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Predicting interactions between recolonising marine mammals and fisheries: Defining precautionary management

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Interactions between fisheries and marine mammals have created costly and unresolved issues throughout the world. This study examines the spatial and resource overlaps between recolonising New Zealand sea lions, Phocarctos hookeri (Grey) (using satellite tracking) and local fisheries (using spatio-temporal catch database) on the Otago coast, New Zealand. Around Otago, spatial and resource overlaps existed year-round and it is predicted that incidental deaths in fishing gear and resource competition may arise as the sea lion population increases. Preventive management methods (e.g. marine protected areas) and monitoring studies (e.g. fish stock assessments) are proposed. The use of precautionary management could ensure sustainable profitable fisheries and successful recolonisation by sea lions around Otago, and it could be used as a case study for other areas with recovering marine mammal populations that interact with fisheries.
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Predicting interactions between recolonising marine
mammals and sheries: dening precautionary
management
A. A. AUGE
´
School of Surveying/Department of Zoology, University of Otago, Dunedin, New Zealand
ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Australia
A. B. MOORE
School of Surveying, University of Otago, Dunedin, New Zealand
B. L. CHILVERS
Aquatic and Threats Unit, Department of Conservation, Wellington, New Zealand
Abstract Interactions between sheries and marine mammals have created costly and unresolved issues throughout
the world. This study examines the spatial and resource overlaps between recolonising New Zealand sea lions,
Phocarctos hookeri (Grey) (using satellite tracking) and local sheries (using spatio-temporal catch database) on the
Otago coast, New Zealand. Around Otago, spatial and resource overlaps existed year-round and it is predicted that
incidental deaths in shing gear and resource competition may arise as the sea lion population increases. Preventive
management methods (e.g. marine protected areas) and monitoring studies (e.g. sh stock assessments) are proposed.
The use of precautionary management could ensure sustainable protable sheries and successful recolonisation by
sea lions around Otago, and it could be used as a case study for other areas with recovering marine mammal
populations that interact with sheries.
KEYWORDS: bycatch, competition, shery management, marine protected area, Otago Peninsula, seals.
Introduction
Fisheries and marine mammals often have overlapping
ranges as they both target similar species, especially in
coastal areas. Three main interactions arise from this
spatial overlap: incidental deaths (bycatch) of marine
mammals in shing gear, depredation (predation of sh
in shing nets; both direct interactions) and competition
for resources (indirect interaction). Bycatch of marine
mammals in sheries and depredation are worldwide
issues, and competition is thought to exist in several
marine areas (Read 2008; Kovacs et al. 2011). All are
detrimental to sheries owing to damaged gear (inclu-
ding for recreational shing) and lost time during opera-
tions. Restrictions of shing activities to limit bycatch of
marine mammals also lead to loss of revenues by sher-
ies (Bisack 2008). Depredation by marine mammals and
damage to nets can also cause major shing losses
(Wickens 1996; Varjopuro 2011) and has led to illegal
killing of marine mammals directly during shing activi-
ties (Loughlin & York 2000). Bycatch in commercial
and recreational shing activities also poses a threat to
the sustainability of many marine mammal populations
(Read 2008). Consequently, there are numerous incen-
tives for both shers and conservationists to avoid
bycatch and depredation.
Competition for resources between sheries and
marine mammals is more difcult to assess than direct
interactions as it requires data on diet, energetic require-
ments and amount of sh taken by marine mammal
Correspondence: A. A. Augé, School of Surveying/Department of Zoology, University of Otago, Dunedin, New Zealand (e-mail: amelie.auge@
gmail.com)
© 2012 Blackwell Publishing Ltd. doi: 10.1111/j.1365-2400.2012.00861.x
Fisheries Management and Ecology, 2012
1
Fisheries Management
and Ecology
populations combined with shery catches. It has been
the centre of debate in several parts of the world as
resource overlaps (i.e. marine mammals and sheries tar-
geting the same sh species) often exist (Wickens et al.
