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Trophic ecology and food web modelling of mid-slope demersal fishes off southern Tasmania, Australia


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Bulman, Cathy 2002 , 'Trophic ecology and food web modelling of mid-slope demersal fishes off southern Tasmania, Australia', PhD thesis, University of Tasmania.

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The trophic ecology and food web dynamics of the mid-slope demersal fish
community (700-1200 m) off southern Tasmania were investigated. The top
predators in the community were orange roughy, the oreos and squalids. Orange
roughy Hoplostethus atlanticus is dominant on the flat ground but even more so on
the seamounts, and consequently fishing has been intense on these seamounts. Oreos
are also fished on the seamounts. During 10 research cruises around south-eastern
Australia, more than 9000 stomachs from orange roughy and 23 other species were
collected and examined. Orange roughy ate predominantly mesopelagic and
benthopelagic fish, crustaceans and squid as adults, and mainly crustaceans as
juveniles suggesting resource partitioning between juveniles and adults. Orange
roughy, warty dory Allocyttus verrucosus, squalids and macrourids are benthopelagic
omnivores. In contrast, the smooth oreo Pseudocyttus maculatus, and the
alepocephalids ate pyrosomes.
Daily rates of food consumption for adult orange roughy were 1.15% body
weight and for juveniles were 0.91%. The metabolism of orange roughy estimated
from a mass balance model, was similar to that of active, migratory mesopelagic
fishes and greater than non-migratory bathypelagic fishes. The use of enzyme
activity rates of white muscle as proxies for oxygen consumption was investigated
for orange roughy and seven other dominant species in the community. Lactate
dehydrogenase (LDH), malate dehydrogenase (MDH) & citrate synthase (CS)
activities were assayed. The fishes were all anaerobically poised, with LDH activities
greater than CS activities. The LDH activities of smooth oreo, dogfish
Centroscymnus crepidater and orange roughy were higher than the majority of deepliving
species studied previously. The oxygen consumption rate for orange roughy,
estimated from the bioenergetic model, was best estimated from LDH activities.
Oxygen consumption for the seamount-associated fish similar to orange roughy,
might also be best predicted from LDH activities.
Food web models using Ecopath with Ecosim models were developed to
examine scenarios of fishing impacts and pelagic inputs to the community through
advection. Diet composition, species composition, biological and physiological
parameters for each food web group, collected from the research cruises, as well as
fishery catch statistics, were used in construction of the models. After simulating a
decade of fishing, orange roughy declined to about 60% of the starting biomass but
recovered to 99% of starting biomass over the next 40 years once fishing ceased. The
oreos declined more and only recovered to 57% once fishing ceased. Advection of
prey was the most important mechanism by which the community biomass on the
seamounts could be sustained. High rates allowed the orange roughy stocks to
recover in less than 20 years and oreos in 55 years While low advection rates would
allow recovery to only two-thirds pre-fishing biomass for both fisheries.

Item Type: Thesis - PhD
Authors/Creators:Bulman, Cathy
Keywords: Fishes, Predation (Biology), Food chains (Ecology), Marine ecology
Copyright Holders: The Author
Copyright Information:

Copyright 2002 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2002. Includes bibliographical references

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