is unavailable to run stock assessments, this study suggests that sardine fishery CPUEs could be used in SPMs to monitor biomass trends over time and may also provide stock status proxies. Additionally, with rapid climate and other environmental changes, sardine stocks must be regularly monitored with consistent and comparable scientific methodologies and updated fisheries time series data.

Computing bias and variance for Pacific sardine (Sardinops sagax) biomass estimated from aerial surveys in California nearshore waters

Pacific sardine (Sardinops sagax) stocks off the U.S. Pacific coast undergo boom and bust cycles modulated by decadal changes in oceanic and atmospheric conditions. During periods of low abundance, Pacific sardine may contract into nearshore waters, making it more challenging to be surveyed by research vessels that cannot operate in the shallowest habitats, 0 to 40.00 m. In response, a new transect-based design and methods were developed to compute bias and variance of biomass estimated from a collaborative aerial survey implemented in nearshore waters. From experimental aerial surveys conducted in 2010 and from 2018 to 2020, two professional aerial fish spotters underestimated school biomass by 10.5% and 12.6%, whereas most of the variability of aerial biomass was due to within-transect variance, with no significant contribution from the among-transect variance. Implementation of the new transect-based design to aerial surveys from 2020 to 2023 in southern and northern California showed that a substantial biomass of Pacific sardine occurred in nearshore waters, representing 69.9% of total biomass estimated from acoustic surveys in spring 2021, and 36.5% in summer 2021. Seasonal biomass estimates were variable within each region, affected by school dynamics during daytime in nearshore waters and the timing of aerial surveys as determined by weather and environmental conditions. Given that nearshore aerial biomass comprised a measurable proportion of total biomass estimates for Pacific sardine during the recent period of low abundance, it has been used to inform acoustic survey catchability, which is no longer assumed to be 1.0 in recent Pacific sardine stock assessments.

Estimation of spawning stock biomass and spawning areas of sardine, (Sardina pilchardus) with winter time ichthyoplankton sampling in the Sea of Marmara, Türkiye

The spawning areas and spawning stock biomass of sardine were studied with ichthyoplankton sampling in the winter period from the 32 stations, in the Marmara Sea. The mean fish egg and larvae biomass in a unit area were calculated as 18.4 ± 5.3 eggs/10 m2 and 2.5 larvae/10 m2, respectively. Three main spawning areas were detected as Karacabey Floodplain area, Gönen, and Büyükçekmece estuarine area. The larvae are mostly located in the western part. The batch fecundity of sardine was detected between 2415.9 and 16738.3, with a mean of 6899.8 ± 255.7 eggs. The sex ratio (R), spawning fraction (S), mortality rate, and daily egg production (Po) were calculated as 0.53, 0.098, 0.62, and 9.25 eggs/m2 in the Marmara Sea. The spawning stock biomass (B) is estimated at 2998 tonnes in the Marmara Sea. Both ichthyoplankton biomass and spawning stock biomass were found relatively lower. It is recommended to apply stricter management sanctions for the sustainability of sardine stocks.

Bayesian joint longitudinal models for assessing the exploitation rates of sardine stock in the Mediterranean Sea

AbstractThe European sardine is a pelagic species of great ecological importance for the conservation of the Mediterranean Sea as well as economic importance for the Mediterranean countries. Its fishing has suffered a significant decline in recent years due to various economic, cultural and ecological reasons. This paper focuses on the evolution of sardine catches in the Mediterranean Sea from 1985 to 2018 according to the fishing Mediterranean country and the type of fishing practised, artisanal and industrial. We propose three Bayesian longitudinal linear mixed models to assess differences in the temporal evolution of artisanal and industrial fisheries between and within countries. Overall results confirm that Mediterranean fishery time series are highly diverse along their dynamics and this heterogeneity is persistent throughout the time. Furthermore, our results highlight a positive correlation between artisanal and industrial fishing. Finally, the study observes a consistent decreasing time trend in the quantity of fish landings. Although the causes of this feature could be also linked to economic motivations (such as a reduction in demand or the reorientation of fleets towards more commercially beneficial species), it may indicate a potential risk to the stock of this species in the Mediterranean Sea.

