Pelagic Species Research Articles

Fossil evidence for earlier radiation in istiophorid billfishes (Teleostei, Istiophoriformes) uncovered by comparative morphology of the caudal vertebrae

ABSTRACT Billfishes include some of the largest pelagic teleostean species, but several aspects about their morphology, paleobiology, and evolution remain ambiguous. Their fossil record is fragmentary and mostly represented by rostral and skull remains. Here, we present a comparative study of the caudal vertebral morphology of extant istiophorid species and we use this information to describe two fossil vertebrae from the Gatun and Chagres formations, both from the late Miocene of Panama. The caudal vertebra from the Gatun Fm. is characterized by the presence of a lateral apophysis and identified as Makaira sp., while the vertebra from the Río Indio Member of Chagres Fm. lacks this structure and its morphology indicates a different genus. The estimated total length of the Makaira sp. specimen from Gatun Fm. is about 5.18 m, the largest size calculated for a marlin, while the Rio Indio specimen was about 2.56 m long. Phylogenies show that the radiation of most living istiophorid species seemingly occurred during the Pliocene. However, our results highlight that the genus Makaira and the taxa lacking the lateral apophyses occurred during the late Miocene, showing that the radiation of istiophorids most likely occurred before the Pliocene (ca. 5 Ma).

Diel Vertical Habitat Use Observations of a Scalloped Hammerhead and a Bigeye Thresher in the Northern Gulf of Mexico

Understanding habitat use of elasmobranchs in pelagic environments is complicated due to the mobility of these large animals and their ability to move great distances in a three-dimensional environment. The Gulf of Mexico is a region where many highly migratory pelagic shark species occur, while in close proximity to coastal, anthropogenic activity including recreational and commercial fisheries. This study provides summary information on the vertical habitat use for a single male scalloped hammerhead and a single male bigeye thresher that were each caught and tagged with an archiving satellite tag. The scalloped hammerhead occupied shallow depths (<100 m) over the continental shelf during the 90 d deployment. The bigeye thresher exhibited strong patterns of diel vertical migrations by occupying depths below the thermocline (>350 m) during the day, then occupying shallower depths (50–100 m) during the night. By providing summary information, this note urges future research to provide scientific information on pelagic, highly migratory species for management efforts in the Gulf of Mexico region.

Interactions between demersal fish body condition and density during the regime shift of the Gulf of Lions

Abstract Environmentally driven changes in small pelagic fish condition and size have been observed in the Gulf of Lions (GOL) since 2008, leading to a significant fishery crisis. However, the effect of changes in environment and/or in the small pelagic community on the demersal community remain unknown. For the first time, this study examines the body condition (bc) and population density of 22 demersal species since 1994, using dynamic factor analysis (DFA). Most (but not all) of demersal species have shown a common shift between 2006 and 2009, which is synchronous with that observed in small pelagic species and the environmental conditions in the GOL. It had been concluded that the environmentally driven changes detected in the pelagic fish community also affected the demersal fish community, but with less drastic and lasting consequences. As the DFA revealed that the bc displayed important variations for several species, notably hake (Merlucius merluccius), the interaction between the bc and population density was investigated using the Multivariate Autoregressive (MAR) model on hake population at three life stages (recruits, juveniles, and adults). Results showed that adult bc, while negatively affected by density, had a positive effect on recruitment. So hake bc could have affected population dynamics by promoting higher recruitment at low densities. Further work is needed to ascertain whether such effects exist in other demersal species.

An ecosystem approach to manage pelagic thresher shark (Alopias pelagicus) based in Kutaraja Ocean Fishing Port, Aceh

