Shell Shape and Meat Condition in Selectively Bred Sydney Rock Oysters, Saccostrea glomerata (Gould, 1850): The Influence of Grow‐out Methods

The Australian edible oyster industry has been severely impacted by disease and declining yields since the 1970s. Selective breeding of Saccostrea glomerata is one measure addressing these problems by producing fast‐growing, disease‐resistant oysters. Farmers report that selected oysters have different growth characteristics than their wild counterparts using conventional grow‐out methods. This study investigated how different grow‐out methods influence commercially valuable oyster characteristics including shell length, shape, surface growth deformities and meat condition. In June 2015, selectively bred S. glomerata spat were deployed in two estuaries (Hawkesbury River and Georges River) in NSW, Australia, using three grow‐out methods (fixed trays, Stanway cylinders and floating baskets). In November 2015, oysters were transferred among grow‐out methods to test for the effects of changing grow‐out methods on oyster growth patterns. Oysters transferred from baskets to cylinders and from trays to cylinders had, on average, deeper and wider shells, a higher meat condition and fewer shell surface deformities than oysters in other grow‐out method combinations. However, these oysters were smaller than oysters not grown in cylinders. While there were some differences in growth patterns between the estuaries, overall it was the grow‐out methods that most influenced oyster characteristics. This was attributed to differences in the amount and magnitude of movement oysters experienced in the grow‐out methods, as recorded by motion sensors. This study demonstrates how grow‐out methods can be managed to achieve desired growth trajectories and therefore improve marketability among selective bred S. glomerata

Habitat characteristics predicting distribution and abundance patterns of scallops in D'Entrecasteaux Channel, Tasmania

This project was funded by the Fishwise Community Grants Scheme administered by the Department of Primary Industries, Parks, Water and Environment, Australia. The first author was supported by an Endeavour International Postgraduate Research Scholarship (EIPRS).Habitat characteristics greatly influence the patterns of distribution and abundance in scallops, providing structure for the settlement of spat and influencing predation risk and rates of survival. Establishing scallop-habitat relationships is relevant to understanding the ecological processes that regulate scallop populations and to managing critical habitats. This information is particularly relevant for the D'Entrecasteaux Channel, south-eastern Tasmania (147.335 W, 43.220 S), a region that has supported significant but highly variable scallop production over many years, including protracted periods of stock collapse. Three species of scallops are present in the region; the commercial scallop Pecten fumatus, the queen scallop Equichlamys bifrons, and the doughboy scallop Mimachlamys asperrima . We used dive surveys and Generalized Additive Modelling to examine the relationship between the distribution and abundance patterns of each species and associated habitat characteristics. The aggregated distribution of each species could be predicted as a function of sediment type and species-specific habitat structural components. While P. fumatus was strongly associated with finer sediments and E. bifrons with coarse grain sediments, M. asperrima had a less selective association, possibly related to its ability to attach on a wide range of substrates. Other habitat characteristics explaining P. fumatus abundance were depth, Asterias amurensis abundance, shell and macroalgae cover. Equichlamys bifrons was strongly associated with macroalgae and seagrass cover, whereas M. asperrima abundance was greatly explained by sponge cover. The models define a set of relationships from which plausible hypotheses can be developed. We propose that these relationships are mediated by predation pressure as well as the specific behavioural characteristics of each species. The findings also highlight the specific habitat characteristics that are relevant for spatial management and habitat restoration plans.Publisher PDFPeer reviewe

Population genetic signatures of a climate change driven marine range extension

Shifts in species distribution, or 'range shifts', are one of the most commonly documented responses to ocean warming, with important consequences for the function and structure of ecosystems, and for socio-economic activities. Understanding the genetic signatures of range shifts can help build our knowledge of the capacity of species to establish and persist in colonised areas. Here, seven microsatellite loci were used to examine the population connectivity, genetic structure and diversity of Octopus tetricus, which has extended its distribution several hundred kilometres polewards associated with the southwards extension of the warm East Australian Current along south-eastern Australia. The historical distribution and the range extension zones had significant genetic differences but levels of genetic diversity were comparable. The population in the range extension zone was sub-structured, contained relatively high levels of self-recruitment and was sourced by migrants from along the entire geographic distribution. Genetic bottlenecks and changes in population size were detected throughout the range extension axis. Persistent gene flow from throughout the historical zone and moderate genetic diversity may buffer the genetic bottlenecks and favour the range extension of O. tetricus. These characteristics may aid adaptation, establishment, and long-term persistence of the population in the range extension zone

