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Autumn diet of recolonising female New Zealand sea lions based at Otago Peninsula, South Island, New Zealand

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New Zealand (NZ) sea lions (Phocarctoshookeri) are slowly recolonising the Otago coast, South Island, New Zealand. The increase in their numbers may lead to resource competition with other marine predators and fisheries. We determined the diet of female NZ sea lions at Otago during autumn. In total, 571 scats and 110 regurgitations were collected on Otago Peninsula during 2008 and 2009. Barracouta (Thyrsites atun) and jack mackerel (Trachurus sp.) were the two main prey species and accounted for 26% and 31% of the reconstituted biomass, respectively. This was consistent between two years. Only five other species contributed > 5% of the diet by biomass in either year. Prey species are all found on the narrow continental shelf surrounding Otago Peninsula. The main prey species of Otago NZ sea lions may be of higher energy content than prey in the Auckland Islands (remnant breeding area). Resource overlap with other marine predators and fisheries appears to occur around Otago Peninsula. A marine trophic model of the area off Otago Peninsula would help understanding potential competition between marine predators and fisheries in this area.
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Autumn diet of recolonising female
New Zealand sea lions based at Otago
Peninsula, South Island, New Zealand
AA Augé a , C Lalas b , LS Davis a & BL Chilvers c
a Department of Zoology, University of Otago, Dunedin, New
Zealand
b Department of Marine Science, University of Otago, Dunedin,
New Zealand
c Department of Conservation, Aquatic and Threats Unit,
Wellington, New Zealand
Version of record first published: 11 Oct 2011.
To cite this article: AA Augé, C Lalas, LS Davis & BL Chilvers (2012): Autumn diet of recolonising
female New Zealand sea lions based at Otago Peninsula, South Island, New Zealand, New Zealand
Journal of Marine and Freshwater Research, 46:1, 97-110
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Autumn diet of recolonising female New Zealand sea lions based at Otago
Peninsula, South Island, New Zealand
AA Auge
´
a
*, C Lalas
b
, LS Davis
a
and BL Chilvers
c
a
Department of Zoology, University of Otago, Dunedin, New Zealand;
b
Department of Marine Science,
University of Otago, Dunedin, New Zealand;
c
Aquatic and Threats Unit, Department of Conservation,
Wellington, New Zealand
(Received 26 March 2011; final version received 14 July 2011)
New Zealand (NZ) sea lions (Phocarctos hookeri) are slowly recolonising the Otago coast, South
Island, New Zealand. The increase in their numbers may lead to resource competition with other
marine predators and fisheries. We determined the diet of female NZ sea lions at Otago during
autumn. In total, 571 scats and 110 regurgitations were collected on Otago Peninsula during
2008 and 2009. Barracouta (Thyrsites atun) and jack mackerel (Trachurus sp.) were the two main
prey species and accounted for 26% and 31% of the reconstituted biomass, respectively. This
was consistent between two years. Only five other species contributed 5% of the diet by
biomass in either year. Prey species are all found on the narrow continental shelf surrounding
Otago Peninsula. The main prey species of Otago NZ sea lions may be of higher energy content
than prey in the Auckland Islands (remnant breeding area). Resource overlap with other marine
predators and fisheries appears to occur around Otago Peninsula. A marine trophic model of
the area off Otago Peninsula would help understanding potential competition between marine
predators and fisheries in this area.
Keywords: pinniped; prey species; foraging; competition; recolonisation; feeding; Otago
Peninsula; Hooker’s sea lion; New Zealand sea lion; Phocarctos hookeri
Introduction
Investigating the diet of animals allows an
understanding of their needs in term of prey
availability and quality (Capitani et al. 2004;
McKenzie & Wynne 2008; Herreman et al. 2009;
Chilvers et al. 2010). Firstly, prey species vary
geographically, have different handling times
and risks, and do not all have the same energy
content (Rosen & Trites 2000; Bowen et al. 2002;
Meynier, Morel, Mackenzie et al. 2008). Sec-
ondly, large marine predators can compete for
resources with fisheries (Bjørge et al. 2002;
Alonzo et al. 2003; Wilkinson et al. 2003;
Huckstadt & Krautz 2004). Knowing the diet
of marine mammals can consequently improve
our understanding of their habitat needs and
help manage their interactions with fisheries.
New Zealand (NZ) sea lions, Phocarctos
hookeri (Gray 1844), were extirpated from the
New Zealand mainland by the 1830s but they
have now started recolonising the Otago coast,
on the east coast of the South Island of New
Zealand, for approximately 50 years (Wilson
1979; Childerhouse & Gales 1998; McConkey,
Heinrich et al. 2002). However, consistent breed-
ing only started in 1994 on Otago Peninsula
(45850?S, 172800??E; McConkey, McConnell
et al. 2002). Up to 2010, 45 pups had been born
there (Auge
´2010). A population of large marine
predators is consequently increasing in number
and may compete with other marine predators
*Corresponding author. Email: amelie.auge@gmail.com
New Zealand Journal of Marine and Freshwater Research
Vol. 46, No. 1, March 2012, 97110
ISSN 0028-8330 print/ISSN 1175-8805 online
#2012 The Royal Society of New Zealand
http://dx.doi.org/10.1080/00288330.2011.606326
http://www.tandfonline.com
Downloaded by [JAMES COOK UNIVERSITY] at 17:34 30 September 2012
and fisheries. Resource competition can signifi-
cantly affect established populations of smaller
and less competitive species when a larger spe-
cies that was previously absent re-establishes in
an area (Herreman et al. 2009; Richard et al.
2010). Otago Peninsula is a breeding area for the
endangered yellow-eyed penguin (Megadyptes
antipodes) (Seddon et al. 1989) and for the New
Zealand fur seal (Arctocephalus fosteri) (mini-
mum estimate of 20,000 fur seals [Lalas 2008]).
The recolonisation of the area by NZ sea lions
may affect these populations.
In this paper, we determined the diet of
female NZ sea lions based at Otago Peninsula,
southeast South Island, New Zealand, during
autumn using undigested prey remains in scats
and regurgitations. The identification of undi-
gested remains of prey (bones, body parts,
feathers etc.) in scats and regurgitations is
commonly used to investigate the diet of carni-
vores, including pinnipeds, as it is non-invasive,
low-cost, and samples can easily be collected on
land (McLellan & Hovey 1995; Capitani et al.
2004; Ruhe et al. 2008; Paralikidis et al. 2010).
By identifying remains in these samples, the prey
species, number of prey species and sizes of prey
can be determined, hence revealing the diet of
the animals. Typically, the identification is only
conducted on otoliths for fish, and on beaks for
cephalopods (McKenzie & Wynne 2008) but the
digestion of otoliths is species-dependant and
this overestimates the amount of larger fish
(Browne et al. 2002). Along with otoliths, the
identification of other species-specific remains
increases the accuracy of the method by detect-
ing more prey items, including from species that
were not present or under-represented in the
reconstructed diet using otoliths only (Browne
et al. 2002; Tollit et al. 2003; Tollit et al. 2007;
Trites & Calkins 2008). While some studies have
only used scat samples, there is a large bias
against larger fish and cephalopods in this case
and the combination of scats and regurgitations
appears to represent the diet of pinnipeds more
reliably (Lalas 1997). It is possible to estimate
length and mass of prey from the size of remains
whenever allometric relationships are available.
In case several different bones from the same
species are found in a sample, these prey size
estimates can be used to determine from how
many different prey they came from. Along with
direct counts of parts when only single remains
per species were found, this enables the estima-
tion of the minimum number of prey of each
species that were taken. Biomass reconstruction
calculated from the mass estimates of prey
provides a more accurate assessment of diet
than frequencies of occurrence in samples or
numerical abundances of prey when looking at
energy intake and resource overlap based on
available biomass (Tollit et al. 2007).