Long-term comparison between the Japanese sardine (Sardinops melanostictus) stock level and simulated zooplankton density around the Kuroshio region

Long-term comparison between the Japanese sardine (Sardinops melanostictus) stock level and simulated zooplankton density around the Kuroshio region

An updated model of potential habitat for northern stock Pacific Sardine (Sardinops sagax) and its use for attributing survey observations and fishery landings

AbstractThree years after the 2015 collapse of the northern stock of Pacific Sardine that is predominantly located off the west coast of the United States, acoustic‐trawl (A‐T) surveys documented an increase in the presence and persistence of the southern stock off coastal Southern California. Then in 2020, the biomass of Sardine that was landed in Mexico and attributed to the northern stock exceeded the estimated biomass for the entire northern stock. To investigate if the landings were incorrectly classified, we revisit a model of northern‐stock potential habitat and the associated range of sea‐surface temperature (SST) used to apportion the A‐T survey data and monthly fishery landings to the two stocks, respectively. We update the probabilistic model of potential habitat with data on sardine‐egg presence and absence and concomitant satellite‐sensed SST and chlorophyll‐a concentration through 2019 and apply the new model to more accurately attribute the A‐T observations and fishery landings data to the northern or southern stock. The addition of recent data, with increased coverage in SSTs between 15°C and 17°C, improves the model accuracy and spatial precision of the stock attribution. The attribution accuracy is critically dependent on the temporal and spatial coincidence of the environmental and survey or landings data and should be corroborated with other characteristics indicative of biological isolation such as spatial separation, distinct spawning areas and seasons, and uncorrelated demographics.

Fish morphometric body condition indices reflect energy reserves but other physiological processes matter

Morphometric indices of body condition are assumed to reflect an animal’s health and ultimately its fitness, but their physiological significance remains a matter of debate. These indices are indeed usually considered as proxies of energy reserves, ignoring other physiological processes involved in animal health such as nutritional, immune and hormonal states. Given the wide variety of ecological processes investigated through morphometric body condition indices in marine sciences, there is a clear need to determine whether morphometric indices reflect primarily individuals’ energy reserves or their broader integrated physiological status. To address this issue, we used morphometric and physiological data (cortisol level, oxidative stress, digestive enzymes activity, and both fatty acids percentage and total amount) collected in three stocks of the European sardine (Sardina pilchardus) presenting contrasted patterns of growth and body condition. We found that morphometric body condition indices are indeed mainly and consistently linked to a proxy of the amount of lipid reserves (i.e., fatty acids amount), but also significantly to quality of lipid reserves (i.e., fatty acids percentage) and fish chronic stress (scale cortisol levels). We found no significant relationship between morphometric indices of body condition and both oxidative stress proxies and variables measuring digestive enzymes activity. Our study confirmed that morphometric body condition indices primarily reflect the variance in individuals’ lipid reserves and to a lesser extent the actual composition of these reserves (linked to differences in fish diet) and scale cortisol levels (indicating fish metabolism and/or their chronic stress levels). Therefore, some non-energetic aspects should be considered when studying individuals’ responses to environmental changes and other key physiological processes (oxidative stress proxies, activity of digestive enzymes) should be investigated directly to support scientific-based decision-making in the context of climate change.

Impact of Drought and Wildfires in Recent Trends of Diarrhetic Shellfish Toxins in Cockles from Northwest Portugal and Its Similarities with Sardine Stock Trends in the Period 2001–2022

