Trachurus Research Articles

Redescription of Bomolochus decapteri Yamaguti, 1936 (Copepoda, Cyclopoida, Bomolochidae) recovered from three species of Carangidae (Pisces, Perciformes) in Japan, with the first description of the male of the species

Abstract Bomolochus decapteri Yamaguti, 1936 is redescribed based on specimens recovered from the bucco-branchial cavity of three species of Carangidae (Pisces, Perciformes), the roughear scad Decapterus tabl Berry, 1968, the whitefin trevally Carangoides equula (Temminck & Schlegel, 1844), and the Japanese jack mackerel Trachurus japonicus (Temminck & Schlegel, 1844) in Japan. The male of the species is described for the first time. The possession of postantennal processes and lateral processes was verified in the genus, next to Nothobomolochus.

Effect of interannual variations of Kuroshio–Tsushima Warm Current system on the transportation of juvenile Japanese jack mackerel (Trachurus japonicus) to the Pacific coast of Japan

AbstractRecruitment of Japanese jack mackerel (Trachurus japonicus) has been decreasing continuously since 2000 in the Pacific coastal waters of Japan. The reasons and mechanisms for this phenomenon are still unclear. Particle‐tracking experiments were performed using a data assimilation model to elucidate the effect of a current system on the transportation processes of T. japonicus from the main spawning ground in the southern East China Sea to the Pacific coastal waters. The experiments demonstrated that T. japonicus were transported from the southern East China Sea to the Pacific waters around western Japan through the Tokara Strait, and the number of particles transported to the Pacific decreased from 2000 to 2017. The particles passing through the northwest Tokara Strait tended to be transported to the Pacific side during 2000–2005 and to the Sea of Japan during 2006–2017. The bifurcation toward the Sea of Japan was due to an amplification of the northward current where the Tsushima Warm Current originates (west of Kyushu). This change was induced by a rising sea level west of Kyushu due to Kuroshio's northward shift along the western Pacific coast of Japan, which induced the Tsushima Strait through flow to strengthen. The decrease in larval transportation due to the current system change can be one of the causes for the recruitment decline of T. japonicus along the Pacific coast.

Apparent digestibility coefficients of animal feed ingredients for olive flounder (Paralichthys olivaceus)

Apparent digestibility coefficients (ADCs) of dry matter, crude protein, crude lipid, nitrogen-free extract, energy and essential amino acids in animal-based feed ingredients were determined for olive flounder (Paralichthys olivaceus). A reference diet (RF) was formulated to contain 1.0% chromic oxide (Cr2O3) as an inert indicator. Nine test diets were formulated to contain RF and one of the feed ingredients (pollock meal [PM], jack mackerel meal [JMM], anchovy meal [AM], cod meal [CM], sardine meal [SM], sand eel meal [SEM], tuna meal [TM], meat meal [MM] and squid liver meal [SLM]) at a 7:3 ratio in each diet designated as PM, JMM, AM, CM, SM, SEM, TM, MM and SLM, respectively. Olive flounder, averaging 150 ± 8.0 g, were stocked at a density of 25 fish per tank in 400-L fiberglass tanks attached with fecal collection columns. Feces were collected from triplicate groups of fish one time a day for four weeks. Dry matter and crude protein ADCs of CM and SEM were significantly higher than the other tested ingredients. Lipid ADCs of JMM, CM and SEM were significantly higher than the other test ingredients. Energy ADCs of CM and SEM were significantly higher than that of the other tested ingredients. The availability of amino acids in CM was generally higher than the other animal protein sources. PM exhibited the lowest amino acid availability among the treatments. Interestingly, MM exhibited significantly higher nutrient digestibility than several marine-based ingredients. However, CM and SEM are seeming to be highly digestible and effective to use in olive flounder diet compared to the other tested ingredients. Overall, the results of this study provide information about the bioavailability of nutrients and energy in animal feedstuffs to apply when formulating cost-effective practical feeds for olive flounder.