Sharks is the dominant bycatch of purse seine and bottom longline vessels that landed in Kutaraja ocean fishing port, particularly pelagic thresher shark species (Alopias pelagicus). The management of shark fisheries in Aceh water is not well implemented. According to the IUCN red list, the pelagic thresher shark has been classified as an endangered species. The capture and trade of pelagic thresher sharks are regulated by CITES (Appendix II). So that Indonesia has to comply with the procedures of CITES due to it has been adopted through the Decree of Minister of Marine Affairs and Fisheries of the Republic of Indonesia Number 61/PERMEN-KP/2018. However, the exploitation and trading of the A. pelagicus continues and is not properly managed. It will threaten the extinction of the pelagic thresher shark population and in terms of a negative image of fisheries management in Indonesia, in particular. Thus, integrated management such as the ecosystem approach to fisheries management (EAFM) is needed to solve this problem. This study aims to evaluate the fisheries management status of the pelagic thresher shark based on EAFM indicator of fish resources domain, focusing in the Kutaraja ocean fishing port. This research was conducted by field measurement and interviews with key stakeholders. Data were analyzed using a multi-criteria analysis (MCA) approach through development of a composite index. The results showed that the trend of CPUE tends to fluctuate in the last 5 years. The total length of the sharks was relatively constant. The proportion of juvenile pelagic thresher sharks was 16% male, and 28% (female), and the shark was bycatch (1%) of the purse seine fishery, the fishing ground was getting further away and seemed to go close to the shark habitat. Based on this assessment, one could conclude that shark's fishery resources were in 'good' category, however, some indicators need to improve through better fisheries management actions. Keywords: EAFM; Alopias pelagicus; pelagic thresher shark; Kutaraja ocean fishing port

Analysis of Owner Requirements of Purse Seine Vessel 180 GT for Fishing Activities on Fishing Line III-Fisheries Management Area (FMA) 572

Fish resources in FMA 572 have not been managed optimally, especially small pelagic species of 82,573 tons. These waters with high wave conditions of 0.2 – 6 meters are located around the waters of West Aceh, the West Indian Ocean of Aceh, the waters of Nias–Sibolga, the waters of the Indian Ocean–West Lampung, and the Sunda Strait. The purpose of this study was to analyze the owner requirements for 180 GT purse seine vessels as a basis for planning the ship's technical specifications. The research method using a single case study with research respondents is purposive sampling. The research findings explain that the Ship dimension is around 35 meters, the Service velocity of 8 knots, the propulsion system is I line engine model, the auxiliary engine system is a dual-engine model, the Fish storage system uses Cargo hold freezer system, and Fishing aids using Fish Aggregating Devices (FADs) and light lamps, Total crew of 27 Personnel, Fish detection equipment using fish finder equipment, Fishing gear pulling with winch mechanical and power block and the ship's operating time 50 days as well. To increase productivity, it is recommended to standardize purse seine vessels with modern equipment to improve fuel efficiency, and ship crew and reduce ship production costs, so that the price of ships is affordable for fishery business actors .

4D marine conservation networks: Combining 3D prioritization of present and future biodiversity with climatic refugia.

Given the accelerating rate of biodiversity loss, the need to prioritize marine areas for protection represents a major conservation challenge. The three-dimensionality of marine life and ecosystems is an inherent element of complexity for setting spatial conservation plans. Yet, the confidence of any recommendation largely depends on shifting climate, which triggers a global redistribution of biodiversity, suggesting the inclusion of time as a fourth dimension. Here, we developed a depth-specific prioritization analysis to inform the design of protected areas, further including metrics of climate-driven changes in the ocean. Climate change was captured in this analysis by considering the projected future distribution of >2000 benthic and pelagic species inhabiting the Mediterranean Sea, combined with climatic stability and heterogeneity metrics of the seascape. We identified important areas based on both biological and climatic criteria, where conservation focus should be given in priority when designing a three-dimensional, climate-smart protected area network. We detected spatially concise, conservation priority areas, distributed around the basin, that protected marine areas almost equally across all depth zones. Our approach highlights the importance of deep sea zones as priority areas to meet conservation targets for future marine biodiversity, while suggesting that spatial prioritization schemes, that focus on a static two-dimensional distribution of biodiversity data, might fail to englobe both the vertical properties of species distributions and the fine and larger-scale impacts associated with climate change.

