Since the discoveries of vertebrate bioapatite’s ability to record oxygen isotopecomposition of ambient seawater were made (Kolodny, 1983), oxygen isotopes have beenwidely used as a climatic and oceanographic proxy. The δ18OP aquatic vertebrate apatite isa function of the δ18Ow value of the ambient water, yet “vital effects” on the δ18OP compositionhave been reported previously (Venneman et al., 2013). I have analysed δ18O compositionin the teeth of six extant shark and ray (chondrichthyan) species from the tropical ocean tankof the Blackpool Sea Life Center, UK. The teeth were naturally shed and collected from thetank substrate.Preparation of samples was performed in the Laboratory of Isotope Geology at the NaturalHistory Museum of Stockholm (Sweden), and the δ18O was measured at the NordSIM facility,using secondary ionization mass spectrometry (SIMS) by a high precision and high spatialresolutionCAMECA IMS 1280 ion microprobe.Data treatment was followed by statistical analysis. Results show significant δ18O differencesat inter-tissue level. I could also illustrate the impact of organics-pretreatment on the finalδ18O values, with the outcome of one more favourable pretreatment for SIMS analysis. Intertaxonvariability was observed, without much statistical confidence, but I hypothesize that itmay be due to the difference in tissue crystallization and organic quantity between species.

The chondrichthyan (shark, batoid and holocephalan) bycatch of the Queensland East Coast Trawl Fishery (ECTF) was examined through a series of fishery-independent trawl surveys, together with fishery-dependent (opportunistic) sampling. Project aims were to document the chondrichthyan bycatch composition in order to test the effectiveness of turtle exclusion devices (TEDs) and bycatch reduction devices (BRDs), to examine biological aspects of bycatch species, and to combine data collected through these parts to assess the conservation status and sustainability of bycatch species. A total of 37 chondrichthyan species (one holocephalan, 19 batoids and 17 sharks) from 18 families were recorded in the bycatch of the fishery. The most speciose families recorded were the stingrays (Dasyatidae; 7 species), the requiem sharks (Carcharhinidae; 5 species), the catsharks (Scyliorhinidae; 4 species) and the stingarees (Urolophidae; 3 species). Chondrichthyan bycatch was highly variable between fishery sectors; catch rates were low in the tiger/Endeavour prawn sector (north Queensland; 0.02–0.12 individuals ha-1 trawled) and in the eastern king prawn (deepwater) sector (southern Queensland; 0.08 individuals ha-1 trawled), intermediate in Hervey Bay (southern Queensland; 0.25 individuals ha-1 trawled) and in the scallop sector (central Queensland coast; 0.31 individuals ha-1 trawled) and highest in the eastern king prawn (shallow water) sector (southern Queensland; 0.96 individuals ha-1 trawled). Chondrichthyan bycatch in the eastern king prawn (shallow water) sector was dominated by the three batoids Aptychotrema rostrata, Trygonoptera testacea and Urolophus kapalensis (~92% of the chondrichthyan bycatch by number), in the eastern king prawn (deepwater) sector by the skate Dipturus polyommata and the two catsharks Asymbolus rubiginosus and Figaro boardmani (~83% of the chondrichthyan bycatch by number), in the scallop sector by the three batoids A. rostrata, Neotrygon kuhlii and Neotrygon picta (~91% of the chondrichthyan bycatch by number), and in the tiger/Endeavour prawn sector by the two batoids Himantura astra and Gymnura australis and the two sharks Chiloscyllium punctatum and Hemigaleus australiensis (~67% of the chondrichthyan bycatch by number). The testing of TEDs and BRDs, which are mandatory throughout the fishery, demonstrated only a limited ability to reduce chondrichthyan bycatch in the ECTF, which is comprised mainly of relatively small species. The shorter trawl durations of the surveys compared with normal commercial activities may have under-represented larger species. No significant reductions in chondrichthyan bycatch were found using a TED and a radial escape section BRD in the eastern king prawn (shallow water) sector, using a TED and a square-mesh codend BRD in the eastern king prawn (deepwater) sector, or using a TED and a fisheye BRD in Hervey Bay. There was however, a significant difference in the probability of capturing the group ‘sharks and guitarfishes’ (comprised largely of A. rostrata) between codend types in the scallop sector, with the lowest probability of capture in nets fitted with both a TED and a square-mesh codend BRD (the difference was largely attributed to the effects of the TED). In the tiger/Endeavour prawn sector, in which three different BRDs were trialed (fisheye, square-mesh codend, square-mesh panel), the probability of capturing chondrichthyans was significantly lower in nets fitted with a fisheye BRD than in the standard (control) net, and the probability of capturing batoids was significantly