ORCID Profile
0000-0001-9670-5854
Current Organisation
University of Tasmania
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Publisher: Oxford University Press (OUP)
Date: 28-05-2015
Abstract: Early post-settlement mortality is one of the main processes determining distribution and abundance patterns of marine benthic invertebrates. Most scallops have an attached phase as spat before they release the byssus and move onto the soft sediments. Thus, spat differ from other stages of life in their use of microhabitat, lack of mobility, and therefore in their vulnerability to mortality processes such as predation. However, the contribution of predation to explain levels of mortality experienced by spat and early juvenile scallops is unknown. Complex habitats such as seagrasses and algae provide a substrate upon which spat can attach and might confer an advantage as a refuge from predation. This study investigates the contribution of early post-settlement predation on abundance of Pecten fumatus and determines the role of the algae Hincksia sordida as a refuge from predation. Data were collected using field observations, a predator exclusion experiment, and tethering techniques. Mortality of up to 85% during the first weeks after settlement appeared to have prevented the establishment of an adult population at our study site. Mats of the macroalgae H. sordida provided a settlement substrate for P. fumatus spat. However, increased algal biomass did not provide greater protection from predation to juvenile scallops than lower algal biomass. Our study suggests that prey survival in submersed vegetation is likely to be dynamic among years, and affected by prey behaviour and density as well as the characteristics of the submerged vegetation.
Publisher: Canadian Science Publishing
Date: 08-2013
Abstract: Changes to the global climate are driving alterations to boundary current-influenced marine ecosystems. The diet of a pelagic teleost, Arripis trutta, was examined in the East Australian Current (EAC)-dominated coastal waters of southeastern (SE) Australia. The diet of A. trutta was dominated by pelagic baitfish, primarily Australian sardine (Sardinops sagax) and scads (Trachurus spp.). Diet varied substantially with both latitude and season linked to variability in the distribution and abundance of key prey species. An ontogenetic diet shift occurred, with crustaceans and polychaetes making up a large proportion of the diet of small fish compared with the dominance of baitfish at larger sizes. The diet of A. trutta has undergone a dramatic shift from one dominated by krill (Nyctiphanes australis) historically to baitfish today. This change is consistent with a well-documented regime shift caused by the increasing intensity of the EAC on coastal SE Australian waters. Understanding the temporal dynamics of this ecosystem is crucial for management of coastal fisheries and also for understanding the impacts of climate change on boundary current-dominated marine ecosystems worldwide.
Publisher: CSIRO Publishing
Date: 1995
DOI: 10.1071/MF9950819
Abstract: An egg survey was carried out in 1992 to estimate the biomass of the orange roughy stock that spawns off north-eastern Tasmania. Spawning occurs at depths of 700-1000 m around a single seamount from early July through early August. Orange roughy have determinate fecundity, and their fecundity and the depth distribution and development rate of the eggs are described elsewhere. A random stratified survey was designed for a limited area around the spawning site in order to s le the eggs fully during their first day of development. The eggs were s led with vertical tows from 1000 m to the surface. There was no evidence of significant mortality or other egg loss during the first day after spawning, when the eggs are mostly below 400 m. Subsequently, egg numbers declined rapidly at an instantaneous loss rate of 0.036 h-1, primariIy through advection out of the survey area. The estimated biomass of spawning fish was 27 445 t. From the proportion of non-spawning fish in the population (29% of females and 10% of males) and estimated catch of spawners, total mid-season stock biomass in 1992 was estimated to be 34 593 t with a coefficient of variation (CV) of 47%. A bootstrap estimate of the variance indicated a somewhat lower CV of 41%. The point source of spawning activity appears to give rise to a highly patchy egg distribution, which results in the high variance of the biomass estimate. From the catch history of the fishery, virgin biomass of the stock was estimated to be approximately 96 900 t, and the stock was at 28% of virgin biomass at the end of season. An acoustic survey of the spawning orange roughy provided a similar estimate of stock size. The acoustic survey had greatly reduced statistical confidence limits (CV = 6%) but far greater non-statistical sources of uncertainty, i.e. the species composition of acoustic targets and the target strength of these species.
