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153 pages, 97 figures, 10 tables, 2 appendixes, Recent studies have shown that coastal and shelf cephalopod populations have increased globally over the last six decades. Although cephalopod landings are dominated by the squid fishery, which represents nearly 80% of the worldwide cephalopod catches, octopuses and cuttlefishes represent ∼10% each. Total reported global production of octopuses over the past three decades indicates a relatively steady increase in catch, almost doubling from 179,042 t in 1980 to 355,239 t in 2014. Octopus fisheries are likely to continue to grow in importance and magnitude as many finfish stocks are either fully or over-exploited. More than twenty described octopus species are harvested from some 90 countries worldwide. The current review describes the major octopus fisheries around the globe, providing an overview of species targeted, ecological and biological features of exploited stocks, catches and the key aspects of management, IGG has been supported by the Japan Science and Technology Agency (Grants J130000263 and AS2715164U). RV has been supported by the Spanish Ministry of Education and Culture (Grant PRX17/00090), Spanish Ministry of Science, Innovation and Universities (OCTOSET project, RTI2018-097908-B-I00, MCIU/AEI/FEDER, EU) and by the Direcció General de Pesca i Afers Marítims, Generalitat de Catalunya. FAFA was supported by a predoctoral fellowship of the MINECO (BES-2013-063551) and an Irish Research Council - Government of Ireland Postdoctoral Fellowship (Ref. GOIPD/2019/460)

Octopus fisheries are expanding worldwide to meet demand and fill market gaps left by overexploited species, a trend that is increasingly apparent in Australia. However, a lack of biological and ecological data is impeding the sustainable development of octopus fisheries. This is the first study to characterise the catch demographics and region-specific abundance of commercially harvested octopus in a remote fishery in southern Australia. Through field surveys, octopus and egg presence was monitored across four seasons and five sampling locations. A sub-sample of octopus from summer and winter were retained and examined. Octopus and eggs were present all year, with peaks of abundance in autumn and low abundance in summer. The catch consisted of large-egged holobenthic species, which were predominantly Octopus berrima (94 %) and Octopus pallidus (6%). Octopus were more abundant in the small and relatively hypersaline bays, but smaller, compared to octopus collected from the more exposed Gulf regions. For O. berrima, females made up 73 % of the catch, were 38 % smaller than males and only 32 % were mature. In contrast, 70 % of the males were mature. Based on the biological and ecological data, recommendations are provided for the sustainability and development of the fishery. As underutilised invertebrate fisheries become increasingly important to global food security, fundamental monitoring studies, such as this, are critical to ensure longevity and conservation of wild populations and fishery resources. Refereed/Peer-reviewed

Otolith (ear stone) chemistry provides powerful insights into the lives of fish. Although frequently used to reconstruct past environments, the influence of physiology remains unsettled. As such, we investigated the relationships between otolith chemistry, physiological factors and environmental factors in an iconic fishery species, snapper (Chrysophrys auratus). Lifetime otolith profiles were analysed of carbon (δ13C) and oxygen (δ18O) isotopes, and elemental concentrations of lithium (Li: Ca), magnesium (Mg: Ca), manganese (Mn: Ca), strontium (Sr: Ca), and barium (Ba: Ca). Mixed-effects modelling alongside a detailed literature review was used to investigate physiological (age, otolith growth rate, fish size, sex) and environmental influences (sea-surface temperature and chlorophyll-a) on otolith chemistry. Carbon isotopes and magnesium related to physiological factors, suggesting their potential as physiological proxies. Physiology also weakly related to strontium and lithium. By contrast, oxygen isotopes, barium, and manganese (except for natal signatures) were suggested to provide insights into past environments. Our study stresses the importance of consistency in biological characteristics for study designs, and highlights the potential of physiological proxies for distinguishing between populations in uniform water bodies. This study has not only reinforced our confidence in field applications of otolith chemistry, but has furthered our understanding of the influence of physiology. Refereed/Peer-reviewed