lower in nets fitted with a fisheye BRD or with a square-mesh codend BRD than in the standard (control) net. The small sample size of chondrichthyan catches in some sectors may have reduced to power to detect bycatch reduction. The biology of several bycatch species from the families Rajidae, Rhinobatidae, Urolophidae and Scyliorhinidae was examined. For D. polyommata, size at birth was estimated at ~100–110 mm total length (LT), size at first feeding at ~105–110mm LT, size at 50% maturity (LT50 and 95% CI) at 321 (305–332) mm LT for females and 300 (285–306) mm LT for males. Diet (described by the index of relative importance as a percentage) was predominantly crustacean based, with carid shrimps (53.6%) and penaeoid prawns (23.3%) being the most significant prey groups. For A. rostrata, size at birth was estimated at <170 mm LT, size at 50% maturity (LT50 and 95% CI) at 640 (618–663) mm LT for females and 597 (551–649) mm LT for males, and litter size was 9–20 (n = 9; mean ± S.E. = 15.1 ± 1.2). For T. testacea, size at birth was estimated at 77–100 mm disc width (WD), size at 50% maturity (WD50 and 95% CI) at 163 (156–169) mm WD for females and 146 (140–150) mm WD for males, and litter size was always one (n = 6). For U. kapalensis, size at birth was estimated at 75–100 mm WD, size at 50% maturity (WD50 and 95% CI) at 154 (145–160) mm WD for females and 155 (149–159) mm WD for males, and litter size was always one (n = 16). The catsharks A. analis, A. rubiginosus and F. boardmani were all confirmed as single oviparous species (carrying only one egg case in each uterus at one time). Ovarian fecundity (the number of vitellogenic follicles) averaged 13.6 (range 13–20) in A. analis, 13.5 (range 5–23) in A. rubiginosus and 10.4 (range 9–13) in F. boardmani. While only limited data were available from southern Queensland, several indicators suggest that Asymbolus catsharks are reproductively active year-round. A general lack of small-sized or immature catsharks captured during the study made assessments of size at maturity difficult for these species. The conservation status of ECTF bycatch species was examined through the application of the IUCN Red List of Threatened SpeciesTM Categories and Criteria, which considers extinction risk at the global level. Of the 24 ECTF chondrichthyan bycatch species evaluated against the IUCN Red List Categories and Criteria, four have been assessed globally as Vulnerable (a threatened category indicating that a species is ‘facing a high risk of extinction in the wild’), seven as Near Threatened, 11 as Least Concern and two as Data Deficient. While the four globally threatened species (A. nichofii, Heteroscyllium colcloughi, Rhynchobatus australiae and Urolophus sufflavus) were only minor components of the ECTF bycatch, their global conservation status warrants that fisheries management and industry should act to ensure minimal impacts on these species. An ecological risk assessment method (Susceptibility-Recovery Analysis) was used to assess the relative sustainability or risk of individual species to the fishing activities of the ECTF. Two separate approaches were taken to the technique, which considers sustainability to be dependent on the susceptibility of a species to the fishery and the recovery potential of a species after depletion by fishing activities. The first approach applied the precautionary principal when data were lacking for the calculation of recovery attributes, while the second used biological data from similar species when species-specific data were lacking. The precautionary approach tended to overestimate risk to poorly known oviparous species. The biological approach suggested that A. nichofii, F. boardmani, Rhizoprionodon acutus, Rhizoprionodon taylori and Rhynchobatus palpebratus face the least risk (i.e. were the most sustainable) while several medium-large batoids and the sharks Loxodon macrorhinus and Heteroscyllium colcloughi were the species most at risk (i.e. least sustainable). Demonstrating ecological sustainability of the ECTF will need to be a continued management objective into the future. To further improve the ecological sustainability of the fishery in relation to sharks, batoids and holocephalans, a number of management recommendations are proposed: (1) give warranted conservation consideration to listed threatened species as well as species identified as being at risk; (2) expand required logbook information on chondrichthyan species to include recording of catches of these species; (3) encourage safe release practices for all chondrichthyans to maximise survivorship of discards; (4) initiate research into the survivorship of discards; (5) ensure long-term observer coverage on commercial vessels to monitor bycatch levels; and, (6) test and quantify reduced TED bar spacings (presently 120 mm) in fishery sectors which show the highest chondrichthyan bycatch levels, that is, the eastern king prawn (shallow water) and scallop sectors.