1992; Bjørge et al. 2002; Atkinson et al. 2008). Recrea-
tional sheries can also have signicant impacts on sh
stocks and be involved in resource competition with
marine mammals (Coleman et al. 2004). Competition
may be increased by shing activities damaging or
destroying benthic habitats that support marine mammal
resources (Friedlander & DeMartini 2002).
Deaths of threatened New Zealand sea lions, Phocarc-
tos hookeri (Grey), as bycatch in commercial sheries
around the Auckland Islands, New Zealand (50.4°S,
166.3°E), have been a long, costly and controversial
issue since the 1980s (Chilvers 2008). The Auckland
Islands host two of the three breeding areas of this spe-
cies, since being extirpated from North and South
Islands of New Zealand by subsistence hunting and seal-
ing (Childerhouse & Gales 1998). The seasonal squid
shery regularly catches Phocarctos hookeri in trawl
nets and possibly competes with them (Robertson &
Chilvers 2011). Numerous and expensive studies and
management measures have been undertaken, incurring
large economic losses to the shing industry and large
cost to the New Zealand government (West et al. 1999;
Breen et al. 2003; Chilvers 2008), but have been unsuc-
cessful at mitigating the issue (Robertson & Chilvers
2011).
An initial population of breeding Phocarctos hookeri
has established itself on the Otago Peninsula, South
Island, New Zealand (45.5°S, 170.4°E) since 1994
(McConkey et al. 2002). This is currently the rst recol-
onisation attempt by this species onto the South Island
of New Zealand. The population is increasing at a slow
rate as it was initiated by a single female (as of 2012
there were only approximately 12 live breeding adult
females, all descended from that female). However, the
increase is exponential and an estimated population of
250 animals should live on the Otago Peninsula by
2031, rising to 1000 animals by 2044 (Lalas &
Bradshaw 2003). These numbers could be reached faster
if other immigrating females join the population and also
start breeding there. Bycatch in shing activities (com-
mercial or recreational) affects all marine mammals and
seabirds that occur around the Otago Peninsula in higher
numbers than the current population of sea lions
(Dawson 1991; Darby & Dawson 2000; Bremner et al.
2009). Female Phocarctos hookeri around Otago forage
in areas where shing occurs (mostly in two critical hab-
itats, shallow rocky reefs and bryozoan thickets) and
prey on commercially and recreationally important sh
species (Augé et al. 2011a,b). Consequently, there may
be risks that bycatch in and competition with sheries
will arise for Phocarctos hookeri around Otago when
sea lion numbers increase, possibly causing socio-eco-
nomic problems and/or impeding the recolonisation pro-
cess within 20 or 30 years without management
planning. Identifying these risks may help produce pre-
cautionary management measures that will avoid a situa-
tion where detrimental interactions between sheries and
sea lions arise in the future.
This study presents evidence that such detrimental
interactions will start as the recolonisation by sea lions
progresses and more animals forage in the area. It pro-
poses management options that could progressively be
implemented by shers and conservationists to avoid
conict. The study aimed to determine the spatial over-
lap between foraging areas of recolonising female Phoc-
arctos hookeri around Otago and the spatial and
temporal distribution of commercial and recreational
sheries. It also aimed to establish the resource overlap
between commercial and recreational sheries and these
sea lions based on their diet and estimates of their
energy requirements and shery catches. The results pre-
dict where risks of bycatch and competition will likely
arise in this rst recolonising area as the sea lion popula-
tion increases. Finally, precautionary management
options are discussed.
Materials and methods
Spatial overlap
The foraging areas of 13 Otago female Phocarctos hook-
eri (including all adults around Otago) were studied dur-
ing the autumns of 2008, 2009 and 2010 using satellite
telemetry (see Augé et al. (2011a), and Augé (2010) for
details on methods and analyses). Foraging areas in
other seasons were not investigated because of nancial
and logistical constraints but these animals resided
almost permanently on or close to the Otago Peninsula
from January 2008 to June 2010 (the study period) and
exhibited site delity for foraging areas between years
(as presented in Fig. 1 and in more detail in Augé
2010). Consequently, they are likely to use the same for-
aging areas year-round and the spatial overlap between
foraging areas and shing activities can be determined
accurately.
