S Tracey

The Spatial Expansion and Ecological Footprint of Fisheries (1950 to Present)

Using estimates of the primary production required (PPR) to support fisheries catches (a measure of the footprint of fishing), we analyzed the geographical expansion of the global marine fisheries from 1950 to 2005. We used multiple threshold levels of PPR as percentage of local primary production to define ‘fisheries exploitation’ and applied them to the global dataset of spatially-explicit marine fisheries catches. This approach enabled us to assign exploitation status across a 0.5° latitude/longitude ocean grid system and trace the change in their status over the 56-year time period. This result highlights the global scale expansion in marine fisheries, from the coastal waters off North Atlantic and West Pacific to the waters in the Southern Hemisphere and into the high seas. The southward expansion of fisheries occurred at a rate of almost one degree latitude per year, with the greatest period of expansion occurring in the 1980s and early 1990s. By the mid 1990s, a third of the worlds ocean, and two-thirds of continental shelves, were exploited at a level where PPR of fisheries exceed 10% of PP, leaving only unproductive waters of high seas, and relatively inaccessible waters in the Arctic and Antarctic as the last remaining ‘frontiers.’ The growth in marine fisheries catches for more than half a century was only made possible through exploitation of new fishing grounds. Their rapidly diminishing number indicates a global limit to growth and highlights the urgent need for a transition to sustainable fishing through reduction of PPR.

Inter-annual plasticity of squid life history and population structure: ecological and management implications

Population size and structure, as well as individual growth rates, condition, and reproductive output, respond to environmental factors, particularly in short-lived and fast-growing squid species. We need to understand the mechanisms through which populations respond to environmental conditions, to predict when or if established relationships, used as management tools to forecast recruitment strength, might break down completely. Identifying characteristics of successful recruits who have grown under different environmental scenarios may improve our understanding of the mechanistic connections between environmental conditions and the temporal variation in life history characteristics that ultimately affect recruitment. This 5-year study sought to determine the association between key life history characteristics of southern calamary Sepioteuthis australis (growth rate, body size, and patterns of repro-somatic energy allocation) and the environmental conditions experienced by individuals on the east coast of Tasmania, Australia. Among years, all population and individual parameters examined were highly variable, despite the environmental regime during the study not encompassing the extremes that may occur in this dynamic region. Temperature was not clearly associated with any of the individual or population differences observed. Populations of apparently similar abundance were composed of individuals with strikingly different biological characteristics, therefore seeking relationships between abundance and environmental parameters at gross levels did not shed light on the mechanisms responsible for population size. Importantly, inter-annual differences in squid size, condition, reproductive investment, and possibly growth rate, were sex-specific, indicating that males and females responded differently to similar factors. Among years differences in body size were extreme, both among the male component of the population and between genders. The relative importance of many size-based processes that contribute to population size and structure (e.g. predation, starvation, competition, and reproductive success) will therefore vary inter-annually.

Marine foods sourced from farther as their use of global ocean primary production increases

The growing human population must be fed, but historic land-based systems struggle to meet expanding demand. Marine production supports some of the worlds poorest people but increasingly provides for the needs of the affluent, either directly by fishing or via fodder-based feeds for marine and terrestrial farming. Here we show the expanding footprint of humans to utilize global ocean productivity to feed themselves. Our results illustrate how incrementally each year, marine foods are sourced farther from where they are consumed and moreover, require an increasing proportion of the oceans primary productivity that underpins all marine life. Though mariculture supports increased consumption of seafood, it continues to require feeds based on fully exploited wild stocks. Here we examine the oceans ability to meet our future demands to 2100 and find that even with mariculture supplementing near-static wild catches our growing needs are unlikely to be met without significant changes.

High survivorship after catch-and-release fishing suggests physiological resilience in the endothermic shortfin mako shark (Isurus oxyrinchus)

We used satellite tags and blood based analyses to examine the impacts of catch and release angling on the shortfin mako shark. We report high survivorship seemingly unaffected by fight time or physiological stress and recommend that circle hooks should be used to reduce physical damage to these sharks.

Exploiting seasonal habitat use of the common carp, Cyprinus carpio, in a lacustrine system for management and eradication.

