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Foraging ecology of shy albatrosses Thalassarche cauta breeding in Australia : implications for interactions with longline fisheries

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Hedd, A (1999) Foraging ecology of shy albatrosses Thalassarche cauta breeding in Australia : implications for interactions with longline fisheries. PhD thesis, University of Tasmania.

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Abstract

Globally, bycatch associated with longline fisheries poses the most serious threat to
albatross populations. Almost half of the populations for which adequate data exist are
either currently, or in the recent past they have been in decline, and there is widespread
acknowledgment that bycatch in longline fisheries is responsible for these declines. Within
the Australian Fishing Zone (AFZ), large numbers of seabirds have been killed in both the
Japanese and Australian domestic pelagic longline fisheries targeting Southern bluefin tuna
Thunnus maccoyii. Attracted to the vessels by baits and offal discharge, seabirds, mainly
albatrosses and petrels, ingest baited hooks, become entangled and subsequently drown.
Conservative estimates of seabird mortality for the Japanese portion of the fishery indicated
that at least 1,000-3,500 birds were killed annually within the AFZ. The Australian
domestic longline fishery also has a serious seabird by-catch problem, but the overall
mortality rates have yet to be quantified.
Shy albatrosses constitute a significant component of the seabird by-catch in longline
fisheries within the AFZ, where an estimated 5,000 individuals have been killed in the
Japanese portion of the fishery in the past decade. Shy albatrosses are also the most
frequently caught species in the Australian domestic longline fishery. Shy albatrosses
Thalassarche cauta are endemic to Australia, and they breed in three colonies off the coast
of Tasmania; Albatross Island to the north, and Pedra Branca and Mewstone off the south
coast. The breeding population size approximates 12,300 pairs annually. Despite the
prevalence of this species as bycatch in longline fisheries, their ecology was poorly known.
This study, which has examined integrated aspects of both the breeding biology on land and
the foraging behaviour at sea, was undertaken to redress the lack of ecological information
for the species, and to quantify their degree of overlap with longline fisheries operating
within the AFZ. The foraging ecology was investigated in three main ways; using satellite telemetry to
identify the foraging zones at sea; using archival recorders to determine both the diving
behaviour and at-sea activity patterns; and by collecting diet samples throughout the chickrearing
period. Parental breeding and provisioning strategies were also investigated using a
combination of VHF telemetry and artificial nests which continually recorded chick mass.
Patterns of attendance by adults at the colony were also quantified during the breeding and
non-breeding periods. All aspects of the foraging ecology and parental provisioning
strategies were examined across three breeding seasons to quantify the magnitude of interannual
variation. Finally, using the full suite of satellite tracking data, an assessment was made of degree of overlap between the three Shy albatross populations and longline
fisheries operating within the AFZ.
Adult Shy albatrosses from all breeding sites in Tasmania foraged locally during the
breeding season, being distributed at-sea within 200-300 km of their colonies. Foraging
occurred exclusively in neritic waters over the southeast Australian continental shelf, and,
at the population level, the foraging locations were highly consistent between years.
Despite the spatial proximity of the three colonies, the birds used mutually exclusive
foraging zones during the breeding season. While the birds were active at sea during both
the day and night, much , of their travelling 80%) was undertaken during daylight hours.
Diving formed a significant component of the foraging repertoire of Shy albatrosses. With
birds diving to depths of almost 8 m, they substantially exceeded their designation as
surface-feeders. Diving occurred exclusively during daylight hours, and as the deepest
depths were attained at or near midday, prey capture appeared to be largely visually cued.
The diet of Shy albatrosses was dominated by fish, and to a lesser extent by cephalopods,
with tunicates and crustaceans also taken. Jack mackerel Trachurus declivis, Redbait
Emmelichthys nitidus, and Gould's squid Nototodarus gouldi were the three most important
prey species in all sampling years. These species are common in the shelf region of
Tasmania, where they are known to surface school during the day. Information on the
behaviour of the birds at sea, coupled with behavioural information on the main prey
species combine to indicate that Shy albatrosses have largely predatory foraging habits.
Given that the main prey species occur in surface waters during the day, Shy albatrosses
could obtain the majority of their food live from surface waters. Almost year-round attendance at the colony by adults from Albatross Island indicated that
the birds likely remained within southeast Australian waters year-round. Unlike any other
albatross species studied, Shy albatrosses spend a significant portion of their non-breeding
period attending the colony, suggesting that prey remain locally available throughout the
year. The provisioning pattern of adults was consistent with short foraging trip durations
and neritic foraging habits. Chicks were provisioned at 400 g/day from the end of the
brooding period until fledging, and they were fed at the highest frequency recorded for any
albatross species. The flexibility offered by locally abundant prey resources was
exemplified during the chick-rearing period. Parents were able to increase provisioning
rates when their chicks were hungry, and even faced with nest abandonment by their mates,
some single parents were able to successfully raise their chick.
The segregated at-sea distribution of the three Shy albatross populations results in different likely impacts from fisheries. Given the distribution of effort in longline fisheries within
the AFZ and the bird's consistent foraging locations between years, it is likely that birds
breeding at Pedra Branca and Mewstone suffer substantially from overlap with longline
fisheries. However, seemingly during both the breeding and non-breeding periods adult
birds from Albatross Island remain relative remote from fishing operations. The unknown
status of the populations at Pedra Branca and Mewstone, along with the little known
distribution of juveniles, is therefore of considerable concern. Future research on Shy
albatrosses must endeavor to identify the foraging grounds of non-breeding birds (both
adults and juveniles), and determine the demographic parameters and status for the three
populations.
This study has examined a number of aspects of the foraging ecology of the Shy
albatrosses, elevating the species from one of the least known (Croxall 1998) to one of the
better understood. It is clear that only armed with a through understanding of albatross
ecology coupled with widespread adoption of - appropriate and effective mitigation
measures, that we can begin securing a future for albatrosses and succeed in ensuring their
long-term survival.

Item Type: Thesis (PhD)
Keywords: Albatrosses
Copyright Holders: The Author
Copyright Information:

Copyright 1999 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:

Chapter 2 appears to be the equivalent of a post-print article finally published as: Hedd, A.; Gales, R.; Brothers, N., (1998), Reliability of morphometric measures for determining the sex of adult and fledgling shy albatrosses, Diomedea cauta cauta, in Australia, Wildlife research, 25(1), 69-79

Chapter 3 appears to be the equivalent of the peer reviewed version of the following article: Brothers, N.; Gales, R.; Hedd, A.; Robertson, G., (1998), Foraging movements of the Shy Albatross Diomedea cauta breeding in Australia; implications for interactions with longline fisheries, Ibis, 140(3), 446-457, which has been published in final form at http://dx.doi.org/10.1111/j.1474-919X.1998.tb04606.x This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.

Chapter 4 appears to be the equivalent of the peer reviewed version of the following article: Hedd, A.; Gales, R.; Brothers, N.; Robertson, G. (1997), Diving behaviour of the Shy Albatross Diomedea cauta in Tasmania: initial findings and dive recorder assessment, Ibis, 139(3), 452-460, which has been published in final form at http://dx.doi.org/10.1111/j.1474-919X.1997.tb04658.x This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.

Date Deposited: 19 Dec 2014 02:38
Last Modified: 11 Mar 2016 05:54
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