Publisher: Wiley
Date: 07-01-2013
Publisher: Wiley
Date: 02-2019
DOI: 10.1002/PAN3.9
Publisher: Inter-Research Science Center
Date: 2005
DOI: 10.3354/MEPS299167
Publisher: Wiley
Date: 23-03-2021
DOI: 10.1002/AQC.3579
Abstract: The Maugean skate, Zearaja maugeana , is endemic to two isolated western Tasmanian (Australia) estuaries. The species' persistence in one of these estuaries (Bathurst Harbour) is uncertain, while the other estuary (Macquarie Harbour), potentially the remaining stronghold for the species, is an anthropogenically impacted system. Key life‐history parameters were studied to inform conservation actions for this species. Reproductive information was obtained using non‐lethal methodologies, circulating concentrations of sex steroids and ultrasonography. Growth and age parameters were estimated based on vertebral sections from a small s le of in iduals. Females and males reached 870 and 760 mm total length, respectively. The species reached a maximum age of at least 10 years. Females and males attained 50% sexual maturity at 665 and 633 mm total length, respectively, probably maturing somewhere between four and six years of age. Females displayed an asynchronous, discontinuous reproductive cycle, being able to reproduce throughout the year, with a probable decline in reproductive activity during summer. No egg cases were observed in‐utero . Males produce sperm all year round, with a peak in testosterone production during spring–autumn. Conservation strategies for Z . maugeana will need to focus on reducing anthropogenic impacts on the environmental health, the primary impacts being altered river flows associated with the production of hydroelectricity and increased nutrient load associated with salmonid aquaculture. There is a need to better understand how reproductive success, egg survival and recruitment are affected by these environmental challenges if the future well‐being of this species is to be secured.
Publisher: Elsevier BV
Date: 05-2007
Publisher: Oxford University Press (OUP)
Date: 14-01-2022
Abstract: Recreational fishing (RF) is a popular pastime resulting in substantial fish mortality in many regions. Yet inclusion of RF in fishery harvest strategies is limited, because the sector's objectives are poorly understood, as are the data required to track their performance. To address this, we reviewed RF data sources available from a region of globally high participation (New South Wales [NSW], Australia) and evaluated their utility for RF-specific performance indicators within harvest strategies. We then linked these data sources to RF objectives they may be used to monitor. A total of 21 RF data sources were identified in NSW over the past two decades, spanning all major aquatic environments and 146 fished species. Numerous data sources were available to monitor ecological objectives, providing time-series and potential reference points for key indicators such as catch-per-unit-effort. Few data sources were available for social, economic, and institutional objectives, consistent with a global paucity of these data. We found that most social objectives of RF lie outside the scope of traditional harvest strategies, although some are linked to underlying ecological performance. Harvest strategy performance for RF will depend on the relative importance of social objectives and whether these can be achieved by controlling harvest.
Publisher: Oxford University Press (OUP)
Date: 2015
Publisher: Elsevier BV
Date: 07-2016
Publisher: Elsevier BV
Date: 02-2006
Publisher: Elsevier BV
Date: 08-2019
Publisher: CSIRO Publishing
Date: 2007
DOI: 10.1071/MF07137
Abstract: Banded morwong, Cheilodactylus spectabilis, a long-lived sedentary temperate reef fish, has undergone rapid changes in its growth and maturity characteristics along the east coast of Tasmania, Australia. Over a period of 10 years, growth of young males and females has consistently accelerated, such that in 2005, 3-year-old fish were up to 40 mm or 13% longer compared with 1996, and age at 50% maturity for females had declined from 4 to 3 years. The magnitude and speed of the observed changes were unexpected given the species’ longevity (maximum age of over 95 years). The underlying mechanisms for the changes remain unclear but density-dependent responses to changes in population size and age composition, possibly mediated through reduced competition for shelter and intra-specific interactions, may have been contributing factors. Increasing sea surface temperatures over part of the period of change does not appear to have been a major driver and a genetic response to fishing seems unlikely. Notwithstanding any uncertainty, C. spectabilis populations have become more productive in recent years, challenging the general approach towards stock assessment where life-history characteristics are assumed to remain stable across contrasting levels of stock abundance and environmental conditions.
