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The Value of Subsea Pipelines to Marine Biodiversity
Abstract
As offshore oil and gas infrastructure reaches the end of its operational life, owners and regulators will question the best options available to decommission it, with decisions requiring information about the potential ecological value of these structures and the environmental impact of their removal. Using a combination of existing industrial underwater Remotely Operated Vehicle video data and marine scientific remote stereo-video surveys, we describe and compare the fish assemblage on pipelines with those on the adjacent natural seafloor of the North West Shelf of Western Australia. Using these video observations of commercially important fish species on pipelines we were able to summarise the potential monetary value of commercial fish found on pipelines to commercial fisheries. Greater numbers of fish were observed on pipelines, compared with that seen on adjacent seafloor areas, and the monetary value of the fish found on the pipelines was estimated to be ca. six times greater than that of fish in surrounding areas lacking subsea infrastructure. Pipeline spans had high fish abundance, with fish appearing to utilise these spans as refuges. These results, together with allied assessments of marine growth on pipelines, suggest over the course of their operating lives, pipelines gain ecological and fishery value, enhancing the diversity and abundance of fish (including important commercial species) which can be translated to a monetary value for commercial fisheries. With an extensive array of pipeline infrastructure spread across the North West Shelf of Western Australia, knowledge of the ecological and fisheries value of subsea infrastructure is imperative to understanding the environmental and economical consequences of removing infrastructure as part of decommissioning. Where pipelines add value to marine biodiversity and fisheries in Western Australia, engineers and ecologists can work towards quantifying this value and preserving it – and potentially also enhancing it – via novel evidence-based abandonment strategies.
... Similarly, Bond et al. (2018c) found the value of fish to be * 2-3 times higher on the Griffin pipeline, which is also located within the PTMF. Differences in the catch value on and off-pipelines reported by Bond et al. (2018d) were attributed to the higher abundance of valuable species, including Pristipomoides multidens, Epinephelus multinotatus, Lutjanus sebae, L. malabaricus, and L. russellii. Two of these species, L. sebae and E. multinotatus, were in the top three species landed by commercial fisheries in the Pilbara in 2017 (Newman et al. 2019). ...
Over 1400 km of oil and gas pipeline infrastructure exists within the boundaries of the Pilbara Trap Managed Fishery (PTMF) operating on the North West Shelf of Australia. Some of this infrastructure has reached the end of its operational life and requires decommissioning. Location and speed data collected from 2008 to 2018 using vessel monitoring systems onboard all trap fishing vessels (n = 3) operating in the PTMF were used to understand how fishing activity near pipelines has changed through time, and to identify the best predictive variables to explain hours spent fishing km−2 week−1. The proportion of fishing activity within 200 m of a pipeline increased over the survey decade and averaged 4.2% across all years. Hours spent fishing km−2 within 200 m of any pipeline was found to be 8.0 h km−2, ~ 11.4 times more than that recorded, on average, for the remaining area of the PTMF (0.7 h km−2), and ~ 4.6 times more than the western portion of the PTMP (1.7 h km−2) where all pipeline infrastructure exists. Fishing activity within 1 km of pipelines increased after their installation, and hence time since installation was the best predictor of fishing. This study demonstrated that trap fishers in the PTMF allocate a small proportion of their time targeting pipeline infrastructure, with the area close to a pipeline experiencing a relatively greater magnitude of fishing than that elsewhere in the PTMF. As such, the results of this study provide decision makers with an understanding of the intrinsic value of this infrastructure to trap fishers.
... The majority of the research on the ecological values of oil and gas infrastructure comes from the temperate waters of the North Sea (e.g., Jørgensen et al., 2002;Jørgensen, 2012;Fujii and Jamieson, 2016;Todd et al., 2020) and California (Love et al., 2005;Love and York, 2006;Claisse et al., 2014) and the sub-tropical waters of the GoM (Hastings et al., 1976;Stanley and Wilson, 1997). Recently, there has been a surge of research from the tropical North West Shelf of Australia (Bond et al., 2018;McLean et al., 2018;Schramm et al., 2020Schramm et al., , 2021. ...