Fisheries‐based approach to disentangle mackerel (Scomber scombrus) migration in the Cantabrian Sea

AbstractMackerel is an important commercial pelagic species present in the western and eastern North Atlantic. The Northeast Atlantic Mackerel (NEAM) stock has its southernmost spawning area mainly located western Iberian Peninsula and southern Biscay. This species performs extensive annual migrations. The present study is focused on the distribution of this species along the Cantabrian Sea, an essential area of the South Spawning Component (SSC), and the environmental drivers that can affect its migration phenology. We have used data from Vessel Monitoring System and Logbooks of the hand line fishery to estimate the catch per unit of effort (CPUE) as a proxy of its distribution and abundance. CPUEs data of fisheries targeting NEAM provided us with a tool to discriminate the most important predictors for both its prespawning and the postspawning behavior. Among the drivers that can affect mackerel migration, we have analyzed wind speed and direction, temperature at surface (SST) and at 200 m depth, chlorophylla, mixed layer depth, upwelling intensity, and the most representative geographical variables: depth, slope of the seafloor, and distance to coast. We used generalize additive models to highlight the predictors most closely related to the phenology of the species and to shape the spatial–temporal abundance of NEAM in the southern Bay of Biscay waters. Temperature and wind speed and direction are the most important factors that affect prespawning and postspawning migration of NEAM SSC and shape its niche tracking leading to a gradual advance of the spawning season.

Long-Term Change of a Fish-Based Index of Biotic Integrity for a Semi-Enclosed Bay in the Beibu Gulf

The Beibu Gulf in the northwestern South China Sea is one of the world’s most productive fishing grounds, yet its biotic resources appear to be in rapid decline because of overexploitation. Assessments of the health status of the fisheries’ resources in the gulf provide a foundation for their conservation and management. As fish accounted for 84% to 97% of the total catch in the Beibu Gulf in the period 1962–2017, a Fish-based Index of Biotic Integrity (F-IBI) was developed for the Beibu Gulf, and data from otter trawl surveys during the period 1962–2017 were used to measure variations in the fish community. The assessment revealed a generally downward trend in total fish catch density (kg/km2), catch density of 12 traditional commercial demersal fish species, and percentage of nektonic-feeding species, but an upward trend for the percentage of fishes with a planktivorous or detritus diet, percentage of pelagic species, and percentage of the dominant species. The dominant species varied greatly over the 50 year period and showed a tendency towards small-sized species. The synthetic F-IBI variable showed a downward trend and has indicated a ‘fair’ state since 1998. The decline in the F-IBI over the last three decades suggests that anthropogenic disturbances, especially overfishing, have had a serious impact on the fish community of the Beibu Gulf. The F-IBI is currently at risk of becoming ‘poor.’ Consequently, we suggest that rigid and enforceable fishery management measures should be taken by both China and Vietnam to prevent further deterioration of the fisheries’ resources in the gulf.

Climate change and fishing are pulling the functional diversity of the world's largest marine fisheries to opposite extremes

AbstractAimMarine biodiversity is increasingly threatened by overfishing and climate change, but it is still unclear how these drivers have shaped the functional diversity (FD) of marine fish. Here, we explore how the FD of commercial marine fish communities responds to climate change and fishing pressure.Major taxa studiedMarine fish.LocationChina Seas.Time period1989–2018.MethodsWe used a catch database of four individual species and 12 species groups that were reported continuously in China from 1989 to 2018. Seven traits were selected to calculate FD. We adopted generalized linear mixed models to analyse the complex relationship among climate change, fishing pressure and several metrics of marine fish FD. We identified the percentage change in diversity for communities to assess the relative contribution of each species or species group by removing individual species or a species group from the dataset.ResultsClimate change and fishing pressure exerted statistically significant opposing effects on the functional evenness (FEve) and functional divergence (FDiv) of commercial fish communities. Increasing sea surface temperature had a significant positive effect on FEve but a negative effect on FDiv. In contrast, increasing fishing pressure had the opposite effects on FEve and FDiv. These results were driven by the significantly varying relative contributions of fish species or species groups to the functional space, whereby low‐trophic‐level pelagic fish species or species groups are closer to the boundaries of the functional trait space than high‐trophic‐level demersal fish species or species groups.Main conclusionsThe FD of commercial marine fish communities responds significantly to climate warming and increasing fishing pressure, with opposite effects driven by different response patterns of fish species or species groups. Our results suggest that management actions should address the two issues simultaneously, because considering only one will unleash greater functional changes in the other.

