Journal of Fish Biology (2014) 84, 247–255 doi:10.1111/jfb.12274, available online at wileyonlinelibrary.com
Fish assemblages associated with oil industry structures on the continental shelf of north-western Australia N. Pradella*†, A. M. Fowler*, D. J. Booth* and P. I. Macreadie‡§ *Centre for Environmental Sustainability, School of the Environment, University of Technology, Sydney, P. O. Box 123, 2007 Broadway, Australia and ‡Plant Functional Biology and Climate Change Cluster, School of the Environment, University of Technology, Sydney, P. O. Box 123, 2007 Broadway, Australia (Received 5 August 2013, Accepted 11 October 2013) This study provides the first assessment of fish associations with oil and gas structures located in deep water (85–175 m) on Australia’s north-west continental shelf, using rare oil industry video footage obtained from remotely operated vehicles. A diverse range of taxa were observed associating with the structures, including reef-dependent species and transient pelagic species. Ten commercially fished species were observed, the most abundant of which was Lutjanus argentimaculatus, with an estimated biomass for the two deepest structures (Goodwyn and Echo) of 109 kg. © 2013 The Fisheries Society of the British Isles
Key words: artificial reef; decommissioning; Lutjanus argentimaculatus; rigs-to-reefs; video analysis.
Currently, there are more than 7500 oil industry structures (e.g. rigs and platforms) deployed in offshore waters worldwide, and c. 85% of them will become obsolete and require decommissioning within the next decade (Parente et al., 2006). Decommissioning of obsolete structures usually involves complete removal from the seabed and deconstruction on land; however, a proposed alternative is to convert obsolete structures into artificial reefs (Macreadie et al., 2011). The ‘rigs-to-reefs’ (RTR) alternative is largely based on the suggestion that rigs provide fishes with important habitat and improve fisheries production (Helvey, 2002; Love et al., 2006). Indeed, some rigs have been found to support high abundances of reef-associated species (Hastings et al., 1976; Rooker et al., 1997; Stanley & Wilson, 2000; Love & York, 2005; Love et al., 2005), including commercially important species that are in decline on natural reefs (Love et al., 2006). Almost all research on fish assemblages associated with oil industry structures has been conducted in two regions of the U.S.A. §Author to whom correspondence should be addressed. Tel.: + 61 2 9514 4038; email: [email protected] †Present address: School of Arts and Sciences, Australian Catholic University, PO Box 968, North Sydney 2059, Australia.
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(southern California and the Gulf of Mexico), and little is known about fish associations with oil structures in other regions. Consequently, the general importance of oil industry structures as fish habitat cannot be evaluated, and most regions of the world cannot make informed decisions on whether or not to leave their obsolete structures in place (Macreadie et al., 2012). This study provides a ‘first look’ at the fish assemblages associated with oil structures on the north-western Australia continental shelf (NWS), where hundreds of structures, including rigs, platforms and well heads, will require decommissioning within the next decade (N.R. Anthony, B.F. Ronaldo & E. Fakas, unpubl. data). Remotely operated vehicle (ROV) footage opportunistically obtained from standard industry operations is used to examine the fish assemblages associated with obsolete well heads (Fig. 1), a common oil industry structure on the NWS. The aims of this study were to: (1) identify fish species associated with well heads on the NWS, particularly commercially important species and (2) determine any differences in assemblages among well heads, and thereby assess the variability of assemblages on these structures. A modified visual census method is also described, which allows collection of fish assemblage data from short (1 min) sections of video footage obtained from the oil industry (i.e. non-scientifically collected footage). Three obsolete well heads (Wanaea, Goodwyn and Echo) were surveyed on the outer NWS (c. 150 km north north-east of Barrow Island, 20◦ 47 53 S; 115◦ 24 22 E) over three voyages between 7 June and 19 July 2008. The seabed on the outer NWS is composed of fine sand and mud (Lyne et al., 2006), and video observations confirmed that each structure was located on soft sediment with no hard substrata present within at least 100 m. The well heads were located at a range of depths (Wanaea 84 m, Goodwyn 133 m and Echo 175 m), and were separated by distances of 29–73 km. They had dimensions of 2·6 m × 2·6 m × 4 m (the last dimension is height) and provided complex habitats, with high vertical relief and numerous holes and overhangs of a range of sizes. They were heavily encrusted
XLS 19
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DPTH 149·1 ALT 1·65 HDG 83·2
E 366270·9 N 7820053·46
Fig. 1. Example of remotely operated vehicle footage showing fish associated with a well head.
