Context Dipturus johannisdavisi is a little known deep-sea skate from the Indian Ocean, with limited biological information and a Data Deficient IUCN listing. Aim This study provides baseline information on size structure, life-history traits, diet, and fishery interactions to support future conservation assessment. Methods Specimens (N = 61) were collected from shrimp-trawl bycatch off south-western India (200–600-m depth). These were examined to describe exploited length classes and life-history characteristics. Key results Individuals ranged from 23.5 to 74.7 cm TL, the latter representing the maximum confirmed size for the species. Females were more abundant than males (2.39:1) and attained larger sizes. Growth was near isometric (b = 3.103; r2 = 0.9715). Approximately one-third of individuals were mature, with slightly larger lengths at 50% sexual maturity (L50) values in females than males. Diet was dominated by crustaceans, particularly deep-sea shrimps, followed by teleosts and cephalopods. A single mature female contained elasmobranch prey, representing a rare record of elasmobranch consumption. Conclusions This study has provided the first detailed life-history information for Dipturus johannisdavisi, which is regularly captured as shrimp-trawl bycatch, including reproductively active individuals, indicating vulnerability to deep-sea trawling. Implications Ongoing deep-sea trawling may pose a risk to this data-deficient species, and the data presented here provide a baseline for future assessment and management.
Context Poor labelling of shark products is a global problem that hampers sustainable fisheries and limits consumer choice. Aims We conducted a detailed assessment of mislabelling and species composition in cooked ‘shark’ products from Western Australian fish and chip shops. Methods COI sequencing was used to identify species in cooked ‘shark’ fillets. Key results We identified 11 shark, 2 chimaera and 3 teleost species in 167 products from 132 shops. Most products were labelled ambiguously (56%) or mislabelled (35%), and only 26% provided origin information. Products labelled ‘shark’ (53%) mostly contained dusky, gummy or whiskery sharks. For species-specific labels, most products (92%) were advertised as ‘gummy’ or ‘bronze whaler’ and identified as gummy, whiskery or dusky sharks. Because these species have similar prices, mislabelling likely reflects complex commercial fishing operations and supply chains. Overall, species composition differed from products tested in other Australian states. Only one sample involved a species in a ‘threatened’ category under Australian IUCN assessments. Conclusions Cooked shark products sold in Western Australian fish and chip shops showed a high incidence of ambiguous labelling and mostly contained dusky, gummy and whiskery sharks. Implications Our findings underscore the need to strengthen seafood labelling legislation in Australia.
Context Understanding growth patterns is essential for effective fisheries management and conservation of freshwater fishes, for economically important species with limited otolith-based growth studies. Cirrhinus reba, a valuable minor carp in the Ganga River, lacks comprehensive otolith-based growth studies despite its significance to subsistence fisheries and aquaculture. Aim This study establishes otolith morphometric relationships and validates back-calculation methods for growth reconstruction of C. reba from four sites along the Ganga River. Methods We analysed relationships between fish body size and otolith measurements by using linear regression and Spearman correlation on 235 specimens, and compared five back-calculation functions and three growth models by using linear mixed-effects and non-linear approaches. Key results The strongest relationships were between otolith weight and fish length (R2 = 0.76–0.78, ρ = 0.85–0.86). The Monastyrsky scale proportional hypothesis best estimated length-at-age. Von Bertalanffy and Gompertz models showed spatial variation; asymptotic length varied from 96 to 205 mm and growth coefficient from 0.44 to 0.74 year−1 across sites. Conclusion Otolith morphometric relationships and validated back‑calculation methods provide a solid foundation for reconstructing growth in C. reba. Implications This validated framework enables otolith-based size and age reconstruction, facilitating evidence-based fisheries management, including minimum catch-size regulations, seasonal fishing restrictions, and habitat prioritisation as site-specific conservation strategies for C. reba under varying environmental conditions throughout the Ganga River.