The chondrichthyan (shark, batoid and holocephalan) bycatch of the Queensland East Coast Trawl Fishery (ECTF) was examined through a series of fishery-independent trawl surveys, together with fishery-dependent (opportunistic) sampling. Project aims were to document the chondrichthyan bycatch composition in order to test the effectiveness of turtle exclusion devices (TEDs) and bycatch reduction devices (BRDs), to examine biological aspects of bycatch species, and to combine data collected through these parts to assess the conservation status and sustainability of bycatch species. A total of 37 chondrichthyan species (one holocephalan, 19 batoids and 17 sharks) from 18 families were recorded in the bycatch of the fishery. The most speciose families recorded were the stingrays (Dasyatidae; 7 species), the requiem sharks (Carcharhinidae; 5 species), the catsharks (Scyliorhinidae; 4 species) and the stingarees (Urolophidae; 3 species). Chondrichthyan bycatch was highly variable between fishery sectors; catch rates were low in the tiger/Endeavour prawn sector (north Queensland; 0.02–0.12 individuals ha-1 trawled) and in the eastern king prawn (deepwater) sector (southern Queensland; 0.08 individuals ha-1 trawled), intermediate in Hervey Bay (southern Queensland; 0.25 individuals ha-1 trawled) and in the scallop sector (central Queensland coast; 0.31 individuals ha-1 trawled) and highest in the eastern king prawn (shallow water) sector (southern Queensland; 0.96 individuals ha-1 trawled). Chondrichthyan bycatch in the eastern king prawn (shallow water) sector was dominated by the three batoids Aptychotrema rostrata, Trygonoptera testacea and Urolophus kapalensis (~92% of the chondrichthyan bycatch by number), in the eastern king prawn (deepwater) sector by the skate Dipturus polyommata and the two catsharks Asymbolus rubiginosus and Figaro boardmani (~83% of the chondrichthyan bycatch by number), in the scallop sector by the three batoids A. rostrata, Neotrygon kuhlii and Neotrygon picta (~91% of the chondrichthyan bycatch by number), and in the tiger/Endeavour prawn sector by the two batoids Himantura astra and Gymnura australis and the two sharks Chiloscyllium punctatum and Hemigaleus australiensis (~67% of the chondrichthyan bycatch by number). The testing of TEDs and BRDs, which are mandatory throughout the fishery, demonstrated only a limited ability to reduce chondrichthyan bycatch in the ECTF, which is comprised mainly of relatively small species. The shorter trawl durations of the surveys compared with normal commercial activities may have under-represented larger species. No significant reductions in chondrichthyan bycatch were found using a TED and a radial escape section BRD in the eastern king prawn (shallow water) sector, using a TED and a square-mesh codend BRD in the eastern king prawn (deepwater) sector, or using a TED and a fisheye BRD in Hervey Bay. There was however, a significant difference in the probability of capturing the group ‘sharks and guitarfishes’ (comprised largely of A. rostrata) between codend types in the scallop sector, with the lowest probability of capture in nets fitted with both a TED and a square-mesh codend BRD (the difference was largely attributed to the effects of the TED). In the tiger/Endeavour prawn sector, in which three different BRDs were trialed (fisheye, square-mesh codend, square-mesh panel), the probability of capturing chondrichthyans was significantly lower in nets fitted with a fisheye BRD than in the standard (control) net, and the probability of capturing batoids was significantly lower in nets fitted with a fisheye BRD or with a square-mesh codend BRD than in the standard (control) net. The small sample size of chondrichthyan catches in some sectors may have reduced to power to detect bycatch reduction. The biology of several bycatch species from the families Rajidae, Rhinobatidae, Urolophidae and Scyliorhinidae was examined. For D. polyommata, size at birth was estimated at ~100–110 mm total length (LT), size at first feeding at ~105–110mm LT, size at 50% maturity (LT50 and 95% CI) at 321 (305–332) mm LT for females and 300 (285–306) mm LT for males. Diet (described by the index of relative importance as a percentage) was predominantly crustacean based, with carid