© 2013 The Fisheries Society of the British Isles, Journal of Fish Biology 2014, 84, 247–255
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with fouling organisms, including sponges, soft corals and barnacles. Well heads were between 16 and 22 years old at the time of surveying. Video footage of the well heads was opportunistically obtained from standard industry surveys conducted with an ROV using a single camera. All available footage (c. 20 h) was assessed to identify species associating with the well heads. To avoid bias arising from non-standardized surveys a sub-set of footage was selected for comparative analyses of assemblages among well heads. Selected footage was: (1) stationary, (2) taken ≤2 m from the structure, (3) had ≥5 m visibility and (4) included the top section of the structure (where most species were located). The resulting field of view sampled c. 50% of the structure, and included a water volume of c. 13·5 m3 . The duration of suitable footage for comparisons was restricted; therefore, species accumulation over time was assessed to determine the minimum survey period that provided representative data. Eighty per cent of species observed on the well heads were encountered in the first minute of footage; therefore, 1 min survey periods were used. This allowed 6 day and 4 night surveys at Wanaea, 9 day and 5 night surveys at Goodwyn and 9 day and 6 night surveys at Echo when ROV dives were pooled across voyages. Footage analysed for each well head included surveys from at least two voyages. ROV lights were required during both day and night surveys owing to the low light conditions at depth. While this may have influenced abundances of some taxa, no reaction (attraction or repulsion) to the light was observed. Because lights were consistently used across all surveys, relative comparisons between sites and diel periods are unlikely to be affected. Assemblage structure was assessed using the rapid visual technique (RVT; Jones & Thompson, 1978). This method uses a rank-based scoring system to determine relative abundance indices (%) for each taxon, and is useful for examining assemblage structure when identification of all individuals within a taxon is difficult. Surveys are divided into regular time intervals, and the time interval that a taxon is encountered is recorded, rather than the actual abundance. Taxa that are encountered earlier in the survey or are encountered multiple times during a survey, or both, receive higher scores than those encountered later in the survey, or infrequently, or both. Replicate surveys are used to generate multiple scores for each taxon, and a relative index is calculated by comparing summed scores to the total score including all taxa. Total fish density (including all taxa) was estimated for each survey using a categorical scoring system. Biomass of the most abundant species [mangrove jack Lutjanus argentimaculatus (Forssk˚al 1775)] was calculated for each structure by multiplying the maximum number of fish by their mass, determined from total length (LT ) estimations and the established LT and mass relationship for the species (Froese & Pauly, 2011). The LT was estimated using objects of known size in the field of view for calibration. Multiple objects were used for calibration, depending on where the individual was located in the field of view. This minimized the potential error associated with estimating LT of fish that differed in distance from the camera. Data were examined at the family level owing to the difficulty in identifying all taxa to genus and species. Exceptions were small ( 0·05). Fish density (categorical) was higher at Wanaea than Echo (Tukey’s test: P < 0·05), but did not differ between other structures (Tukey’s test: P > 0·05 for all). Both richness and density were higher during the day than during the night (richness: ANOVA: F 1,33 = 19·88, P < 0·001; density: ANOVA: F 1,33 = 19·88, P < 0·001). RVT survey analysis indicated that small (50 individuals were also observed outside the survey field of view on some occasions. Mean ± s.e. LT of L. argentimaculatus was estimated to be 526 ±14 mm at Goodwyn and 540 ±15 mm at Echo, and these values did not differ significantly (t-test; d.f. = 9, P > 0·05). This size range corresponds to recently matured individuals (mean length at which 50% are mature, L50 , male = 452 mm fork length, LF , mean L50 female = 461 mm LF ) between 4 © 2013 The Fisheries Society of the British Isles, Journal of Fish Biology 2014, 84, 247–255
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Table I. Fish species associated with the three oil industry structures Family Apogonidae Caesionidae Carangidae
Glaucosomatidae Lutjanidae
Orectolobidae Pomacentridae Rhincodontidae Rhinobatidae Scorpaenidae
Serranidae
Sparidae Tetraodontidae