Climate-induced small pelagic fish blooms in an overexploited marine ecosystem of the South China Sea

Marine ecosystems are a primary conservation concern because of the separate and synergistic effects of overfishing and climate change on their productivity and biodiversity. For the purpose of implementing ecosystem-based fisheries management, it is essential to understand how fish stocks respond to climate change in marine ecosystems, especially those that have been overexploited. The Beibu Gulf in the northwestern part of the South China Sea has long been one of China’s major fishing grounds. After the collapse of the demersal ecosystem in 1990 s, small pelagic fishes, including Japanese jack mackerel (Trachurus japonicus) and Japanese scad (Decapterus maruadsi), have occupied a more-important ecological niche in this gulf. However, insufficient research on how small pelagic fish respond to climate change creates great uncertainty for implementing the current management measures. This study used fish data of trawl surveys and environmental data to investigate possible mechanisms leading to dramatic fluctuations in small pelagic fish populations and their possible effects on the Beibu Gulf marine ecosystem. Abnormal blooms of small pelagic fish, especially T. japonicus and D. maruadsi, occurred following four La Niña events (in 2007/2008, 2010/2011, 2011/2012, and 2020/2021). Moreover, the dominant fish species shifted observably and regularly, Shannon–Wiener diversity and Pielou’s evenness decreased significantly in the northeastern coastal waters of the gulf, and the spatial pattern of the fish community was reorganized in this ecosystem. The small pelagic fish blooms in summers probably resulted from a combination of climate change, overfishing, and a summer fishing moratorium, which thereby caused a series of responses in the marine ecosystem. Fluctuations in the small pelagic fish populations after La Niña events seemed more dramatic after the collapse of demersal fish stocks. Therefore, we emphasize the need for implementing ecosystem-based, preventive, and adaptive fisheries management.

Vertical habitat shifts of juvenile jack mackerel estimated using otolith oxygen stable isotope

Japanese jack mackerel (Trachurus japonicus) is distributed in the semi-demersal layer of the continental shelf of the East China Sea (ECS), whereas their larvae are distributed on the surface. Notably, a smooth vertical habitat layer shift (HLS) to a deeper layer during their juvenile stage is crucial for the survival of this species. However, the determination of the start and duration of the HLS and the factors controlling HLS are not yet optimized. To elucidate the timing of the HLS, we analyzed the otolith oxygen stable isotope ratio (δ18Ooto), which increases at lower temperatures and higher salinity (the conditions that the fish experience in the deeper layers of the ECS), at a high temporal resolution of minimum 5 days intervals. From the profile of the δ18Ooto in otoliths of juvenile T. japonicus in the demersal layer, the HLS timing was estimated using two different indices, namely, HLS moment and HLS duration, which represent the highest δ18Ooto gap signal and gradual δ18Ooto change, respectively. Consequently, the average HLS moment was estimated to be 35.1 ± 10.3 days post-hatching (dph). The HLS started at 23.1 ± 9.6 dph, and its duration lasted for 31.3 ± 17.2 days on average. Generalized additive model (GAM) analyses indicated that the standard length and growth conditions influenced the HLS timing, which suggested that energy demand might regulate the HLS timing. To determine the order of HLS and life-history events, the ages of T. japonicus were compared among HLS, metamorphosis and maximum growth rate. The results showed that the start of HLS duration, metamorphosis, the HLS moment, and maximum growth rate occurred in that sequence. The experienced change of δ18Ooto suggested that T. japonicus juveniles shift their habitat layer gradually, rather than rapidly at a specific life-history event.

Environmental correlates of temporal variation in the prey species of Australian fur seals inferred from scat analysis.

Marine ecosystems in southeastern Australia are responding rapidly to climate change. We monitored the diet of the Australian fur seal (Arctocephalus pusillus doriferus), a key marine predator, over 17 years (1998–2014) to examine temporal changes. Frequency of occurrence (FO) of prey was used as a proxy for ecosystem change. Hard part analysis identified 71 prey taxa, with eight dominant taxa in greater than 70% of samples and predominantly included benthic and small pelagic fish. FO changed over time, e.g. redbait (Emmelichthys nitidus) reduced after 2005 when jack mackerel (Trachurus declivis) increased, and pilchard (Sardinops sajax) increased after 2009. Using generalized additive models, correlations between FO and environmental variables were evident at both the local (e.g. wind, sea surface temperature (SST)) and regional (e.g. El Niño–Southern Oscillation Index (SOI), Southern Annular Mode (SAM)) scales, with redbait and pilchard showing the best model fits (greater than 75% deviance explained). Positive SAM was correlated to FO for both species, and wind and season were important for redbait, while SOI and SST were important for pilchard. Both large-scale and regional processes influenced prey taxa in variable ways. We predict that the diverse and adaptable diet of the Australian fur seal will be advantageous in a rapidly changing ecosystem.