Publisher: Wiley
Date: 02-2012
Publisher: Springer Science and Business Media LLC
Date: 08-09-2012
Publisher: Wiley
Date: 06-04-2011
DOI: 10.1111/J.1095-8649.2011.02959.X
Abstract: The influence of freshwater inflows and salinity on spawning success of black bream Acanthopagrus butcheri (Sparidae) was investigated over 2 years in a small estuary on the east coast of Tasmania, Australia. The in idual spawning seasons experienced quite different freshwater inflows 2004-2005 was characterized by low flows throughout the season whereas during 2005-2006 there were three relatively large discharge events in the first part of the season. Macroscopic gonad staging of adults was used to define the spawning season and daily increment analysis of otoliths from recently settled recruits was used to backcalculate spawning dates. Gonad staging indicated that adults were in spawning condition over a 3 to 4 month period during spring and summer. The timing and duration of successful spawning, however, differed markedly between years and was linked to the timing of freshwater inflows and salinity conditions, with successful spawning occurring during periods of low freshwater discharge and when salinities in the upper estuary were above c. 15. Growth rates of the recently settled recruits did not differ between years, nor did the timing of spawning within the season influence growth rates. While the latter finding was unexpected, especially given within season temperature variability, these results imply that by the onset of winter earlier spawned fish would be larger than later spawned in iduals, potentially conferring advantages for survival and competition for food. Climate change predictions for eastern Tasmania indicate a decrease in river flows in spring and an increase during summer, potentially increasing environmental variability between and within years, with implications for spawning success and subsequent recruitment.
Publisher: CSIRO Publishing
Date: 2017
DOI: 10.1071/MF17130
Abstract: Determining the dynamics of ecological communities following periods of anthropogenic change is critical to assessing the effectiveness of management strategies. Several coastal areas in south-eastern Australia were proclaimed shark refuge areas (SRAs) following overfishing of the school shark (Galeorhinus galeus) during the 1940s and 1950s. In conjunction with catch reduction measures, these areas provide spatial protection for juvenile G. galeus. In the present study, we compared recent (2012–14) and historic (1991–97) longline catch rates to determine whether young-of-year (YOY) and juvenile G. galeus continue to use these nursery areas (42°47′60.00″S, 147°30′0.00″E). Our data suggest that YOY abundances in the SRAs may have increased, or at least have remained stable, since the 1990s. Data from research fishing conducted from 1947 to 1956 showed that YOY abundance in the SRA correlated well with overall stock abundance in the past. If this relationship still holds, our longline data indicate that the stock may be showing signs of recovery. However, the present-day importance of the SRA to overall stock recruitment, as well as the relationship between YOY abundance in the SRA and stock health, need to be resolved before monitoring of YOY abundance in the SRA can be used as a fisheries-independent stock-assessment tool.
Publisher: Elsevier BV
Date: 07-2011
Publisher: Elsevier BV
Date: 03-2009
Publisher: Public Library of Science (PLoS)
Date: 18-11-2016
Publisher: Wiley
Date: 04-08-2023
DOI: 10.1111/FAF.12781
Abstract: Recreational fishing (RF) is a large yet undervalued component of fisheries globally. While progress has been made in monitoring, assessing, and managing the sector in isolation, integration of RF into the management of multi‐sector fisheries has been limited, particularly relative to the commercial sector. This marginalises recreational fishers and reduces the likelihood of achieving the sector's objectives and, more broadly, achieving fisheries sustainability. We examined the nature and extent of RF inclusion in harvest strategies (HSs) for marine fisheries across 15 regions in 11 nations to define the gap in inclusion that has developed between sectors. We focused on high‐income nations with a high level of RF governance and used a questionnaire to elicit expert knowledge on HSs due to the paucity of published documents. In total, 339 HSs were considered. We found that RF inclusion in HSs was more similar to the small‐scale sector (i.e., artisanal, cultural, or subsistence) than the commercial sector, with explicit operational objectives, data collection, performance indicators, reference points, and management controls lacking in many regions. Where specified, RF objectives focused on sustainability, economic value and catch allocation rather than directly relating to the recreational fishing experience. Conflicts with other sectors included competition with the commercial sector for limited resources, highlighting the importance of equitable resource allocation policies alongside HSs. We propose that RF be explicitly incorporated into HSs to ensure fisheries are ecologically, economically, and socially sustainable, and we recommend that fisheries organisations urgently review HSs for marine fisheries with a recreational component to close the harvest strategy gap among sectors.