Potential competition between fisheries and
NZ sea lions around the main remnant breed-
ing areas of NZ sea lions in the Auckland
Islands (50840?S, 166810??E) is of concern as
fisheries may affect the resource availability of
prey species of sea lions (Childerhouse et al.
2001; Meynier et al. 2009; Meynier et al. 2010;
Robertson & Chilvers 2011). It is, therefore,
important to determine the likelihood of this
situation around Otago Peninsula as the popu-
lation grows. This will allow precautionary
management decisions to ensure the establish-
ment of new breeding colonies on the New
Zealand mainland as this is the main step to
remove the species from its ‘nationally critical’
conservation status (Department of Conserva-
tion 2009; Baker et al. 2010). The diet of male
NZ sea lions was previously investigated on
Otago Peninsula (Lalas 1997). However, sexual
segregation in diet is often found in pinniped
species (Beck, Iverson et al. 2007; Meynier,
Morel, Chilvers et al. 2008; Trites & Calkins
2008; Breed et al. 2009). Consequently, the
investigation of the diet of the female compo-
nent of the Otago population was essential.
Material and methods
Scats and regurgitations of female NZ sea lions
were collected from 23 March to 28 May 2008
and 2009 at Victory Beach and Papanui Inlet
(45850?S, 170843??E) on Otago Peninsula. This
area was the main site used by all Otago-born
98 AA Auge´ et al.
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female NZ sea lions aged two years and over in
2008 (n14) during this study period, and was
where all lactating females nursed their pups
(Auge
´2010). Consequently, the entire popula-
tion of females from Otago Peninsula was
sampled. When a female sea lion was found,
any fresh scat or regurgitation nearby was
collected in a zip-lock plastic bag (Minigrip
Redline, Kennesaw, USA). The study area was
searched at least twice daily and females’ loca-
tions and identities (each female could be
individually identified, see Auge
´[2010]) were
recorded. Occasionally, males were found in a
part of the area, in which case samples were not
collected and all scats or regurgitations found in
this part were covered with soil or vegetation so
they were not re-sampled later. Regurgitation
samples were kept chilled after collection, and
later stored in a 20 8C freezer within 15 days
of collection and until further analyses to avoid
putrefaction of flesh often present. Scat samples
were soaked in water with liquid detergent
(laundry soap) in zip-lock plastic bags for up
to a week to allow the soft part of the scats to
break down. The undigested remains in scats
were recovered by washing the contents of the
bags with water through a sieve of mesh size 0.6
mm. All remains collected were stored in fresh
water in small bottles and kept in a fridge until
further analysis. Regurgitations were placed in
large containers in water with detergent the day
before identification process, and sieved with the
same mesh size as the scats before identification.
All scat and regurgitation samples from each
female during one year were gathered and
organised by date so that each sample could be
attributed to a foraging trip (i.e. period at sea)
based on presenceabsence of the females in the
study area. This limited the bias of repetitive
sampling of the same prey in multiple scats or
regurgitations. Foraging trip was defined as the
sampling unit in the analyses.
All remains found after sieving were chec-
ked for possible identification. Those non-
identifiable remains (either broken, too eroded
or unknown) were discarded. The identification
of the undigested remains was completed using
the reference drawings in Furlani et al. (2007)
for otoliths, in Leach (1997) for fish jaw bones,
in Lu and Ickeringill (2003) and Lalas (2009)
for beaks of cephalopods, and the private
collection held by Chris Lalas for all remains of
species not described in these references (this
collection was used in Lalas [1997], Fea et al.
[1999] and Mattern et al. [2009]). Cephalopods
were mainly identified from beaks, but we
also used undigested body parts (e.g., radula or
arms) to assess the occurrence of this group.
Otoliths and jaw bones were mainly used to
determine fish species, although other parts
contributed to more identifications than these
in some species (e.g. lateral scutes of jack
mackerel [Trachurus sp.], green bones of green-
bone [Odax pullus], caudal peduncle and teeth
of barracouta [Thyrsites atun], denticles of rough
skate [Raja nasuta] and spines of spiny dogfish
[Squalus acanthias]). The occurrence of crusta-
ceans corresponded to the recovery of exoskele-
tal remains. Species of birds were identified from
feathers and feet.
For remains with a set number in each prey
but no allometric equation available or remains
that were broken or too eroded to be measured,
but were still identifiable, it was possible to
determine the correspondent minimal number
of prey ingested during the trip by identifying
the side (left or right) of the structure whenever
possible. Owing to the large amount of feathers
often ingested during seabird predation, if a
definite occurrence was detected during a fora-
ging trip, the sole presence of a few feathers in
the samples of the following trip was attributed
to the previous occurrence. This allowed the
determination of the minimal numerical abun-
dance of each prey taken during each foraging
trip. When allometric equations were available,
the estimated fork length for fish and wet mass
for all prey were calculated based on the
remains. In this case, if all structures of the
same species gave approximately similar sizes
and there was no replication of the same
structure, they were attributed to the same
prey item. Allometric equations were from
Leach et al. (1996) for barracouta, Leach,
Diet of Otago female NZ sea lions 99
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Davidson & Horwood (1997) for blue cod
(Parapercis colias), Leach et al. (2001) for red
cod (Pseudophycis bachus), Leach, Davidson,
Samson et al. (1997) for wrasses, Labridae spp.,
Lalas (2009) for Maori octopus (Macroctopus
maorum), and equations obtained from diag-
nostic structures in Furlani et al. (2007) or the
reference collection held by Chris Lalas, for all
other species.
The percentage of sampled foraging trips
during which each prey species was identified
(percentage of occurrence) and the minimal
number of individuals of each prey species
(numerical abundance) were determined. All
numbers calculated for these two values are
given as minimal numbers. The diet was
described by calculating the percentage that a
particular species contributed to the overall
total reconstituted biomass of prey taken dur-
ing each study season (percentage of reconsti-
tuted biomass).
Results
Totals of 166 and 405 scats and 42 and 68
regurgitations were collected, respectively in
2008 and 2009. At least one scat or regurgita-
tion was collected for 104 foraging trips in 2008
and 154 foraging trips in 2009. We identified
386 prey in 2008, and 551 prey in 2009, from 38
different species including 27 fish, 2 cephalo-
pods, 4 crustaceans, 3 seabirds and 2 salps.
Twenty of the prey species were found during
both years. Pieces of bryozoans were also
detected during 21 foraging trips. Reconstituted
biomasses added up to totals of 243 kg in 2008
and of 401 kg in 2009.
Only nine species were taken during more
than 10% of the sampled foraging trips in
any one year, and 22 species were represented
by fewer than 10 individual prey items in the
diet (Table 1). Barracouta and jack mackerel
were taken during 4060% of the foraging
trips while all other species were found in less
than 25% of the trips. Fourteen species were
identified in the samples of only one individual
(seven species during a single foraging trip).
Mean sizes of the prey species of female NZ
sea lions at Otago are presented in Table 2. The
largest prey species taken by female NZ sea
lions at Otago consisted of yellow-eyed penguin
(Megadyptes antipodes) (5.4 kg), and trumpeter
(Latris lineate) (4.1 kg). Neither was found in
the top five prey species of the diet, which made
up 74.0% and 81.4% of the reconstituted
biomass during 2008 and 2009. All other prey
were less than 2.5 kg. All of the top five prey
species in the diet were relatively large prey
(range of mean masses 0.51.6 kg). During
both study years, jack mackerel and barracouta
were the main prey species, adding up to 51.0%
and 62.5% of the total reconstituted biomass,
in 2008 and 2009 respectively. Only four other
species made up more than 5% of the female
diet during any one year (Table 1).
From Table 1, the inter-annual difference in
diet at the population level can be assessed.