Common name Unidentified cardinalfish sp. 1 Unidentified cardinalfish sp. 2 Unidentified fusilier sp. 1 Banded trevally Bluefin trevally Greater amberjack Highfin amberjack Blotched fantail ray Deepsea jewfish Mangrove jack Darktail snapper Malabar snapper Moses perch Red snapper Wobbegong sp. 1 Smokey chromis Whale shark Guitarfish Deepwater firefish Guam Scorpionfish Unidentified firefish sp. 1 Tomato rockcod Blunt-headed rockcod Malabar grouper Small-toothed cod Rankin cod Unidentified grouper sp. 1 Deepsea fairy basslet Unidentified basslet sp. 1 Long spined snapper Narrow-lined pufferfish
Scientific name
Carangoides ferdau Caranx melanpygus Seriola dumerili Seriola rivoliana Taeniura meyeni Glaucosoma burgeri Lutjanus argentimaculatus Lutjanus lemniscatus Lutjanus malabaricus Lutjanus russelli Lutjanus sebae Chromis fumea Rhincodon typus Rhynchobatus sp. Pterois mombasae Scorpaenodes guamensis Pterois sp. Cephalopholis sonnerati Epinephelus amblycephalus Epinephelus malabaricus Epinephelus microdon Epinephelus multinotatus Epinephelus sp. Pseudanthias rubrizonatus Pseudanthias sp. Argyrops spinifer Arothron malinensis
and 7 years of age (Pember et al., 2005). Biomass of this species was estimated to be 4·08 kg m−3 at Goodwyn and 4·01 kg m−3 at Echo, resulting in a total biomass estimate of 55·08 and 54·14 kg within the 13·5 m3 survey field of view for Goodwyn and Echo. This study provides the first data on fishes associated with oil industry structures in Australia, and results support the findings from southern California and the northern Gulf of Mexico, which show that numerous species associate with oil industry structures, including commercial species (Hastings et al., 1976; Rooker et al., 1997; Stanley & Wilson, 2000; Love & York, 2005; Love et al., 2005, 2006). Similar to these regions, however, the ecological importance of fish associations
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6·0
(a)
Taxonomic richness
5·0
b a
a
4·0 3·0 2·0 1·0 0
Density (categorical)
3·0
(b)
a ab
2·5
b 2·0 1·5 1·0 0·5 0 Wanaea
Goodwyn
Echo
Fig. 2. Mean ± s.e. of (a) taxonomic richness (number of species) and (b) total fish density (categorical: video footage was frozen on the frame which contained the maximum number of individuals, and a score of 1 was given for 500 individuals) on the three well heads. Values that share a lower case letter were not significantly different (P > 0·05) according to Tukey’s multiple comparison test.
with oil structures on the NWS remains unclear. Because of the narrow period of investigation (June to July 2008), the extent to which mobile species (including commercial species) use the oil structures as habitat could not be assessed. Longer term assessments of fish associations, as well as site fidelity, are required to determine the habitat role of oil structures on the NWS for mobile species. In contrast, oil structures probably provided permanent habitat for smaller site-attached reef species (e.g. anthiine serranids), owing to the absence of other reef within at least 100 m (Fowler & Booth, 2012). A key aspect of the habitat value of oil structures is whether they produce fish biomass or simply attract individuals from surrounding natural habitat [the ‘attraction v . production’ debate (Bohnsack, 1989)]. The extent to which the two processes are operating on structures in this study cannot be determined owing to the lack of long-term data. The biomass of L. argentimaculatus was probably produced inshore, however, and subsequently attracted to the offshore structures, because L. argentimaculatus recruits to estuaries and only moves offshore at larger sizes [400+ mm LF (Russell & McDougall, 2005)]. The structures may still have contributed to the © 2013 The Fisheries Society of the British Isles, Journal of Fish Biology 2014, 84, 247–255
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(a)
(b)
(c)
(d)
(e)
(f)
30 20 10 0 40 30
Relative abundance (%)
20 10 0 40 30 20 10 0 40
Wanaea
(g)
Goodwyn
Echo
30 20 10 0 Wanaea
Goodwyn
Echo
Fig. 3. Relative abundance indices of (a) small (
Fish assemblages associated with oil industry structures on the continental shelf of north-western Australia N. Pradella*†, A. M. Fowler*, D. J. Booth* and P. I. Macreadie‡§ *Centre for Environmental Sustainability, School of the Environment, University of Technology, Sydney, P. O. Box 123, 2007 Broadway, Australia and ‡Plant Functional Biology and Climate Change Cluster, School of the Environment, University of Technology, Sydney, P. O. Box 123, 2007 Broadway, Australia (Received 5 August 2013, Accepted 11 October 2013) This study provides the first assessment of fish associations with oil and gas structures located in deep water (85–175 m) on Australia’s north-west continental shelf, using rare oil industry video footage obtained from remotely operated vehicles. A diverse range of taxa were observed associating with the structures, including reef-dependent species and transient pelagic species. Ten commercially fished species were observed, the most abundant of which was Lutjanus argentimaculatus, with an estimated biomass for the two deepest structures (Goodwyn and Echo) of 109 kg. © 2013 The Fisheries Society of the British Isles
Key words: artificial reef; decommissioning; Lutjanus argentimaculatus; rigs-to-reefs; video analysis.