Publisher: Elsevier BV
Date: 05-2016
Publisher: Springer Science and Business Media LLC
Date: 2016
Publisher: Oxford University Press (OUP)
Date: 08-05-2015
Abstract: Protecting essential habitats through the implementation of area closures has been recognized as a useful management tool for rebuilding overfished populations and minimizing habitat degradation. School shark (Galeorhinus galeus) have suffered significant stock declines in Australia however, recent stock assessments suggest the population may have stabilized and the protection of closed nursery areas has been identified as a key management strategy to rebuilding their numbers. Young-of-the-year (YOY) and juvenile G. galeus were acoustically tagged and monitored to determine ontogenetic differences in residency and seasonal use of an important protected nursery area (Shark Refuge Area or SRA) in southeastern Tasmania. Both YOY and juvenile G. galeus showed a distinct seasonal pattern of occurrence in the SRA with most departing the area during winter and only a small proportion of YOY (33%) and no juveniles returning the following spring, suggesting areas outside the SRA may also be important during these early life-history stages. While these behaviors confirm SRAs continue to function as essential habitat during G. galeus early life history, evidence of YOY and juveniles emigrating from these areas within their first 1–2 years and the fact that few YOY return suggest that these areas may only afford protection for a more limited amount of time than previously thought. Determining the importance of neighbouring coastal waters and maintaining the use of traditional fisheries management tools are therefore required to ensure effective conservation of G. galeus during early life history.
Publisher: CSIRO Publishing
Date: 2007
DOI: 10.1071/MF06233
Abstract: This study examined post-release survival in sand flathead (Platycephalus bassensis) and whether there were survival benefits from the use of circle hooks over conventional hook patterns. Anatomical hooking location was the major factor contributing to mortality, with an almost 100% survival rate for fish hooked in the lip, mouth or eye (shallow-hooked) compared with around 64% for fish hooked in the throat or gut (deep-hooked). Mortality in deep-hooked fish was generally associated with injuries to vital organs (gills, heart, liver) and survival was significantly lower if bleeding was associated with injury (54% compared with 85% for non-bleeders). Circle hooks resulted in significantly lower deep-hooking rates (1%) compared with conventional hook types (4–9%) and, based on catch rates, were at least as effective as conventional hook patterns. Estimated survival rates for line-caught sand flathead were high, over 99% for circle hooks and between 94 and 97% for conventional hooks. These findings support the efficacy of management strategies based on size and bag limits and the practice of catch-and-release fishing for sand flathead, as well as a potential conservation benefit from the use of circle hooks.
Publisher: Elsevier BV
Date: 10-2014
Publisher: Springer Science and Business Media LLC
Date: 27-03-2007
Publisher: Canadian Science Publishing
Date: 03-2016
Abstract: Interactions between seals and midwater trawl operations in the Australian Small Pelagic Fishery are common and can be lethal. The nature of interactions and effectiveness of a seal exclusion device (SED) in mitigating lethal interactions was assessed using underwater video. Recent fishing activity and the phase of the trawl operation significantly influenced interaction rates interactions increased with the amount of recent trawl activity and were highest while the trawl was being set. Most seals accessed the trawl via the net entrance and exited via an escape opening located at the base of the SED. The size of the escape opening was the only operational factor that influenced mortality rates — simply enlarging the escape hole reduced lethal interactions by 79%. However, since all deceased seals dropped out of the net before they were brought on board, they would have gone unobserved without video monitoring. Limiting the concentration of fishing activity in space and time and refinement of the SED design, in particular to address dropouts, is recommended if mortality rates are to be reduced.
Publisher: Springer Science and Business Media LLC
Date: 17-04-2011
DOI: 10.1038/NCLIMATE1084
Publisher: Wiley
Date: 15-12-2011
Publisher: Canadian Science Publishing
Date: 09-2011
DOI: 10.1139/F2011-057
Abstract: Atlantic salmon, Salmo salar , and rainbow trout, Oncorhynchus mykiss , are farmed in Tasmania, Australia, where fish sometimes escape into the natural environment. If escapees are able to survive and feed on native fauna, it is likely that they will have ecosystem impacts. Stomach content, body condition (muscle lipid content and Fulton’ K), stable isotope, and fatty acid analysis were used to determine if escaped salmonids feed on native fauna. Results indicate that, in general, escaped salmonids do not feed on native fauna. Salmonids loose condition after escaping, and escapee stomachs were mostly empty or contained non-nutritious material or feed pellets. Nevertheless, almost a quarter of rainbow trout stomachs contained native fauna. The majority of escapees had biochemical composition similar to caged animals, indicating that these fish had not switched to feed on local food sources. However, a small fraction of escapees conclusively showed changes in biochemical parameters indicative of a shift to feeding on native fauna. Given the numbers and frequency of escapes, this can have an important impact on native species and on the ecology of Macquarie Harbour.