Percentages of trips and of reconstituted bio-
mass can be compared between years. The
numerical abundance cannot be directly com-
pared, as the amount of sampled foraging trips
differed between years. There was no difference
in the percentages of reconstituted biomass
made up by the prey species in the diet of
female NZ sea lions between years. Conse-
quently, the diet at the population level ap-
peared similar in 2008 and 2009. This
similarity, however, relied in a large part on
the high proportions made by barracouta and
jack mackerel in the diet as there was a
difference between years for prey species of
lower importance in the diet. The third to sixth
prey species in order of importance in the diet,
constituting more than 5% of the diet of the
population in any one year, varied. Species
making up less than 5% also varied between
years, especially in numerical abundance, as
they had small sizes (Table 2).
100 AA Auge´ et al.
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Table 1 Diet of the female population of New Zealand sea lions in autumns 2008 and 2009 on Otago
Peninsula, New Zealand. Species ranked by biomass in the diet for the two years combined.
Percentage of
occurrence
Numerical
abundance
Percentage of
biomass
Common name Species 2008 2009 2008 2009 2008 2009
Barracouta Thyrsites atun 43.3 58.4 49 110 24.8 33.4
Jack mackerel Trachurus sp. 57.7 57.1 52 95 26.2 29.1
Arrow squid Nototodarus sloanii 20.2 13.6 68 27 15.2 3.7
Red cod Pseudophycis bachus 3.8 22.7 4 50 1.3 9.8
Maori octopus Macroctopus maorum 12.5 9.1 13 15 6.5 5.4
Yellow-eyed penguin Megadyptes antipodes 2.9 1.9 3 2 6.8 2.8
Wrasses Labridae, two spp. 21.2 16.2 24 38 3.5 3.4
Greenbone Odax pullus 11.5 9.7 12 16 3.6 2.9
Blue cod Parapercis colias 24.0 16.2 31 37 2.8 2.0
Little penguin Eudyptula minor 1.9 3.2 2 6 1.2 2.3
Ling Genypterus blacodes 3.8 43.3
Trumpeter
1
Latris lineata 0.6 22.1
Rough skate
1
Raja nasuta 1.9 21.9
Yellow-eyed mullet Aldrichetta forsteri 2.9 3.9 5 16 0.3 0.6
Spiny dogfish Squalus acanthias 4.8 3.9 5 5 0.4 0.3
Catfish Crapatalus sp. 1.9 1.3 4 3 0.5 0.2
Estuary stargazer Leptoscopus macropypus 4.8 11.7 8 23 0.2 0.3
Spotted shag
1
Stictocarbo punctatus 1.0 0.6 1 1 0.6 B0.1
Blue moki
1
Latridopsis ciliaris 0.6 20.3
Rock cod Lotella rhacinus 1.9 3.2 2 5 0.1 0.2
Witch Arnoglossus scapha 1.0 4.5 1 20 B0.1 0.2
Lemon sole Pelotretis flavilatus 1.9 1.3 2 2 0.2 0.1
Marblefish
1
Aplodactylus arctidens 1.0 10.3
Paddle crab Ovalipes catharus 3.8 5.2 4 10 0.1 0.1
Tarahiki
1
Nemadactylus macropterus 0.6 10.2
Opalfish Hemerocoetes sp. 1.9 40.2
Sprat Sprattus sp. 6.7 75 0.2
Pigfish
1
Congiopodus leucopaecilus 1.9 30.2
Lobster
1
Jasus edwardsii 0.6 10.1
Common roughy
1
Paratrachichthys trailli 3.9 24 0.1
Ahuru
1
Auchenoceros punctatus 1.9 27 0.1
Flounder
1
Rhombosolea sp. 1.0 1B0.1
Camouflage crab
1
Notomithrax sp. 0.6 1B0.1
Garfish
1
Hyporhamphus ihi 0.6 1B0.1
Salp Two spp. 6.7 1.3 14 5 B0.1 B0.1
Mantis shrimp
1
Squilla armata 1.0 1B0.1
Note:
1
Species taken by a single individual female sea lion.
Diet of Otago female NZ sea lions 101
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Table 2 Mean sizes (including masses used to calculate the reconstituted masses) of prey species found in the
diet of female New Zealand sea lions on Otago Peninsula, New Zealnd in autumns 2008 and 2009.
Fork length for fish
(cm)
1
Mass (g)
2
Species Mean9se Max. Min. Mean9se Max. Min. n
Mass (g) from
references
3
Ahuru 10.093.9 18.8 5.5 8910 34 8 15
Arrow squid 29.593.3 36.8 22.5 5439218 1218 214 54
Barracouta 61.3913.3 87.3 38.1 12639728 3208 250 72
Blue cod 23.395.6 41.1 15.8 219177 506 51 16
Blue moki 600
Camouflage crab 80 1
Catfish 28.5910.0 32.0 18.7 125956 215 61 4
Common roughy 3.491.3 6.7 1.8 17912 51 8 14
Estuary stargazer 16.693.8 25.9 9.9 56939 161 25 19
Flounder 17.7 120 1
Garfish 25.1 36 1
Greenbone 35.398.2 49.0 23.3 7349604 1869 100 12
Jack mackerel 42.496.3 50.1 26.5 12259232 1605 789 29
Lemon sole 22.6915.4 38.8 8.1 2259128 638 105 4
Ling 2000
Little blue penguin 1100
Lobster 500
Mantis shrimp 10
Marblefish 32.8 778 1
Maori octopus 14.493.9 21.0 6.3 144191013 3783 133 17
Opalfish 35.5913.0 51.7 21.5 1779124 399 46 4
Paddle crab 57931 161 18 19
Pigfish 200
Red cod 38.498.9 49.3 25.5 7819583 2437 64 36
Rock cod 23.795.1 29.2 25.5 162994 285 117 7
Rough skate 69.5 2284 1
Salp B1
Spiny dogfish 39.7 217 1
Spotted shag 1200
Wrasses 20.498.1 33.2 5.8 3569250 1093 31 44
Sprat 8.691.0 12.5 7.0 59320 3 61
Tarahiki 34.0 714 1
Trumpeter 63.7 65.2 62.3 4145 4430 3860 2
Witch 17.395.1 28.0 10.7 49951 173 9 14
Yellow-eyed mullet 20.593.8 28.7 18.8 155998 313 62 5
Yellow-eyed penguin 5400
Notes:
1
For squid and octopus, this is the mantle length;
2
obtained from the undigested remains of this study;
3
obtained
from references Ayling & Cox (1982), Robertson & Heather (1999), Paul (2000) and Paulin et al. (2001).
102 AA Auge´ et al.
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Discussion
Prey species of female NZ sea lions around
Otago Peninsula
This first study of the diet of female NZ sea
lions based on Otago Peninsula showed that
barracouta and jack mackerel were the most
consumed prey and likely represent critical prey
species for female NZ sea lions during autumn
at least. Only two other species (arrow squid
and red cod) were taken in significant amounts
by the female population of NZ sea lions at
Otago (representing approximately 10% and
over of reconstituted biomass during any one
year; see Table 1). Barracouta and jack mack-
erel are pelagic but can be found near the
seafloor from 0 to 200 m depth within the
continental shelf (Ayling & Cox 1982). Both are
schooling fish during the day but barracouta
disperse at night, when they may be feeding at
the bottom (O’Driscoll & McClatchie 1998).
Arrow squid diurnally migrate in the water
column from the bottom to surface waters over
the continental shelf (Paul 2000). Red cod are
demersal and abundant in any type of habitat
from sand to rock at depths up to 150 m
(Beentjes et al. 2002). The pieces of bryozoans
found in several samples indicated that several
females foraged in the bryozoan thickets found
off Otago Peninsula (50100 m deep, around
815 km offshore [Batson & Probert 2000]), at
least during some foraging trips. No species
predominantly living at more than 200 m depth
(i.e. on the continental slope or beyond) were
recorded in the prey remains from female NZ
sea lions at Otago in autumn. This corroborates
the results of a satellite tracking study on some
of the Otago female NZ sea lions during
autumns 2008 and 2009 as foraging mostly
occurred in coastal waters and on the con-
tinental shelf in the area of bryozoan thickets
(Auge
´et al. 2011).