Decommissioning of offshore oil and gas structures is either occurring, or imminent in most regions of the world. Most jurisdictions require that offshore structures be removed for onshore disposal. However, there is growing interest in understanding the ecological and socio-economic benefits of leaving structures in the water. Descriptions of how fish utilize the vertical structure created by wellhead platform jackets (platforms) will provide insights into possible outcomes of decommissioning alternatives, such as full removal, leave in situ, or translocation to a designated reefing site. We surveyed fish assemblages associated with seven platforms and five reference sites located ∼150 km offshore in the central Gulf of Thailand. The platforms spanned the entire water column (∼75 m) and were a mix of three and four legged structures. We used a Remotely Operated Vehicle (ROV) fitted with an underwater stereo video system to quantify the abundance, size, biomass, and economic value of fish associated with the platforms. We recorded 43 species of fish on the platforms and five reference sites with most fishes on platforms categorized as coral-reef or coral-reef-associated species. We observed a strong vertical zonation in the fish assemblage on the platforms. The Regal demoiselle (Neopomacentrus cyanomos) was numerically dominant (75% of all fish observed). We measured 3,933 kg of fish on the platforms with Caranx sexfasciatus accounting for 76.12% of that. We conservatively estimate each platform had a scaled mean biomass of ∼2,927 kg and the fished species had scaled mean economic value of 175,500 Thai Baht per platform. We estimated that the biomass of fish associated with the seven platforms was at least four times higher per unit area than some of the world’s most productive coral reefs.
... When offshore oil and gas installations reach the end of their production life, operators and regulators must decide the best decommissioning option available, for example, to reduce the environmental impacts (Bond et al., 2018;Sommer et al., 2019). Large subsea infrastructure is installed onto the seabed where oil and gas exploration occur, including platforms, wellheads, and pipelines (umbilical, riser, flowline and trunk line structures) (Rouse et al., 2018). ...
... Although not collected for the purposes of scientific research, historical ROV imagery represents a rare and ready-made resource for ocean observation Levin et al., 2019), with the potential to facilitate investigation of a broad range of ecological, biological, behavioral and oceanographic questions, once adequately screened for quality. Historical ROV imagery has already been used to characterize fauna communities that develop on O&G infrastructure (Pradella et al., 2014;Rouse et al., 2018;Thomson et al., 2018;McLean et al., 2019) and assess the commercial fishery value of pipelines and wells (McLean et al., 2017Bond et al., 2018d). Some archival collections span decades and may even provide insights into the effects of longer-term environmental change on offshore ecosystems. ...
Remotely operated vehicles (ROVs) are used extensively by the offshore oil and gas and renewables industries for inspection, maintenance, and repair of their infrastructure. With thousands of subsea structures monitored across the world’s oceans from the shallows to depths greater than 1,000 m, there is a great and underutilized opportunity for their scientific use. Through slight modifications of ROV operations, and by augmenting industry workclass ROVs with a range of scientific equipment, industry can fuel scientific discoveries, contribute to an understanding of the impact of artificial structures in our oceans, and collect biotic and abiotic data to support our understanding of how oceans and marine life are changing. Here, we identify and describe operationally feasible methods to adjust the way in which industry ROVs are operated to enhance the scientific value of data that they collect, without significantly impacting scheduling or adding to deployment costs. These include: rapid marine life survey protocols, imaging improvements, the addition of a range of scientific sensors, and collection of biological samples. By partnering with qualified and experienced research scientists, industry can improve the quality of their ROV-derived data, allowing the data to be analyzed robustly. Small changes by industry now could provide substantial benefits to scientific research in the long-term and improve the quality of scientific data in existence once the structures require decommissioning. Such changes also have the potential to enhance industry’s environmental stewardship by improving their environmental management and facilitating more informed engagement with a range of external stakeholders, including regulators and the public.
