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Terns and noddies (subfamily Sterninae), comprising almost 15% of all seabird species, are largely piscivorous predators found from temperate to tropical regions in both coastal and pelagic systems. The largest species, the Caspian Tern (Hydroprogne caspia) has a cosmopolitan distribution, but despite this they are largely understudied, especially the finer-scale patterns of their distribution, abundance and foraging ecology throughout non-breeding periods. In south-western Australia, most H. caspia populations are restricted to two or three pairs, except for a large group of approximately 120 birds that breed annually on Penguin Island, Shoalwater Bay. This study investigated the foraging ecology of H. caspia over the first five months of their non-breeding season, from October 2018 to February 2019 on the Ramsar-listed Peel-Harvey Estuary. A single overnight roosting site for H. caspia was identified on the Estuary where a maximum of 147 birds were recorded in mid-February 2019. Tern foraging activity was concentrated at six main areas across the estuary, although tern counts and foraging activity varied between these areas, and foraging activity also differed significantly with time of day throughout the study period – it was greatest in the morning block. Overall, H. caspia were recorded taking 17 prey species (16 fish and one crustacean) on the Estuary, the most common being whitings (Sillaginidae), mullets (Mugilidae) and Eight-lined Trumpeter (Pelates octolineatus), comprising 35.0%, 33.9% and 14.4% respectively of their observed catch. The results of this study highlight the significance of the Peel-Harvey Estuary for the conservation of H. caspia in south-western Australia and the connectivity between the birds on the Estuary in the non-breeding period and those on Penguin Island during the breeding season. In addition, H. caspia appear to be strong candidates as biological indicators of Estuary health. The results of this study provide a basis for an ongoi

The study of ocean sunfishes has for decades been practically synonymous with the study of Mola mola, recently listed as ‘vulnerable’ on a global scale by the International Union for Conservation of Nature. The concerns are high levels of fisheries bycatch worldwide, however sunfish bycatch is rarely identified to species level anywhere, perhaps as a long legacy of taxonomic confusion in the sunfish taxonomy has rendered identification to species level challenging. This includes the Australian and New Zealand longline fisheries, where sunfishes are listed at “High Risk” due to data deficiency. In the popular sunfish SCUBA dive tourism off Bali, Indonesia, another type of anthropogenic pressure is manifested through diver crowding, preventing sunfish from interacting with cleaner-fish on the local reefs. The consequences are difficult to gauge due to a paucity of information on this highly seasonal phenomenon, but have motivated discussions of sunfish protection by Indonesian authorities. In this study, the species identities and zoogeographies of the little studied sunfishes in Australia and New Zealand were explored through biopsy sampling in the longline fisheries, and by reviewing museum collections across both countries. Specimen IDs were established phylogenetically and/or morphologically. Combined, the results revealed a new species of ocean sunfish, Mola tecta, which was diagnosed and described. Furthermore, the results showed that three large species of sunfish dominate the tropical, subtropical/warmtemperate and cold-temperate waters of Australia and New Zealand; Masturus lanceolatus, Mola alexandrini and Mola tecta, respectively. Mola mola appears to be rare. These results imply that the long-term fisheries observer sunfish bycatch data from both countries consists of a mix of species. Bycatch rate analyses within four fishing grounds sub-areas, each presumably dominated by one species of sunfish, did not reveal downwards trends over the 10 - 12 year perio