Publisher: Springer Science and Business Media LLC
Date: 06-08-2015
DOI: 10.1007/S00442-015-3411-6
Abstract: Long-term ecological datasets are vital for investigating how species respond to changes in their environment, yet there is a critical lack of such datasets from aquatic systems. We developed otolith growth 'chronologies' to reconstruct the growth history of a temperate estuarine fish species, black bream (Acanthopagrus butcheri). Chronologies represented two regions in south-east Australia: South Australia, characterised by a relatively warm, dry climate, and Tasmania, characterised by a relatively cool, wet climate. Using a mixed modelling approach, we related inter-annual growth variation to air temperature, rainfall, freshwater inflow (South Australia only), and El Niño-Southern Oscillation events. Otolith chronologies provided a continuous record of growth over a 13- and 21-year period for fish from South Australia and Tasmania, respectively. Even though fish from Tasmania were sourced across multiple estuaries, they showed higher levels of growth synchronicity across years, and greater year-to-year growth variation, than fish from South Australia, which were sourced from a single, large estuary. Growth in Tasmanian fish declined markedly over the time period studied and was negatively correlated to temperature. In contrast, growth in South Australian fish was positively correlated to both temperature and rainfall. The stark contrast between the two regions suggests that Tasmanian black bream populations are more responsive to regional scale environmental variation and may be more vulnerable to global warming. This study highlights the importance of examining species response to climate change at the intra-specific level and further validates the emerging use of growth chronologies for generating long-term ecological data in aquatic systems.
Publisher: Springer Science and Business Media LLC
Date: 21-04-2011
Publisher: CSIRO Publishing
Date: 1997
DOI: 10.1071/MF96074
Abstract: The distribution, abundance, size structure, reproductive biology and diet of warty oreo, Allocyttus verrucosus (Gilchrist), and spiky oreo, Neocyttus rhomboidalis (Gilchrist), from the continental slope region (400-1200 m depth) of south-eastern Australia are described. The depth distributions of the two species overlap, with spiky oreo being more abundant in intermediate depths (600-800 m) and warty oreo abundance peaking at greater depths (900-1200 m). There was evidence of size structuring with depth. Warty oreo juveniles and subadults were comparatively more abundant in depths of less than 1000 m and adults dominated at greater depths. In spiky oreo, juveniles were largely restricted to the depth range of 700-900 m. Size at 50% maturity in females was 28 and 35 cm for warty and spiky oreos, respectively. Males mature at slightly smaller sizes. Spawning occurs in May–June for warty oreo and between August and October for spiky oreo. Just prior to spawning in warty oreo the sexes appear to segregate by depth, with females becoming progressively more dominant with depth. Both species are benthopelagic feeders, consuming a range of prey items including crustaceans, fish and squid. Salps were also an important component of the diet of spiky oreo.
Publisher: Elsevier BV
Date: 05-2009
Publisher: Springer Science and Business Media LLC
Date: 09-10-2014
Publisher: Public Library of Science (PLoS)
Date: 07-06-2017
Publisher: Public Library of Science (PLoS)
Date: 13-01-2014
Publisher: Oxford University Press (OUP)
Date: 22-10-2016
Publisher: Wiley
Date: 16-11-2017
DOI: 10.1111/FAF.12251
Publisher: Wiley
Date: 1992
Publisher: CSIRO Publishing
Date: 2007
DOI: 10.1071/MF07032
Abstract: Generating age estimates for long-lived fish requires particular attention to validation because they are usually difficult to age owing to narrow increment structure. A robust validation of the accuracy and precision of banded morwong, Cheilodactylus spectabilis, s led from Tasmanian waters, was undertaken. Age at the first enumerated increment was established from analysis of juvenile cohorts, and the timing and periodicity of increment formation was established using a quantitative model from oxytetracycline (OTC) mark-recaptures at liberty for periods of up to 8 years. The accuracy of age estimates was examined independently by comparing radiocarbon values in the otolith region corresponding to the first year of growth against the south-western Pacific calibration curve. C. spectabilis is very long-lived, with males and females living to over 90 years of age. Growth modelling revealed a fast initial growth phase, terminating in an abrupt plateau near the asymptotic length. This species displays substantial sexual dimorphism in growth, with males growing to larger sizes than females.