Hypoxic or oxygen-free zones are linked to large-scale mortalities of fauna in aquatic environments. Studies investigating the hypoxia tolerance of fish are limited and focused on marine species and short-term exposure. However, there has been minimal effort to understand the implications of long-term exposure on fish and their ability to acclimate. To test the effects of long-term exposure (months) of fish to hypoxia we devised a novel method to control the level of available oxygen. Juvenile golden perch (Macquaria ambigua ambigua), and silver perch (Bidyanus bidyanus), two key native species found within the Murray Darling Basin, Australia, were exposed to different temperatures (20, 24 and 28 °C) combined with normoxic (6–8 mgO2 L−1or 12–14 kPa) and hypoxic (3–4 mgO2 L−1or 7–9 kPa) conditions. After 10 months, fish were placed in individual respirometry chambers to measure standard and maximum metabolic rate (SMR and MMR), absolute aerobic scope (AAS) and hypoxia tolerance. Golden perch had a much higher tolerance to hypoxia exposure than silver perch, as most silver perch died after only 1 month exposure. Golden perch acclimated to hypoxia had reduced MMR at 20 and 28 °C, but there was no change to SMR. Long-term exposure to hypoxia improved the tolerance of golden perch to hypoxia, compared to individuals held under normoxic conditions suggesting that golden perch can acclimate to levels around 3 mgO2L−1(kPa ~ 7) and lower. The contrasting tolerance of two sympatric fish species to hypoxia highlights our lack of understanding of how hypoxia effects fish after long-term exposure. Refereed/Peer-reviewed

The illegal pet trade facilitates the global dispersal of invasive alien species (IAS), providing opportunities for new pests to establish in novel recipient environments. Despite the increasing threat of IAS to the environment and economy, biosecurity efforts often lack suitable, scientifically-based methods to make effective management decisions, such as identifying an established IAS population from a single incursion event. We present a proof-of-concept for a new application of a stable isotope technique to identify wild and captive histories of an invasive pet species. Twelve red-eared slider turtles (Trachemys scripta elegans) from historic Australian incursions with putative wild, captive and unknown origins were analysed to: (1) present best-practice methods for stable isotope sampling of T. s. elegans incursions; (2) effectively discriminate between wild and captive groups using stable isotope ratios; and (3) present a framework to expand the methodology for use on other IAS species. A sampling method was developed to obtain carbon (δ13C) and nitrogen (δ15N) stable isotope ratios from the keratin layer of the carapace (shells), which are predominantly influenced by dietary material and trophic level respectively. Both δ13C and δ15N exhibited the potential to distinguish between the wild and captive origins of the samples. Power simulations demonstrated that isotope ratios were consistent across the carapace and a minimum of eight individuals were required to effectively discriminate wild and captive groups, reducing overall sampling costs. Statistical classification effectively separated captive and wild groups by δ15N (captive: δ15N‰ ≥ 9.7‰, minimum of 96% accuracy). This study outlines a practical and accessible method for detecting IAS incursions, to potentially provide biosecurity staff and decision-makers with the tools to quickly identify and manage future IAS incursions.

Metabolic rate underpins our understanding of how species survive, reproduce and interact with their environment, but can be difficult to measure in wild fish. Stable carbon isotopes (δ13C) in ear stones (otoliths) of fish may reflect lifetime metabolic signatures but experimental validation is required to advance our understanding of the relationship. To this end, we reared juvenile Australasian snapper (Chrysophrys auratus), an iconic fishery species, at different temperatures and used intermittent-flow respirometry to calculate standard metabolic rate (SMR), maximum metabolic rate (MMR) and absolute aerobic scope (AAS). Subsequently, we analysed δ13C and oxygen isotopes (δ18O) in otoliths using isotope-ratio mass spectrometry. We found that under increasing temperatures, δ13C and δ18O significantly decreased, while SMR and MMR significantly increased. Negative logarithmic relationships were found between δ13C in otoliths and both SMR and MMR, while exponential decay curves were observed between proportions of metabolically sourced carbon in otoliths (Moto) and both measured and theoretical SMR. We show that basal energy for subsistence living and activity metabolism, both core components of field metabolic rates, contribute towards incorporation of δ13C into otoliths and support the use of δ13C as a metabolic proxy in field settings. The functional shapes of the logarithmic and exponential decay curves indicated that physiological thresholds regulate relationships between δ13C and metabolic rates due to upper thresholds of Moto. Here, we present quantitative experimental evidence to support the development of an otolith-based metabolic proxy, which could be a powerful tool in reconstructing lifetime biological trends in wild fish.