Migrations are key events in the annual life cycle for many animal species, including baleen whales. Despite having some of the longest migrations among mammals, relatively little is known about what triggers migration behaviour in baleen whales, and how intrinsic and extrinsic factors influence the timing of migrations. This study investigated the timing of migration in southern right whales (Eubalaena australis) and whether the probability of departure of individuals from winter breeding and calving grounds is determined by intrinsic (maternal body condition and calf size) or extrinsic variables (day length, temperature). Unmanned aerial vehicles were used to record data on the body size (length and width) of right whale mother and calves between the June 24 and September 25, 2016, providing repeated measurements of 40 mother-calf pairs. I used the time interval between sightings of individuals to determine the departure date of whales from the breeding grounds. Generalised linear models were used to determine which variable (maternal body condition, calf size, day length and sea surface temperature) was the best predictor of the departure time of the whales from the breeding grounds. Diurnal period was found to be the best predictor of migration for southern right whales, followed by calf size (i.e. body volume and length), sea surface temperature and maternal body condition. Hence it seems like migration in this population of right whales is determined by calves reaching a large enough body size to facilitate migration, rather than mothers pushing themselves energetically to their lower limit. Apart from improving our understanding of migratory behaviour in large whales, the findings of this study will help determine residency times of southern right whales on their breeding and calving grounds, which can be used to identify key times for protection (e.g. temporary exclusion periods for fisheries) during the winter breeding and calving season.

This project will review information and methodologies for evaluating how small-scale fisheries and aquaculture contribute to household livelihoods in Indonesian coastal communities and review the roles of women in small-scale fisheries. It will also investigate cases where attempts have been made to enhance the livelihoods of small-scale fisheries communities by strengthening or diversifying existing livelihoods or introducing alternative ones. The project will evaluate the effectiveness of initiatives to enhance small-scale fisheries livelihoods and their effect on women. Small-scale fisheries contribute to food security, alleviate poverty and prevent malnutrition in the developing world. 90% of people involved in capture fisheries are part of small-scale fisheries. The number of women involved in Indonesian small-scale fisheries and aquaculture is unknown, but may be up to 50% or more of the people engaged in Indonesian fisheries, based on estimates from comparable fisheries in Africa. This research will study how small-scale fisheries and aquaculture enhance coastal livelihoods, and the opportunities (and constraints) in developing livelihood improvement strategies for coastal communities involved in small-scale fisheries.

This study is the first to describe aspects of reproductive and larval biology required for aquaculture-based enhancement of the Western School Prawn Metapenaeus dalli (Racek, 1957), in south-western Australia. Biological and environmental factors influencing the reproductive dynamics were investigated in a three year study of the population in the Swan-Canning Estuary. Estimates of total population fecundity were made for the first time, based on detailed histological studies of ovarian development. The morphology of different stages of larval development was described to inform subsequent larval rearing trials to investigate their physico-chemical and feeding requirements for large-scale production. Morphological analysis of ovarian development in M. dalli showed that maturation occurs in five stages i.e. immature, early maturing, late maturing, mature and post spawning. Histological methods developed in this study increased the precision of measuring oocyte size by 17 to 40%, for all cell types measured and provided the basis to developing a novel histological technique for quantifying oocyte composition. A study of the reproductive dynamics of female M. dalli in the Swan-Canning Estuary showed that reproduction occurred between November and March, when water temperatures were > 17 ˚C, salinities > 25 ‰ and stratification (bottom – surface salinity) < 3 ‰. Densities of gravid M. dalli were highly seasonal, peaking in November each year when 0+ females matured (19 mm CL), and were highest within the Lower Canning Estuary. Knowledge from the histological studies of oogenesis was used to estimate individual fecundity ranged from 34,000 (18.1 mm CL) to 132,000 ova (27.1 mm CL). This information, which combined with the data on size at maturity and macroscopic ovarian condition, was used to estimate the total egg production by M. dalli in the estuary. Egg production peaked in December/January and differed among the three years. Results suggest that closing fishing bet