In Portugal, high levels of diarrhetic shellfish toxins (DSTs) originating from Dinophysis spp. are accumulated in bivalves, mainly on the northwest coast (NWC). The occurrence of DSTs in spring and early summer is positively related to precipitation. A decrease in average precipitation after 2003 led to a reduction in DSTs after 2008. However, the accumulation of DSTs in the NWC increased in the period 2020–2022. The hydrological year of 2022 was marked by extreme drought. In cockles from the endemic area of Ria de Aveiro, 37.3% of the weeks tested presented samples above the regulatory limit (RL). The previous record was 31.9% in 2005, also an extremely dry year. The average percentage of weeks above the RL in severe drought years surpassed both the low and high precipitation years. In severe dry years, toxicity was dominated mainly by D. acuta toxins. While D. acuminata grows after the abundant river discharges in spring, D. acuta is capable of growing in summer during upwelling favourable conditions. In the last two decades, extensive forest wildfires were recurrent, but the area burnt reduced sharply after 2017 following tighter fire control measures. Low levels of DSTs or low percentage of weeks with cockles above the RL were related to high burnt areas in the previous year. The recent increase in 2020–2022 of DSTs, a planktonic biomarker in bivalves, was also coincident with the similar temporal increase in either the recruitment or the biomass of Sardina pilchardus, a planktivorous fish in decline after 2005/2006. Both low sardine recruitment and biomass were coincident with low precipitation or high burnt areas. Wildfires degrade coastal water quality, as seems reflected both in the cockle’s DST and the sardine stock time series.

Large sardine resource discovered off south-eastern Australia: Potential risks, challenges and benefits of establishing a new fishery

This paper documents the discovery of a large sardine (Sardinops sagax) resource off South-eastern Australia. We use information from three ichthyoplankton surveys for jack mackerel to apply the Daily Egg Production Method (DEPM) to the South-eastern sardine stock. Mean daily egg production was estimated from survey data. Spawning area was estimated from the surveys and using a habitat suitability model to predict presence/absence of eggs in unsurveyed areas. Spawning biomass was calculated using adult parameters from the adjacent Southern stock. The spawning biomass in the area surveyed was 262,564 t (95% CI 125,670–326–438 t). Habitat modelling using a conservative threshold suggested that the total spawning biomass was 346,388 t (95% CI 143,936–548,840 t). These results suggest this stock has the capacity to sustain an annual catch of several tens of thousands of tonnes, which is considerably larger than the recent catch of < 2500 t. Our findings provide further evidence that opportunities exist to increase Australia’s fisheries production. Risks and challenges associated with establishing a new large-scale sardine fishery, including bycatch and ecological impacts, and opposition from conservation groups and recreational fishers are discussed. We also outline the potential socio-economic and environmental benefits, including the use of marine protein and oil from a sustainable local source with low environmental impacts as an input to the AU$1.3B Tasmanian salmon aquaculture industry. We emphasize the need to adopt a precautionary approach to developing a new fishery and the critical importance of conducting comprehensive surveys to confirm our findings and inform ongoing management.

Assessment and management of the temperate stock of Pacific sardine (Sardinops sagax) in the south of California Current System

Knowing the population dynamics and the variations in the abundance of the Pacific sardine is essential for suitable fishing management. Due to the possibility that the different stocks of Sardinops sagax that can inhabit the south of California Current System (CCS) were present in the catches, the caught of the temperate stock were discriminated from the total landed and, subsequently was assessed the dynamics of temperate stock of Pacific sardine (TSPS) for the period from 1989 to 2021. For the above, we use a statistical analysis of catch-at-age (ACE), which is an integrated analysis model that includes three indices of relative abundance (catch rate, acoustic surveys and evaluations of eggs and larvae). Acoustic indices and capture rate (CPUE) denoted changes in population abundance better than the index of eggs and larvae. The total biomass has shown great interannual variability oscillating between 853,476 and 1,592,519 t; a similar trend was shown by the spawning biomass, oscillating between 404,189 t and 770,484 t. With the modified Ricker Stock-Recruitment model, the minimum biomass Bmin = 50,000 t and the exploitation rate in Emrsy = 0.251 year−1 were estimated. Considering behavior of proportion between the recorded catch and the estimated biologically acceptable catch to each year (Cobs/BAC), we can infer that the TSPS has been sustainably exploited throughout analyzed period, except for 2014 and 2017 fishing seasons, when the BAC was exceeded by around 20%. Harvest control rule, by depending on a biomass fraction, estimated with an integrated model ACE, is considered a management suitable strategy to TSPS.