Identification of Anisakis sp. larvae in jack mackerel fish sold in the city of Cajamarca

The objective of the research was to identify the presence of larvae of the parasite Anisakis sp. in muscle of jack mackerel fish (Trachurus symmetricus murphyi) marketed in the city of Cajamarca - Peru. A total of 120 samples of different sizes and weights were collected from three main markets in the city of Cajamarca between May and July 2016, which were transported to the Laboratorio de Parasitología Veterinaria y Enfermedades Parasitarias de la FCV-UNC. Of the 120 samples analyzed, one larva (L3) of the nematode parasite (0.83%) was found in one sample, which according to its morphological characteristics identified by microscopy corresponded to Anisakis sp. Therefore, we can conclude that positivity to Anisakis sp larvae is relatively low in jack mackerel fish marketed in the city of Cajamarca.

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

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.

Extracting daily isotopic records on fish otolith (Trachurus japonicus) by combining micro-milling and micro-scale isotopic analysis(MICAL-CF-IRMS).

The recent progress in micro-scale isotopic analytical techniques for otoliths has enabled the reconstruction of the experienced water temperature history of fish in every few days resolution using the stable oxygen isotope ratio (δ18 O) of otoliths. We aimed to improve those techniques and extract the daily δ18 O records of otoliths formed during the juvenile period. Growth rings were formed daily in fish otoliths. We precisely distinguished the daily rings in otoliths of Japanese jack mackerel Trachurus japonicus, and milled them along daily growth rings using a high-spatial resolution micromilling system (Geomill326). Then, we determined the stable carbon and oxygen (δ13 C, δ18 O) isotopic compositions using a high-precision micro-scale isotopic analytical system (MICAL3c with IsoPrime 100). We successfully milled each daily ring with width ranging from 14.0 to 62.9μm (average 27.0μm) during the high growth period (30-70 days after hatching), and determined the isotopic compositions of otolith aragonite. Our improved micro-scale analytical method is the first to determine the daily δ18 O history of fish otoliths. By using our method together with the δ18 O - water temperature equation, the daily history of experienced water temperature can be elucidated. Our high-resolution milling and analytical technique can also be applied to high-resolution isotope analysis for stalactites, clams, and corals.

Understanding common dolphin and Australasian gannet feeding associations from nutritional and ethological perspectives

Abstract Prey detection and subsequent capture is considered a major hypothesis to explain feeding associations between common dolphins and Australasian gannets. However, a current lack of insight on nutritional strategies with respect to foraging behaviours of both species has until now, prevented any detailed understanding of this conspecific relationship. Here we combine stomach content analysis (SCA), nutritional composition of prey, a multidimensional nutritional niche framework (MNNF) and videography to provide a holistic dietary, nutritional, and behavioural assessment of the feeding association between dolphins and gannets in the Hauraki Gulf, New Zealand. Dolphins consumed ten prey species, including grey mullet (Mugil cephalus) as the most representative by wet mass (33.4%). Gannets preyed upon six species, with pilchards (Sardinops pilchardus) contributing most of the diet by wet mass (32.4%) to their diet. Both predators jointly preyed upon pilchard, jack mackerel (Trachurus spp.), arrow squid (genus Nototodarus), and anchovy (Engraulis australis). Accordingly, the MNNF revealed a moderate overlap in the prey composition niche (0.42) and realized nutritional niche (0.52) between dolphins and gannets. This suggests that both predators coexist in a similar nutritional space, while simultaneously reducing interspecific competition and maximizing the success of both encountering and exploiting patchily distributed prey. Behavioural analysis further indicated that dolphin and gannets feeding associations are likely to be mutually beneficial, with a carouselling foraging strategy and larger pod sizes of dolphins, influencing the diving altitude of gannets. Our approach provides a new, more holistic understanding of this iconic foraging relationship, which until now has been poorly understood.

