Jackass Morwong Research Articles

Contribution of offshore platforms and surrounding habitats to fish production in the Bass Strait, south-east Australia

Information on the contribution of offshore oil and gas (O&G) platforms to fish productivity is required to contribute to the decision-making process to remove, partially remove, or retain these structures during decommissioning after petroleum production ceases. The present study assesses the biomass and fish production of one common and abundant fish species (Caesioperca lepidoptera – butterfly perch) and two commercially fished species (Helicolenus percoides – reef ocean perch; Nemadactylus macropterus – jackass morwong) on eight O&G platforms and in surrounding natural habitats in the Bass Strait, south-east Australia, where options for decommissioning are being assessed. High-definition stereo-video imagery was collected by remotely operated vehicle (ROV) from eight platform facilities, their immediate benthic surrounds, reference areas reflective of the likely pre-installation seabed state (sand-dominated) and a nearby natural ‘reef’ area referred to as south-east reef (some limestone foundation). The biomass of all three species was low in the benthic surrounds of platforms, at reference locations and at south-east reef where minimal cover by benthic organisms was recorded and, as such, there was little to no fish production for the three study species in these areas. We observed a total fish biomass of 2.85 tonnes across the eight platforms for the three fish species surveyed, with high variability across platforms. Total production (P) across all platforms was estimated at 1244 kg/year for the three species, with a mean fish production density of 82 g/m2/year. Approximately 79% of total production is considered ‘new’ production (984 kg/year i.e., the production attributed to the presence of the platforms; with a mean production density of 64 g/m2/year). The remaining 21% could be retained or redistributed into the surrounding area if platforms were removed. C. lepidoptera accounted for the majority (90%) of biomass and of total production for all three species across all locations surveyed. Despite only accounting for a small proportion of platform surface area, the bottom 5 m sections of platforms had 41% of the total biomass observed and accounted for 46% of total production of these three study species. Production measures for platforms surveyed here are relatively high compared to other artificial reefs and habitats around the world. Total removal of these platforms will likely result in a reduction of fish biomass and fish productivity (incl. several fishery species) in the immediate vicinity.

Modelling perspective on the climate footprint in south east Australian marine waters and its fisheries

Abstract South eastern Australia is a global warming hotspot, and is also home to ~70% of Australia’s population and one of Australia’s largest fisheries—the South East Scalefish and Shark Fishery. This fishery spans shelf to deep waters, subtropical to temperate waters, employs many gears, and interacts with over 100 species. Despite following best practice fisheries management principles, including taking an ecosystem perspective to overall fisheries interactions, management interventions have failed to arrest or recover the decline of some focal species. Using an Atlantis ecosystem model developed for the fishery over the past 20 years, this paper presents simulations that suggest climate change may be a major contributor to the trajectories seen for a number of species—such as jackass morwong (Nemadactylus macropterus), blue warehou (Seriolella brama), and gemfish (Rexea solandri). This kind of climate influence poses many challenges for fisheries management into the future, raising questions about what to do when climate change undermines or overrides fisheries management actions and objectives.

Industry remotely operated vehicle imagery for assessing marine communities associated with subsea oil and gas infrastructure on the continental shelf of South-East Australia

Introduction Offshore oil and gas (O & G) infrastructure provides hard substrata of structural complexity in marine environments and has been shown to have ecological value, particularly in oligotrophic environments. As infrastructure approaches end of life, understanding such values is critical to inform decommissioning decisions. MethodsThis study uses a decade of industry remotely operated vehicle (ROV) imagery to describe fish, invertebrate, and benthic communities on gas field infrastructure. Sampling was conducted over 22 km of flowline, three wells and one manifold in the temperate waters of Bass Strait, south east Australia in depths of 155 to 263 m.ResultsA total of 10,343 mobile animals from 69 taxa were observed. A higher diversity of fishes were observed on flowlines (28 taxa) compared to wells (19 taxa). Fish and invertebrate communities observed along flowlines were distinct from those observed on wells/manifold, however, there was also high spatial variability among the different flowlines surveyed and between the three wells and manifold. These differences appear to be driven by habitat and depth preferences of the species observed. Many sand-affiliated species were associated with buried sections of flowlines (Tasmanian giant crab Pseudocarcinus gigas, Balmain bug Ibacus peronii, slender sand burrower Creedia haswelli, red cod Pseudophycis spp., blue grenadier Macruronus novaezelandiae) whilst reef-associated and schooling species were observed on the wells/manifold (jackass morwong Nemadactylus macropterus, redbait Emmelichthys nitidus, splendid perch Callanthias australis). Species of ecological importance were also noted including the Australian fur seal (Arctocephalus pusillus doriferus), long-lived foxfish (Bodianus frenchii), and handfish (Brachionichthyidae spp).DiscussionThis study describes the habitat value of oil and gas infrastructure in a data poor temperate region that is important for understanding how the decommissioning of these structures may affect local marine ecosystems and fisheries. Therefore, it is critical to understand the habitat value of O&G infrastructure to marine life in the Bass Strait and whether decommissioning of these structures affect local marine ecosystems and fisheries. This study shows the complexity of determining temporal change in biodiversity values associated with these O & G structures from historical industry datasets that will be key for informing future decommissioning options. We also provide some guidance on how future quantitative data can be obtained in a systematic way using industry ROV data to better inform ecological investigations and decommissioning options.