Lay summary It is poorly understood whether fish can acclimate to prolonged low-oxygen conditions (or hypoxia). Our study shows that prior long-term exposure to low-oxygen conditions improves tolerance to low-oxygen in a freshwater fish. The results of our study aid our understanding of long-term responses of freshwater fish to low-oxygen to hypoxic events., Persistent hypoxic or low-oxygen conditions in aquatic systems are becoming more frequent worldwide, causing large-scale mortalities to aquatic fauna. It is poorly understood, however, whether species can acclimate to long-term hypoxic conditions. In two experiments, we exposed juvenile freshwater fish (Murray cod, Maccullochella peelii) to low-oxygen conditions and investigated acclimation effects. Experiment 1 determined how responses could be modified by exposure to different temperatures (20, 24 and 28°C) and oxygen conditions (control 6–8 mgO2 L−1 and low-oxygen 3–4 mgO2 L−1) over 30 days. Experiment 2 determined the acclimation ability of fish exposed to two temperatures (20 and 28°C) and low-oxygen conditions (3–4 mgO2 L−1) for three different acclimation periods (7, 14 and 30 days). Responses were measured by determining critical oxygen tension (Pcrit), loss of equilibrium and aerobic capacity using resting respirometry. In experiment 1, resting oxygen requirements were negatively affected by long-term low-oxygen exposure except at the highest temperature (28°C). However, long-term acclimation in low-oxygen improved tolerance as measured by loss of equilibrium but not Pcrit. In experiment 2, fish could tolerate lower oxygen levels before reaching loss of equilibrium after 7 days acclimation, but this declined overtime. Murray cod were most tolerant to low-oxygen at the lowest temperature (20°C) and shortest exposure time (7 days). Extended low-oxygen exposure resulted in reduced aerobic capacity of fish particularly at the lowest temperature. While prior exposure to low-oxygen may allow fish to cope with hypoxic conditions better in the long-term, acclimation time was inversely related to tolerance, suggesting that resistance to hypoxia might decrease as a function of exposure time. Our study fills a much-needed gap in our understanding of how freshwater species acclimate to hypoxia, and in particular, how exposure to prolonged periods of low-oxygen and elevated temperatures affect organisms physiologically.

Human activities have substantially changed the world’s oceans in recent decades, altering marine food webs, habitats and biogeochemical processes. Cephalopods (squid, cuttlefish and octopuses) have a unique set of biological traits, including rapid growth, short lifespans and strong life-history plasticity, allowing them to adapt quickly to changing environmental conditions. There has been growing speculation that cephalopod populations are proliferating in response to a changing environment, a perception fuelled by increasing trends in cephalopod fisheries catch. To investigate long-term trends in cephalopod abundance, we assembled global time-series of cephalopod catch rates (catch per unit of fishing or sampling effort). We show that cephalopod populations have increased over the last six decades, a result that was remarkably consistent across a highly diverse set of cephalopod taxa. Positive trends were also evident for both fisheries-dependent and fisheries-independent time-series, suggesting that trends are not solely due to factors associated with developing fisheries. Our results suggest that large-scale, directional processes, common to a range of coastal and oceanic environments, are responsible. This study presents the first evidence that cephalopod populations have increased globally, indicating that these ecologically and commercially important invertebrates may have benefited from a changing ocean environment, SI