The control of invasive species is a major challenge to the preservation of native ecosystems, both terrestrial and aquatic. A population of the invasive common carp, Cyprinus carpio, was detected in Lakes Sorell and Crescent, Tasmania, Australia, in the mid-1990s. Early detection allowed for the containment of their population to this lacustrine system. Radio-telemetry was subsequently used over a 5-year period to understand seasonal distribution of carp in relation to environmental parameters to guide efficient eradication strategies. The present study found that fish displayed increased mobility during spring–summer periods, moving into shallow habitat rich in macrophytes, particularly during years of high lake levels. During years of low lake levels, this pattern was altered with frequent use of a rocky ‘secondary’ habitat in Lake Sorell. During winter, carp congregated in deeper habitat in Lake Sorell, whereas no habitat-specific winter aggregations were found in Lake Crescent. The increased knowledge of spatio-temporal preferences of carp provided a basis for deploying barriers to facilitate the capture of fish and sabotage spawning events. The results have led to the eradication of carp from Lake Crescent and a significant reduction of their population in Lake Sorell.

Super Trawler Scuppered in Australian Fisheries Management Reform

ABSTRACT In response to an intense social media campaign led by international conservation groups, Green politicians, and recreational fishers, the Australian government imposed a moratorium on the operations of a large factory trawler. This moratorium overrode the governments own independent fisheries management process by making amendments to its key environmental legislation just days prior to the commencement of fishing by this vessel. Concurrently, the government announced a comprehensive review of Australias fisheries management legislation. Whereas science is usually deployed in support of conservation in natural resource conflicts, in this case science-based fisheries management advice took a back seat to vociferous protest by interest groups, perpetuated by the media (in particular social media), ultimately culminating in a contentious political decision.

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

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.

Long term trends of Hg uptake in resident fish from a polluted estuary.

Mercury contamination of fish is dependent upon a systems ability to transform inorganic Hg into biologically available forms; however, fish biometrics also play an important role. To assess long term trends in Hg concentrations in sand flathead (Platycephalus bassensis) a polynomial model, corrected for fish length, was used to evaluate temporal trends and spatial variability, while growth rates were estimated using the Von Bertalanffy length-at-age model. Hg concentrations showed no decrease over time, and generally remained near recommended consumption levels (0.5 mg kg(-1)). Previously reported spatial differences in Hg concentrations were not supported by the data once the models were corrected for fish length. Growth rate variation accounted for a large part of the previously published spatial differences. These results suggest that inclusion of fish biometrics is necessary to facilitate an accurate interpretation of spatial and temporal trends of contaminant concentrations in long term estuarine and marine monitoring programs.

Southernmost records of two Seriola species in an Australian ocean-warming hotspot

Changes in marine species distributions in response to climate warming are being observed globally. However, there is great variation in the magnitude and rate of species responses. South-eastern Australia represents a global hotspot for ocean warming and, subsequently, numerous poleward extensions in marine species distributions are evident within the region. We report on two species of Carangid not previously found in this region, recorded through photo-verified observations by citizen scientists. This includes the first record of Amberjack (Seriola dumerili) in eastern Tasmania and an extension of the previously most southern reported observation of a similarly mobile congener, the Yellowtail kingfish (Seriola lalandi) along south-eastern Tasmania. Out-of-range observations may simply represent vagrant individuals; however, there is also evidence that they are often indicators of future colonisation potential. Moreover, the observations presented here are potentially representative of a range of climate-driven changes to marine biodiversity in this region and highlight the utility of community observations in acting as an effective early-warning system for reporting changes in the marine environment. Early detection and reporting of distributional changes are important for proactive environmental management, and is enhanced by establishing an informed community and mechanisms for conveying these observations to science and management authorities.

Changing windows of opportunity: past and future climate-driven shifts in temporal persistence of kingfish ( Seriola lalandi ) oceanographic habitat within south-eastern Australian bioregions

Climate-driven shifts in species distributions are occurring rapidly within marine systems and are predicted to continue under climate change. To effectively adapt, marine resource users require information relevant to their activities at decision-making timescales. We model oceanographic habitat suitability for kingfish (Seriola lalandi) from southeastern Australia using multiple environmental variables at monthly time steps over the period 1996–2040. Habitat predictions were used to quantify the temporal persistence (months per year) of suitable oceanographic habitat within six coastal bioregions. A decline in temporal habitat persistence is predicted for the northernmost (equatorward) bioregion, whereas increases are predicted for the three southernmost (poleward) bioregions. We suggest that temporal habitat persistence is an important metric for climate change adaptation because it provides fishery-relevant information. Our methods demonstrate how novel metrics relevant to climate adaptation can be derived from predictions of species’ environmental habitats, and are appropriate for the management of fisheries resources and protection of high conservation value species under future climate change.