The world’s ocean stores ~90% of the excess heat generated by anthropogenic global warming, making sustained ocean observations essential for understanding physical, biological and climate processes. Here, we describe how the Integrated Marine Observing System (IMOS) Animal Tagging Facility, in collaboration with national and international partners, has established a unique animal-borne ocean-observing system. Wide-ranging, deep-diving marine predators provide critical observations from remote and under-sampled regions, particularly the Australian Antarctic sector and tropical northern Australia, complementing traditional observing networks. Since 2004, IMOS Animal Tagging has deployed 1023 instrumented tags on southern elephant (n = 746) and Weddell seals (n = 125), Australian sea lions (n = 50), Australian (n = 8) and New Zealand fur seals (n = 24), and olive ridley (n = 24), green (n = 10) and flatback turtles (n = 16). These deployments have yielded more than 420,000 temperature–salinity–depth profiles spanning the Antarctic to the tropics. The resulting observations have advanced understanding of ocean structure, bathymetry, climate processes and the ecology of wide-ranging marine vertebrates, while providing valuable data to operational oceanography and climate research. Twenty years of sustained observations have demonstrated the importance of long-term, continuous animal-borne data streams as a core component of Australia’s IMOS.
Context Climate-driven droughts increasingly threaten freshwater species, and emergency rescue and repatriation is a critical conservation intervention. The platypus (Ornithorhynchus anatinus), a semi-aquatic monotreme endemic to eastern Australia, is increasingly exposed as droughts intensify. Aims We quantified the post-release movement ecology of repatriated platypuses to evaluate the emergency rescue-and-return intervention. Methods After the severe 2017–19 drought, seven platypuses were rescued from Tidbinbilla Nature Reserve and held at Taronga Zoo; five were returned to their capture sites after ~5 months. Acoustic telemetry across 11 sites over 18 months recorded movements, and Hidden Markov Models identified behavioural states and site-to-site transitions. Key results All five gained body condition in captivity (mean weight gain 36.9%, range 20.6–54.4%). Four were detected for 290–553 days post-release; one female was lost to follow-up after 39 days (minimum first-year survival 0.80). The four females established consistent site preferences; the single male used all 11 sites with more frequent transitions. Activity was positively associated with Hemiptera, Diptera and Gastropoda and negatively with Plecoptera. Conclusions Repatriated platypuses re-established typical movement and foraging patterns within days of release. Implications Emergency rescue and repatriation offers a viable conservation tool for freshwater wildlife under intensifying climate-driven droughts.
Context Fish production from Gayatri Reservoir in India remains substantially below the estimated potential, highlighting a considerable gap with actual yield, underscoring need for fisheries management. Aims To bridge the gap, trophic model of the reservoir was constructed to assess ecosystem functioning and inform science-based fisheries management. Methods Ecopath model developed with 14 ecological groups using monthly data from April 2022 to March 2023 and was parametrised using monthly biological and fisheries data collected from seven stations. Ecological carrying capacity of economically important groups, Indian major carp (Labeo catla, L. rohita and Cirrhinus mrigala), prawns (Macrobrachium rosenbergii and M. malcolmsonii) and Nile tilapia (Oreochromis niloticus), was estimated. Key results Ecological stability indices, such as total primary productivity : total respiration (6.12) and total primary productivity : total biomass (28.42), indicated that the ecosystem is in developmental phase. Ecological carrying capacity of Indian major carp, prawns and Nile tilapia were estimated at 7.875 5.925 and 5.39 Mg km−2 respectively. Conclusion Fish seed stocking within ecosystem limits can enhance fish production and Ecopath framework effectively guides carrying capacity estimation and fisheries management. Implications This investigation will be useful for developing strategies to maintain ecosystem stability and to formulate fish seed stocking programs in a scientific manner to ensure sustainable fisheries.
Context Mesophotic temperate habitats are among the world’s most poorly studied ecosystems, yet they support a wide range of ecosystem services, including fisheries production. Aims In this study, we aimed to compare the epibenthic communities occurring on mesophotic plain v. reef habitats off the western coast of Kangaroo Island, South Australia. Methods We annotated autonomous underwater vehicle imagery collected from 2 years, using the Australian Morphospecies Catalogue to compare community structure differences. Key results Results identified that the two habitats differed greatly in structure and complexity of epibenthic communities, with greater morphospecies richness across reefs. A greater proportion of hydroids than other cnidaria was identified across reef outcrops, which is unique to temperate mesophotic reefs described globally. For mesophotic plains, model predictions showed that refining soft substrate into finer categories can be useful for predicting morphospecies counts. Conclusion The findings of this study have provided new information of the epibenthic structure of mesophotic reef and plain habitats in the Southern Ocean. Implications These baselines will be important for future integration into benthic assessment and management programs in the deep continental shelf waters of southern Australia.