Age and Growth of European Sardine (Sardina pilchardus) in the Central Mediterranean Sea: Implication for Stock Assessment

Understanding the drivers of fish growth is essential for predicting productivity, stability, and resilience of exploited populations. For the European sardine (Sardina pilchardus) in the Strait of Sicily (Central Mediterranean Sea, GSA16), growth parameters or length at age estimates have never been published before. To fill this data gap, the length and age as well as the von Bertalanffy parameters (the most widely used growth model) were estimated. Data from landing samples during the period 2009–2019 were collected by two methods (purse seine and mid-water pelagic trawl). Temporal trends in average length at age, as well as an overall age-length key were obtained and compared with other areas across the geographical distribution range of sardine in the Mediterranean Sea. The observed age range was 0–3 years with most of the individuals belonging to Age 1 (52%) and Age 2 (43%). The mean length at age, for the entire study period, was 11.7 (±0.08) cm for Age 0; 13.4 (±0.09) cm for Age 1; 15 (±0.1) cm for Age 2; and 16.6 (±0.11) cm for Age 3. Furthermore, during the considered period, a reduction in the length at age was observed in the older classes (Age 2 and Age 3). The estimated parameters of the von Bertalanffy growth model were Linf = 18 (±1.15) cm, K= 0.459 (±0.018), and t0 = −1.99 (±0.008) and, accordingly, the mortality vector was obtained according to Gislason’s model, for each age class, these values were 0.99 (0.98–1.02) C at Age 0; 0.71 (0.7–0.73) y−1 at Age 1; 0.6 (0.59–0.62) y−1 at Age 2; 0.54 (0.53–0.56) y−1 at Age 3; and 0.51 (0.49–0.53) y−1 at Age 4. Results appeared in agreement with literature from other areas of the Mediterranean Sea and suggested a poor condition status of the sardine stock in the GSA16.

What drives the recruitment of European sardine in Atlanto-Iberian waters (SW Europe)? Insights from a 22-year analysis

The European sardine (Sardina pilchardus) is the most abundant and socio-economically important small pelagic fish species in Western Iberia Upwelling Ecosystem. As a result of a long series of low recruitments, sardine biomass off Western Iberia has greatly reduced since the 2000s. Recruitment of small pelagic fish is mainly dependent on environmental factors. In order to identify the key drivers of sardine recruitment, it is essential to understand its temporal and spatial variability. To achieve this goal, a comprehensive suite of atmospheric, oceanographic, and biological variables spanning 1998–2020 (22 years) were extracted from satellite datasets. These were then related to in situ recruitment estimates obtained from yearly spring acoustic surveys carried out along two different hotspots of sardine recruitment of the southern Iberian sardine stock (NW Portugal and Gulf of Cadiz). Sardine recruitment in Atlanto-Iberian waters appears to be driven by distinct combinations of environmental factors, although sea surface temperature was identified as the main driver in both regions. Physical conditions that favour larval feeding and retention, such as shallower mixed layers and onshore transport, were also seen to play a vital role in modulating sardine recruitment. Furthermore, high sardine recruitment in NW Iberia was associated with optimal conditions in the winter (January–February). In contrast, recruitment strength of sardine off the Gulf of Cadiz were associated with the optimal conditions during late autumn and spring. The results from this work provide valuable insights to further understand the dynamics of sardine off Iberia, with potential to contribute to the sustainable management of sardine stocks in Atlanto-Iberian waters, particularly under climate change.