shrimps (53.6%) and penaeoid prawns (23.3%) being the most significant prey groups. For A. rostrata, size at birth was estimated at <170 mm LT, size at 50% maturity (LT50 and 95% CI) at 640 (618–663) mm LT for females and 597 (551–649) mm LT for males, and litter size was 9–20 (n = 9; mean ± S.E. = 15.1 ± 1.2). For T. testacea, size at birth was estimated at 77–100 mm disc width (WD), size at 50% maturity (WD50 and 95% CI) at 163 (156–169) mm WD for females and 146 (140–150) mm WD for males, and litter size was always one (n = 6). For U. kapalensis, size at birth was estimated at 75–100 mm WD, size at 50% maturity (WD50 and 95% CI) at 154 (145–160) mm WD for females and 155 (149–159) mm WD for males, and litter size was always one (n = 16). The catsharks A. analis, A. rubiginosus and F. boardmani were all confirmed as single oviparous species (carrying only one egg case in each uterus at one time). Ovarian fecundity (the number of vitellogenic follicles) averaged 13.6 (range 13–20) in A. analis, 13.5 (range 5–23) in A. rubiginosus and 10.4 (range 9–13) in F. boardmani. While only limited data were available from southern Queensland, several indicators suggest that Asymbolus catsharks are reproductively active year-round. A general lack of small-sized or immature catsharks captured during the study made assessments of size at maturity difficult for these species. The conservation status of ECTF bycatch species was examined through the application of the IUCN Red List of Threatened SpeciesTM Categories and Criteria, which considers extinction risk at the global level. Of the 24 ECTF chondrichthyan bycatch species evaluated against the IUCN Red List Categories and Criteria, four have been assessed globally as Vulnerable (a threatened category indicating that a species is ‘facing a high risk of extinction in the wild’), seven as Near Threatened, 11 as Least Concern and two as Data Deficient. While the four globally threatened species (A. nichofii, Heteroscyllium colcloughi, Rhynchobatus australiae and Urolophus sufflavus) were only minor components of the ECTF bycatch, their global conservation status warrants that fisheries management and industry should act to ensure minimal impacts on these species. An ecological risk assessment method (Susceptibility-Recovery Analysis) was used to assess the relative sustainability or risk of individual species to the fishing activities of the ECTF. Two separate approaches were taken to the technique, which considers sustainability to be dependent on the susceptibility of a species to the fishery and the recovery potential of a species after depletion by fishing activities. The first approach applied the precautionary principal when data were lacking for the calculation of recovery attributes, while the second used biological data from similar species when species-specific data were lacking. The precautionary approach tended to overestimate risk to poorly known oviparous species. The biological approach suggested that A. nichofii, F. boardmani, Rhizoprionodon acutus, Rhizoprionodon taylori and Rhynchobatus palpebratus face the least risk (i.e. were the most sustainable) while several medium-large batoids and the sharks Loxodon macrorhinus and Heteroscyllium colcloughi were the species most at risk (i.e. least sustainable). Demonstrating ecological sustainability of the ECTF will need to be a continued management objective into the future. To further improve the ecological sustainability of the fishery in relation to sharks, batoids and holocephalans, a number of management recommendations are proposed: (1) give warranted conservation consideration to listed threatened species as well as species identified as being at risk; (2) expand required logbook information on chondrichthyan species to include recording of catches of these species; (3) encourage safe release practices for all chondrichthyans to maximise survivorship of discards; (4) initiate research into the survivorship of discards; (5) ensure long-term observer coverage on commercial vessels to monitor bycatch levels; and, (6) test and quantify reduced TED bar spacings (presently 120 mm) in fishery sectors which show the highest chondrichthyan bycatch levels, that is, the eastern king prawn (shallow water) and scallop sectors.