Context The assessment of population abundance, dynamics and spatial use of coastal dolphins is essential for guiding conservation management measures. Aim This study investigated the long-term abundance, site fidelity, residency patterns and habitat use of Indo-Pacific bottlenose dolphins (Tursiops aduncus) within the Cape Byron Marine Park. Methods Photo-identification data collected from 115 vessel-based surveys (591 h) between 2003 and 2023 were used to assess population structure and areas of core use. Key results The population was composed of a high proportion of transients (59.9%; n = 659), alongside individuals exhibiting varying degrees of site fidelity. Four residency clusters were identified, including a core community with multi-decadal presence, reaching a maximum abundance of 62.2 individuals (95% CI = 54.51–71.05) in 2014. Non-resident abundance peaked at 411.4 (95% CI = 382.86–442.02) in 2014. Spatial analysis showed long-term consistency in the use of core habitats. Conclusions Population densities in the study area appear among the highest reported for the species in Australia and, together with the long-term use of critical habitat areas, highlight the region’s high conservation value. Implications The findings from this study have important implications for the management of the marine protected area and enhance the limited knowledge of this species along the eastern coast of Australia.
Context Flooding of freshwater turtle eggs has been identified as a threatening process that could negatively affect freshwater turtle population function. Aims Experiments were conducted to identify the effects of inundation of Emydura macquarii krefftii eggs in response to (1) duration and (2) timing on hatching success of eggs and hatchling phenotypes as measures of both direct and indirect impacts. Methods Four treatments of eggs, namely, control (no submersion time), 30 min of submersion, 1 h of submersion and 6 h of submersion, were tested by flooding at nine periods during incubation (within the first 24 h, then every week following). Key results Inundation for any length of time caused a significant increase in egg mortality compared with zero inundation with control eggs. The developmental age at which inundation treatments were applied also had a significant effect on hatching success. Conclusion It is concluded that E. m. krefftii eggs are very sensitive to even brief episodes of inundation, especially within the first 24 h of incubation. Implications It is expected that the eggs of other turtle species that have a brief post-oviposition embryonic diapause will exhibit similar sensitivities to inundation.
Context Effective maritime governance depends on understanding the complex relationships among diverse institutional actors. Aims This study applies social network analysis (SNA) to Iran’s maritime governance system, drawing on the ‘Comprehensive Plan for the Implementation of General Policies for Maritime Development’ (GMDP) approved in 2024, which outlines a multidimensional strategy across economic, social, environmental and security domains involving 44 guiding articles and a broad spectrum of organisations. Methods Through a systematic review and coding of the GMDP, this research constructs and analyses the governance network, evaluating cooperation, coordination and the distribution of power and dependency among actors. Key results Results reveal a moderately dense and reciprocal network, with a cohesive core of government ministries and the private sector, but also notable fragmentation at the periphery, particularly among research and innovation-focused organisations. The private sector emerges as a key influencer, whereas the presence of distinct subgroups highlights both the potential for specialisation and the risk of policy fragmentation. Conclusions These findings are broadly consistent with international studies of marine governance, underscoring the need for stronger integration of peripheral actors and enhanced cross-sectoral collaboration. Implications The study offers practical insights for optimising institutional arrangements to support Iran’s sustainable maritime development.