Diets of any animal populations vary to
accommodate usual seasonal variations in food
resources (McLellan & Hovey 1995; Fea et al.
1999; Womble & Sigler 2006; McKenzie &
Wynne 2008). Female NZ sea lions at Otago
may also change prey species or the percentages
that each species makes in their diet during the
year. Lalas (1997) found significant differences
in the diet of male NZ sea lions at Otago
between seasons, with some prey species being
taken only during specific months. Jack mack-
erel, one of the two main prey species in the diet
of female NZ sea lions in autumn, is likely a
migratory species and unusual off Otago
outside summer and autumn (Lalas 1997;
O’Driscoll & McClatchie 1998). Jack mackerel
was absent from scats and regurgitations col-
lected in winter at the beginning of July 2009
(H. Anderson, unpubl. data). This reinforces
that this food resource is likely only available
during summer and autumn and a seasonal
variation in diet probably occurs.
It will be necessary to conduct a year-round
diet study of female NZ sea lions at Otago over
several years to determine the extent of dietary
variations. However, in autumn 2010, the
constant presence of several highly mobile
juvenile and sub-adult males in the area where
females were found prevented sample collection
to investigate female diet from remains in scats
and regurgitations. The increase in number of
the breeding group of NZ sea lions at Otago
Peninsula may make it harder to obtain sam-
ples from females only. Outside summer, fe-
male NZ sea lions in established breeding
colonies typically disperse and become less
gregarious (Auge
´et al. 2009) and this may still
allow female diet studies using undigested
remains. Investigation of the diet of female
NZ sea lions could also be conducted by using
more invasive methods such as fatty acid
analyses of blubber or milk samples (Iverson
et al. 1997; Iverson et al. 2004; Beck, Rea et al.
2007; Meynier, Morel, Chilvers et al. 2008;
Cooper et al. 2009).
Female NZ sea lions based on Otago
Peninsula were previously reported as feeding
on yellow-eyed penguins and this raised con-
cerns for the viability of particular local popu-
lations of this endangered seabird species (Lalas
et al. 2007). We found that only two Otago-
born New Zealand female sea lions preyed on
Diet of Otago female NZ sea lions 103
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seabirds, including yellow-eyed penguins, dur-
ing each year. These two females were not
mother and daughter and their respective
daughters never fed on seabirds. The predation
by NZ sea lions on yellow-eyed penguins
consequently appears potentially to be an
individually learnt behaviour that is not trans-
mitted through generations.
Comparison with sub-Antarctic data
At Enderby Island, in the Auckland Islands, the
diet of NZ sea lions by mass (based on the
digested stomach content of by-caught adult
females and juveniles of both sexes with no
significant differences between all) was princi-
pally composed of octopus (27.8%), arrow squid
(20.8%), hoki (Macruronus novaezelandiae) and
hake (Merluccius australis) (together 19.2%),
opalfish (Hemerocoetes sp.) (4.7%) and red
cod (4.3%) (Meynier et al. 2009) during a simi-
lar season as our study (end of summer and
autumn). This was consistent with the spe-
cies found in faecal samples analysed by
Childerhouse et al. (2001). The diet of NZ sea
lions consequently differed between the Auck-
land Islands populations and Otago Peninsula
females on the mainland of New Zealand. Jack
mackerel and barracouta were taken only in
negligible numbers at the Auckland Islands
(Childerhouse et al. 2001; Meynier et al. 2009).
While the two main prey species of the
Otago females (barracouta and jack mackerel,
on average 57% of the diet) have energy con-
tent of 6.1 kJ.g
1
and 7.6 kJ.g
1
, respectively
(Pickston et al. 1982; Vlieg 1984), the two main
prey species (octopus and squid, 49% of the
diet) at the Auckland Islands have lower energy
content on average9sd (3.890.4 kJ.g
1
and
6.390.6 kJ.g
1
, respectively) (Meynier, Morel,
Mackenzie et al. 2008; Meynier et al. 2009).
Cephalopods were part of the prey range of the
Otago females but constituted only 20.2% and
13.6% of their diet each autumn (2008 and 2009,
respectively). Consequently, the food resources
at the Auckland Islands seem to be of lower
quality than the food resources available to
female NZ sea lions at Otago at least during
autumn, potentially supporting the hypothesis
that the Auckland Islands are marginal marine
habitat for this species (Chilvers et al. 2006;
Meynier et al. 2009). However, more studies on
energy content of prey throughout the year and
specifically off Otago Peninsula will be needed
to confirm this.
Resource overlap with other marine predators
Male NZ sea lions are found at Otago most of
the year, except during the breeding season
(December and January) when many migrate to
the breeding colonies in the Aucklands and
Campbell Islands (McConkey, Heinrich et al.
2002; Robertson et al. 2006). The best estimate
of the number of male NZ sea lions using
Otago Peninsula is currently 75 (S. McConkey,
New Zealand Sea Lion Trust, pers. comm.).
Male NZ sea lions at Otago had a similar prey
range as females during autumn, at least for the
main prey species in the reconstituted biomass
(Table 3), although they foraged on some
deeper water species than females. Neverthe-
less, because male diet was investigated more
than 10 years prior to this study, a concurrent
comparative investigation of Otago male and
female NZ sea lion diets during the same period
is needed to determine the overlap. In many
pinnipeds, males and females forage in different
areas and/or have segregated diets (Koen et al.
2000; Beck, Iverson et al. 2007; Trites &
Calkins 2008), including potentially NZ sea
lions at the Auckland Islands (Meynier, Morel,
Chilvers et al. 2008; Geschke & Chilvers 2009).
Southern elephant seals (Mirounga leonine),
leopardseals(Hydrurga leptonyx), orcas (Orcinus
orca), and several species of dolphins are only
occasionally sighted at Otago (J. Fyfe, DOC
Coastal Otago ranger, pers. comm.). Conse-
quently, the only other large marine mammal
that potentially competes for food resources with
female NZ sea lions at Otago is the New Zealand
fur seal. Fur seals breed in large numbers on
Otago Peninsula (between 20,000 and 30,000
fur seals [Lalas 2008]). Their main prey varies
104 AA Auge´ et al.
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between arrow squid in summer and autumn,
and barracouta, jack mackerel and octopus in
winter and spring (Carey 1992; Fea et al. 1999).
Red cod is taken during the entire year (Fea
et al. 1999). Although resource overlap between
fur seals and sea lions appeared limited during
autumn, both predators may target similar spe-
cies during half the year, and red cod all year.
All diet studies on New Zealand fur seals were,
however, conducted more than 10 years prior
to this study. To assess possible competition
between these two species, concurrent diet studies
could be conducted.
The other marine predators inhabiting the
Otago Pensinula are seabirds that all tend to
forage near Otago Peninsula (McClatchie et al.
1989; Moore 1999). Yellow-eyed penguins nest-
ing on Otago Peninsula feed mainly on blue cod
(18.3% of reconstituted biomass), opalfish
(28.6%), arrow squid (14.4%), and red cod
(7.4% [Moore & Wakelin 1997]). Three of these
species constituted a significant part of the diet
of female NZ sea lions, indicating some reso-
urce overlap but penguins feed on smaller prey
than sea lions (Moore & Wakelin 1997). Jack
mackerel was not part of the diet of yellow-eyed
penguins, and barracouta was rarely consumed
(Moore & Wakelin 1997). Most other seabird
species feed predominantly on small fish, krill
and invertebrate larvae (McClatchie et al. 1989).