The chondrichthyan (shark, batoid and holocephalan) bycatch of the Queensland East Coast Trawl Fishery (ECTF) was examined through a series of fishery-independent trawl surveys, together with fishery-dependent (opportunistic) sampling. Project aims were to document the chondrichthyan bycatch composition in order to test the effectiveness of turtle exclusion devices (TEDs) and bycatch reduction devices (BRDs), to examine biological aspects of bycatch species, and to combine data collected through these parts to assess the conservation status and sustainability of bycatch species. A total of 37 chondrichthyan species (one holocephalan, 19 batoids and 17 sharks) from 18 families were recorded in the bycatch of the fishery. The most speciose families recorded were the stingrays (Dasyatidae; 7 species), the requiem sharks (Carcharhinidae; 5 species), the catsharks (Scyliorhinidae; 4 species) and the stingarees (Urolophidae; 3 species). Chondrichthyan bycatch was highly variable between fishery sectors; catch rates were low in the tiger/Endeavour prawn sector (north Queensland; 0.02–0.12 individuals ha-1 trawled) and in the eastern king prawn (deepwater) sector (southern Queensland; 0.08 individuals ha-1 trawled), intermediate in Hervey Bay (southern Queensland; 0.25 individuals ha-1 trawled) and in the scallop sector (central Queensland coast; 0.31 individuals ha-1 trawled) and highest in the eastern king prawn (shallow water) sector (southern Queensland; 0.96 individuals ha-1 trawled). Chondrichthyan bycatch in the eastern king prawn (shallow water) sector was dominated by the three batoids Aptychotrema rostrata, Trygonoptera testacea and Urolophus kapalensis (~92% of the chondrichthyan bycatch by number), in the eastern king prawn (deepwater) sector by the skate Dipturus polyommata and the two catsharks Asymbolus rubiginosus and Figaro boardmani (~83% of the chondrichthyan bycatch by number), in the scallop sector by the three batoids A. rostrata, Neotrygon kuhlii and Neotrygon picta (~91% of the chondrichthyan bycatch by number), and in the tiger/Endeavour prawn sector by the two batoids Himantura astra and Gymnura australis and the two sharks Chiloscyllium punctatum and Hemigaleus australiensis (~67% of the chondrichthyan bycatch by number). The testing of TEDs and BRDs, which are mandatory throughout the fishery, demonstrated only a limited ability to reduce chondrichthyan bycatch in the ECTF, which is comprised mainly of relatively small species. The shorter trawl durations of the surveys compared with normal commercial activities may have under-represented larger species. No significant reductions in chondrichthyan bycatch were found using a TED and a radial escape section BRD in the eastern king prawn (shallow water) sector, using a TED and a square-mesh codend BRD in the eastern king prawn (deepwater) sector, or using a TED and a fisheye BRD in Hervey Bay. There was however, a significant difference in the probability of capturing the group ‘sharks and guitarfishes’ (comprised largely of A. rostrata) between codend types in the scallop sector, with the lowest probability of capture in nets fitted with both a TED and a square-mesh codend BRD (the difference was largely attributed to the effects of the TED). In the tiger/Endeavour prawn sector, in which three different BRDs were trialed (fisheye, square-mesh codend, square-mesh panel), the probability of capturing chondrichthyans was significantly lower in nets fitted with a fisheye BRD than in the standard (control) net, and the probability of capturing batoids was significantly lower in nets fitted with a fisheye BRD or with a square-mesh codend BRD than in the standard (control) net. The small sample size of chondrichthyan catches in some sectors may have reduced to power to detect bycatch reduction. The biology of several bycatch species from the families Rajidae, Rhinobatidae, Urolophidae and Scyliorhinidae was examined. For D. polyommata, size at birth was estimated at ~100–110 mm total length (LT), size at first feeding at ~105–110mm LT, size at 50% maturity (LT50 and 95% CI) at 321 (305–332) mm LT for females and 300 (285–306) mm LT for males. Diet (described by the index of relative importance as a percentage) was predominantly crustacean based, with carid shrimps (53.6%) and penaeoid prawns (23.3%) being the most significant prey groups. For A. rostrata, size at birth was estimated at <170 mm LT, size at 50% maturity (LT50 and 95% CI) at 640 (618–663) mm LT for females and 597 (551–649) mm LT for males, and litter size was 9–20 (n = 9; mean ± S.E. = 15.1 ± 1.2). For T. testacea, size at birth was estimated at 77–100 mm disc width (WD), size at 50% maturity (WD50 and 95% CI) at 163 (156–169) mm WD for females and 146 (140–150) mm WD for males, and litter size was always one (n = 6). For U. kapalensis, size at birth was estimated at 75–100 mm WD, size at 50% maturity (WD50 and 95% CI) at 154 (145–160) mm WD for females and 155 (149–159) mm WD for males, and litter size