Currently, there are more than 7500 oil industry structures (e.g. rigs and platforms) deployed in offshore waters worldwide, and c. 85% of them will become obsolete and require decommissioning within the next decade (Parente et al., 2006). Decommissioning of obsolete structures usually involves complete removal from the seabed and deconstruction on land; however, a proposed alternative is to convert obsolete structures into artificial reefs (Macreadie et al., 2011). The ‘rigs-to-reefs’ (RTR) alternative is largely based on the suggestion that rigs provide fishes with important habitat and improve fisheries production (Helvey, 2002; Love et al., 2006). Indeed, some rigs have been found to support high abundances of reef-associated species (Hastings et al., 1976; Rooker et al., 1997; Stanley & Wilson, 2000; Love & York, 2005; Love et al., 2005), including commercially important species that are in decline on natural reefs (Love et al., 2006). Almost all research on fish assemblages associated with oil industry structures has been conducted in two regions of the U.S.A. §Author to whom correspondence should be addressed. Tel.: + 61 2 9514 4038; email: [email protected] †Present address: School of Arts and Sciences, Australian Catholic University, PO Box 968, North Sydney 2059, Australia.
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(southern California and the Gulf of Mexico), and little is known about fish associations with oil structures in other regions. Consequently, the general importance of oil industry structures as fish habitat cannot be evaluated, and most regions of the world cannot make informed decisions on whether or not to leave their obsolete structures in place (Macreadie et al., 2012). This study provides a ‘first look’ at the fish assemblages associated with oil structures on the north-western Australia continental shelf (NWS), where hundreds of structures, including rigs, platforms and well heads, will require decommissioning within the next decade (N.R. Anthony, B.F. Ronaldo & E. Fakas, unpubl. data). Remotely operated vehicle (ROV) footage opportunistically obtained from standard industry operations is used to examine the fish assemblages associated with obsolete well heads (Fig. 1), a common oil industry structure on the NWS. The aims of this study were to: (1) identify fish species associated with well heads on the NWS, particularly commercially important species and (2) determine any differences in assemblages among well heads, and thereby assess the variability of assemblages on these structures. A modified visual census method is also described, which allows collection of fish assemblage data from short (1 min) sections of video footage obtained from the oil industry (i.e. non-scientifically collected footage). Three obsolete well heads (Wanaea, Goodwyn and Echo) were surveyed on the outer NWS (c. 150 km north north-east of Barrow Island, 20◦ 47 53 S; 115◦ 24 22 E) over three voyages between 7 June and 19 July 2008. The seabed on the outer NWS is composed of fine sand and mud (Lyne et al., 2006), and video observations confirmed that each structure was located on soft sediment with no hard substrata present within at least 100 m. The well heads were located at a range of depths (Wanaea 84 m, Goodwyn 133 m and Echo 175 m), and were separated by distances of 29–73 km. They had dimensions of 2·6 m × 2·6 m × 4 m (the last dimension is height) and provided complex habitats, with high vertical relief and numerous holes and overhangs of a range of sizes. They were heavily encrusted
XLS 19
14 Jul 2008
16:29:53
WEL Severance ECHO 1
DPTH 149·1 ALT 1·65 HDG 83·2
E 366270·9 N 7820053·46
Fig. 1. Example of remotely operated vehicle footage showing fish associated with a well head.