Targeted fisheries for shark fin are one of the main causes driving the unprecedented decline of shark populations. Despite widespread concern for sharks and calls for their conservation, a lack of data often delays regulatory action for shark fisheries. For over two decades, Indonesia has reported higher average shark landings than any other nation, but information on its shark fisheries is extremely limited. The eastern Indonesian shark fishery, here defined to extend from East Nusa Tenggara to Papua, is virtually data-less and beyond the focus of central fisheries agencies. The lack of essential information, including the location of fishing grounds, catch composition and fishing effort, as well as biological and socio-economic characteristics of harvested species and the livelihoods they support, impedes the development of effective fisheries management in this region. This thesis uses a transdisciplinary approach to address these knowledge gaps. My findings are based on extensive field studies in three remote coastal communities with fishing grounds in the Seram, Halmahera, Aru-Arafura and Timor Seas. During my stay in each community, I involved fishers in collecting and interpreting fishery data, studied local fishing practices and patron-fisher relationships, and conducted in-depth interviews with fishers, shark fin bosses and other community members. This allowed me to portray the fishery from biological, economic and sociological perspectives (Chapter 2), and to investigate the reliability and accuracy of fisher data. The description of a range extension for the vulnerable fossil shark Hemipristis elongata demonstrates that fisher’s species identifications are not only reliable, but can lead to serendipitous findings on species occurrences (Chapter 3). Expanding on the application of fisher data, I then use diverse data sources to provide the first sustainability assessment of the eastern Indonesian shark fishery (Chapter 4). The fishery targets over 40 spe

Coastal and estuarine systems worldwide suffer from a range of anthropogenic influences, such as eutrophication and high fishing pressure. Portunid crabs are abundant in such systems globally and the magnitude of degradation and variations in environmental conditions can influence the dynamics of the fisheries they support. This Thesis investigated two major components relating to portunid crabs: (i) a review and summary of the literature on portunid biology and behaviour and an assessment of how they vary among species and regions (Chapter 2); and (ii) a study of the dietary composition of the Blue Swimmer Crab Portunus armatus and how it varies among two estuaries and a coastal embayment and seasons in temperate south-western Australia (Chapter 3). Portunids are highly fecund, fast growing, short-lived species, with high natural mortalities and are opportunistic predators. These characteristics vary among species, but also between different populations. The dynamics of portunid fisheries are therefore reliant not only on the biology of the fished species but also on the local environmental conditions, through their influence on portunid biology. These factors need to be taken into consideration by fishery managers. The diet of P. armatus is dominated by shelled molluscs, polychaetes and small crustaceans. Dietary composition varied significantly between the Peel-Harvey and Swan-Canning estuaries and three sites (habitats) within Cockburn Sound and this variation was greater in magnitude than the seasonal variation. The diet of crabs in the Peel-Harvey Estuary was distinct from that of crabs in the Swan-Canning Estuary and Cockburn Sound because of greater consumptions of the bivalves A. semen and S. trigonella and fragments of their shells in the former. Differences in the dietary composition follow closely the known variation in the benthic macroinvertebrates assemblages, i.e. the prey availability, between systems and sites. Seasonal variation was greater in the

The taxonomy of the ocean sunfishes (Molidae) has a complicated history. Currently, three genera and four species are recognized, including two in the genus Mola (M. mola and M. ramsayi). In 2009, a genetic study revealed a potential third species, Mola species C, in Southeast Australian waters. Concentrating on this region, we obtained samples and morphological data from 27 Mola sp. C specimens, genetically confirmed the existence of this species (mtDNA D-loop and cytochrome c oxidase 1), and established its morphology across a size spectrum of 50–242 cm total length. Mola sp. C is diagnosed by clavus meristics [15–17 fin rays (13–15 principal, 2 minor), 5–7 ossicles, paraxial ossicles separate], clavus morphology (prominent smooth band back-fold, rounded clavus edge with an indent), and body scale morphology (raised conical midpoints, non-branching). This species does not develop a protruding snout, or swollen dorso- or ventrolateral ridges. Body proportions remain similar with growth. A review of the historic literature revealed that Mola sp. C is a new, hitherto undescribed species, M. tecta, which we describe and diagnose, and that it is the first proposed addition to the genus Mola in 125 years. Its core distribution is likely in the temperate waters of the Southern Hemisphere.