was always one (n = 16). The catsharks A. analis, A. rubiginosus and F. boardmani were all confirmed as single oviparous species (carrying only one egg case in each uterus at one time). Ovarian fecundity (the number of vitellogenic follicles) averaged 13.6 (range 13–20) in A. analis, 13.5 (range 5–23) in A. rubiginosus and 10.4 (range 9–13) in F. boardmani. While only limited data were available from southern Queensland, several indicators suggest that Asymbolus catsharks are reproductively active year-round. A general lack of small-sized or immature catsharks captured during the study made assessments of size at maturity difficult for these species. The conservation status of ECTF bycatch species was examined through the application of the IUCN Red List of Threatened SpeciesTM Categories and Criteria, which considers extinction risk at the global level. Of the 24 ECTF chondrichthyan bycatch species evaluated against the IUCN Red List Categories and Criteria, four have been assessed globally as Vulnerable (a threatened category indicating that a species is ‘facing a high risk of extinction in the wild’), seven as Near Threatened, 11 as Least Concern and two as Data Deficient. While the four globally threatened species (A. nichofii, Heteroscyllium colcloughi, Rhynchobatus australiae and Urolophus sufflavus) were only minor components of the ECTF bycatch, their global conservation status warrants that fisheries management and industry should act to ensure minimal impacts on these species. An ecological risk assessment method (Susceptibility-Recovery Analysis) was used to assess the relative sustainability or risk of individual species to the fishing activities of the ECTF. Two separate approaches were taken to the technique, which considers sustainability to be dependent on the susceptibility of a species to the fishery and the recovery potential of a species after depletion by fishing activities. The first approach applied the precautionary principal when data were lacking for the calculation of recovery attributes, while the second used biological data from similar species when species-specific data were lacking. The precautionary approach tended to overestimate risk to poorly known oviparous species. The biological approach suggested that A. nichofii, F. boardmani, Rhizoprionodon acutus, Rhizoprionodon taylori and Rhynchobatus palpebratus face the least risk (i.e. were the most sustainable) while several medium-large batoids and the sharks Loxodon macrorhinus and Heteroscyllium colcloughi were the species most at risk (i.e. least sustainable). Demonstrating ecological sustainability of the ECTF will need to be a continued management objective into the future. To further improve the ecological sustainability of the fishery in relation to sharks, batoids and holocephalans, a number of management recommendations are proposed: (1) give warranted conservation consideration to listed threatened species as well as species identified as being at risk; (2) expand required logbook information on chondrichthyan species to include recording of catches of these species; (3) encourage safe release practices for all chondrichthyans to maximise survivorship of discards; (4) initiate research into the survivorship of discards; (5) ensure long-term observer coverage on commercial vessels to monitor bycatch levels; and, (6) test and quantify reduced TED bar spacings (presently 120 mm) in fishery sectors which show the highest chondrichthyan bycatch levels, that is, the eastern king prawn (shallow water) and scallop sectors.

La gestion et la conservation des pêcheries sont problématiques pour la plupart des chondrichthiens; cela tient principalement au manque de données scientifiques causé par les défis logistiques impliqués par les prélèvements par grandes profondeurs. De plus, plusieurs les techniques analytiques, à l’exemple du contenu stomacal et des mesures morphologiques, demandent des quantités d’échantillons importantes difficilement obtenues. De nouvelles techniques exigent moins d'échantillons, en particulier celles mettant en oeuvre la biochimie qui sont de plus en plus utilisées pour résoudre des questions écologiques et biologiques complexes au niveau individuel et démographique des populations. Cette thèse a testé plusieurs techniques biochimiques (analyses de lipide, mercure, et isotope de carbone et azote) pour mieux comprendre les aspects de la reproduction, de l'écologie trophique, de l'amplification du mercure et de la physiologie de chondrichthiens des profondeurs. La plupart des espèces font partie de l'Ordre des Squaliformes. D'autres espèces appartiennent à différentes Familles: Chimaeridae, Rhinochimaeridae, Scyliorhinidae et Hexanchidae. Tous les échantillons ont été capturés dans les filets de pêcheurs dans les eaux du plateau continental et des marges du sud-est de l'Australie. L’analyse de la composition en lipides de différents tissus révèlent que le foie des chondrichthiens est riche en lipides (38 à 70% de la masse