© 2013 The Fisheries Society of the British Isles, Journal of Fish Biology 2014, 84, 247–255
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with fouling organisms, including sponges, soft corals and barnacles. Well heads were between 16 and 22 years old at the time of surveying. Video footage of the well heads was opportunistically obtained from standard industry surveys conducted with an ROV using a single camera. All available footage (c. 20 h) was assessed to identify species associating with the well heads. To avoid bias arising from non-standardized surveys a sub-set of footage was selected for comparative analyses of assemblages among well heads. Selected footage was: (1) stationary, (2) taken ≤2 m from the structure, (3) had ≥5 m visibility and (4) included the top section of the structure (where most species were located). The resulting field of view sampled c. 50% of the structure, and included a water volume of c. 13·5 m3 . The duration of suitable footage for comparisons was restricted; therefore, species accumulation over time was assessed to determine the minimum survey period that provided representative data. Eighty per cent of species observed on the well heads were encountered in the first minute of footage; therefore, 1 min survey periods were used. This allowed 6 day and 4 night surveys at Wanaea, 9 day and 5 night surveys at Goodwyn and 9 day and 6 night surveys at Echo when ROV dives were pooled across voyages. Footage analysed for each well head included surveys from at least two voyages. ROV lights were required during both day and night surveys owing to the low light conditions at depth. While this may have influenced abundances of some taxa, no reaction (attraction or repulsion) to the light was observed. Because lights were consistently used across all surveys, relative comparisons between sites and diel periods are unlikely to be affected. Assemblage structure was assessed using the rapid visual technique (RVT; Jones & Thompson, 1978). This method uses a rank-based scoring system to determine relative abundance indices (%) for each taxon, and is useful for examining assemblage structure when identification of all individuals within a taxon is difficult. Surveys are divided into regular time intervals, and the time interval that a taxon is encountered is recorded, rather than the actual abundance. Taxa that are encountered earlier in the survey or are encountered multiple times during a survey, or both, receive higher scores than those encountered later in the survey, or infrequently, or both. Replicate surveys are used to generate multiple scores for each taxon, and a relative index is calculated by comparing summed scores to the total score including all taxa. Total fish density (including all taxa) was estimated for each survey using a categorical scoring system. Biomass of the most abundant species [mangrove jack Lutjanus argentimaculatus (Forssk˚al 1775)] was calculated for each structure by multiplying the maximum number of fish by their mass, determined from total length (LT ) estimations and the established LT and mass relationship for the species (Froese & Pauly, 2011). The LT was estimated using objects of known size in the field of view for calibration. Multiple objects were used for calibration, depending on where the individual was located in the field of view. This minimized the potential error associated with estimating LT of fish that differed in distance from the camera. Data were examined at the family level owing to the difficulty in identifying all taxa to genus and species. Exceptions were small ( 0·05). Fish density (categorical) was higher at Wanaea than Echo (Tukey’s test: P < 0·05), but did not differ between other structures (Tukey’s test: P > 0·05 for all). Both richness and density were higher during the day than during the night (richness: ANOVA: F 1,33 = 19·88, P < 0·001; density: ANOVA: F 1,33 = 19·88, P < 0·001). RVT survey analysis indicated that small (50 individuals were also observed outside the survey field of view on some occasions. Mean ± s.e. LT of L. argentimaculatus was estimated to be 526 ±14 mm at Goodwyn and 540 ±15 mm at Echo, and these values did not differ significantly (t-test; d.f. = 9, P > 0·05). This size range corresponds to recently matured individuals (mean length at which 50% are mature, L50 , male = 452 mm fork length, LF , mean L50 female = 461 mm LF ) between 4 © 2013 The Fisheries Society of the British Isles, Journal of Fish Biology 2014, 84, 247–255