Aquaculture-based enhancement, a method of releasing cultured organisms into the wild to boost fishery productivity, is becoming increasingly popular as a management option for restoring depleted fish stocks and increasing fishery yields. In the first section of this Thesis, I review and synthesise how the effectiveness of aquaculture-based enhancements can be optimised to maximise survival of released individuals. Two specific areas were identified that have a major influence on the short-term survival of released animals (i) “training” or acclimation in the hatchery to conditions in natural systems, e.g. habitats, water flows, natural (live) food and the smell and sight of predators through predator avoidance training and (ii) the development of a sound release strategy, involving the selection of site, time and size at release. The objective of the second section of this Thesis was to create a tool to inform the development of an optimal release strategy, by evaluating site selection and time of release for the release of post-larval Western School Prawns Metapenaeus dalli in the Swan-Canning Estuary. This was achieved by developing the Survival-Maximisation-At-Release-Tool (SMART), a quantitative tool that collated factors and variables considered to influence the survival of released M. dalli at potential sites around the estuary to determine a SMART score (0-100) for each potential release site and time (Month, Year, Day/Night). Statistical analyses on the resultant SMART scores determined that region of release was the most influential factor for the survival of released M. dalli, followed by year and then month. Due to the wide range of values for the salinity variable and sediment composition and predation factors among sites and time, these had the most influence on overall SMART score. Across the 16 nearshore sites sampled in five consecutive months in each of three years, the optimal site of release was at Deep Water Point in the Lower Canning Estuary du

Little information is available on the contribution of macroalgae to the food web of the Ningaloo lagoon and its importance in the diets of fish associated with it. This information is important for understanding potential trophic flows from macroalgae to juvenile fish and provides the fundamental data for constructing ecosystem models. In my Honours research, I have examined: the significance of macroalgae, its associated epibionts and infauna in the diets of juvenile and subadult fish in the Ningaloo lagoon, focussing on: 1. the significance of macroalgae in the diets of juvenile fish and how this varies between summer (February) and winter (July) (Chapter 3); and 2. the development and use of an Ecopath with Ecosim ecosystem model to assess trophic flows of macroalgae to functional fish groups (Chapter 4). Fish were sampled in macroalgal beds by a variety of techniques (herding into fence nets by SCUBA, hand spear, and rod and line fishing) in February and July, 2015. A total of 181 fish were caught representing 11 species, with six species caught in both months. Stomach contents were identified to the lowest taxonomic resolution possible and the percent volume of items recorded. Multivariate analyses were used to identify guilds (species with similar diets), and to assess differences in diets between February and July. The results showed that: fleshy macroalgae (e.g. Sargassum spp.) were not as important as filamentous algae to the diets of the juveniles of two nominally herbivorous fish species in February, but became more important in July. Macroalgae were not an important component in the diets of juvenile Lethrinidae, Lutjanidae, or Mullidae, though the infauna associated with the macroalgal beds was important in the diets. Analysis of feeding specialisation found that the smaller size classes of fish in February had a narrower trophic width and a more specialised feeding strategy than larger bodied fish of the same species in July. At this time, fish tended