Fine‐tuning the performance of abundance estimation based on environmental DNA (eDNA) focusing on eDNA particle size and marker length

AbstractReliable abundance estimation is a primary challenge in environmental DNA (eDNA) analysis, which has been addressed by considering the effects of eDNA transport and degradation. However, these eDNA spatial dynamics depend on the cellular and molecular structure of eDNA, with its persistence state (particle size and DNA fragment length) being essential for improved abundance estimation. To address the issue, we used datasets obtained from two types of aquarium experiments (targeting zebrafish [Danio rerio] and Japanese jack mackerel [Trachurus japonicus]) and compared the relationships between eDNA concentration and species abundance among different eDNA size fractions and target marker lengths. We reared the fish in experimental tanks with different individual numbers or biomass densities, filtered rearing water using different pore size filters, and quantified eDNA concentrations targeting different fragment lengths or genetic regions. Consequently, both experiments showed that the accuracy and sensitivity in abundance estimation were improved (i.e., R2 values and slopes of linear regressions increased) when targeting eDNA at the 3‐ to 10 μm size fraction. On the contrary, targeting eDNA at the >10 μm size fraction yielded a lower R2 value. This result indicates that the relationship between eDNA concentration and species abundance can be worsened when extremely larger size fractions are targeted. Conversely, the target marker length negatively affected the R2 value. This study proposes that the relationship between eDNA concentration and species abundance relies on the complex interactions between the particle size, persistence, and spatial heterogeneity of eDNA in water.

Analysis of the Persistence and Particle Size Distributional Shift of Sperm-Derived Environmental DNA to Monitor Jack Mackerel Spawning Activity.

Environmental DNA (eDNA) analysis holds great promise as an efficient and noninvasive method to monitor not only the distribution of organisms but also their spawning activity. In eDNA analysis-based monitoring of spawning activity, the detection of sperm-derived eDNA is a key point; however, its characteristics and dynamics are completely unknown. The present study focuses on the persistence and particle size distribution (PSD) of eDNA derived from the sperm of Japanese jack mackerel. First, we investigated the time-dependent degradation and the PSD of sperm-derived eDNA by artificially adding sperm to seawater. Next, we kept fish in tanks and examined the changes in eDNA concentration and PSD before and after spawning. The results of two experiments showed that the degradation of sperm-derived eDNA proceeded rapidly, with PSD shifting to a smaller size regardless of the DNA region (Cyt b or ITS1). Additionally, it was shown that the nuclei and mitochondria released from sperm through degradation had a size distribution that was not simply dependent on each organelle size. These results will contribute to elucidating the characteristics and dynamics of eDNA specifically during the spawning season and to further developing eDNA analysis as a powerful tool for the monitoring of spawning activity.

Bomb Radiocarbon, Otolith Daily Increments and Length Modes Validate Age Interpretations of Chilean Jack Mackerel (Trachurus murphyi)

Ages of Chilean jack mackerel (Trachurus murphyi) in the southern Pacific Ocean were validated using three methods: 1) daily microincrement readings in sagittal otoliths of young-of-the year (YOY) fish to validate the first annulus; 2) modal progression of strong year-classes (PSYC) to validate the first, second and third annuli, and 3) bomb radiocarbon analysis of otolith cores to validate the absolute age in older fish >38 cm fork length (FL). A Laird-Gompertz (LG) model was fitted to fork length (cm) at age (days) relationship in fish ranging from 3.4 to 25.0 cm FL and from 56 to 550 days in age. The LG model estimated a mean FL of 22 cm at the end of the first year of life, which was large compared with the mean FL estimated through conventional ageing in whole otoliths. The comparison between daily age with annual growth bands from whole otoliths, showed a false increment formed at 185 ± 34 days and a second translucent increment formed at 352 ± 79 days, corresponding to the first annulus for fish with the mean FL of 21.4 ± 1.8 cm. The PSYC coinciding with the recruits of 2008 (age 0), was tracked through three subsequent years with high accuracy, attaining 23, 27 and 30 cm FL in 2009, 2010 and 2011, respectively. These modes identified as age 1, age 2 and age 3 in the PSYC, matched to the mean length of fish with 2, 4 and 5 translucent increments in sagittal otoliths. Results from bomb radiocarbon analysis confirmed that most of the ages were correct, because the Δ14C content of adult otolith core matched the reference chronology. The absolute mean ages for the assayed otoliths, based on the comparison with the reference chronology, ranged from 7 to 13 years for sizes between 39 and 60 cm FL. The age validation for T. murphy as addressed in the current study provided crucial information for enhancing stock assessment output of this important transboundary commercial species.