Context Swordfish are among the most abundant top predators in the Indian Ocean, and play a key role in pelagic food webs. However, their feeding habits and ocean-wide trophic niche remain poorly known. Investigating swordfish foraging behaviour, diet variability and trophic position can provide important information on predator–prey dynamics and improve our understanding of open-ocean ecosystems functioning. Aims This study aims to evaluate the ecological role of swordfish in pelagic food webs across major biogeochemical provinces of the Indian Ocean and adjacent waters of the Atlantic. Methods We investigated the trophic ecology of swordfish using stomach content analysis and stable isotopic value (δ13C and δ15N) measurements from white muscle tissue. On the basis of 872 non-empty stomachs and 759 muscle samples collected between 1998 and 2011 across five biogeochemical provinces, we described swordfish prey composition, prey size structure and size-related prey biomass. We further analysed feeding patterns and swordfish’s relative trophic position within the pelagic ecosystem. Key results Epipelagic and vertically-migrating mesopelagic fishes, together with cephalopods, constituted the principal prey groups by number and reconstituted weight, alternating in dominance among provinces. Ommastrephid squids formed the primary component of the cephalopod prey group, a pattern consistently reported across ocean basins. Stomach content analysis showed an ontogenetic dietary shift, with dominance transitioning from fish to cephalopod prey. Although micronektonic prey dominated numerically, more than 70% of the total consumed prey biomass originated from large nektonic species, highlighting their crucial importance for swordfish populations. Muscle δ15N values increased with body size, indicating a rise in trophic position during growth, which was likely to be driven by the consumption of larger fish prey and an increasing contribution of cephalopods to the diet. Conclusions Swordfish exhibit a flexible and opportunistic feeding strategy, with their diet being largely composed of a limited number (5–7) of dominant prey species that vary across provinces and seasons. Muscle δ13C and δ15N values indicated a distinct isotopic niche within each Indian Ocean province, suggesting mid-term (months) residential behaviour at the provincial scale. Implications Residential behaviour may increase swordfish vulnerability to local depletion under excessive fishing pressure, potentially leading to mesopredator-release effects and broader trophic cascades. Continuous long-term monitoring of the Indian Ocean pelagic ecosystem is therefore essential to support sound management and sustainable exploitation of pelagic resources. This should include larger-expanded stomach-content sampling, improved δ13C and δ15N baseline and mid-trophic-level values and modelling of their pathways. In addition, estimates of tissue turnover rates, currently unavailable for swordfish, are needed to improve the evaluation of migratory and residential behaviour and refine interpretation of stable isotope data.
Context Overabundant echinoderms can dramatically alter reefs, with this problem being exemplified along Australia’s coast, with recurrent outbreaks of crown-of-thorns starfish (CoTS) (Acanthaster cf. solaris) on the Great Barrier Reef (GBR) and high densities of long-spined sea urchins (Centrostephanus rodgersii) on the eastern Great Southern Reef (GSR). Aim To foster cross-system knowledge exchange on ‘prickly problems’ across reef systems. Methods Synthesise and compare the ecology and management of CoTS and C. rodgersii, focusing on the GBR and GSR. Key results Population dynamics differ, with recurrent boom-and-bust outbreaks in CoTS, whereas C. rodgersii can increase to high-density stable populations, forming urchin barrens that last decades or more. Differences in nutritional ecology (obligate corallivore, CoTS, v. omnivore, C. rodgersii) and regeneration rate of nutritional resources are linked to population dynamics. For both species, there is evidence of effective, local, top-down active management by culling or harvesting, but large differences in funding exist (funding for GBR CoTS management is >40-fold higher than for Tasmanian urchin management). Conclusions Spatially structured management aimed at prevention is more efficient and cost effective than reactive control efforts. Implications The review emphasises the value in bridging research and sharing knowledge across parallel but largely independent research fields across tropical and temperate reefs.
Context Artificial structures are increasing in coastal environments owing to population expansion, necessitating an understanding of their impacts. Jetties are common in estuaries and can affect aquatic vegetation, yet effects on fish, and whether they are density dependent, remain unclear. Aims Examine the effect of private jetties and their density on fish assemblages and seagrass meadows in Lake Macquarie, New South Wales (NSW), Australia. Methods Fish assemblages were quantified using remote underwater video systems and remotely operated vehicles, with fish and seagrass metrics compared among control, low-density (≤6 jetties per 150 m) and high-density (≥10 jetties per 150 m) treatments. Key results Compared with controls, jetty sites had altered fish assemblage composition and greater species diversity, abundance and fisheries important species including Acanthopagrus australis. Seagrass cover and canopy height were reduced adjacent to jetties at two of three locations. Jetty density effects were complex, with both low- and high-density treatments showing inconsistent responses across locations. Conclusions Jetties modified fish assemblages by adding structure into the seascape, although this occurs at the expense of adjacent seagrass habitat. Implications These findings improve understanding of jetty impacts to guide future development, emphasising the need to assess environmental impacts and protect seagrasses while providing socio-economic benefits from infrastructure.