Coincident recruitment patterns of Southern Hemisphere fishes

Three dominant recruitment patterns were identified across 30 stocks from Australia, New Zealand, Chile, South Africa, and the Falkland Islands using data from 1980 to 2010. Cluster and dynamic factor analysis provided similar groupings. Stocks exhibited a detectable degree of synchrony among species, in particular the hakes and lings from Australia, New Zealand, Chile, and South Africa. We tested three climate indices, the Interdecadal Pacific Oscillation (IPO), Southern Annular Mode (SAM), and Southern Oscillation Index (SOI), to explore their relationship with fish stock recruitment patterns. The time series of IPO and SOI showed the strongest correlation with New Zealand hoki (blue grenadier, Macruronus novaezelandiae) and Australian jackass morwong (Nemadactylus macropterus) (r = 0.50 and r = –0.50), and SAM was positively related to Australian Macquarie Island Patagonian toothfish (Dissostichus eleginoides) (r = 0.49). Potential linkages in recruitment patterns at sub-basin, basin, and multibasin scales and regional and global climate indices do account for some of the variation, playing an important role for several key Southern Hemisphere species.

The impacts of fish body size changes on stock recovery: a case study using an Australian marine ecosystem model

Abstract Many fished stocks show long-term reductions in adult body size. Such changes could lead to new feeding interactions and alter stock productivity, introducing new levels of uncertainty in fisheries management. We use a marine ecosystem model parameterized for Southeast Australia to explore how reductions (up to 6% in 50 years) in size-at-age of fished species affect stock recovery after an implementation of a fishing moratorium. We show that reduction in body size can greatly elevate predation mortality and lower the post-fishing biomass of affected species. In our simulations, the recovery period after the fishing moratorium was characterized by two phases. In the initial readjustment phase, the ecosystem dynamics was largely determined by the rapid changes in the biomasses of recovering species and changes in body size had negligible effects. In contrast, fish body sizes had the major impact on the biomasses in the second, semi-equilibrium state and the final biomasses were generally not affected by the harvest rate during the fishing period. When reduced size-at-age elevated predation mortality in most age groups of a species (tiger flathead Platycephalus richardsoni or silver warehou Seriolella punctata in our simulations), the species' equilibrium biomass was considerably lower compared with the scenarios of no change in body size. For other species (pink ling Genypterus blacodes and jackass morwong Nemadactylus macropterus), a predation increase in some age groups was balanced by the decrease in others. The latter reduction in predation mortality occurred when major predators of species with reducing size-at-age were decreasing in size themselves, or when cannibalism was an important source of juvenile mortality (in blue grenadier Macruronus novaezelandiae). We suggest that decreased size-at-age will be most detrimental to stock recovery when the main predators of the stock are not affected by the drivers causing changes in body size.

Management implications of including a climate-induced recruitment shift in the stock assessment for jackass morwong (Nemadactylus macropterus) in south-eastern Australia

Fishery responses to climate change are occurring on time-scales relevant to the provision of short-term management advice. This is especially the case in climate change ‘hotspots’ such as south-eastern Australia, where the rate of ocean-warming is 3–4 times the global average. The application of harvest strategies utilizing biological reference points that do not take into account the effect of the changing environment on fish productivity may lead to unsustainable catch recommendations. Jackass morwong (Nemadactylus macropterus) is a moderately long-lived demersal species inhabiting continental shelf waters of the southern hemisphere. The most recent Stock Synthesis assessment for the species suggests that this stock has recently declined in abundance off south-eastern Australia. The stock assessment attributes the decline to mostly below average recruitment since 1985, but the recommended catch levels are based on an assumption of average recruitment from a stationary stock–recruitment relationship. The ability of Stock Synthesis to include an environmental variable to adjust the stock–recruitment relationship is used to model a regime shift on the average level of recruitment. Management strategy evaluation (MSE) is then used to examine the consequences of using the wrong recruitment assumption in the assessment used in the harvest strategy for setting the catches. The MSE shows that the consequences of mis-specifying the assessment model are greater if the assessment continues to assume that no shift in recruitment has occurred. Thus the more precautionary approach for management wishing to meet all the aims of the Australian government Harvest Strategy Policy is to assume that a shift in recruitment has occurred. A possible mechanism for how observed oceanic changes could be impacting jackass morwong recruitment is presented.