Resource overlap with recreational fisheries
Both recreational and commercial fisheries
occur along the Otago coast. While commercial
fishing is well documented by the Ministry of
Fisheries, data on species and quantities taken
by recreational fishermen are sparse. Only one
survey conducted in 1991 enabled the evalua-
tion of this fishery (Teirney & Kilner 2002). The
main species taken by recreational fishermen at
Otago that overlapped with the prey range of
female NZ sea lions were blue cod (48% of
the total number of prey caught by fisher-
men), barracouta (10%), spiny dogfish (7%),
wrasse (3%), red cod (2%) and greenbone (2%).
Consequently, there is a resource overlap in
targeted species between female NZ sea lions
and recreational fisheries and potential compe-
tition around Otago Peninsula. However, there
is no estimate of biomass taken by recrea-
tional fishermen. This only survey of recrea-
tional fishing activities at Otago was also
conducted almost 20 years prior to this study
(Teirney & Kilner 2002). Recreational fishing
could be monitored in order to detect the
Table 3 Comparison of the top 10 prey species by percentage of biomass in the diet of male and female New
Zealand sea lions at Otago Peninsula, New Zealand.
Females during autumn
1
Males during autumn
2
Males year-round
2
Prey species % biomass Prey species % biomass Prey species % biomass
Barracouta 30 Jack mackerel 30 Barracouta 25
Jack mackerel 28 Barracouta 23 Maori octopus 14
Arrow squid 8 Maori octopus 16 Jack mackerel 13
Red cod 7 Ling 9 Skate 10
Maori octopus 6 Rough skate 7 Flounder 9
Yellow-eyed penguin 4 Red cod 3 Paddle crab 4
Wrasse 3 Greenbone 2 Ling 4
Greenbone 3 Flounder 1 Greenbone 4
Blue cod 2 Wrasse 1 Red cod 4
Little blue penguin 2 Paddle crab B0.1 Brill 2
Total 93 Total 92 Total 90
Notes:
1
Present study (mean across the two study years);
2
Lalas (1997).
Diet of Otago female NZ sea lions 105
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trend in increase or decrease in catch of parti-
cular species, and potential consequences for
the marine life foraging in the coastal area
off Otago Peninsula and adjacent coastlines,
including sea lions.
Resource overlap with commercial fisheries
Barracouta and jack mackerel have been in the
top five New Zealand commercially targeted
fish species by weight managed in the Quota
Management System (QMS, see Clark [1993])
at least since 2005 (Ministry of Fisheries 2010).
Except for wrasse and octopus (not taken in
commercial fishing activities) and seabirds, all
top 15 species in the diet of female NZ sea lions
at Otago in autumn are commercially targeted
around Otago Peninsula and managed in the
QMS (Ministry of Fisheries 2010). There is
consequently a resource overlap between NZ
sea lions and commercial fisheries, including
with three of the main New Zealand fisheries
(arrow squid, barracouta and jack mackerel, all
occurring in the marine areas around Otago
Peninsula [Ministry of Fisheries 2010]).
Marine food resources at Otago may have
been altered while the NZ sea lion was absent
from the mainland owing to fishing activities by
early Ma
¯ori and predominantly by large-scale
commercial fishing since the 1970s. Fur seals
have reached large numbers at Otago following
recolonisation, but the populations now seems
to have stabilised (Lalas 2008). Whether this is
because of the carrying capacity of the marine
habitat or of the terrestrial habitat is not
understood (Bradshaw et al. 2002). In order
to determine potential competition between NZ
sea lions and fishing activities around Otago
Peninsula, it will be necessary to gain detailed
data including primary production, available
biomass of prey species and their distribution
and migration, and masses taken out by sea
lions, other marine predators and fisheries to
integrate them into a complex marine trophic
model.
Conclusion
In autumn, the female NZ sea lions foraging
around Otago Peninsula fed predominantly on
barracouta and jack mackerel, but also to a
lesser extent on a wide range of cephalopods,
other bony fish, seabirds, cartilaginous fish,
crustaceans and salps. All prey species were
found in coastal waters or on the continental
shelf, hence highlighting that they foraged
exclusively in this area. There appears to be a
large resource overlap between female NZ sea
lions and other resident marine predators of
Otago Peninsula and recreational and commer-
cial fisheries that could lead to resource com-
petition as the population of sea lions grows.
More research is needed into marine produc-
tion around Otago Peninsula to evaluate this
possibility. Comparison between the diet of
female NZ sea lions at Otago and the diet of
NZ sea lions foraging around the Auckland
Islands indicated that prey quality may be
higher at Otago. Year-round diet studies of
male and female NZ sea lions at both sites are
needed to confirm this.
Acknowledgements
We would like to thank Nathan McNally for his help
in the field, Vivienne McNaughton and Kim Garrett
(Zoology Department, Otago University) for finding
the required gear and lab space, Jim Fyfe (DOC,
Coastal Otago) for his safety contact role, and two
anonymous reviewers for helpful comments on an
earlier draft of this manuscript.
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... During the summer and autumn, NZSL on the Otago Peninsula feed predominately on snake mackerel (Thyrsites atun) and jack mackerel (Trachurus spp.), which occur on the continental shelf (Augé et al., 2012b). However, the winter diet of the females in our study may differ, as jack mackerel were absent from prior analysis of scat collected during the winter (Augé et al., 2012b;Lalas, 1997 (Augé et al., 2012b). ...
... During the summer and autumn, NZSL on the Otago Peninsula feed predominately on snake mackerel (Thyrsites atun) and jack mackerel (Trachurus spp.), which occur on the continental shelf (Augé et al., 2012b). However, the winter diet of the females in our study may differ, as jack mackerel were absent from prior analysis of scat collected during the winter (Augé et al., 2012b;Lalas, 1997 (Augé et al., 2012b). ...
... During the summer and autumn, NZSL on the Otago Peninsula feed predominately on snake mackerel (Thyrsites atun) and jack mackerel (Trachurus spp.), which occur on the continental shelf (Augé et al., 2012b). However, the winter diet of the females in our study may differ, as jack mackerel were absent from prior analysis of scat collected during the winter (Augé et al., 2012b;Lalas, 1997 (Augé et al., 2012b). ...
Article
New Zealand sea lions (NZSL, Phocarctos hookeri) were extirpated from mainland New Zealand during pre‐European subsistence hunting. They began reoccupying South Island in 1994, and the newest breeding colony arose in 2006 along the Catlins Coast on southeastern South Island and currently consists of <10 individuals. The goal of this study was to use animal‐borne satellite telemeters and miniature data recorders (MDRs) to determine home ranges, three‐dimensional movements, and foraging strategy of female NZSL along the Catlins Coast during the austral winter of 2019. Total home ranges were small (97 km2) and primarily restricted to nearshore areas. Dives were shallow (8.9 m), short in duration (1.4 min), and had a mean swimming speed of 1.5 m s−1. We identified three dive types based primarily on total dive duration, mean maximum depth, total distance swam, and path linearity. The estimated at‐sea metabolic rate varied among dive types because of differences in flipper stroke frequency and swim speed. Female NZSL along the Catlins Coast have smaller home ranges and make shorter foraging trips compared with females in the Auckland Islands, and suitable habitat for breeding and prey availability along the southeast coast are encouraging for future population growth.
... The diet of New Zealand sea lions has been well researched for all populations except Stewart Island. This has been undertaken through scat, re gur gitation, stable isotope, and fatty acid analysis (Milne 1996, Childerhouse et al. 2001, Meynier et al. 2008a, Augé et al. 2012, Stewart-Sinclair 2013, Lalas & Webster 2014, Roberts & Lalas 2015, Chilvers 2017, 2019, 2021. Several of these studies investigated diet for the Auckland Islands population over a longer term using either fatty acid analysis (Meynier et al. 2008a(Meynier et al. , 2010, a long-term data series of scat sampling (Stewart-Sinclair 2013), or foraging behaviour and whisker stable isotope ana lyses (Chilvers 2019). ...