Gelatinous Carbon Impacts Benthic Megafaunal Communities in a Continental Margin

Post-collapse of seasonal blooms of gelatinous zooplankton (Cnidaria, Ctenophora, and Thaliacea) sinking carcasses transports labile carbon (jelly-C) to benthic continental margins and the deep sea. In recent decades, bloom frequency and intensity have increased globally; however, how sinking jelly-C affects benthic communities is poorly known. Further, as climate change and other anthropogenic impacts may increase gelatinous blooms in the future, understanding the contributions and impacts of jelly-C upon benthic communities is of pivotal importance. Thus, in this study, we assessed jelly-C deposits post-intense blooming of a pelagic species of marine colonial gelatinous tunicate in the Thaliacean class, Pyrosoma atlanticum. We studied the seabed using a remotely operated vehicle (ROV) from 26 to 1,276 m, documenting jelly-C deposits and species of the megafaunal benthic community. Environmental variables from water column profiles at transects near our own off the Ivory Coast of West Africa were used in assessments. Jelly-C biomass peaked at 400 m (1,500 grC 100 m−2) and remained at the average (300 grC 100 m−2) through 1,276 m. Typically, in depth strata between 300 and 800 m, peaks in jelly-C biomass (500 to 1,500 grC 100 m−2) corresponded to areas with significantly reduced benthic megafaunal species abundances as well as diversity. From 800 to 1,276 m, we noted patchier jelly-C biomass deposits where individual megafauna species abundances and diversity correspondingly increased, yet total organism counts remained low. We observed 11 species from 5 phyla directly feeding on jelly-C and 10 single-species aggregations triggering megafaunal dominance events at various localized depth strata. Although such dynamics have been hypothesized and examined for some time with respect to phytodetritus biomass, they have been rarely described for jelly-C. Thus, our novel findings for jelly-C dynamics in the offshore regions can help to provide a better understanding of the ecological role that this component plays in marine benthic ecosystems and continental margins.

Evaluating the influence of environmental factors on the early life history growth of chub mackerel (Scomber japonicus) using a growth and migration model

Chub mackerel is one of the most important fisheries target species worldwide. These fish have large fluctuations in biomass, the mechanism of which remains unclear. This study developed a bioenergetics individual-based model for chub mackerel distributed in the Northwest Pacific and evaluated the dominant environmental factors that affect their early life history. The parameters in the bioenergetics model were obtained or estimated from previous studies, and a migration model with a gradient area search algorithm was coupled. The growth rate of chub mackerel was calibrated to in situ growth data by adjusting the half-saturation constant of consumption (K). During 2002–2016, the growth and migration of chub mackerel were reproduced using the model with satellite-derived forcing. The migration routes and growth were tightly coupled: individuals located to the north of the Kuroshio axis experienced a better prey environment, showed a relatively higher growth rate, and entered a better prey field by self-selected swimming. Years with more high-growth individuals in the model corresponded to observed higher recruitment (R) and recruitment per spawner (RPS). These results support the hypothesis that a higher growth rate in the early stage results in higher recruitment, because individuals with higher growth can migrate into a better prey environment. A negative correlation was found between R and the distance of the Kuroshio axis from the Boso Peninsula, indicating that when the Kuroshio axis was located closer to the Boso Peninsula, the water temperature of the coastal area increased, resulting in an increase in coastal-dominant zooplankton species, which positively affected the growth of chub mackerel in the early life stage. In addition, interannual variations in prey zooplankton species composition and the relative position of the Kuroshio to the spawning grounds partially influenced the early growth of chub mackerel. The results demonstrate the complex mechanisms of ocean currents and prey fields controlling the recruitment of small pelagic species.

Fisheries bycatch mitigation measures as an efficient tool for the conservation of seabird populations