Abundance indices for main commercial fish species caught by trawl from the south-eastern Australian continental shelf from 1918 to 1957

Per-haul records of catches by steam trawlers on the south-eastern Australian continental shelf from 1918 to 1957 were examined for the main commercial species tiger flathead (Neoplatycephalus richardsoni), jackass morwong (Nemadactylus macropterus), redfish (Centroberyx affinis), latchet (Pterygotrigla polyommata) and chinaman leatherjacket (Nelusetta ayraudi). Catch rates in weight per haul per species were standardised to annual indices of abundance using a log-linear model. Standardised annual index trends for flathead, latchet and leatherjacket indicate a strong to severe decline during the period covered by the data. All species showed seasonal patterns, but the peak season varied depending on the species. The distribution of standardised catch rate by area also differed greatly by species, and no single area showed consistent differences across all species. Day trawls caught more flathead, redfish and latchet, while night trawls caught more morwong and leatherjacket. Moon phase had less influence on catch rates than other factors. The correlation of annual index trends to a number of annual mean environmental factors was examined and no strong correlations were found.

In situ examination of the behaviour of fish in response to demersal trawl nets in an Australian trawl fishery

In situ examination of the behaviour of fish was undertaken with underwater cameras positioned on demersal trawl gear used by Australia’s South East Trawl Fishery. Blue grenadier (Macruronus novaezelandiae), pink ling (Genypterus blacodes) and whiptails (Coelorinchus spp.) swam in an anguilliform mode whereas other species displayed a carangiform swimming mode. Tiger flathead (Neoplatycephalus richardsoni) and ocean perch (Heliocolenus spp.) were active in response to the approaching trawl net compared with the generally passive activity of whiptails, New Zealand dory (Cyttus novaezelandiae), and jackass morwong (Nemadactylus macropterus). However, when in the body of the trawl, gemfish were active while ocean perch, whiptails and New Zealand dory were generally passive. Some blue grenadier, ocean perch and whiptails escaped capture by passing through open meshes in the trawl mouth, whereas tiger flathead passed under the ground gear. In the trawl body, small numbers of blue grenadier passed through open meshes in the top panel whereas numerous spotted warehou swam faster than the towing speed, presumably escaping capture by swimming forwards and out of the trawl. Interspecific behavioural variation in escape response could be utilised to design more efficient trawl gears.

Evaluation of management tools for Australia's South East Fishery.2. How well can management quantities be estimated?

The ability to estimate some of the quantities relevant to the management of South East Fishery species is examined using Monte Carlo simulation. The analyses are based on scenarios for four of the species of this fishery (spotted warehou, tiger flathead, jackass morwong and pink ling). Integrated Analysis was found to perform best out of six potential methods of fisheries stock assessment (Schaefer and Fox production models, age-structured production model, Integrated Analysis, ad hoc tuned VPA and ADAPT) that are, or have been, applied to data for South East Fishery species. However, its performance, particularly for spotted warehou, is nevertheless relatively poor. The sensitivity of estimation ability to many factors including model uncertainty and the extent of observation and process error is examined. Factors that influence estimation performance markedly include: violation of the assumption of no population spatial structure; time-trends in catchability; the depletion of the resource at present; and uncertainty about the value of the instantaneous rate of natural mortality. Little improvement in estimation performance can be expected without resolution of issues related to model structure. This highlights the importance of considering model uncertainty in future studies of the estimation performance of stock assessment methods.