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Table I. Fish species associated with the three oil industry structures Family Apogonidae Caesionidae Carangidae
Glaucosomatidae Lutjanidae
Orectolobidae Pomacentridae Rhincodontidae Rhinobatidae Scorpaenidae
Serranidae
Sparidae Tetraodontidae
Common name Unidentified cardinalfish sp. 1 Unidentified cardinalfish sp. 2 Unidentified fusilier sp. 1 Banded trevally Bluefin trevally Greater amberjack Highfin amberjack Blotched fantail ray Deepsea jewfish Mangrove jack Darktail snapper Malabar snapper Moses perch Red snapper Wobbegong sp. 1 Smokey chromis Whale shark Guitarfish Deepwater firefish Guam Scorpionfish Unidentified firefish sp. 1 Tomato rockcod Blunt-headed rockcod Malabar grouper Small-toothed cod Rankin cod Unidentified grouper sp. 1 Deepsea fairy basslet Unidentified basslet sp. 1 Long spined snapper Narrow-lined pufferfish
Scientific name
Carangoides ferdau Caranx melanpygus Seriola dumerili Seriola rivoliana Taeniura meyeni Glaucosoma burgeri Lutjanus argentimaculatus Lutjanus lemniscatus Lutjanus malabaricus Lutjanus russelli Lutjanus sebae Chromis fumea Rhincodon typus Rhynchobatus sp. Pterois mombasae Scorpaenodes guamensis Pterois sp. Cephalopholis sonnerati Epinephelus amblycephalus Epinephelus malabaricus Epinephelus microdon Epinephelus multinotatus Epinephelus sp. Pseudanthias rubrizonatus Pseudanthias sp. Argyrops spinifer Arothron malinensis
and 7 years of age (Pember et al., 2005). Biomass of this species was estimated to be 4·08 kg m−3 at Goodwyn and 4·01 kg m−3 at Echo, resulting in a total biomass estimate of 55·08 and 54·14 kg within the 13·5 m3 survey field of view for Goodwyn and Echo. This study provides the first data on fishes associated with oil industry structures in Australia, and results support the findings from southern California and the northern Gulf of Mexico, which show that numerous species associate with oil industry structures, including commercial species (Hastings et al., 1976; Rooker et al., 1997; Stanley & Wilson, 2000; Love & York, 2005; Love et al., 2005, 2006). Similar to these regions, however, the ecological importance of fish associations
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6·0
(a)
Taxonomic richness
5·0
b a
a
4·0 3·0 2·0 1·0 0
Density (categorical)
3·0
(b)
a ab
2·5
b 2·0 1·5 1·0 0·5 0 Wanaea
Goodwyn
Echo
Fig. 2. Mean ± s.e. of (a) taxonomic richness (number of species) and (b) total fish density (categorical: video footage was frozen on the frame which contained the maximum number of individuals, and a score of 1 was given for 500 individuals) on the three well heads. Values that share a lower case letter were not significantly different (P > 0·05) according to Tukey’s multiple comparison test.
with oil structures on the NWS remains unclear. Because of the narrow period of investigation (June to July 2008), the extent to which mobile species (including commercial species) use the oil structures as habitat could not be assessed. Longer term assessments of fish associations, as well as site fidelity, are required to determine the habitat role of oil structures on the NWS for mobile species. In contrast, oil structures probably provided permanent habitat for smaller site-attached reef species (e.g. anthiine serranids), owing to the absence of other reef within at least 100 m (Fowler & Booth, 2012). A key aspect of the habitat value of oil structures is whether they produce fish biomass or simply attract individuals from surrounding natural habitat [the ‘attraction v . production’ debate (Bohnsack, 1989)]. The extent to which the two processes are operating on structures in this study cannot be determined owing to the lack of long-term data. The biomass of L. argentimaculatus was probably produced inshore, however, and subsequently attracted to the offshore structures, because L. argentimaculatus recruits to estuaries and only moves offshore at larger sizes [400+ mm LF (Russell & McDougall, 2005)]. The structures may still have contributed to the © 2013 The Fisheries Society of the British Isles, Journal of Fish Biology 2014, 84, 247–255
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(a)
(b)
(c)
(d)
(e)
(f)
30 20 10 0 40 30
Relative abundance (%)
20 10 0 40 30 20 10 0 40
Wanaea
(g)
Goodwyn
Echo
30 20 10 0 Wanaea
Goodwyn
Echo
Fig. 3. Relative abundance indices of (a) small (