... A number of fish species were observed in the vicinity of the subsea pipelines. The presence of ling underneath North Sea pipeline free spans (sections of pipeline unsupported by the substratum) is consistent with observations of fish aggregations under free spanning pipelines sections in Australian and Californian waters (Love and York, 2005;McLean et al., 2017;Bond et al., 2018c). Pipeline free spans are likely to offer shelter or refuge for the fish species observed in these habitats. ...
Oil and gas pipelines that lie exposed on the seabed can function as “artificial reefs,” providing habitat for fish and benthic species, including some that are listed under conservation designations. As the offshore hydrocarbon industry matures, operators and national governments must decide whether decommissioned pipelines should be left in situ or removed for onshore disposal. In most jurisdictions, there is a requirement to evaluate the environmental consequences of different pipeline decommissioning options in a comparative assessment. To do this effectively requires an understanding of the associations between pipelines and fauna. Pipeline operators routinely collect video footage for inspection and maintenance purposes using remotely operated vehicles (ROV). This footage has the potential to provide insight into interactions between the marine environment and offshore pipelines. This study uses inspection footage from eight pipelines to quantify the presence and abundance of species and features listed under a number of EU and United Kingdom conservation designations; 12 such features and species were observed on the pipelines or neighboring sediments. The soft coral Alcyonium digitatum was present in the highest densities on pipelines located on mud, while Sabellaria sp. and Echinus esculentus were more common on pipelines in sand. Gadoids, anemones and hermit crabs were also frequently observed around pipelines. The study identifies the limitations to the use of industry ROV footage for ecological purposes, but shows that with consideration of taxon size, image resolution, ROV speed and altitude, this can be a valuable approach to gain additional insights into environment-infrastructure interactions. The results suggest that removal of pipelines will remove established colonies of epibenthic species, some of which have conservation value. The ecological significance of this loss, however, must be weighed against the broader considerations during pipeline decommissioning including cost, technical feasibility and impacts to other marine users.
Context. Remotely operated vehicles (ROVs) are routinely used to inspect oil and gas infrastructure for industry’s operational purposes and scientists utilise this video footage to understand how fish interact with these structures.
Aim. This study aims to clarify how fish abundance data obtained from ROV video compares to that collected using baited remote underwater video (BRUV). Method. This study compares fish assemblages observed using an industry ROV and BRUVs along a pipeline located in 130-m water depth in north-west Australia.
Key results. Both methods recorded 22 species of fish, however each method observed 15 unique species. The fish assemblage recorded by each method was statistically different at all sites. Differences in the fish assemblages correlated with the caudal fin aspect ratio of each species: the mean caudal fin aspect ratio of fish recorded using BRUVs was 2.81, compared to
1.87 for ROV observations.
Conclusions. We interpret this to indicate differences in site attachment, with site-attached species having generally lower caudal fin aspect ratios that are associated with slower swimming speeds with a burst and glide pattern. Implications. Our results show that these remote video methods predominantly sample different fish assemblages and demonstrates how different sampling methods can provide different insights into fish interactions with subsea infrastructure.
In recent years, video footage obtained from routine industry surveys using remotely operated vehicles (ROVs) has been used to assess fish assemblages associated with offshore oil and gas infrastructure. However, as industry moves towards using autonomous underwater vehicles (AUVs), it is important to understand how such a change may affect assessments of fish assemblages and whether these data collected from AUVs can be directly compared to those collected from historic and future ROV footage. In an extremely rare opportunity, we compare fish assemblages surveyed by an industrial ROV and an industrial hybrid-AUV (H-AUV) along the same 2,060-m section of subsea pipeline, at the same time of day, within 1 day of each other. A total of 206 transects, each 20 m in length, were analyzed, recording 406 fish from 10 species. The H-AUV recorded all 10 fish species, while the ROV recorded seven. Mean species richness was ~4% higher for H-AUV, and mean abundance was ~21% higher for ROV; these differences can be considered negligible. Multivariate analysis revealed nonsignificant differences in species composition between survey methods. This result suggests that future surveys of fish at this pipeline using a similar H-AUV can yield comparable results to ROV and, as such, facilitate comparison to historical ROV imagery. Future surveys of pipelines with AUV should consider adding extra lighting and high-definition cameras onto booms similar to those operating on ROVs, which will provide a useful field of view into pipeline spans and make it easier to identify fish. Our study provides insight into the utility and comparability of industry ROV and AUV pipeline inspection footage for the assessment of fish assemblages associated with subsea pipelines, which is used to inform policies and practices on the installation and decommissioning of subsea infrastructure.