des tissus humides), en majeure partie des lipides neutres et des acides gras mono-saturés. Le foie est un tissu multifonctionnel, qui joue un rôle essentiel dans la distribution de la biosynthèse lipidique, le stockage de l’énergie et la régulation de la flottaison. A l’inverse, le tissu musculaire est un organe structurel, à faible concentration en lipide (<2 %) qui se compose essentiellement de lipides polaires. La composition des lipides rénaux et pancréatiques montre que leur fonctionnement métabolique est complexe. L'analyse des lipides des organes reproducteurs a révélé que l’énergie utile à la gestation chez les adultes chondrichthiens en pré-ovulation nécessite un pourcentage important de lipide (follicule ovarien 18 à 34 %). Les variations de triacylglycérols (8 à 48 %), des éthers diacylglycéryls (0,2 à 28 %) et des cires (0,5 à 20 %) ont été observées dans tous les échantillons. Ces variations impliquent l'utilisation de classes lipidiques multiples pour favoriser le développement embryonnaire. Les réserves maternelles sont différentes entre espèces ovipares et vivipares et entre les élasmobranches et les holocéphales. L’allocation la plus important de lipides est trouvée chez les requins vivant dans les environnements les plus profonds. Cette observation suggère que leur fécondité est plus faible et que leur vulnérabilité face à la pêche est plus importante. Le régime alimentaire des requins a été déterminé par des techniques complémentaires: traceurs lipidiques et analyses du contenu stomacal. 41 taxons de proie ont été identifiés. Ils étaient surtout composés de poissons et de céphalopodes du domaine demersal. En utilisant les profils des acides gras, la variabilité de la composition de nourriture a été établie pour chaque espèce en associant la signature de ces profils dans les tissus des chondrichthiens aux profils de plusieurs proies. Les deux techniques ont montré que les chondrichthiens sont des prédateurs opportunistes qui consomment une large gamme de proie. Les concentrations en mercure et sa distribution des tissus ont été examinés pour accéder à sa bioamplification dans ce type d’organisme et de déterminer des niveaux de contamination pour la consommation publique. Le mercure total (THg : toutes formes chimiques confondues) et le méthylmercure (MeHg : la forme la plus toxique et bioaccumulable) ont été dosées. Pour la plupart des espèces, les niveaux de THg étaient supérieurs au seuil maximal recommandé par les législations en vigueur dans plusieurs pays dont l’Australie (>0,1 mg kg-1 pois humide, ph) et une concentration aussi forte que 6,6 mg kg-1 (ph) a été enregistrée. L' / Analyse de spéciation a montré que le mercure est présent à plus de 91 % sous forme de MeHg, et même avec des taux supérieurs à 95 % chez les espèces des environnements les plus profonds. Les concentrations maximales en THg ont été trouvés dans les tissus musculaires (59 à 82 % de charge corporelle). Les reins et le foie possèdent aussi des taux élevés, respectivement de 0,3 à 4,2 et 0,5 à 1,5 mg kg-1 (ph), tandis que la peau enregistre les concentrations les plus faibles (> 0,3 mg kg-1, ph). Cette étude de l’organotropisme permet de conclure que les reins et le foie sont associés au métabolisme du métal, à l'élimination et au stockage à court terme, alors que le muscle est le sites le plus important du stockage du mercure à long terme. Les isotopes stables de carbone et d’azote ont été utilisés pour évaluer l'influence de la position trophique (d15N) et de la source de carbone (d13C) sur l'accumulation du THg chez les chondrichthiens. Le d15N varie entre 12,4 à 16,6 ‰ démontrant la large gamme de positions trophiques occupées par ces espèces. La variation interspécifique du d13C est quant à elle minimale (–18,7 à –17,1 ‰). Les concentrations en mercure notées chez la plupart des requins augmentent en fonction de la taille, de la position trophique (d15N) et du stade de maturité de l’animal. Dans la communauté des chondrichthiens des profondeurs on observe des taux modérés de bioamplification du mercure, ceci est révélé par la faible pente de la relation, log (THg mg kg-1 ww) = 0,2 (d15N) – 2,4 (R2 = 0,35 ; P <0,05). Le THg et les acides gras de 61 espèces appartenant aux niveaux trophiques intermédiaires ont été analysés dans le but d’étudier les régimes alimentaires des proies et la bioaccumulation de ce métal à travers la chaîne alimentaire démersale. L'utilisation intégrée de ces techniques biochimiques a fourni des données fondamentales sur la reproduction, l'accumulation en mercure et l'écologie trophique des chondrichthiens des profondeurs. La compréhension de ces fonctions est impérative non seulement pour la mise en place d’une gestion durable des pêcheries, mais aussi pour la protection des habitats des chondrichthiens et leurs écosystèmes associés. / For most deepwater chondrichthyans, fisheries and conservation management is problematic, largely due to the lack of scientific data resulting from inherent logistical