... It would be useful to have direct diet research undertaken for this colony to understand the species, number, and indication of the size of prey that are being taken by the Stewart Island sea lions. Given the remoteness of this colony and how sparsely distributed the individuals are in the colony, this could not easily be undertaken using the normal diet study techniques of analysis of hard parts in regurgitation or faeces (Childerhouse et al. 2001, Augé et al. 2012, Stewart-Sinclair 2013, Lalas & Webster 2014. Instead, it would be recommended that DNA analysis of faeces be undertaken on the small number of samples that could be found in a field trip to have a broader picture of the diet than could be reached using hard parts only on small sample sizes. ...
Article
Full-text available
New Zealand sea lions Phocarctos hookeri have experienced a 46% decline in pup production in the last 25 yr, driven by female deaths in trawl fisheries around the Auckland Islands. The only colony for this species recorded away from the subantarctics and this fishing impact is on Stewart Island. Despite the Stewart Island colony only being 1% of the species, it is significant, as it is currently the only stable population and is located in an area away from most on-land human impacts, although not away from potential fisheries pressures. To ensure this colony’s persistence, more information is needed on these sea lions’ diet, foraging behaviour, and local fisheries interactions for management that promotes their protection. The present research investigates the long-term foraging behaviour, and infers the diet, of female New Zealand sea lions on Stewart Island using their known foraging behaviour and linking this to their proximal and full-length whisker stable isotope values. Previous foraging studies found that these animals have small foraging areas with consistent mesopelagic diving behaviours. These behaviours, linked with their whisker stable isotope values, show consistency in foraging behaviour and inferred diet across their entire adult life. Currently, there are no known commercial fisheries bycatch issues for sea lions around Stewart Island. However, precautionary measures ensuring fisheries pressure does not increase and management to safeguard that deepwater trawling and finfish aquaculture remain absent would be proactive steps that should be undertaken for the protection of this new colony and for this Endangered species as a whole.
... These low TP estimates may also be due to the TP estimation method used, or alternatively, it may suggest that those females predated on organisms at lower trophic levels than previously assumed during the summer. However, as scat analysis is known to be biased to prey with hard parts, alternative genetic (DNA) metabarcoding analysis of scat samples from females from Marion Island could provide valuable insights into prey consumption (Augé et al. 2012, McInnes et al. 2017, Cavallo et al. 2018. ...
Article
Full-text available
The Southern Ocean exhibits substantial spatio-temporal variation in biogeochemical processes that shape interactions and productivity across food webs. Stable isotopes in marine predators provide an opportunity to capture such variations, yet few studies have accounted for variability in the isotopic baseline when interpreting predator isotope values. Using bulk δ ¹⁵ N and δ ¹³ C values and the δ ¹⁵ N values of amino acids (AAs) of blood from female Antarctic fur seals (AFSs) Arctocephalus gazella , we investigated spatial and seasonal variation in baseline δ ¹⁵ N (δ ¹⁵ N baseline ) values across 3 Southern Ocean basins (Indian, Pacific and Atlantic) to facilitate robust comparison of consumer trophic ecology. We detected spatial and seasonal differences in δ ¹⁵ N baseline values across the basins, using the source AAs phenylalanine (Phe) and lysine (Lys), consistent with the latitudinal gradient of AFS colonies and seasonal changes in seal foraging movement. The δ ¹⁵ N values of source AAs from Marion Island and Cape Shirreff were representative of particulate organic matter δ ¹⁵ N values in the Indian and southwest Atlantic sector, respectively, whereas more complex patterns were observed in the Atlantic sector around Bird Island. Variations in bulk δ ¹⁵ N values can also be attributed to changes in AFS diet, with females foraging in the Atlantic and Pacific targeting higher trophic level prey in winter. Trophic position estimation using Phe and leucine (Leu) suggested that females encompass more than 2 trophic levels. Our study highlights the utility of using Lys alongside Phe to assess seasonal and ocean basin-level variations in the isotopic baseline and Leu/Phe for AFS trophic position estimation.
... This food web included predator-prey interactions inferred from diet studies of free-living species occurring off the coast of Otago or the surrounding area, including data from Allum & Maddigan (2012), Augé et al. (2012), Bennett & Randhawa (2019), Cruz et al. (2001), Fea et al. (1999), Flemming et al. (2013), Graham (1938), Hanchet (1991), Harcourt et al. (2002), Heather & Robertson (2015), Imber (1999), James & Stahl (2000), Lalas (1977Lalas ( , 1983 Robertson (1992) and van Heezik (1990). For instance, if a species of shark was reported as having a crustacean species present in its gut contents or was observed consuming a crustacean species in nature, then we considered that a predator-prey interaction existed between the shark and crustacean. ...
Article
Parasites comprise a significant proportion of species on Earth yet are seldom included or realistically represented in studies of food web ecology. As ecosystems continue to change in response to natural and anthropogenic pressures, it is important now more than ever to include parasites to improve our understanding of their role, now and in the future. A large-scale biodiversity survey of the coastal marine ecosystem of Otago, New Zealand, provided a unique opportunity to assess what contribution parasitological studies can make toward revealing trophic interactions between species when creating food webs. Here, we created 4 increasingly complex food web depictions of Otago and compared network properties between them to assess changes with each addition of new types of data (first excluding and then including parasite species). We also assessed how parasites influence the functioning of Otago’s food web by simulating extinction scenarios for each web, estimating their robustness to biodiversity loss. The inclusion of parasites altered food web structure, such as decreasing connectance and increasing path length, modularity and species clustering. In both extinction scenarios, including parasites resulted in a lower robustness of the food webs to biodiversity loss. Our results suggest that neglecting parasite taxa in food web studies may lead to inappropriate estimates of ecosystem structure and functioning and possibly an overestimation of an ecosystem’s resilience to change. Above all, we reveal the huge potential of parasitological studies to advance our understanding of predator-prey interactions.
... Based on the results from the tracking off the Otago Peninsula in winter 2022, it appears that the bryozoan thickets are also used in winter, but perhaps, with a lower intensity. Several prey species in the diet of the Otago Peninsula female sea lions are migratory and this may lead to a seasonal change in marine habitat use (Augé et al., 2012a). Interestingly, sea lion foraging patterns may indicate the presence of bryozoan thickets or other similar deep biogenic habitats that would provide special foraging grounds. ...