Full-subsets information theoretic approaches are becoming an increasingly popular
tool for exploring predictive power and variable importance where a wide range of
candidate predictors are being considered. Here, we describe a simple function in the
statistical programming language R that can be used to construct, fit, and compare a
complete model set of possible ecological or environmental predictors, given a re-
sponse variable of interest and a starting generalized additive (mixed) model fit. Main advantages include not requiring a complete model to be fit as the starting point for
candidate model set construction (meaning that a greater number of predictors can
potentially be explored than might be available through functions such as dredge);
model sets that include interactions between factors and continuous nonlinear pre-
dictors; and automatic removal of models with correlated predictors (based on a user
defined criterion for exclusion). The function takes continuous predictors, which are
fitted using smoothers via either gam, gamm (mgcv) or gamm4, as well as factor vari-
ables which are included on their own or as two- level interaction terms within the
gam smooth (via use of the “by” argument), or with themselves. The function allows
any model to be constructed and used as a null model, and takes a range of arguments
that allow control over the model set being constructed, including specifying cyclic
and linear continuous predictors, specification of the smoothing algorithm used, and
the maximum complexity allowed for smooth terms. The use of the function is dem-
onstrated via case studies that highlight how appropriate model sets can be easily
constructed and the broader utility of the approach for exploratory ecology.
The industrialization of the deep sea is expanding worldwide. Increasing oil and gas exploration activities in the absence of sufficient baseline data in deep-sea ecosystems has made environmental management challenging. Here, we review the types of activities that are associated with global offshore oil and gas development in water depths over 200 m, the typical impacts of these activities, some of the more extreme impacts of accidental oil and gas releases, and the current state of management in the major regions of offshore industrial activity including 18 exclusive economic zones. Direct impacts of infrastructure installation, including sediment resuspension and burial by seafloor anchors and pipelines, are typically restricted to a radius of ~100 m on from the installation on the seafloor. Discharges of water-based and low-toxicity oil-based drilling muds and produced water can extend over 2 km, while the ecological impacts at the population and community levels on the seafloor are most commonly on the order of 200–300 m from their source. These impacts may persist in the deep sea for many years and likely longer for its more fragile ecosystems, such as cold-water corals. This synthesis of information provides the basis for a series of recommendations for the management of offshore oil and gas development. An effective management strategy, aimed at minimizing risk of significant environmental harm, will typically encompass regulations of the activity itself (e.g., discharge practices, materials used), combined with spatial (e.g., avoidance rules and marine protected areas), and temporal measures (e.g., restricted activities during peak reproductive periods). Spatial management measures that encompass representatives of all of the regional deep-sea community types is important in this context. Implementation of these management strategies should consider minimum buffer zones to displace industrial activity beyond the range of typical impacts: at least 2 km from any discharge points and surface infrastructure and 200 m from seafloor infrastructure with no expected discharges. Although managing natural resources is, arguably, more challenging in deep-water environments, inclusion of these proven conservation tools contributes to robust environmental management strategies for oil and gas extraction in the deep sea.