Context Boops boops is a commercially important sparid species widely distributed in the Mediterranean Sea. Comparative information on its population dynamics in the south-western Marmara Sea and the northern Aegean Sea remains limited. Aims This study aimed to investigate population dynamics of Boops boops in the south-western Marmara Sea and the northern Aegean Sea, Türkiye, and to assess regional differences in growth patterns and fishing pressure. Methods In total, 748 individuals were sampled monthly between January and December 2024, including 370 specimens from the Marmara Sea and 378 from the Aegean Sea, by using gillnets and purse seines. Age determination was based on otolith readings. Von Bertalanffy growth parameters were estimated separately for females and males in both regions. Mortality rates and exploitation ratios were calculated. Key results Age ranges were 1–6 years in the Marmara Sea and 1–5 years in the Aegean Sea. Marmara Sea individuals showed lower growth rates, but larger asymptotic lengths, whereas Aegean Sea individuals exhibited faster growth and smaller maximum sizes. Exploitation rates exceeded sustainable levels in both regions (E = 0.65; E = 0.59). Conclusions Results indicated that Boops boops populations in both regions are overexploited. Implications Region-specific fisheries management strategies are required for sustainability.
Context Natural causes of sea turtle mortality can significantly affect populations. Defensive mechanisms of prey species, such as porcupinefish (Diodontidae family), may pose risks to predators such as loggerhead turtles (Caretta caretta (Linnaeus, 1758)). Aims This study aimed to investigate the stranding records of loggerhead turtles to identify porcupinefish ingestion as a cause of mortality. Methods Between 2015 and 2025, a total of 30 stranded loggerhead turtles were recorded along the coasts of Rio Grande do Norte and Ceará States, in the north-eastern of Brazil. Morphological data and life-stage classification were recorded, and necropsies and macroscopical analysis were conducted to confirm the presence of porcupinefish and evidence of asphyxiation and the presence in other parts of gastrointestinal portions of specimens. Key results Necropsies and macroscopical analysis showed that buccal and oesophageal obstruction in all loggerhead turtles due the morphological adaptations of the fish’s defence. The fish were also found in other organs of the gastrointestinal system. This represents the highest recorded mortality from this cause in the north-eastern Atlantic Ocean region. Conclusions Porcupinefish ingestion is a recurring and under-reported cause of loggerhead turtle mortality, principally in the population of the the Atlantic Ocean. Opportunistic feeding may increase risks, particularly for juveniles. Implications Further research is needed to better understand these predator–prey interactions, other ecological drivers and their impact on sea turtle populations. Continued monitoring is crucial for effective conservation strategies.
Context The discharge of heavy metals into freshwater and marine environments is a serious environmental concern globally. Aims The objectives of this study were to determine the distribution of heavy metals in economically important fish species (Merluccius merluccius, Sardinella aurita, Sparus aurata) and the parasitic nematode, Hysterothylacium sp., from the Mersin Bay, and to evaluate potential human health implications. Methods Fish samples were collected to determine metal (aluminium, Al; chromium, Cr; manganese, Mn; iron, Fe; cobalt, Co; nickel, Ni; copper, Cu; zinc, Zn; cadmium, Cd; lead, Pb) concentrations and evaluate potential health risks. Key results The study results showed that only S. aurata was parasitised by Hysterothylacium sp. Additionally, the mean metal concentrations were found to vary between 1.54 and 2.00 mg kg−1 wet weight (WW) for Al, 0.20–0.45 mg kg−1 WW for Cr, 0.08–0.25 mg kg−1 WW for Mn, 1.26–5.36 mg kg−1 WW for Fe, 0.006–0.014 mg kg−1 WW for Co, 0.11–0.27 mg kg−1 WW for Ni, 0.13–0.23 mg kg−1 WW for Cu, 1.70–2.47 mg kg−1 WW for Zn, 0.001–0.002 mg kg−1 WW for Cd and 0.03–0.05 mg kg−1 WW for Pb, for the unparasitised fish samples. Additionally, findings of this study showed that the metal concentrations in nematodes were 4–14 times higher than those measured in the fish samples, suggesting high bioaccumulation of metals in the parasites. Conclusions Screening-level risk indices indicated potential human health concerns associated with carcinogenic Ni and Cu in the studied fish species from Mersin Bay.