A Collaborative Aerial Survey of Coastal Pelagic Species in Nearshore California Waters

Pacific Sardine Sardinops sagax and Northern Anchovy Engraulis mordax are commercially important West Coast fish stocks managed within the Coastal Pelagic Species (CPS) complex by the Pacific Fishery Management Council and National Marine Fisheries Service. Before 2020, survey indices used in Pacific Sardine stock assessments did not explicitly account for nearshore biomass, which presumably had been relatively small compared to the total biomass of the population, but since 2015, has been a more substantial component of total biomass. During the recent Pacific Sardine stock decline, the California Department of Fish and Wildlife and the California Wetfish Producers Association collaborated on an aerial survey off California to estimate nearshore (within 3,600 m from shore) CPS biomass to inform assessments. This project has also involved federal fisheries biologists and Pacific Fishery Management Council advisory bodies and committees, representing a unique collaborative effort to improve data used in CPS fisheries management. We will discuss successes, issues, and challenges in implementing this nontraditional survey and how these data can continue to inform future stock assessments.

Allometry and Individual Growth of the Temperate Pacific Sardine (Sardinops sagax) Stock in the Southern California Current System

We analyzed individual growth and body mass allometry of the temperate stock of Sardinops sagax from samples collected on commercial fleet during 2005 to 2014 in the southern California Current System. Ages were estimated on otolith growth ring reading. Age (years) and standard length (SL; mm) data were fitted using four growth models: von Bertalanffy (VBM), Gompertz (GM), logistic (LM), and Schnute (SM) models. Parameters of each model were calculated by the maximum likelihood method using Akaike information criterion and Akaike’s weight (WAICi) to select the model with the greatest plausibility. Additionally, the interannual growth performance (φ′) variation was described. Body mass allometry was established from the relationship between total body mass (TM; g) and standard length. The sardine samples ranged in size from 114 to 226 mm SL and in weight from 20 to 192 g TM; ages varied from 0.5 to 6.0 years. The allometric parameter (b) was estimated to be 3.155 (3.154–3.156), showing a hyper-allometry growth type. On the basis of raw data, we found that the LM model fit the original data better (WAICi ~35%). When models were fitted to data bolstered with simulated values, the VBM model obtained the greatest weight (WAICi = 60.9%), but the LM model had null plausibility. Consequently, we determined that the Pacific sardine growth pattern was best described by the VBM model, which appears to be more robust against biased data. The φ′ showed interannual variation (2.13–2.51), with an average of φ′ = 2.25. An apparent inverse relationship was observed between φ′ and the Oceanic Niño Index (ONI) or the Pacific Decadal Oscillation (PDO) and the apparent positive relationship between Upwelling Index (UI) and φ’.

Seasonal approach to forecast the suitability of spawning habitats of a temperate small pelagic fish under a high-emission climate change scenario

Spawning habitats of cold-water, European small pelagic fishes have shifted poleward in the last three decades coincident with gradual ocean warming. We predicted present-day, season-specific habitat suitability for spawning by European sardine Sardina pichardus in the Atlantic Ocean and Mediterranean and Black Seas, and projected climate-driven changes in suitable areas from 2050-2099 under the IPCC – RCP 8.5 scenario. Sea surface temperature and distance to the coast had the greater influences in spawning habitats, reflecting the temperature- and coastal-dependent spawning of sardines. Chlorophyll-a was the third most important explanatory variable for spawning in winter to summer. Winds were predominantly important during autumn, whilst sea surface salinity was an important driver during spring and summer. Present-day, “hotspots” for spawning were identified in regions of highly productive, salty waters, where SST was between 6 and 18°C from autumn to spring or 16 and 25°C during summer and favourable winds occurred that would retain eggs and larvae closer to the coast (&amp;lt; 250 km). For future scenarios, forecasts indicate that environmental optima for spawning is projected to be in regions where SST varies between 11°C and 18°C from autumn to spring; and between 18°C and 24°C during summer. However, a negative relationship between phytoplankton productivity and habitat suitability induced by warming is likely to occur in the future. Projections suggest that suitable spawning habitats in all seasons will shift to higher latitudes, with a prominent range expansion along the coast of Norway during winter and autumn (&amp;gt; 83%). The total spawning area, however, was projected to contract in the future during spring (-10.5%) and autumn (-4.1%) due to losses of currently suitable areas along the Atlantic African Coast and Mediterranean Sea. Such regions currently support the greatest sardine stocks but climate-driven warming and decreased plankton productivity are projected to make these areas unsuitable for spawning and likely also for sardine fisheries in future.