Influence of mesoscale oceanographic processes on larval distribution and stock structure in jackass morwong (Nemadactylus macropterus: Cheilodactylidae)

The distribution of morwong larvae in the southwestern Tasman Sea was investigated during autumn/early winter over three consecutive years (1992-1994). Larvae were confined to surface tows and large numbers (6-30 mm in length) were captured up to 250 km east of Tasmania (the limit of sampling). The jackass morwong (Nemadactylus macropterus) dominated samples, although larvae of the banded morwong (Cheilodactylus spectabilis) were also recorded. N. macropterus larvae were found within water masses derived from the East Australian Current (EAC) and Sub-tropical Convergence Zone (STCZ). Back-calculated spawning dates, significant differences in otolith microstructure, and inferred current patterns suggest that larvae from within each water mass originate from different spawning regions: a northern one (probably southern New South Wales and eastern Victoria) and a southern one (probably western and southern Tasmania). There was a significant positive relationship between larval age and distance offshore. Seasonal movements of the major water masses provide mechanisms that may facilitate regionally self-sustaining populations in northern and southern regions with an area of recruitment derived from both regions covering eastern Tasmania and Bass Strait. Larval distribution and advection processes suggest spatially variable levels of mixing between spawning regions. These data provide an explanation for both the lack of previously detected population sub-structuring from genetics studies and the multiple spawning population scenario suggested by otolith microchemistry studies.

Age, growth and spatial and interannual trends in age composition of jackass morwong, Nemadactylus macropterus, in Tasmania

Transverse sections of sagittae were examined. The first and second annual increments were defined by examination of the progression of otolith radius and length of the 0+ and 1+ cohorts. Growth in both sexes is rapid until ~5 years old (32–35 cm), and then slows appreciably. There was a broad range of lengths within individual age-classes, with a maximum of 12 age-classes present in a 1 cm length-class. Maximum ages of males and females were 41 and 30 years, respectively, which is considerably higher than previously estimated from whole otoliths. There was no significant difference in the growth curves between males and females, although this is influenced by the large number of juveniles and by the examination of relatively few large, older fish. The sex-specific von Bertalanffy growth parameters are: L∞ 38.4 cm FL, t0 –0.07 years, K 0.36 year–1 for females and L∞ 36.2 cm FL, t0 0.15 years, K 0.42 year–1 for males. The age composition was dominated by 4–7 year olds but showed evidence of considerable recruitment variability, particularly in the strong 1988 year-class. The relationship between the life-history strategy of N. macropterus and recruitment variability is discussed.

Spatial and temporal variations in abundance and distribution of juvenile and adult jackass morwong, Nemadactylus macropterus, in south-eastern Tasmania

Depth-stratified random demersal trawl surveys of the shelf of southern and eastern Tasmania from summer 1993 to summer 1995 showed seasonal variations in abundance of N. macropterus in all depth strata, although the trend varied between years, with abundance peaking in summer 1993 and winter 1994. This variation is attributed to the seasonal movement of fish from south-eastern Tasmanian shelf waters, although some seasonal change in size composition is also evident. Catch rates were highest on the outer shelf and lowest on the inner shelf, reflecting the distinct size-structuring, with juveniles concentrated on the inner and mid shelf and mature fish on the outer shelf. Size compositions differed among shelf regions, with few mature fish on the mid shelf of Storm Bay compared with the same stratum on the east coast, indicating that the bay is primarily a nursery area for the species. Settlement from the pelagic post-larval phase occurred in spring and early summer at 7–9 cm, with evidence of movement between inner-and mid-shelf strata by autumn. Abundance of 0+ fish was highest in 1993 and 1994 and a considerable decrease in the abundance in both regions in 1995. The influences of local hydrography and the large size at settlement are discussed.

Mitochondrial DNA Diversity in Jackass Morwong (Nemadactylus macropterus: Teleostei) from Australian and New Zealand Waters

The jackass morwong (Nemadactylus macropterus), a commercially valuable marine fish in the Australian–New Zealand region, was surveyed for genetic variation as part of a larger project aimed at clarifying its stock structure. Mitochondrial DNA variation in 166 jackass morwong from seven southern Australian localities was examined using nine restriction enzymes. The 28 haplotypes identified gave an overall nucleon diversity of 0.671. Mean nucleotide diversity per sample was 0.458%, with a (corrected) nucleotide divergence among samples of 0.001%. There was no significant spatial patterning. Five hundred individuals from eight southern Australian localities and one New Zealand locality were examined using three restriction enzymes detecting polymorphic cut sites. The 33 haplotypes identified gave an overall nucleon diversity of 0.635. Mean nucleotide diversity per sample was 1.247%, with a (corrected) nucleotide divergence among samples of 0.002%. No differentiation was detected among the Australian localities. The New Zealand sample showed weak but significant divergence from the Australian samples. These results were similar to those from a concurrent allozyme analysis, and we conclude that there is appreciable nuclear and mitochondrial DNA gene flow among Australian localities, while the Tasman Sea separating Australia from New Zealand acts as a partial barrier.