Context We lack basic scientific knowledge of coastal fish faunal diversity and distribution in the islands of the Bismarck Sea, such as New Britain. High-flow rivers and microtidal conditions result in a patchwork of salinity regimes, which creates a diversity of unique environmental settings and habitat features, such as extensive, low-salinity Nypa fruticans mangrove-palm swamps adjoining major rivers. Aims Focusing on coastal, estuarine and lowland freshwater systems, we investigated the environmental settings present, the habitat features they contain and the patterns of utilisation by different fish species, to better understand the potential for adverse impacts from human activities. Methods We used remote underwater video to define fish assemblages and habitat associations. Key results Fish assemblages contained a unique mix of species with diverse habitat and physical requirements. Conclusions A large proportion of New Britain’s coastal and lowland fish use multiple environmental settings, underlining the importance of hydrological connectivity in enabling day-to-day and life-history migration requirements of the fish community. Implications The complex inter-setting utilisation of New Britain coastal and lowland fishes, their reliance on unique habitats (some derived from local and upstream forests), and intact watersheds, places them at risk from the landscape impacts stemming from extensive logging and oil palm.
Context The North Sea hosts numerous historic shipwrecks. Two World War II vessels with ferrous hull were investigated, namely, a German Sperrbrecher 141 and Allied HMS Basilisk. Aims Their disturbance of the coastal seabed was determined. More specifically, the microbial composition, diversity and introduction of iron, aluminium, sulfur and zinc was measured in marine sediment samples. Methods Elemental analysis was conducted by microwaved-assisted HF destruction prior to inductively coupled plasma–optical emission spectroscopy (ICP-OES). Microbial characterisation involved the use of flow-cytometry, ATP spectroscopic assay and 16S rRNA amplicon sequencing. Key results The wrecks cause enrichment in sulfur and largely varying iron concentrations (4.6–153 mg kg−1). Aluminium, which was less abundant, correlated to some extent with the bacterial cell density. Marine bacteria detected include Verrucomicrobiaceae, Woeseia and Flavobacteriaceae, next to sulfur and iron cyclers, similar to Desulfocapsaceae, Sulfurovaceae, Desulfuromonas and B2M28 that are active in dissimilatory iron reduction. Close to the wrecks, the alpha diversity in the seabed was significantly decreased. Conclusions Hence, the submerged wrecks still alter the coastal sediment geochemistry and microbiology. Implications Marine ecosystems near sunken war ships show an adaptive response that microbially cycle iron and sulfur, enriched in those environments. Results show special relevance to recent off-shore structures in coastal areas.
Context Flathead fishes (family Platycephalidae) have economic and cultural significance, but species-specific pigmentation and morphological characteristics used for identification of larvae, and information on their distribution and seasonality, are largely unknown. Aims To infer timing and location of spawning from the spatial, seasonal and interannual distributions of the larval assemblages in eastern Australian waters. Methods DNA barcoding of flathead larvae, by using a particular gene, facilitated species-specific identification of larvae obtained from monthly samples collected between 2014 and 2021 at three oceanographic National Reference Stations (NRS) off eastern Australia. Key results Distinct larval flathead assemblages characterised each NRS, and larval diversity decreased with an increasing latitude, from seven species and six genera off North Stradbroke Island (27°S), five species and two genera at Port Hacking (34°S), to two species within the genus Platycephalus at Maria Island (42.6°S). Conclusions Larval flathead assemblages vary spatially and seasonally relating to oceanographic influences. Diversity of taxa increases towards the equator. Some species show potential of reproductive plasticity. Implications Species-specific identification of larvae enables an understanding of the larval phase of key species that are commercially and recreationally important and provides insights into spatial, seasonal and oceanographic influences on their distribution.