Alternative harvest control rules for achieving sustainable fisheries under the revised Fisheries Act in Japan: case studies in two Japanese sardine stocks

Alternative harvest control rules for achieving sustainable fisheries under the revised Fisheries Act in Japan: case studies in two Japanese sardine stocks

Discrimination of the sardine stocks by using a morphometric and meristic analysis along the Moroccan Atlantic coast

Discrimination of the sardine stocks by using a morphometric and meristic analysis along the Moroccan Atlantic coast

Predictions of sardine and the Portuguese continental shelf ecosystem dynamics under future fishing, forced-biomass and SST scenarios

We used the Ecopath with Ecosim ecosystem model to assess the future effects of multiple stressors on sardine and the Portuguese continental shelf ecosystem. We assessed individual and combined impacts of changes in sardine fishing pressure, biomass of sardine competitors and predators and sea surface temperature (SST). This study demonstrated that the greatest impact on sardine stock is caused by projected SST rise whose effect is dominant and detrimental to sardine stock regardless of other conditions, including sardine fishing at maximum sustainable yield (FMSY). The largest impact on ecosystem stability, maturity and diversity of flows was observed under the forced-biomass scenarios that simulate changes in biomass of sardine predators and competitors. Moreover, these stressors alongside FMSY are projected to play an important role in the future evolution of the sardine stock. Results presented in this study can assist long-term and strategic management of the Iberian sardine stock.

Spatio-temporal variability of the zooplankton community in the SW Mediterranean 1992–2020: Linkages with environmental drivers

Variability in the spatial and temporal distribution of the mesozooplankton abundance in the N Alboran Sea (SW Mediterranean) was assessed intermittently from 2010 to 2020, and compared with 1992–2000 historical time series data. Total abundance of mesozooplankton was significantly higher in the coast than in the shelf and slope waters. There were significant differences in mesozooplankton abundance between 1992–2000 and 2010–2020 at the three zones. Copepods dominated the mesozooplankton during winter and spring, but cladocerans and doliolids also became important components of the community in summer and autumn. We found significant increases between the first and the second decadal periods in the abundance of copepods, appendicularians, holoplanktonic gastropods and siphonophores in the shelf. However, in the coast, copepod nauplii, doliolids, gastropods and siphonophores increased, while euphausiids abundance decreased significantly. These trends contrast with the ongoing decline of the sardine stocks in European waters. Increasing temperature and decreasing predation pressure are suggested to be the main drivers of mesozooplankton variability.

Are Cape Cormorants Phalacrocorax capensis losing the competition? Dietary overlap with commercial fisheries

Cape Cormorants Phalacrocorax capensis breed in southern Africa’s Benguela upwelling system and in 2013 were listed as Endangered by the IUCN following a population decrease of >50% over their three most recent generations. This decrease was associated with reduced prey availability, particularly of the pelagic shoaling fishes Cape anchovy Engraulis encrasicolus and sardine Sardinops sagax. The diet of Cape Cormorants was examined from 929 regurgitated prey samples collected at 11 localities off west South Africa from 1988 to 2007. By number, anchovy was the most important prey in all years, except 2007, in which the geographical distribution of samples was limited. Overall anchovy contributed 85% of all prey items eaten and sardine 6%. However, from 1988 to 1997, sardine formed 93% of the diet by mass in the southwest. The proportional contribution of anchovy to the diet increased between 1988–1997 and 1998–2007, whereas that of sardine decreased. Anchovy eaten in the northwest were smaller than those caught in the central west and southwest were. Small, immature sardine were eaten in all regions, but mature sardine only in the southwest, the spawning ground of the western sardine stock. Anchovy and sardine are targeted by South Africa’s purse-seine fishery. Most anchovy and sardine eaten by Cape Cormorants had caudal lengths of 5–9 cm and 15–21 cm, respectively, and showed considerable overlap with sizes harvested by the fishery. This highlights the potential for competition between Cape Cormorants and the fishery for anchovy and sardine.