Technical Report
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A small breeding population of New Zealand sea lions/pakake/whakahao (NZSL) has been recolonising The Catlins/Te Akau Tai Toka since 2007, in a human-modified landscape. Interactions with vehicles (accidents and disturbance) are a known risk. There are also concerns for interactions with fishing gear and recreational boating. Detailed understanding of the land and marine habitat uses of the Catlins female NZSL is needed to manage and mitigate these risks. From June to August 2022, five adult female NZSL were instrumented with fastloc-GPS satellite tags, and one juvenile female with a GPS logger, in The Catlins. This was a follow-up on a previous tracking study in 2019. The tags recorded land and marine locations and dive depths of these animals for up to 80 days each with a high location accuracy (~20 m). This report presents the analyses of the data from the 2022 tracking project and the results most relevant to management, and provides recommendations for achieving the goals of the NZSL Threat Management Plan and for future research. Adult female NZSL spent on average 48% of their time on land. During periods on land, they used between nine and 18 land sites each between the Clutha River/Mata-au Mouth and Wallace Head, with a concentration of sites from Campbell Point/Taumatakōtare/Ōwaea to Jacks Bay/Ōtemakura. Each female had one site each where they spent more time than any other (29-55% of their time onshore). Surat Bay was overall the most used beach (33% of time on land across all females). Female NZSL spent on average 20% of their time on land within 20 m of a road, primarily along The Nuggets Road. They spent on average 77% of time on land at beaches with vehicle access, notably Surat Bay and Cannibal Bay/Ōrakiutuhia. Adult female NZSL foraged almost exclusively within 300 m from land on shallow rocky reefs (79% of marine locations). The core foraging range (65% Kernel density) was a small area around the tip of Tokatā/ Nugget Point (known as 'The Nuggets'). The rest of the foraging range was concentrated in discreet areas all along the coast from Campbell Point to Jacks Bay, but did not include estuaries, other than the mouth of the Catlins River/Pounawea Estuary. This estuary was used regularly but for very short periods (overall <2% of their time at sea) by females to travel to and from land sites. The mean dive depth was 10.5 m, with 97% of all dives < 30 m depth; 69% of the dives were benthic. The deeper dives were in the 'offshore area', considered a part of their foraging range but seldom used in winter, at depths of 40-70 m about 4-13 km off Nugget Point. There were only 3.5 days of data (only land locations and dives) from the juvenile female (1.5 year-old) due to tag malfunction. She used land sites along Kaka Point Road and The Nuggets Road, crossing the road at Campbell Point. Her diving behaviour was very different from any of the adults i.e. exclusively diving at night, continuously and at constant depth (i.e. not on rocky reefs). Comparisons with the results of a previous 2019 winter tracking of female NZSL in The Catlins were only qualitative due to the difference in accuracy of locations (ARGOS locations vs fastloc-GPS locations). The diving behaviours in 2019 were within the range of the 2022 study. Adult female NZSL used the same general areas for foraging and as land sites but there might be differences in core foraging range between 2019 and 2022. Some land locations are specific to individuals and therefore, there were differences because different females were studied (one adult female was studied in both years and used similar sites in 2019 and 2022). Recommendations for management included (1) for land sites with risks from vehicles, speed reduction for key coastal roads, 'safe zone' investigation, better signage, education, fences, and warning systems, (2) recreational fisher surveys to determine interactions at sea in coastal areas, and (3) for Catlins River Estuary, assessing boat speed limits, education, set net regulations. Future science needs identified were (1) year-round land habitat use (using existing data, future resights and structured studies), (2) year-round diet (proxy for seasonal changes in foraging range), (3) fishery overlap analyses (recreational and commercial), and (4) marine habitat use outside winter and marine habitat use of yearlings.
... The shelf break front can be recognized by strong gradients in temperature, salinity, and nutrients where warm, salty, high-silicate, macronutrient-poor STW meets cool, fresh, low-silicate, macronutrient-rich SAW water (Boyd et al., 1999;Currie et al., 2011;Jones et al., 2013). This region's ecosystem supports several endemic and endangered marine species (Augé et al., 2012), in addition to significant commercial fisheries (Leathwick et al., 2006), highlighting the need to understand mechanisms driving phytoplankton variability along the OSB. Early remotely-sensed studies of this region (Murphy et al., 2001) identified maximum monthly averaged surface chlorophyll-a (Chl-a) concentrations (>1 mg/m 3 ) occurring in the subtropical front regions to the east and west of ANZ from 3 years of 9 km binned SeaWiFS monthly composite data. ...
Article
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This study investigates the influence of along‐front wind forcing on chlorophyll‐a (Chl‐a) at the Otago Shelf Break (OSB) in southeast Aotearoa/New Zealand using remotely‐sensed and in situ data. Summer wind stress over the OSB was shelf‐aligned, oscillating between upfront and downfront. Surface Chl‐a concentrations along the OSB were shown to increase episodically (≤10 days duration) following upfront wind stress. This response occurred over most of the 350 km long shelf break, and was most intense north of the Otago Peninsula. Peak Chl‐a enhancement at the shelf break occurred following periods of upfront winds, exhibiting a lagged response of approximately 5 days. Moored thermistor data indicated that upfront wind events were followed by increased thermal stratification over the mid‐shelf, whereas downfront wind events were followed by a well‐mixed water column. In situ temperature, salinity, and nutrient measurements suggested an offshore movement of the surface expression of the front following upfront winds, and a reduction in nitrate over the shelf break. From these observations a model of Ekman restratification driven by upfront winds is proposed for this system, wherein off‐shelf Ekman transport converts strong horizontal isopycnal gradients at the shelf break front into vertical stratification. This stratification holds phytoplankton in the upper water column, allowing increased access to light, which is marked by the increased drawdown of nitrate at the shelf break. Downfront winds break down this stratification, move the shelf break front onshore, and mix phytoplankton through the water column, reducing the surface expression of chlorophyll.
... including Chile (Bahamonde, 1951;Duarte et al., 2007), the western Atlantic coast of South Africa (Griffiths, 2002(Griffiths, , 2002(Griffiths, , 2003Isaacs, 2013), the southern coast of Australia and the coast of New Zealand (Augé, Lalas, Davis, & Chilvers, 2012;Mehl, 1969). Nowadays, snoek is absent from the coasts of Argentina and the subantarctic waters of the Beagle Channel, where the SST is between 5°C and 10°C (Lloris & Rucabado, 1991;López et al., 1996;Zangrando, Ponce, et al., 2016). ...
Article
Stable carbon and nitrogen isotope ratios in the skeletal elements of both ancient and modern marine species from the Beagle Channel were used to compare the structure of Late Holocene and modern food webs, and predict potential changes as a result of a Sea Surface Temperature (SST) increase in the region. Complementary, ancient and modern shells of limpets and mussels were isotopically analysed to explore changes in the isotopic baseline and compare marine food webs through time after an appropriate correction for baseline shifts. Results confirmed a declining pattern of marine primary productivity during the Late Holocene in the Beagle Channel. In general, the isotopic niches overlapped largely in the ancient food web in comparison to the current marine one, with the exception of that of cormorants (Phalacrocorax sp.). Our data suggest that all the species that have undergone intense human exploitation (Arctocephalus australis, Otaria flavescens and Merluccius sp.) significantly increased their trophic levels. The most important finding of this work was the very high isotopic overlap between snoek (Thyrsites atun) and hake (Merluccius sp.) during the Late Holocene. Increasing SST as a result of global warming could favour the recolonization of the southern South‐Western Atlantic Ocean by snoek from the South‐Eastern Pacific Ocean, with a potential impact on the landings of the economically important Argentine and Austral hake. These findings highlight the relevance of using zooarchaeological remains for providing predictions about marine food webs changes in the near future. This article is protected by copyright. All rights reserved.
Thesis
Shark declines may cause trophic cascades, which is partially dependent on how sharks influence prey abundance and behaviour. Rays are mesopredators that play a unique role in ecosystems as bioturbators. My dissertation investigates whether sharks induce changes in ray sightings, behaviour, and habitat use across multiple spatial and temporal scales. First, I reviewed the ray ecology literature and found limited evidence for risk-induced ray trait responses (Chapter 1). Next, using a baited remote underwater video station (BRUVS) survey, I found that southern stingray (Hypanus americanus) sightings were negatively associated with shark abundance throughout the tropical Western Atlantic Ocean (Chapter 2). Other important predictors of southern stingray sightings in the region included habitat complexity, geomorphology, and bottom fishing gear. At a smaller spatial scale inside the Glover’s Reef Marine Reserve in Belize, a BRUVS survey revealed southern stingray sightings and behaviour remained stable between 2009 – 2019 despite a concurrent decline in the relative abundance of Caribbean reef sharks (Carcharhinus perezi) (Chapter 3). Habitat complexity explained southern stingray sightings and behaviour on BRUVS, which may be due to their preference for soft bottom habitats and/or because we are less likely to detect stingrays on BRUVS in areas with high reef relief. Passive acoustic telemetry showed Caribbean reef and lemon (Negaprion brevirostris) sharks use shallow lagoon habitat, which was also the preferred habitat of southern stingrays, suggesting it is unlikely a refuge from predators. Finally, using accelerometry and hidden Markov models, I found that southern stingray activity is crepuscular and nocturnal, with high individual variation (Chapter 4). Southern stingrays were highly active in shallow water (<5 m), which is likely associated with prey activity and availability. My findings emphasize the context dependent nature of predation risk effects and the need to take a multimethod approach to understand ray behaviour and habitat use.