An oil pipeline and its surrounding seafloor, located in the Santa Barbara Channel, southern California, were surveyed for fishes using a manned research submersible. The parts of the pipeline and seafloor surveyed were situated in waters 95235 m deep. Some sections of the surveyed pipe were covered with both sessile and motile invertebrates, such as sea anemones (Metridium cf. farcimen) and sea urchins (Allocentrotus fragilis), sea stars (particularlyHippasteria cf. spinosa andStylasterias cf. forreri ), basket stars (Gorgonocephalus eucnemis ), spot prawns (Pandalus platyceros), and king crabs (Paralithodes californiensis). Based on differences in fish assemblages, four habitats (shallow and deep pipeline and shallow and deep seafloor) were categorized. Fish densities along the shallow portion of the pipeline were about seven times higher than on the adjacent seafloor and densities along the deep pipeline portion were nearly six times that of the deeper seafloor. Along the pipeline, rockfishes comprised 84% of the fishes and included 22 species. Unidentified sanddabs (probably most or all Citharichthys sordidus), forming 33.2%, and combfishes (Zaniolepis frenata and Z. latipinnis), comprising 19% of the total, were most often observed on the seafloor. Most of the fishes living on the pipeline were either juveniles of such larger taxa as blackgill (Sebastes melanostomus), flag (S. rubrivinctus), and vermilion (S. miniatus) rockfishes, cowcod (S. levis), and lingcod (Ophiodon elongatus), or diminutive species such as halfbanded (S. semicinctus) and stripetail (S. saxicola) rockfishes, combfishes (Zaniolepis spp.), and poachers (Family Agonidae). Higher densities of fishes were often noted in areas of the pipeline that had been undercut. Of particular interest were the relatively high densities of juvenile cowcod along the deeper parts of the pipeline, densities that were far higher than any seen at over 80 natural outcrops and at ten platforms. We suggest that, in the process leading to oil platform and pipeline decommissioning, it is important to understand the role that human-made structure plays as fish habitat.
Demersal fishes on the continental rise and slope were sampled by trawl, baited trap and a baited camera. Seventy-one different species were trawled, but only 18 species approached baits. At rise soundings (4100 m to 2250 m) Coryphaenoides (Nematonurus) armatus was dominant at baits and comprised 41·5% of the trawl catch. On the slope (<2250 m) Synaphobranchus kaupi was dominant at baits and comprised 32·7% of the trawl catch. At 1500–2501 m Antimora rostrata competed at baits and comprised 5–10% of trawl catches. At 1500–1650 m Centroscymnus coelolepis also consumed baits but was not captured by trawl. For C. (N.) armatus abundance was proportional to tarr2 (where tarr= arrival time), demonstrating that arrival time of the first fish at baits provides an estimate of population density. Maximum estimated abundance at 2897 m was 877 km-2, more than five times the abundance on the abyssal plain. Halosauropsis macrochir, Lepidion eques, Coryphaenoides guentheri, Gadiculus argenteus and Coryphaenoides rupestris were important in trawl samples but absent or rare at baits.
The modification of the physical environment by organisms is a critical interaction in most ecosystems. The concept of ecosystem engineering acknowledges this fact and allows ecologists to develop the conceptual tools for uncovering general patterns and building broadly applicable models. Although the concept has occasioned some controversy during its development, it is quickly gaining acceptance among ecologists. We outline the nature of some of these controversies and describe some of the major insights gained by viewing ecological systems through the lens of ecosystem engineering. We close by discussing areas of research where we believe the concept of organisms as ecosystem engineers will be most likely to lead to significant insights into the structure and function of ecological systems.
Remote Operated Vehicles are routinely used to undertake inspection and maintenance activities of underwater pipelines in north-west Australia. In doing so, many terabytes of geo-referenced underwater video are collected at depths, and on a scale usually unobtainable for ecological research. We assessed fish diversity and abundance from existing ROV videos collected along 2–3 km sections of two pipelines in north-west Australia, one at 60–80 m water depth and the other at 120–130 m. A total of 5962 individual fish from 92 species and 42 families were observed. Both pipelines were characterised by a high abundance of commercially important fishes including: snappers (Lutjanidae) and groupers (Epinephelidae). The presence of thousands of unidentifiable larval fish, in addition to juveniles, sub-adults and adults suggests that the pipelines may be enhancing, rather than simply attracting, fish stocks. The prevalence and high complexity of sponges on the shallower pipeline and of deepwater corals on the deeper pipeline had a strong positive correlation with the fish abundance. These habitats likely offer a significant food source and refuge for fish, but also for invertebrates upon which fish feed. A greater diversity on the shallower pipeline, and a higher abundance of fishes on both pipelines, were associated with unsupported pipeline sections (spans) and many species appeared to be utilising pipeline spans as refuges. This study is a first look at the potential value of subsea pipelines for fishes on the north-west shelf. While the results suggest that these sections of pipeline appear to offer significant habitat that supports diverse and important commercially fished species, further work, including off-pipeline surveys on the natural seafloor, are required to determine conclusively the ecological value of pipelines and thereby inform discussions regarding the ecological implications of pipeline decommissioning.