Growth, reproduction, and feeding habits of striped bonito, Sarda orientalis, in the East China Sea

We evaluated the growth, reproduction, and feeding habits of striped bonito (Sarda orientalis) in the East China Sea. We collected a total of 289 specimens and determined their age from polished otoliths. The estimated growth function was FLt=586.98{1−exp[−0.76exp(t+0.33)]}, where FLt represents fork length (mm) at age t. Males reached spermiation in April through September, and females spawned in May through July. The main spawning periods for females were May and June. The smallest sexually mature female and male reached 445 and 436 mm in FL, respectively, and were both age 1. The principal prey species were jack mackerel (Trachurus japonicus), scad (genus Decapterus), and anchovy (Engraulis japonicus). The mean carbon and nitrogen stable isotope ratios of the striped bonito were −16.6‰ and 13.7‰, respectively. The relative contribution of prey species based on stable isotope ratios indicates that the striped bonito is an opportunistic feeder of small pelagic fishes. These biological and ecological data on the striped bonito will be of great importance for stock assessment and the development of ecosystem-based fisheries management schemes.

Impact of squid predation on juvenile fish survival

Predation is a major source of mortality during the early life stages of marine fishes; however, few studies have demonstrated its impact—especially that of squid predation—on survival processes. Here, we examined the feeding habits and predation impacts of swordtip squid on a major prey fish, juveniles of jack mackerel, in the East China Sea. Otoliths of the juveniles extracted from the squid stomach were used to reconstruct the age–length relationship and the growth trajectory of the consumed juveniles, and they were compared to those of juveniles collected with a net using a newly developed statistical framework. The juveniles consumed by squid had significantly shorter body lengths and smaller body sizes during the late larval and early juvenile stages than the netted juveniles, suggesting that smaller juveniles with slower growth rates have a higher probability to be selected. The body mass ratio of the predator squid to prey juveniles (predator–prey mass ratio, PPMR) ranged from 7 to 700, which was remarkably lower than the PPMR reported in various marine ecosystems based on analyses of fishes. Our findings demonstrate that squid predation can significantly impact the early life survival of fish and the trophodynamics in marine ecosystems.

Dietary optimum inclusion level of jack mackerel meal for olive flounder (Paralichthys olivaceus, Temminck & Schlegel, 1846)

Feed stimulants are used to incite feeding behavior in fish to improve feed consumption and growth. This study investigated the effect of jack mackerel meal (JM) as dietary attractant and/or stimulants on olive flounder on growth, feed utilization, chemical composition, plasma chemistry, and non-specific immune responses. In addition, the attractiveness of the experimental diets containing various levels of JM to olive flounder was evaluated. Six hundred and seventy five juveniles were randomly assigned to 27 tanks each containing 25 fish [initial weight of 5.3 ± 0.01 g (SEM)] in the 8-week feeding trial. The control diet (JM0) contains 60% fish meal (FM). The graded levels (1, 3, 5, 20, 20, 40, 60, and 100%) of JM were included at the expenses of FM, referred to as the JM1, JM3, JM5, JM10, JM20, JM40, JM60, and JM100 diets, respectively. Fish were hand-fed to visual satiation in triplicate groups of each diet twice daily for 8 weeks. To determine the attractiveness of the experimental diets, thirty fish were confined in the acclimatization chamber at a time and a knockout comparison of the experimental diets was applied. The strongest feeding attractant response of olive flounder was observed in the JM60 diet. Attractiveness of fish to the JM40 diet was also higher than that of fish to the JM20 diets. Weight gain and SGR of fish fed the JM20 diet was significantly (P < 0.0001) greater than those of fish fed the JM0, JM1, JM3, JM5, JM10, and JM100 diets, but not significantly (P > 0.05) different from those of fish fed the JM40 and JM60 diets in the 8-week feeding trial. The highest feed consumption was obtained in fish fed the JM20 diet. None of the organosomatic indices (condition factor, and viscerosomatic and hepatosomatic indices), biochemical parameters, non-specific immune responses (superoxide dismutase and lysozyme activities), chemical composition and amino acid and fatty acid profiles of the fish whole-body were affected by the experimental diets. In conclusion, the strongest attractiveness of fish was observed in the JM60 diet, but the optimal inclusion level of JM in the diets seemed to be 20% for juvenile olive flounder.