The incidental capture of cetaceans in fisheries threatens several species with extinction and represents a global conservation challenge. In order to assess the impacts of bycatch on dolphins in a north-western Australian trawl fishery, I (i) examined bycatch reported in skippers’ logbooks and independent observer data; (ii) applied genetic methods to estimate dolphin population structure and connectivity; and (iii) conducted an aerial survey to estimate dolphin abundance across the fishery, simultaneously undertaking boat-based photo-identification to infer fidelity to the fishery. From 2003-2009, between 180 and 366 dolphins were caught across all management areas, depths and seasons. Independent observers reported more than double the dolphin bycatch reported in skippers’ logbooks. Significant predictors of dolphin bycatch were fishing vessel, time-of-day and whether nets included Bycatch Reduction Devices (BRDs). Genetic evidence showed one panmictic population of trawler-associated common bottlenose dolphins (Tursiops truncatus), but isolation from all adjacent, coastal populations of Indo-Pacific bottlenose dolphins (T. aduncus). Abundance was estimated at 2,000-3,000 T. truncatus across 25,880 km2. While the lack of correction factors for availability bias mean this is likely an underestimate, it is lower than previously thought. Trawler-associated individuals were photographically and genetically matched over periods of days to years. Recent skippers’ logbook data suggest dolphin bycatch rates have increased since the BRDs were introduced. These results indicate that (i) only a considerable reduction in trawling effort is likely to reduce dolphin bycatch; (ii) the impacted population does not recruit from the adjacent coastal populations; and (iii) the number of dolphins interacting with trawlers is fewer than expected. The chronic bycatch of this protected species may affect the dolphin population’s conservation status. As a consequence, the classification

Coastal dolphin populations are exposed to non-consumptive human activities that can pose conservation challenges. Consequently, effective management strategies, using rigorous scientific assessments of exposed populations, are needed to mitigate any potential negative impacts of these activities. To inform management decisions for the conservation of the Hawaii Island spinner dolphin (Stenella longirostris) stock, I: (i) estimated abundance and survival rates; (ii) measured the effectiveness of various sampling scenarios to detect changes in abundance; (iii) identified important spinner dolphin resting habitats; and (iv) measured cumulative exposure to human activities. Between September 2010 and March 2013, boat-based and land-based sampling was undertaken to collect dolphin photo-identification, group behaviour and acoustic data from both inside and outside four important spinner dolphin resting bays on the Kona Coast of Hawaii Island. Between years, independent survival rate estimates were similar (0.97 ± 0.05 SE), and abundance estimates of 631 (95% CI 524-761) and 668 (95% CI 556-801; CV =0.09) were very consistent. At this precision, and with 95% power and a monitoring interval of three years, a 5% change in abundance would not be detected for 12 years. I documented that should resting spinner dolphins be displaced from resting bays, they are unlikely to engage in rest behaviour elsewhere. When resting inside bays, dolphins were most likely to rest between 10:00-14:00, and over sandy substrates. Individual spinner dolphins spent between 49.5% and 69.4% of daytime resting (mean = 61.7%). Dolphins were chronically and repeatedly exposed to human activities during daytime hours (> 82% of time), with a median duration of only ten min between interactions. The short interval between interactions may prevent recovery from disturbance and deprive individuals of rest and change their sleep state from “deep” to “light”. Rest deprivation and the disruption of sleep can

Background New Zealand (NZ) sea lions (Phocarctos hookeri) are one of the rarest otariids (i.e. eared seals) in the world. They are listed as "Nationally Critical" under NZ conservation policy and are recognized as "Vulnerable" in the International Union for the Conservation of Nature's (IUCN) Red List of Threatened Species. Currently, the Auckland Islands population of NZ sea lions is in decline and facing persistent threats from commercial trawl fisheries. This population is at-risk of fisheries interactions which may result in bycatch and/or resource competition, particularly with the Southern Arrow squid (Nototodarus sloani) trawl fishery (referred to as 'SQU6T' in New Zealand fisheries management policy). Bycatch of NZ sea lions in the Southern Arrow squid trawl fishery has been historically biased towards females, and resource limitation from competition with this fishery may also be influencing female fecundity. This female-bias in fishery interactions appears to be a result of sex differences in habitat use among adult NZ sea lions. Recent research suggests that sex differences in habitat use may also extend to juvenile age classes. Juvenile sea lions are particularly susceptible to fisheries-induced resource competition because of: (a) age- and size-specific constraints affecting juvenile foraging success; and possibly (b) greater risk of capture in trawling gear due to weaker swimming and diving capabilities, and inexperience. Understanding juvenile NZ sea lion habitat use in relation to the SQU6T trawl fishery is therefore essential to assessing and managing fisheries interactions. Thesis aims The aims of this Thesis are to: (1) identify discrete behaviours from juvenile NZ sea lion dive data through the development and application of a statistical modelling approach, known as a state-space model (SSM); (2) describe the spatio-temporal features of the vertical distribution of those behaviours, and examine how they are influenced by biological factors; and