Initial impacts of the COVID-19 pandemic on Australian fisheries production, research organisations and assessment: shocks, responses and implications for decision support and resilience

Australia’s fisheries have experience in responding individually to specific shocks to stock levels (for example, marine heatwaves, floods) and markets (for example, global financial crisis, food safety access barriers). The COVID-19 pandemic was, however, novel in triggering a series of systemic shocks and disruptions to the activities and operating conditions for all Australia’s commercial fisheries sectors including those of the research agencies that provide the information needed for their sustainable management. While these disruptions have a single root cause—the public health impacts and containment responses to the COVID-19 pandemic—their transmission and effects have been varied. We examine both the impacts on Australian fisheries triggered by measures introduced by governments both internationally and domestically in response to the COVID-19 pandemic outbreak, and the countermeasures introduced to support continuity in fisheries and aquaculture production and supply chains. Impacts on fisheries production are identified by comparing annual and monthly catch data for Australia’s commercial fisheries in 2020 with averages for the last 4–5 years. We combine this with a survey of the short-term disruption to and impacts on research organisations engaged in fisheries monitoring and assessment and the adaptive measures they deployed. The dominant impact identified was triggered by containment measures both within Australia and in export receiving countries which led to loss of export markets and domestic dine-in markets for live or fresh seafood. The most heavily impact fisheries included lobster and abalone (exported live) and specific finfishes (exported fresh or sold live domestically), which experienced short-term reductions in both production and price. At the same time, improved prices and demand for seafood sold into domestic retail channels were observed. The impacts observed were both a function of the disruptions due to the COVID-19 pandemic and the countermeasures and support programs introduced by various national and state-level governments across Australia to at least partly mitigate negative impacts on harvesting activities and supply chains. These included protecting fisheries activities from specific restrictive COVID-19 containment measures, pro-actively re-establishing freight links, supporting quota roll-overs, and introducing wage and businesses support packages. Fisheries research organisations were impacted to various degrees, largely determined by the extent to which their field monitoring activities were protected from specific restrictive COVID-19 containment measures by their state-level governments. Responses of these organisations included reducing fisheries dependent and independent data collection as required while developing strategies to continue to provide assessment services, including opportunistic innovations to harvest data from new data sources. Observed short run impacts of the COVID-19 pandemic outbreak has emphasised both the vulnerability of fisheries dependent on export markets, live or fresh markets, and long supply chains and the resilience of fisheries research programs. We suggest that further and more comprehensive analysis over a longer time period of the long-run impacts of subsequent waves of variants, extended pandemic containment measures, autonomous and planned adaptive responses would be beneficial for the development of more effective counter measures for when the next major external shock affects Australian fisheries

World squid fisheries

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Dynamics of growth and development in tropical loliginid squid Photololigo species