Unravelling the spatial-temporal population structure of Trachurus picturatus across the North-East Atlantic using otolith fingerprinting

The blue jack mackerel Trachurus picturatus is one of the most important pelagic fish captured in the Macaronesian islands of the Azores and Madeira. However, in the last years' landings registered substantial decreases. Fluctuations may be related to oscillations in the cohorts’ recruitment rates, although no information regarding the species movements and connectivity is available. The present study applies laser ablation inductively coupled-plasma mass spectrometry (LA-ICP-MS) to investigate the otolith chemical fingerprints (core and edge) of three cohorts sampled off the Azores, Madeira, Canaries and Peniche (Portuguese coast) in 2013, 2016 and 2019. Otoliths from juveniles (age 0+ and 1+) and adults (age 3+) were examined to infer the scale of geographical variation among fishing grounds and years. Univariate analyses showed significant differences among locations based on Li:Ca, Mg:Ca, Sr:Ca and Ba:Ca concentration ratios. Multi-elemental analyses allocated 70% (2013), 43% (2016) and 43% (2019) of the individuals to their original location based on core elemental fingerprint, and 63% (2013), 75% (2016) and 83% (2019) based on the edge elemental signature. The natal signature suggests that there is some degree of self-recruitment in the fishing grounds and that the subpopulations are connected essentially by dispersal of larvae/juveniles. Furthermore, data suggests that self-recruitment is variable among the cohorts sampled. The discrimination of individuals observed at the time of collection suggests that T. picturatus populations across the north-eastern Atlantic should be regarded as different population units and manage accordingly, as previously observed. Future works should focus on identifying the natal sources of each fishing ground and assess the impact of environmental changes on the distance and direction of larval dispersal.

A pilot study one stimating the biomass of chub mackerel and jack mackerel in the northwestern sea of Jeju Island using trawl survey and frequency characteristics

A pilot study one stimating the biomass of chub mackerel and jack mackerel in the northwestern sea of Jeju Island using trawl survey and frequency characteristics

Modelling Fish Growth with Imperfect Data: The Case of Trachurus picturatus

Growth modelling is essential to inform fisheries management but is often hampered by sampling biases and imperfect data. Additional methods such as interpolating data through back-calculation may be used to account for sampling bias but are often complex and time-consuming. Here, we present an approach to improve plausibility in growth estimates when small individuals are under-sampled, based on Bayesian fitting growth models using Markov Chain Monte Carlo (MCMC) with informative priors on growth parameters. Focusing on the blue jack mackerel, Trachurus picturatus, which is an important commercial fish in the southern northeast Atlantic, this Bayesian approach was evaluated in relation to standard growth model fitting methods, using both direct readings and back-calculation data. Matched growth parameter estimates were obtained with the von Bertalanffy growth function applied to back-calculated length at age and the Bayesian fitting, using MCMC to direct age readings, with both outperforming all other methods assessed. These results indicate that Bayesian inference may be a powerful addition in growth modelling using imperfect data and should be considered further in age and growth studies, provided relevant biological information can be gathered and included in the analyses.

Safeguarding Seafood Security, Marine Biodiversity and Threatened Species: Can We Have Our Fish and Eat It too?

The ocean contains an abundance of biodiversity that is vital to global food security. However, marine biodiversity is declining. Marine protected areas and marine reserves have been used to protect biodiversity, conserve threatened species and rebuild exploited species, but are perceived as restrictive to fishing, which has slowed progress towards ocean protection targets. Here, we perform a spatial prioritisation of the ocean to protect biodiversity, threatened species and food security. Food security was quantified using catch in tonnes per km2, per 0.5-degree cell of the ocean, using data from the Sea Around Us, a global database of industrial, artisanal, subsistence, and recreational fishing catches. Using Representative Biodiversity Areas [RBAs (the top 30% of the ocean based on holistic measures of biodiversity)], maps of 974 threatened species, and catch data for 2,170 exploited species, we find that these multiple, competing objectives are achievable with minimal compromise. Protecting 30% of the ocean using a multi-objective solution could protect 89% of RBAs, 89% of threatened species and maintain access to fishing grounds that provide 89% of global catch. Even when prioritising food security above conservation objectives we find significant protection for biodiversity and threatened species (85% RBAs, 73% threatened species). We highlight four exploited species for improved management, as they are consistently caught in areas of high conservation importance (skipjack tuna,Katsuwonus pelamis; yellowfin tuna,Thunnus albacares; Atlantic cod,Gadus morhua; Chilean jack mackerel,Trachurus murphyi). We show that a globally coordinated approach to marine conservation and food security is necessary, as regional scale strategies are shown to be less efficient and may result in conflict between food security and conservation objectives. Our results add support for calls to protect 30% of the ocean by 2030, and show where protection would best protect food security and conserve biodiversity and threatened species.