Non-indigenous species can have significant deleterious impacts on the ecosystems in which they become established. Following the recent establishment of the Striped Sandgoby Acentrogobius pflaumii in the Swan-Canning Estuary, south-western Australia, a study was initiated to determine its spatial and temporal distribution and biological characteristics. Although A. pflaumii was not recorded in the coarse sandy sediment present in the nearshore, shallow waters of the estuary, substantial numbers were recorded on soft muddy sediments in the deeper waters, where it comprised 55% of the total number of gobies. While A. pflaumii dominated the gobiid fauna in Lower Melville Water (~98%), its contributions declined progressively upstream, indicating a preference for waters with a salinity close to that of full strength sea water. Size and age compositions determined that the oldest individual was 3.9 years old and 89 mm in total length, but that the population is dominanted by 1+ individuals. Population mortality and turn-over rates are therefore likely to be very high. Both males and females attained > 87% of their asymptotic lengths (L∞) of 74.9 and 69.3 mm, respectively, during the first year of life, which is characteristic of smaller, shorter-lived species of fish. The results from gonadosomatic indices and the histological examination of gonads suggest that A. pflaumii is able to spawn throughout most of the year, with a peak from November to February. The presence of mature, spawning and depleted gonads in A. pflaumii suggests that this species spawns within the Swan-Canning Estuary. Acentrogobius pflaumii can be thus considered an estuarine & marine species like Favonigobius lateralis. As A. pflaumii attains high densities over a relatively large part of the estuary and can breed within the system, it is likely to be a permanent resident and further work is needed to determine its impact on the native gobiid fauna.

Although they support many millions of people, the vast majority of the world’s fisheries are small-scale and data-poor, and without the resources or data systems needed for comprehensive stock assessments. There is strong evidence that unmanaged fisheries are a recipe for disaster, with over-exploitation of the stock almost inevitable. Additionally, it is increasingly recognised that the spatial scale of the stocks of many marine species is much smaller than previously thought, which adds another layer of cost to the stock assessment process, as the cost of collecting and analysing such fine-scale data is prohibitive. The overall aim of this thesis was to develop and test novel methods of stock assessment for data-poor and small-scale fisheries, based on the basic biological characteristics of the exploited species. Knowledge of the basic biological parameters of fish stocks, such as the natural mortality rate (M), the growth parameters (commonly described by the von Bertalanffy equation, L¥ and k), and the length at maturity (Lm), is important for many stock assessment methodologies. However, collecting such information is costly, and usually requires sophisticated ageing studies. I conducted a meta-analysis of over 120 marine species, from a range of taxa including teleosts, chondrichthyans, mammals and invertebrates, and examined the variation and patterns in the life-history ratios, and the relationships between size and spawning potential (Chapter 2). These patterns were examined by standardising the age and size of each species so that the relationship between size and spawning-per-recruit for a large range of diverse species could be compared on the same scale. This meta-analysis demonstrated that species that are often considered to be quite different, essentially have the same life-history strategy when viewed on the same relative scale. For example, tuna can be considered as ‘larger, slower’, anchovies, while prawns are ‘smaller, faster’ versions of fish.