Abstract The impact of industrial fisheries on marine biodiversity is conspicuous in large pelagic vertebrate's fisheries bycatch. In seabirds, this led to the decline of many populations since the 1980s following the rise of global fishing effort. Bycatch mitigation measures were implemented since the 2000s, but their effects on the concerned seabird populations remain poorly quantified and understood. We studied the effects of bycatch mitigation measures on the demography of the white‐chinned petrel, one of the most bycatch impacted seabirds whose populations suffered dramatic declines before the implementation of mitigation measures. To do so we (a) built multi‐event capture–recapture models to estimate the demographic parameters of a population from Possession Island (southern Indian Ocean) over 30 years, (b) assessed the effect of climate and fishery covariates on demographic parameters, (c) built a population matrix model to estimate stochastic growth rate according to the management in fisheries bycatch and (d) estimated changes in breeding population density using distance sampling data. The population declined from the 1980s to the mid‐2000s, while trawl and longline fisheries occurred with no bycatch mitigation measures. The negative effects of fishery bycatch through additive mortality and of rat predation on breeding success were likely the main drivers of this decline. Both modelled population growth rate and observed breeding densities showed an increase since the mid‐2000s. We explained this trend by the improvement in survival probability following implementation of fishery bycatch mitigation measures and in breeding success probability with the local control of the rat population and changes in sea ice conditions on foraging grounds. Synthesis and applications. We provide a holistic approach to assess the effects of management measures by analysing datasets from sampling methods commonly employed in seabird studies. Our conclusions should encourage the eradication of invasive predatory species in seabird breeding areas and the strengthening of bycatch mitigation measures for the vulnerable seabird species, especially in international waters, but also the development of such measures considering the other marine large pelagic species threatened by fisheries bycatch (sharks, rays, turtles and marine mammals) since it could be crucial to avoid populations' extinction.

Functional and phylogenetic diversity of sharks in the Northeastern Pacific

AbstractAimThe expansive spatial scale of pelagic communities and the difficulty in acquiring pelagic species' functional traits have stymied an understanding of marine community dynamics. We assembled and analysed a shark trait database and community phylogeny to identify the major axes of trait variation that define shark functional groups. We tested whether membership to biophysical macroecological strata is related to these functional or phylogenetic relationships.LocationNortheastern Pacific, 180–255°E and 0–50°N.TaxonSharks (Class: Chondrichthyes, superorder: Selachimorpha).MethodsWe built a community phylogeny and collected habitat, reproductive, somatic growth, trophic and dentition traits. We used principal coordinates analyses to identify axes of trait variation and hierarchical clustering to classify functional groups. We tested whether functional or phylogenetic relatedness determined species' membership to strata from five macroecological gradients: latitude, habitat type, thermal, carbon source and bathymetry.ResultsWe assembled 38 traits from 1225 records from 130 sources, 260 pictographs from seven sources and 631 teeth from 79 jaw specimens. Life history, r versus K selection, was responsible for the biggest division in the functional dendrogram. Vertical habitat preference, growth rates, diet and dental morphology generated further divisions between r‐ or K‐selected species. Vertical habitat preference, carbon source and biochemical habitat type were significantly dispersed or clustered on the functional dendrogram or phylogram.Main ConclusionsHabitat and reproductive traits were the most important trait suites driving shark functional diversity. Through ordination and clustering, we were able to associate major axes of trait variation to the membership of shark functional groups. The phylogram approximated well the functional dendrogram's backbone but was a poor substitute for the trait diversity at the tips. Given the long evolutionary history of sharks and coincident expansive trait diversity, merging functional and phylogenetic approaches was necessary to capture the dimensions of shark biodiversity.

Deciphering the Stock Structure of White Sardine Escualosa thoracata (Valenciennes, 1847) along the Indian Waters by using Chemometric Analysis of Natural Signature Fatty Acid Profile

Background: Small pelagic species like white sardine gained importance due to their high demand in local markets over years has become important to sustainably harvest the available resources. Thus, the current study was aimed to decipher the stock structure studies based on chemometric analysis of natural signature fatty acid profile which plays an important role in stock identification to the formulation of better sustainable management plans and its conservation. Methods: Samples of Escualosa thoracata were collected from four locations each from two on the east coast (Chennai and Kolkata) and west coast (Mumbai and Kochi) of the Indian peninsula 2019-2020. Heart tissue from the specimen from each location was collected, preserved and fatty acid profiling was performed. The analysis comprised methanolysis, gas chromatography and multivariate statistics. Result: The profile showed a difference between southern and northern populations on both the coast. The trend was more obvious in SAFAs and PUFAs; SAFAs were high content in the southern populations and PUFAs were high content in the northern populations. The separation can be attributed to the latitudinal effects on the deposition of fatty acids.

