L’écologie et la physiologie des chondrichthiens des profondeurs du sud-est de l’Australie : les analyses du mercure, des lipides et des isotope de carbone et d’azote, Ecology and physiology of deepwater chondrichthyans off southeast Australia : mercury, stable isotope and lipid analysis

PHD THESIS
THESE DE DOCTORAT


Ecology and physiology of deepwater chondrichthyans off
southeast Australia: mercury, stable isotope and lipid analysis

L’écologie et la physiologie des chondrichthiens des
profondeurs du sud-est de l’Australie: les analyses du mercure,
des lipides et des isotope de carbone et d’azote



By
Heidi R. Pethybridge
BSc (Griffith University, Australia)
BSc(Hons) (University of Tasmania, Australia)



A thesis submitted in fulfilment of the requirements for the degree of
Doctor of Philosophy
Cotutelle between the University of Tasmania, and
L’Université de Bordeaux 1

June 2010
iiDeclaration

Statement of Originality

This thesis contains no material which has been accepted for a degree or diploma by the
University or any other institution, except by way of background information and duly
acknowledged in the thesis. To the best of my knowledge and belief, no material
previously published or written by another person except where due acknowledgement is
made in the text of the thesis. This thesis may be available for loan and limited copying in
accordance to the Copyright Act 1968.



Heidi R. Pethybridge








“Like the resource it seeks to protect, wildlife conservation must be dynamic, changing as
conditions change, seeking always to become more effective”. (Rachel Carson, 1907 – 1964)

“What is a scientist after all? It is a curious man looking through a keyhole, the keyhole
of nature, trying to know what's going on”. (Jacques Cousteau, 1910 – 1997)


To the unprotected in our oceans………
iiiABSTRACT
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
ivdetermined 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
-1 -1regulatory threshold (>0.1 mg kg ww) and levels as high as 6.6 mg kg 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
-1total body burden of mercury. High levels were also found in kidney (0.3–4.2 mg kg
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
15relationships and to assess the influence of trophic position ( δ N) and carbon sources
13 15( δ C) on THg accumulation. Isotopic nitrogen ( δ N) values ranged from 12.4 to 16.6 ‰
13demonstrating a broad range of trophic positions. Minor variation in carbon ( δ C)
enrichment was observed between species (–18.7 to –17.1‰). In most shark species,
15mercury concentrations increased with size, trophic position ( δ N), 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
15 2slope (log (THg) = 0.2 δ N – 2.4, R = 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.

vRÉSUMÉ
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 œuvre 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 <