challenges working within deep-sea environments. Furthermore, many conventional analytical techniques (stomach content analysis and morphometrics) require large sample sizes and are often quantitatively inadequate. Thus, new and more robust methods requiring fewer specimens are needed. Biochemical ‘tracer’ techniques are increasingly being used to resolve complex ecological and biological questions at individual species and population levels. This research explored the integrated use of multiple biochemical techniques (lipid and fatty acid profiling, stable nitrogen and carbon isotope and mercury analysis) to understand aspects of the reproduction, feeding ecology, metal accumulation and physiology of deepwater chondrichthyans. Most were from the Order Squaliformes. Other species include those from the Families: Chimaeridae, Rhinochimaeridae, Scyliorhinidae and Hexanchidae. All specimens were caught as fisheries bycatch from the continental slope waters off southeast Australia. The examination of lipid composition and partitioning revealed that deepwater chondrichthyans have large, lipid rich (38–70 % wet weight, ww) livers high in neutral lipids and monounsaturated fatty acids. Liver is a multifunctional tissue, playing a vital role in lipid distribution and biosynthesis, buoyancy regulation and storage. In contrast, muscle is a structural organ, low in lipid (<2 %) and consisting primarily of polar lipids. Lipid composition of kidney and pancreas show that they, too, have complex roles in lipid metabolism and storage. Lipid analysis of reproductive tissues revealed high maternal investment in deepwater chondrichthyans as indicated by high lipid content in mature pre-ovulated ovarian follicles (18–34 %). Variable levels of triacylglycerols (8–48 %), diacylglyceryl ethers (0.2–28 %) and wax esters (0.5–20 %) were observed in all specimens, demonstrating the use of multiple lipid classes to fuel embryonic development. The maternal provisions differed between oviparous and viviparous species and between elasmobranchs and holocephalans. Greater lipid investment was displayed by sharks living in deeper environments, suggesting lower fecundity and increased vulnerability to fishing. Diet was examined by complementary lipid biomarker and traditional stomach content techniques. A total of 41 prey taxa were identified using stomach content analysis and consisted mainly of bathyal-demersal fish and cephalopods. Using multidimensional scaling analysis, the extent of variability in composition within each species was determined by grouping the signature fatty acid profiles of shark tissues with profiles for demersal fish, squid and crustaceans. Both techniques showed that deepwater chondrichthyans are opportunistic predators, and that there is some degree of specialisation and overlap between them. Total (THg) and inorganic (monomethyl, MeHg) mercury concentrations and tissue distribution were examined to determine the extent of biomagnification and evaluate levels for human consumption. Mean THg levels for most species were above the regulatory threshold (>0.1 mg kg-1 ww) and levels as high as 6.6 mg kg-1 ww were recorded. Speciation analysis demonstrated that 91% mercury was bound as MeHg with higher percentages (>95%) observed in species occupying deeper environments. Higher levels of THg were stored in muscle which accounted for between 59–82% of the total body burden of mercury. High levels were also found in kidney (0.3–4.2 mg kg-1 ww) and liver (0.5–1.5) with lower levels observed in skin (>0.3). Both the kidney and liver are likely to be associated in metal metabolism, short term storage and elimination procedures, while the muscle is the major site for long term storage. Stable isotopes were used as natural dietary tracers, to further evaluate dietary relationships and to assess the influence of trophic position (d15N) and carbon sources (d13C) on THg accumu / lation. Isotopic nitrogen (d15N) values ranged from 12.4 to 16.6 ‰ demonstrating a broad range of trophic positions. Minor variation in carbon (d13C) enrichment was observed between species (–18.7 to –17.1‰). In most shark species, mercury concentrations increased with size, trophic position (d15N), and maturity stage, but not between location or collection period. As a community, deepwater sharks demonstrated moderate rates of THg biomagnification, as indicated by the regression slope (log (THg) = 0.2 d15N – 2.4, R2 = 0·35, P < 0·05). THg and fatty acid analyses of 61 mid-trophic species were measured for their usage in studies of diet in high-order predators and mercury bioaccumulation in the extended demersal food chain. The integrated use of these biochemical techniques has provided fundamental data on the reproduction, metal accumulation and trophic ecology of deepwater chondrichthyans. Understanding these parameters is imperative not only for the implementation of sustainable management but for habitat protection of deepwater chondrichthyans and their associated ecosystems.