Philopatry as a Tool to Define Tentative Closed Migration Cycles and Conservation Areas for Large Pelagic Fishes in the Pacific

Migrations of large pelagic fishes across the Pacific are usually inferred from tagging or genetic studies. Even though these techniques have improved over time, they still fail to demonstrate large transoceanic migrations, usually proposing ‘routes’ that do not cycle seasonally. The current study uses the concept of ‘philopatry’ in 11 large pelagic fish species, i.e., the tendency for animals to return to their natal site to reproduce. Tentative migration routes and maps emerge by applying this concept to the movements extracted through a comprehensive review of the literature on satellite and conventional tagging, and population and subpopulation linkages inferred from genetic and/or genomic studies. Moreover, when comparing these proposed migration routes and the mapped reconstructed catch (1950–2016, Sea Around Us) of each species in the Pacific, similarities emerge, reinforcing the accuracy of these migration cycles informed by philopatry. Finally, by superposing the migration routes of our 11 species, we identified areas of the Pacific that are part of the inferred migration routes of multiple species, leading to a discussion of possible ‘blue corridors’ that would protect the studied species’ key migration routes and stocks, which are important for the fisheries, culture and nutrition of Pacific islanders.

Community dynamics of estuarine forage fishes are associated with a latitudinal basal resource regime

AbstractForage fishes are an important component of marine, estuarine, and aquatic food webs that facilitate the transfer of energy and nutrients from primary producers to upper trophic levels. Previous studies of forage fishes have focused primarily on pelagic planktivorous species in pelagic environments. However, benthically associated taxa can be just as important as planktivorous species, particularly in highly productive estuarine environments that provide critical habitat for many predators. In this study, we analyzed a 20‐year forage fish community composition and abundance dataset across four eastern Gulf of Mexico estuaries spanning a broad latitudinal gradient to investigate spatiotemporal variability in community structure and quantify associations with habitat. Our analyses revealed significant regional structuring of forage fish communities, coupled with a strong association with habitat characteristics related to latitudinal effects and basal resource regime. Communities in the two northern estuaries and two southern estuaries were associated primarily with planktonically reliant and benthically reliant taxa, respectively. Despite regional differences, we uncovered a coherent annual cycle in forage fish communities across all estuaries related to seasonal shifts in abundances of several abundant and ubiquitous species. We additionally revealed significant subdecadal periodicity potentially associated with bottom‐up effects of global climatic cycles. The significant association of forage fish communities with habitat regime shown in this study underlies the importance of continued monitoring of these communities. This study represents a novel approach to assess this critical ecosystem component in diverse estuarine systems globally.

Microplastic presence in the pelagic fish, Seriola dumerili, from Balearic Islands (Western Mediterranean), and assessment of oxidative stress and detoxification biomarkers in liver

Microplastics (MPs) are characterized by their high persistence in marine ecosystems, and due to their small size, they can be easily ingested by very diverse organisms. Although the presence of MPs in wild fish is well documented, there is still limited information on their potential to induce adverse effects. Pelagic fish species, because of their wide distribution, are considered good bioindicators for monitoring environmental pollution of marine ecosystems. This study investigated the presence of MPs in the gastrointestinal tract of the predatory pelagic fish (Seriola dumerili) in the Balearic Islands (Mediterranean Sea), and the possible relationship with oxidative stress through the analysis of biomarkers in liver tissue. The results showed the presence of MPs in 98% of total samples examined (n = 52) with an average of 12.2 ± 1.3 MPs/individual. A greater amount of fibre-like particles was isolated compared to fragments. No correlation between the presence of MPs in the gastrointestinal contents and the size of the fishes was noted. Antioxidant enzymes (superoxide dismutase and catalase) and the phase II detoxification enzyme glutathione-S-transferase showed increased activities in fish with higher MPs load. The activity ethoxyresorufin-O-deethylase and the levels of malondialdehyde were similar in both groups. In conclusion, the present results provide an important database on the assessment of the presence of MP debris in S. dumerili gastrointestinal tract and, the potential capability to cause oxidative stress.