Technical Report
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This report addresses aspects of the Otago shelf bryozoan ("lace coral") thickets of relevance to the Ministry of Fisheries, namely their distribution and composition, their exposure and vulnerability to mobile fishing gear, and the influence of this community type on commercial and non-commercial species. Bryozoan thickets are a rare habitat type by global standards, and are uncommon in New Zealand waters (Batson 2000). Nevertheless, where bryozoans occur in thicket-forming densities, they are often ecologically and commercially important (Proben et al. 1979, Bradstock & Gordon 1983). Frame-building Bryozoa significantly enhance biodiversity where they occur by providing habitat for numerous sessile and mobile invertebrate species that may otherwise be absent or less abundant (Robert et al. 1979). They may also function as nursery areas for commercially valuable finfish and shellfish species (Vooren 1975). Recognition of the growing role of habitat protection in marine fisheries management has led to increased benthic mapping research in New Zealand's marine estate. The basis of this report was a two-year study conducted by the Marine Science Department, University of Otago, to investigate the distribution and species composition of bryozoan thickets on the Otago shelf. The report is divided into five sections. Because the Bryozoa is a poorly known group, we begin by describing key life history characteristics of the phylum. We then summarise the Otago shelf physical setting, the methods used and findings of our benthic mapping study, and the effects of bryozoan thickets on biodiversity. Finally, we examine fisheries issues relating to bryozoans on the Otago shelf, including their commercial significance and vulnerability to mobile fishing gear.
Article
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The primary objective of the population management plan for New Zealand sea lions, Phocarctos hookeri, is to move the species from its current conservation status of ‘Threatened’ to ‘Non-threatened’. The mechanism by which this will occur is through the establishment of new breeding colonies away from the only existing colonies at Auckland Islands and Campbell Island. Otago, on the southeast coast of the South Island of New Zealand, is one of only three locations where breeding has been recorded away from these islands in modern times. We found only one female at the initiation of our surveys here in 1991, an individual that had been tagged as a pup at Auckland Islands. This female has remained resident at Otago and is now breeding. Her first live birth, in the 1993/94 breeding season, represented the first record of a P. hookeri pup on the New Zealand mainland since the elimination of the species here by humans c. 150 years ago. Up to and including the 2000/01 breeding season she had produced six pups. Her surviving pups have remained at Otago and her eldest two daughters have started breeding, producing a further three pups. From this total of nine live births, two pups have died. Although 6 - 8 other migrant females have been recorded, to our knowledge none have bred at Otago. We conclude that the initiation of breeding by P. hookeri at Otago has been a serendipitous event attributable to atypical behaviour by a single female.
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Thirty measurements were taken on the otoliths, pharyngeal bones, and five of the paired cranial bones of a modern sample of labrids from New Zealand, consisting of 18 Notolabrus celidotus (spotty) and 122 Pseudolabrus miles (scarlet wrasse). Regression analysis was performed on these measurements to estimate live fork length and ungutted weight. A number of regression models were examined (linear, logarithmic, exponential and power curve) to work out the optimum estimator for each bone measurement. It was found that live fork length of this species can be estimated with a standard error of less than ± 21 mm, and live weight to less than ± 94 g. Coefficients are provided for 60 equations linking bone size to live characteristics. This is followed by a study of labrids from an archaeological site at Waihora in the Chatham Islands. Measurements were made on 3,096 archaeological bones with a Minimum Number of Individuals of 1,509. It was found that the labrid catch had non-normal characteristics with a mean fork length of 295 mm and SD of 59 mm. The non-normality is largely attributed to a mixture of three species of labrids in the archaeological collection, which could not be identified to species from bone anatomy. The size-frequency mixture was decomposed into three separate size-frequency diagrams using a recursive technique. This analysis suggested approximate proportions of 7% Notolabrus celidotus (spotty), 66% Pseudolabrus miles (scarlet wrasse), and 27% Pseudolabrus fucicolia (banded parrotfish).
Book
The accurate identification of fish ‘ear-bones’, known as otoliths, is essential to determine the fish prey of marine and terrestrial predators. Fish otoliths are species-specific when combining size, shape and surface features, and can remain undigested for long periods. As a result, they can indicate which fish make up the diet of various predators, including cephalopod, seabird, marine mammal and fish species. Such studies are crucial for understanding marine ecosystems, and trophodynamics in particular. Increasingly, these methods are being used to understand the diet of some terrestrial predators, also extending to that of humans in archaelogical studies. Otoliths of Common Australian Temperate Fish offers users a verified reference collection to assist in the accurate identification of species and size of fish using otoliths. It covers 141 fish species from a broad geographic range of the Australian temperate region and includes commercial and non-commercial fish species. A standardised written description of the otolith structure, size and surface features is provided for each species. Included are brief distribution and ecology notes, and regression for both otolith and fish lengths, together with high-quality SEM photographs of the otolith described. This guide will be an essential reference for marine scientists and marine mammal researchers; ornithologists, fisheries researchers and fish biologists studying age and growth or comparative anatomy; and archaeologists. Winner of the 2008 Whitley Award for Zoological Manual.
Article
This paper describes both the modern and the pristine distribution, breeding range, and relative abundance of the New Zealand sea lion (Phocarctos hookeri). Archaeological data and historical reference were used to determine the pristine status of the sea lion, and its present status was determined from recent scientific studies and observations. The sea lion had a substantially more widespread distribution before the arrival of humans in New Zealand than it does today. The species used to range along the whole length of the coast, from the north of the North Island through to Stewart Island and the subantarctic islands. Although we have no direct estimate of pristine abundance, the present population size is clearly reduced. Subsistence and commercial killing of sea lions is the most likely cause of historical changes in distribution and abundance. Their pristine breeding range extended at least as far north as Nelson and may have extended to the North Island. The present breeding range is restricted to the Auckland Islands and Campbell Island. Within the last 10 years a few individuals have started to breed on mainland New Zealand and Stewart Island, which may reflect a slow recolonisation of earlier breeding grounds. Pup production at Sandy Bay, Enderby Island, has been stable for at least the last three decades, and no major changes in pup production at Dundas Island and Figure of Eight Island are apparent.
Article
Stomach samples were collected by using the water-flushing technique from Yellow-eyed Penguins Megadyptes antipodes from the south-east coast of the South Island, New Zealand. One hundred and ninety-eight samples were collected from 86 individuals during four breeding seasons from February 1991 to December 1993. Unworn otoliths were used to reduce bias in prey biomass calculations. Forty-three types of prey were identified, including 37 fish species, four cephalopod species and several crustacean species. Seven species (six fish and one squid) constituted 90% of the estimated biomass and 60% of the total prey number, and all fish comprised 90% of diet biomass and 80% of prey number. Opalfish Hemerocoetes monopterygius, a demersal (bottom-dwelling) species, was the most important component of the diet in terms of the total biomass, numbers and frequency at which it was eaten. Other important biomass components included demersal species and species often found near the bottom, such as Blue Cod Parapercis colias, Arrow Squid Nototodarus sloani, Silverside Argentina elongata and Red Cod Pseudophycis bachus, although pelagic prey such as Sprat Sprattus antipodum and krill Nyctiphanes australis were also eaten. Mean lengths of the main prey species were 5-17 cm and most prey items were < 25 cm long. There was significant temporal variation in diet composition for several prey species, such as increased proportions of Red Cod and Opalfish, and decreased Blue Cod and Arrow Squid in 1992/93. This coincided with a year of improved breeding success. Individual variation in diet may reflect differing foraging ranges. Nests with adults that were sampled for diet had lower breeding success than other nests.