Temporal and spatial abundance of juveniles of two Photololigo species on the continental shelf off Townsville, Australia was described using light-traps. The two species showed very distinct and separate spatial distribution patterns. Photololigo sp. A was found close to the coast and was the smaller and more abundant of the two species. This species was most abundant in surface waters, although larger individuals were generally caught deeper. There was no evidence of vertical movements during the night. The presence of small and large juvenile Photololigo sp. A during summer and winter months suggests that spawning and recruitment occurs throughout the year. In contrast, Photololigo sp. B was caught predominantly offshore. All sizes of Photololigo sp. B were caught both close to the benthos and in surface waters in the middle of the Great Barrier Reef lagoon, but juveniles were deeper and larger further offshore. This study demonstrated that light-traps are an effective way of sampling and catching small loliginid squid for research. This study approached growth of squid by examining the dynamics of muscle tissue and changes in shape and size of body structures in juvenile and adult Photololigo sp. A. Animals change shape during growth because body structures increase in size at different relative rates. These changes are of particular interest because they are generally concomitant with changes in ecology. Length and mass measurements were taken from squid ranging in size (dorsal mantle length) from 2.77 mm to 117.03 mm. Small squid ( 50 mm dorsal mantle length) were more elongate and narrow and the head was proportionally smaller. As squid reached a dorsal mantle length of 60 mm, the changes in shape with growth become slower and they reached a final shape. Small individuals allocated energy predominantly in the arms and tentacles during early stages of growth, while the viscera and head grew at a much slower rate. Once individuals began producing gametic tissue and gonad growth occurred, the mantle muscle tissue grew more slowly than the gonad. Allocation of energy to somatic and gametic growth was investigated using information about the way muscle tissue grows. Growth of somatic tissue in Photololigo sp. was expressed in terms of muscle fibre recruitment and growth. Muscle blocks and muscle fibres were measured and the size frequency distributions were compared between different size-classes of squid. Muscle blocks increased in size as individuals grew. The size frequency distribution of the muscle fibres suggested that this increase resulted from the generation of new muscle fibres and an increase in the size of existing muscle fibres. The size frequency distribution of muscle fibres was very similar in all size-classes of squid examined and the presence of small muscle fibres in all individuals suggested that muscle fibre recruitment may be continuous. Growth of muscle tissue, by muscle fibre growth and recruitment, provides a mechanism to explain the continuous growth described for tropical squid. Two structural types of muscle fibres; mitochondria-poor and mitochondria-rich, are present in juvenile and adult squid. A poor relationship between the ratio of the muscle fibre types and dorsal mantle length suggests that generation of mitochondria-rich muscle fibres may not be influenced by growth. The presence of what, histologically, appears to be a breakdown in the organisation of circular muscle fibres was dependent upon the size of the individual and its reproductive status. However, there was no evidence to suggest that this is part of the senescence process. An influx of immature individuals was detected in early September and this group of individuals was followed throughout reproductive maturation. From the time female Photololigo began producing primary oocytes to ovulation was less than two months. Four pieces of evidence supported the hypothesis that Photololigo sp. A has the potential to lay multiple, discrete batches of eggs. (1) The ovaries of maturing and mature females contained a large population of primary oocytes. (2) There was a poor correlation between the size of females and both the oviduct mass and the number of eggs per mass of oviduct. (3) Rapid increase in the oviduct mass of mature females indicated that the ovary released batches of ovulated eggs. (4) Gonad mass increased at a relatively slow rate compared to the increase in somatic tissue. There was no evidence, from an examination of the length-weight relationships and microscopic assessment of the mantle muscle tissue, of a cost of egg production

Limited use of stored energy reserves for reproduction by the tropical loliginid squid Photololigo sp.

This study sought to determine if the tropical loliginid squid Photololigo sp. stores energy in the form of lipid, carbohydrate or protein for reproductive investment. Individuals were examined for changes in morphometry, mantle muscle structure and concentrations of water, lipid, carbohydrate and protein in muscle tissue and the digestive gland, associated with the stage of reproductive maturation. Muscle mass was affected by reproductive maturation in females. Mature individuals were lighter for their length compared with females in the early stages of maturation. Concentrations of lipid and carbohydrate in the muscle tissue were very low, and female Photololigo sp. showed equivocal evidence of declining lipid and carbohydrate levels with egg production. There was no evidence of dramatic changes in protein concentration in the mantle muscle with reproductive maturation. Male Photololigo sp. showed a change in the digestive gland with maturation, with water content increasing and protein concentrations decreasing. The digestive gland of both male and female Photololigo sp. increased in size and contained less water with growth. There was little evidence that the storage and transfer of energy for reproduction occurred in Photololigo sp. Instead, it is probable that energy for reproduction is predominantly sourced directly from consumed food

Distribution and abundance of two juvenile tropical Photololigo species (Cephalopoda: Loliginidae) in the central Great Barrier Reef Lagoon

This study quantified the temporal and spatial abundance of juveniles of two Photololigo species on the continental shelf off Townsville, Australia with the use of light-traps. The two Photololigo species (A and B) showed very distinct and separate spatial distribution patterns. Photololigo sp. A was found close to the coast and was the smaller and more abundant of the two species. This species was most abundant in surface waters, although larger individuals were generally caught deeper. There was no evidence of vertical movements during the night. The presence of small and large juvenile Photololigo sp. A during summer and winter months suggests spawning and recruitment occur throughout the year. In contrast, Photololigo sp. B was caught predominantly offshore. All sizes of Photololigo sp. B were caught both near the benthos and at the surface in the mid-lagoon, but farther offshore juveniles were deeper and larger. The presence of small juvenile squid of both species throughout the summer suggests that these species spawn for an extended period during the summer. This study demonstrates that light-traps are an effective way of sampling small cephalopods