Benthic-Pelagic state changes in the primary trophic level of an ancient tropical lake

Many large, ancient lakes support primarily planktonic-driven food webs. In contrast, the lowest trophic levels of the Malili Lakes of Sulawesi Island, Indonesia are dominated by benthic diatom communities composed mainly of endemic species. Centric diatoms are not observed in the current diatom assemblage and pennate pelagic species are rare. Using two deep drill-cores from Lake Towuti, we investigated whether the lake has always been dominated by benthic primary production. Despite the ultra-oligotrophic conditions observed in the lake today, we observed state changes characterized by productive planktonic communities and less productive, benthic-dominated diatom assemblages. Two periods of planktonic production, each lasting approximately 50 kyr, were dominated by a complex mixture of Aulacoseira spp., with valve densities >1.0 × 10 9 valves/g with a maximum biovolume of 3.5 × 10 12 μm 3 /g. A similar planktonic assemblage was observed at much lower abundances (<10 7 valves/g) in the deeper sediments (>1 Ma), during the earliest stages of lake formation. Two periods of increased benthic primary production of approximately ~11 kyr in duration, originating from the littoral zone of the lake, were also observed, one between the two planktonic phases and one above the last planktonic maxima. The benthic periods were dominated by Cymbopleura spp., with valve densities of approximately 2.0 × 10 8 valves/g and a maximum biovolume of 1.2 × 10 11 μm 3 /g. Nonmetric multidimensional scaling analysis of sediment chemistry revealed that the benthic and pelagic states clustered with distinct chemical environments. The benthic phases were associated with well-mixed conditions in the lake whereas the planktonic phases were related to rapidly reoccurring water column mixing followed by intense stratification that generate nutrient recycling events. We conclude that lake mixing and nutrient cycling regimes regulated, in part, the switch between benthic and pelagic states in Lake Towuti. • Major switches between benthic and pelagic states in lake's diatom fossil record • Long-term planktonic diatom dominance in current benthic Lake Towuti • Planktonic communities established and persisted naturally for ~50 ky each • Both planktonic diatom communities had similar composition and abundance • Switches in state potentially linked to shifts in lake mixing regime

Suitability and Sensitivity of Golden Grey Mullet Chelon auratus (Risso, 1810) as a Reference Fish Species for Ecotoxicity Tests in the Black Sea

In recent years, hydrocarbon exploration and production operations have intensified in the Black Sea. Alongside growth in exploration and production activities, the influence of chemical usage across multiple industrial sectors within the Black Sea environment has become increasingly interesting. The aim of this research was to define a protocol for determining the acute toxicity of chemicals using the golden grey mullet, Chelon auratus (Risso, 1810), a native pelagic fish species of the Black Sea. Juvenile golden grey mullets were exposed for 96 h, under semi-static conditions, to dilutions of the reference toxicant 3,5-Dichlorophenol. Results from three reference toxicity tests (LC50 = 1.25 mg/L, 1.739 mg/L, and 1.409 mg/L) indicated that C. auratus is of moderate sensitivity when compared to literature values from EPAs Ecotox database. The protocol described within is intended to ensure Black Sea native organisms are represented by standard hazard assessment practices.

Potential Efficiency of Earth Observation for Optimum Fishing Zone Detection of the Pelagic Sardinella aurita Species along the Mediterranean Coast of Egypt

This research utilizes the efficiency of remotely sensed data and advanced digital image processing techniques to assist in monitoring for the management of marine fisheries in Egypt (south Mediterranean Sea region). A newly developed model is applied to the Sardinella aurita fisheries to determine optimal fishing zones, and is then applied to monitor and detect the potentially optimal fishing zones for other locally important and economic fish species. This approach depends on chlorophyll-a (Chl-a) and sea-surface temperature (SST) characteristics that are that known to control this species communities. The ranges and distribution of SST and Chl-a were obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) aqua as well as Sentinel-3 satellites during the period from 2018 to 2020. The results revealed that there is a strong link between Sardinella abundance and both the SST and the Chl-a concentration. The suitable months for the abundance of this pelagic fish species were defined to be from May to November, producing 75% of the catch (nearly 42 K tons). Low abundances were recorded during the months from December to April, below the suitable harvest levels for this species. This research highlighted the importance of using satellite data as a tool to help scientists to develop appropriate management strategies for the sustainable management of fisheries resources worldwide.