Population age structure and mortality rates of jackass morwong ( Nemadactylus macropterus) in Eastern Bass Strait, Australia

The catch-curve method was used to estimate the instantaneous rate of total mortality ( Z) of jackass morwong ( Nemadactylus macropterus) in south-east Australian waters. Age-frequency distributions were obtained for fish collected from eastern Bass Strait during the 3 years. March 1982–February 1985. Fish were obtained from: (1) demersal research fishing surveys stratified by depth; (2) commercial landings from eastern Bass Strait; (3) commercial landings from the adjacent New South Wales fishery. Jackass morwong were found in water 65–299-m deep, and almost half the biomass was in water 90–179-m deep. Our estimate of the total biomass (from the survey results) of the part of the population in eastern Bass Strait was 15 700 t. The oldest male morwong caught was 11 years old, the oldest female 13 years old. From the survey data, total mortality ( Z) was estimated as 0.45 for males, which is equivalent to an annual survival rate ( S) of 0.64, and as 0.47 for females, equivalent to an S of 0.63. There was substantial annual variation in estimates of Z. For the survey results, the annual mortality rate estimated for males was significantly different from that for females. The instantaneous rate of fishing mortality ( F) estimated from population biomass and mean commercial landings was very low (about 0.024; sensitivity analysis indicated a possible range of 0.012–0.072), and indicated that about 2% (by number; range 1–6%) of the part of the population in eastern Bass Strait was harvested annually. Z values estimated from samples of commercial landings were consistently larger than Z estimated from the survey samples. Using estimates of Z from commercial landings data resulted in high values of M (the instantaneous rate of natural mortality), which were inconsistent with the longevity of the species and the proportion of older fish found in the population. We believe this to be due to bias in the way commercial landings sample the population, and to be an inherent bias in the use of age-frequency data from commercial landings unless some correction for size-selectivity due to commercial fishing gear and fishing behaviour can be made.

Annual total mortality and population stucture of jackass morwong (Nemadactylus macropterus Bloch & Schneider) in eastren Australian waters

Catch curves were analysed to estimate the annual total mortality of jackass morwong landed at the port of Eden between July 1976 and June 1979. The annual total mortality of females was lower in 1978-1979 than in the previous 2 years, reflecting the expansion of the trawl fishery in New South Wales to include previously unexploited deepwater grounds. Males were fully recruited to the commercially exploited population at an earlier age than females. It is suggested that the increased mortality in older males is due to an increase in natural mortality.

Geographical distribution of electrophoretically detected protein variation in Australian commercial fishes. II. Jackass morwong, Cheilodactylus macropterus Bloch & Schneider

The presence of genetic polymorphisms in alcohol dehydrogenase, phosphogluconate dehydrogenase (decarboxylating), phosphoglucomutase, adenosine deaminase and glucosephosphate isomerase in the jackass morwong, or tarakihi, and the distribution of the variation in the fish stocks in the waters of south- eastern Australia are described. Although the Australian and New Zealand stocks are genetically distinct, no evidence of population structuring was found in Australian waters.

Age and growth of jackass morwong (Nemadactylus macropterus Bloch & Schneider) in eastern Australian waters

N. macropterus, landed at the port of Eden, were sampled from July 1976 to June 1979. Saggital otoliths were used for age determination. A hyaline and an opaque ring were found to be formed during winter and summer. respectively. The growth of adult N. macropterus was adequately described by the von Bertalanffy growth curve. Females (K = 0.13, L∞ = 51.13) were found to grow faster, and to a greater age, than males (K = 0.17. L∞ = 45.50). No significant difference between sexes was apparent in the length-weight relationships.

Mercury levels in six species of Australian commercial fish

The total mercury content of six species of Australian commercial fish (John dory. Zeus faber: mirror dory. Zenopsis nebulosus; tiger flathead, Neoplatycephalus richardsoni; rubberlip morwong, Nemadactylus douglasii; jackass morwong, Nemadactylus macroprerus; and sand whiting, Sillago ciliata) is reported. Total mercury content is regressed against fish length and the resultant equations and correlation coefficients are presented for each species. A length-frequency histogram derived from the Sydney Fish Market data and a length-mercury content curve are plotted as an overlay for each of the six species. The integrated average mercury content (mg/kg) has been calculated for each species and these are as follows: sand whiting, 0.08; rubberlip morwong, 0.13; tiger flathead, 0.14; John dory, 0.14; mirror dory, 0.15; and jackass morwong, 0.16. The graphical method adequately demonstrates the relationship between mercury levels and the commercial size range of particular species.