The population dynamics of restocking involves trade-offs between different release scenarios and the conservation of wild stocks and evaluating these trade-offs is an important component of restocking programs. This study used length frequency data and mixture analysis to estimate growth, mortality and reproductive parameters for the western school prawn Metapenaeus dalli in the Swan-Canning Estuary. These biological parameters provide the first quantitative estimates of growth and mortality for M. dalli and were used as inputs into a bioeconomic model developed with the EnhanceFish software used to evaluate the effectiveness of different stocking levels and sizes-at-release. This research had two primary objectives: 1) To use the data from a spatially and temporally comprehensive sampling program for M. dalli in the Swan-Canning Estuary to determine the biological parameters for growth, mortality and size at maturity; and 2) Develop a bioeconomic model using the EnhanceFish software to evaluate the potential increase in population biomass from restocking with different numbers of released prawns and different sizes-at-release. Monthly length frequency data demonstrated that M. dalli exhibits strong seasonal growth and reproductive cycles. Growth was estimated using Somers (1988) seasonal adaptation of the von Bertalanffy growth curve. This analysis demonstrated that females grew significantly larger (L∞ = 33.72 mm CL, k = 1.06) than males (L∞ = 24.20 mm CL, k = 0.97). Gravid females, or females carrying a spermatophore, were only found between November and April, when surface and bottom water temperatures were between 20 and 27 ºC. Pauly’s (1983a, b, 1984) seasonal catch-curve revealed little difference in total instantaneous mortality between female and males (Z = 0.048 and 0.047 week-1, respectively). Whereas Pauly’s (1990) non- seasonal catch-curve showed a larger range in mortality between females (0.067 week-1) and males and (0.052 week-1). Since recreational

The composition of the sediment is known to influence the distribution of estuarine biota, as it can provide both habitat and, either directly or indirectly, a food source for invertebrates and fish. While the flora and fauna of estuaries are often well studied, less focus is typically placed on elucidating the composition of the sediment. Thus, this study characterised and classified the sediments of the nearshore and offshore waters of the Swan-Canning Estuary. Multivariate statistical analyses indicated that the composition of the sediment from 20 nearshore and 16 offshore sites, in two seasons, differed significantly among water depths, seasons and sites, with seasonal changes only being detected in offshore waters. Differences in sediment composition between water depths were particularly marked due to higher contributions of particulate organic matter and finer inorganic grain sizes present in offshore waters. A quantitative classification of the sediment composition using the CLUSTER and SIMPROF procedures identified 11 significantly different sediment types, which were used to produce a comprehensive map of the sediment types present within the Swan- Canning Estuary. A decision tree was then constructed, which provides a set of quantitative thresholds to allow for the sediment type to which any new sample (site) from within the estuary belongs to be identified. As well as a marked decline in the abundance of the Western School Prawn (Metapenaeus dalli) in the Swan-Canning Estuary since the 1980s, anecdotal evidence from recreational fishers also indicated that there had been a spatial shift in their distribution within the estuary, away from the upper reaches. In the past, migration into these areas was thought to be driven by an increase in salinity. Declining rainfall has resulted in this change in salinity occurring earlier and it is hypothesised that a change in sediment composition may be responsible for the shift in the abundance of M. dalli away from

Despite their prominence as species of great interest and conservation significance, currently our understanding of shark movement patterns and their ecological role as predators on small Odontocete populations is far from complete. The first component of my research investigated the movement patterns of the four main commercial species (sandbar, Carcharhinus plumbeus; dusky, Carcharhinus obscurus; whiskery, Furgaleus macki; gummy, Mustelus antarcticus) and several species occasionally caught off the coast of Western Australia (Chapter 2). I analysed long-term (1994 to 2013), conventional tagging data collected by the Department of Fisheries, Western Australia to provide a detailed account of observed movement patterns. The second component of my research investigated the predatory role of sharks on bottlenose dolphins (Tursiops aduncus) off Bunbury, Western Australia (Chapter 3). I examined the prevalence of shark bites on systematically photographed dolphins over an eight year period (2007 to 2014). I also attempted to identify the shark species responsible for the attacks by seeking the expert opinions of three independent reviewers on the bite marks. The analyses of movement patterns from the long-term tagging data (Chapter 2) found mean displacements of < 250 km for the four main commercial species. However, occasional displacements of more than 2,000 km were also observed for all four species. Displacement was positively correlated with time at liberty, size (fork length) and release condition. The swimming speed varied significantly between species, with faster movements observed for larger Carcharhinid sharks. Furthermore, significant differences in sex ratios at release and recapture were observed for gummy and whiskery sharks. A significantly higher proportion of females were released and recaptured for both species. Although, fork length was found to significantly vary for non-recaptured and recaptured sandbar and dusky sharks, results from the analyses w