Sediment transport-induced changes to the embedment of three 26 km long sections of subsea pipeline are analysed and subsequently explained using model scale experiments. Rather than the scour and scour-induced sinking and sagging traditionally thought to dominate post-lay pipeline spanning and embedment change, the change for these pipelines is shown to be caused by sedimentation. The pipelines traverse a range of metocean and soil conditions; the variation in embedment correlates well with the variation in metocean conditions, with most change occurring in an area where multidirectional high-velocity short-duration flows associated with internal waves propagate at near-perpendicular angles to the pipeline. To understand the mechanism driving these changes, a series of model scale tests in O-tube flumes have been completed under flow conditions mimicking those recorded in the field. Good agreement is found between the field and laboratory results, both in terms of the process timescale and the post-sedimentation profile. The consistency of the embedment changes between the pipelines, their correlation with metocean conditions, and the ability to replicate these changes in model scale tests suggests that such changes can be accounted for in more effective pipeline design. Spans are relatively rare along the pipelines but where they do occur fish rather than scour are shown to be the principal agent of span formation.
The generally accepted formation mechanism of pockmarks worldwide is the expulsion of fluid at the seafloor, but such a mechanism does not explain the close association between pockmarks and seabed infrastructure such as pipelines and wellheads within the Stag oil field on the North West Shelf of Australia. Furthermore, certain characteristics of the pockmarks, such as conical mounds of sediment positioned around their perimeters, are strongly suggestive of a biotic origin. Pockmarks in this case are typically 5m in diameter and 1m deep, excavated within a sandy seabed in 45m water depth. Inspection of ROV footage acquired during oilfield operations within the Stag field supports, but does not confirm without doubt, the proposition that the pockmarks are created by fish of the genus Epinephelus.
Effects of three different light wavelengths (blue, red and white) were assessed on the composition, abundance and behaviour of nocturnal fish at the Houtman Abrolhos Islands, Western Australia. The effects of fishing were also considered by further examining the combined effects of lighting and fishing (open vs. closed areas). Data were collected using baited remote underwater stereo-video systems (stereo-BRUVs), which were equipped with red (620–630 nm), white (550–560 nm) or blue (450–465 nm) lights. The total number of individuals, relative abundance of fish and assemblage composition differed under each lighting condition and fishing status. The greatest number of individuals was observed on samples illuminated by red lights (43% of all individuals surveyed). The species Apogon doederleini, Gymnothorax woodwardi, and Pempheris klunzingeri were each more abundant and spent longer in the field of view of the cameras using red lights. In contrast to white and blue light, the wavelength of red light is thought to be beyond the visual sensitivity of these fish species, and may not have affected their behaviour. The heavily targeted species, Pagrus auratus, were twice as abundant on stereo-BRUVs illuminated by blue lights and white lights than on red lights, but only in areas closed to fishing. This higher abundance on blue and white lights may have been due to the attraction of baitfish to these lights. In addition to the effects of lighting, clear effects of fishing were noted on nocturnal populations of P. auratus. Light wavelength can influence observations and measurements made of a nocturnal fish assemblage, and therefore careful consideration of choice of light wavelength should be made for nocturnal studies using artificial illumination on stereo-BRUVs.