Publisher: Wiley
Date: 12-1983
Publisher: Springer Science and Business Media LLC
Date: 09-12-2016
Publisher: Inter-Research Science Center
Date: 22-05-2008
DOI: 10.3354/MEPS07394
Publisher: Wiley
Date: 17-06-2010
DOI: 10.1111/J.1095-8649.2010.02703.X
Abstract: Movement patterns and habitat utilization by black bream Acanthopagrus butcheri (Sparidae), an estuarine resident species, were investigated using acoustic telemetry in a small estuary on the east coast of Tasmania, Australia. Thirty-four adult A. butcheri were tracked for periods of up to 187 days between August 2005 and January 2006. Although able to tolerate a wide range of salinities, the fish spent most of the time within the upper and middle regions of the estuary, where brackish conditions dominated. The species exhibited extensive movements linked to tidal cycles, with small-scale upstream movements during incoming tides and downstream movements during out going tides. The extent of these movements was positively correlated with the tidal height difference between consecutive tidal peaks and troughs. Freshwater inflows and resultant changes in salinity also significantly influenced distribution and movement patterns. Fish moved downstream during the periods of heavy inflows, returning upstream as salinities increased to c. >10. During the peak of spawning period (November to December) fish moved into the upper region of the estuary, where they aggregated to spawn. Periodic increases in freshwater discharge, however, resulted in fish leaving the spawning grounds and moving downstream. Towards the end of the spawning season (January), the fish became more dispersed throughout the entire estuarine system.
Publisher: Oxford University Press (OUP)
Date: 11-09-2014
Abstract: A molecular approach was successfully developed to discriminate between spawned eggs of the pelagic carangids Trachurus declivis and Trachurus novaezelandiae collected during ichthyoplankton surveys conducted in October 2002 and 2003 along shelf waters of Queensland (Qld) and New South Wales (NSW), in southeastern Australia (25o50′–37o30′S). Visually identified Trachurus eggs were subjected to mtDNA analysis by targeting specific fragments of the cytochrome oxidase subunit 1 (CO1) and cytochrome b (Cyt b) genes, with three diagnostic sites (single-nucleotide polymorphisms) within a 297 bp segment of Cyt b (558, 588, 825) providing the best approach to discriminate between species. Polymerase chain reaction lification and sequencing of 608 suspected Trachurus eggs resulted in 586 (96.4%) high-quality sequences that unequivocally identified 315 and 207 eggs as T. declivis and T. novaezelandiae, respectively, as well as 18 “variant haplotype” eggs that exhibited a base substitution at one of the diagnostic sites the remaining 46 sequences aligned to three different genera in GenBank including two carangids, thus highlighting the effectiveness of molecular methods for egg identification. Rehydrated, mtDNA-verified eggs of T. declivis were significantly larger (0.97 ± 0.01 mm) than those of T. novaezelandiae (0.82 ± 0.01 mm), though still proved problematic to identify to species when relying on morphology alone. Egg distributions showed main spawning areas of T. declivis and T. novaezelandiae confined mostly to southern NSW (& °S) and northern NSW/southern Qld (& °S), respectively, with T. novaezelandiae likely to continue spawning further south during summer with the gradual temperature increase associated with the south-flowing East Australian Current. Overall findings support the adoption of comparable molecular protocols to verify identification of wild spawned eggs to species level, especially eggs collected during the application of the daily egg production method to estimate spawning biomass of pelagic species, as well as biological fish studies.
Publisher: Elsevier BV
Date: 08-2008
Publisher: Oxford University Press (OUP)
Date: 18-07-2016
Publisher: CSIRO Publishing
Date: 2001
DOI: 10.1071/MF99136
Abstract: The fishery can be ided into two subfisheries (‘spawning’ and ‘non-spawning’). Commercial catch rates for the ‘non-spawning’ subfishery declined from the late 1980s to 1997, whereas those for the ‘spawning’ subfishery exhibit no obvious temporal trend. An ‘Integrated Analysis’ assessment, of the feasibility of reconciling these differing trends, uses catch (landed and discarded), catch rate, length-at-age, and catch-at-age data and estimates of absolute abundance based on the egg-production method. It emphasizes uncertainty due to model assumptions and the data included in the assessment. Use of the discard data allows more precise estimation of the magnitude of recent recruitments. Spawning biomass is estimated to have declined from a peak in 1989–91 to 1999 although fishing mortality has consistently been %for each subfishery. One main reason for the reduction in population size is the weakness of year-classes spawned from 1988 to 1993. Differences in catch rates between the two subfisheries can therefore be explained by interactions between the components of the population harvested by the two ‘subfisheries’, and the trends in year-class strength. A risk analysis is used to evaluate the consequences of different future levels of harvest for different assessment assumptions. Overall, the spawning biomass is predicted to increase over the next five to ten years as a result of the strong 1994 and 1995 year-classes, although the extent of this increase remains uncertain.
Location: Australia
Location: Australia
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Jeremy Lyle.