The incidental capture of unwanted species along with target species is a common and wasteful aspect of many fisheries. Trawl fisheries in particular have a high rate of incidental capture, or bycatch, due to the low selectivity of their nets. The bycatch of protected, endangered and threatened species is of particular concern and poses significant challenges for the ecologically sustainable management of wild capture fisheries. In the Pilbara Fish Trawl Interim Managed Fishery (PFTIMF), approximately 50 common bottlenose dolphins (Tursiops truncatus) are reportedly caught incidentally every year. Failure to adequately address the bycatch of this protected species has prevented the PFTIMF from attaining ‘Managed Fishery’ status. In this study, I analysed 195 hours of underwater video footage recorded inside active trawl nets in the PFTIMF to address the following aims: Chapter 2: a) examine and describe fine-scale dolphin behaviour in and around the trawl nets, and b) discuss the implications of these interactions for the reduction of dolphin bycatch in the fishery; and Chapter 3: a) assess the efficacy of two bycatch reduction devices (BRDs) at reducing the catch of dolphins and five other taxonomic groups of concern, and b) provide an estimate of the number of wildlife species caught annually in the PFTIMF. Dolphins frequently interacted with active trawl nets, and were recorded inside and outside the net for up to 98% and 99% of the trawl duration, respectively. Inside the net, dolphins exhibited a significantly higher proportion of foraging behaviours than outside the net, which may indicate that dolphins enter trawl nets because they provide a concentrated food source. Outside the net, dolphins most frequently engaged in ‘trampolining’, whereby they bounced on the upper surface of the net, often rubbing different body parts on the mesh. It thus appears that dolphins are motivated by several factors to approach and interact with active trawl nets. Most of the 29

The fishery for the western rock lobster (Panulirus cygnus) is one of the largest and most valuable single species fishery in Australia. However, few studies have examined the behaviour of this species and its interaction with traps (known as ‘pots’) in either the field or laboratory. The life cycle of the lobster incorporates a migratory phase (known as the ‘whites’), in which sub-adult (4 – 5 year old) P. cygnus moult into a creamy pale pink exoskeleton in November and migrate offshore to breed and return to the more sedentary ‘red’ phase. In this study I used direct in situ video observations of P. cygnus to investigate the effect of the migratory phase on trap behaviour. I also used video observations in the laboratory to investigate whether the presence of a large lobster in the trap affected the behaviour of smaller individuals outside the trap. Proportionally, the behaviour of the white migratory lobsters around a trap did not differ significantly from that of lobsters in the more sedentary red phase. However, there were a significantly higher number of observations during the whites phase (n = 224) than during the reds (n = 39). The difference is likely to be a reflection on the performance of the camera trap in the reds phase as there was a significant disparity between the catch rate of the camera trap and three standard control traps and as such, further replicates in a reds phase are required to increase the robustness of this study. On a few occasions, lobsters were observed to exit the trap through the neck entrance, however, a much higher proportion of lobsters in both phases escaped through the escape gap. Laboratory experiments were performed to observe the behaviour of small legal-sized P. cygnus (76 > 85 mm carapace length [CL]) when approaching a trap containing a large lobster (> 98 mm CL). The laboratory observations found that small lobsters of both sexes spent significantly more time on and around a trap containing a large female than one con