This paper summarizes the results of an experimental study on the onset of scour below and self-burial of pipelines in currents/waves. Pressure was measured on the surface of a slightly buried pipe at two points, one at the upstream side and the other at the downstream side of the pipe, both in the sand bed. The latter enabled the pressure gradient (which drives a seepage flow underneath the pipe) to be calculated. The results indicated that the excessive seepage flow and the resulting piping are the major factor to cause the onset of scour below the pipeline. The onset of scour occurred always locally (but not along the length of the pipeline as a two-dimensional process). The critical condition corresponding to the onset of scour was determined both in the case of currents and in the case of waves. Once the scour breaks out, it will propagate along the length of the pipeline, scour holes being interrupted with stretches of soil (span shoulders) supporting the pipeline. As the span shoulder gets shorter and shorter, more and more weight of the pipeline is exerted on the soil. In this process, a critical point is reached where the bearing capacity of the soil is exceeded (general shear failure). At this point, the pipe begins to sink at the span shoulder (self-burial). It was found that the self-burial depth is governed mainly by the Keulegan–Carpenter number. The time scale of the self-burial process, on the other hand, is governed by the Keulegan–Carpenter number and the Shields parameter. Diagrams are given for the self-burial depth and the time scale of the self-burial process.
Western Australia has an extensive coastline ranging from the tropical north to the temperate south, with a high diversity of neritic marine fishes. Distribution data of 1855 neritic fish species were used to compare a range of methods for identifying priority areas for their conservation. Species richness and endemism richness hotspots, biogeographic zoning and complementarity analysis were tested for their efficiency at representing the total suite of species. The hotspot approaches demonstrated low efficiency, as the sections of coastline selected were grouped together in isolated geographic locations and relatively few of the total suite of neritic fish species were represented. Biogeographic zoning divided the coast of Western Australia into six regions, and as such, priority areas were selected around the entire coastline, which resulted in fairly high levels of efficiency. However, the complementarity analysis proved to be the most efficient method, as >95% of all neritic fish species could be represented in six, appropriately located, 100 km long sections of coastline. Complementarity analysis indicated a total of 26 priority areas for neritic fish conservation, which were spread around the entire coast of Western Australia. However, as current marine conservation measures in Western Australia are focused on the west and northwest coasts, this study highlighted the need for marine conservation efforts to be extended to cover the north and south coasts.
A field comparison of baited remote underwater video stations (BRUVS) and prawn (shrimp) trawls was made to assess the sampling options for describing patterns of fish biodiversity in the lagoonal waters of the Great Barrier Reef Marine Park. Replicated comparisons were made during the day and night on trawl grounds with different biophysical characteristics. Each trawl was made close and parallel to a long-shore set of five BRUVS set at regular intervals along one nautical mile. For each species, the sum of the maximum number of fish sighted on BRUVS at any one time (∑MaxN1, …, 5) was compared with the number of fish caught in trawls (N).
The length frequencies and age structures of resident Pseudanthias rubrizonatus (n = 407), a small protogynous serranid, were measured at four isolated artificial structures on the continental shelf of north-western Australia between June and August 2008, to determine whether these structures supported full (complete size and age-structured) populations of this species. The artificial structures were located in depths between 82 and 135 m, and growth rates of juveniles and adults, and body condition of adults, were compared among structures to determine the effect of depth on potential production. All life-history stages, including recently settled juveniles, females and terminal males, of P. rubrizonatus were caught, ranging in standard length (L(s)) from 16·9 to 96·5 mm. Presumed ages estimated from whole and sectioned otoliths ranged between 22 days and 5 years, and parameter ±s.e. estimates of the von Bertalanffy growth model were L(∞) = 152 ± 34 mm, k = 0·15(±0·05) and t(0) = -1·15(±0·15). Estimated annual growth rates were similar between shallow and deep artificial structures; however, otolith lengths and recent growth of juveniles differed among individual structures, irrespective of depth. The artificial structures therefore sustained full populations of P. rubrizonatus, from recently settled juveniles through to adults; however, confirmation of the maximum age attainable for the species is required from natural populations. Depth placement of artificial reefs may not affect the production of fish species with naturally wide depth ranges.
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