Spatial commercial shing data were made available
by the New Zealand Ministry of Fishery via the Ware-
hou Catch Effort database. All commercial shing
vessels of 6 m in length and over are required by the
New Zealand government to report their activities using
specic forms where at least date, latitude and longitude,
type of gear used, duration of shing and species caught
© 2012 Blackwell Publishing Ltd.
A. A. AUGE
´ET AL.
2
and associated weights must be provided. Three out of
ve shing methods used in the shing zone around the
Otago Peninsula were known to result in bycatch of sea
lions and were used in further analyses (i.e. trawling,
seining and long-lining; Shaughnessy et al. 1981; Read
2008; Bremner et al. 2009).
Spatial overlap between shing activities and foraging
areas of sea lions was calculated for the period January
2008 to June 2010. Spatial intensity of shing activities
was mapped using the duration of shing activities. The
Warehou Catch Effort data were reduced to start latitude,
longitude and duration of each shing event. These data
were mapped in ArcGIS (ESRI, Redlands, CA, USA) by
producing a 5-km-resolution raster (to reduce the preci-
sion of data as required by the Warehou database proto-
col) where each cell had the value of the sum of all
duration of shing events (of the three methods with
potential for bycatch) that took place therein. The level
of annual consistency in the distribution of shing
activities was assessed by exploring shing distribution
during seasons each year. Spatial overlap between forag-
ing areas and shing activities was visually represented
by producing 65 and 95% Kernel ranges of foraging
areas (volume contours representing the percentages of
the Kernel probability density distribution of the forag-
ing locations) for all sea lions satellite-tracked. These
Kernel ranges were superimposed on the maps of shing
distribution.
Spatial recreational shing data were not available,
although recreational shing activities usually take place
in coastal waters within 3 km from shore (Teirney &
Kilner 2002). Most of the shing activities reported by
recreational shers did not involve a risk of bycatch of
marine mammals, except gillnetting (Teirney & Kilner
2002).
Resource overlap
The diet of male Phocarctos hookeri around Otago is
presented in Lalas (1997) and female Phocarctos hookeri
around Otago in Augé et al. (2011b). To estimate the
food requirement by mass for sea lion populations, equa-
tions for energetic requirement of sea lions presented in
Winship et al. (2002) were used, with a proportion of
time on land of 50% based on Augé et al. (2011a). The
annual food requirement of the current population of
Phocarctos hookeri around Otago Peninsula and that of
a hypothetical population of 1000 animals (predicted to
be reached by 2044) was determined using the average
energy content of sea lion diet and the food require-
ments, with sex and age group adjustment.
The average annual amount of sh taken by commer-
cial sheries was calculated from the Warehou Catch
Effort database from data obtained between January
2008 and June 2010. Only shing events taking place
within the foraging area of sea lions were used for anal-
yses. This foraging area was dened as the minimum
convex polygon of all foraging locations of sea lions
with a 15-km buffer to accommodate a minimum of sh
stock movement. This area extended over 4953 km
2
.
The amount taken by sheries was only calculated for
the top 10 sh species found in the diet of male and
female Phocarctos hookeri (Lalas 1997; Augé et al.
2011b) and corresponding to over 90% of the diet by
mass of each sex.
The average annual amount of sh taken by recrea-
tional sheries within the foraging area of sea lions was
obtained from Teirney and Kilner (2002). This report
contains estimated number of sh caught by recreational
shers within dened areas of the New Zealand coastline
based on an annual survey of a sample of shers. Esti-
mated annual numbers of sh (only sh found in the diet
Figure 1. Concurrent overlaps between commercial shing activities
(trawling, seining and long-lining) and foraging areas of female New
Zealand sea lions born at the Otago Peninsula, during 2008 (n=4),
2009 (n=7), and 2010 (n=6) autumns. Each shing cell is
595 km.
© 2012 Blackwell Publishing Ltd.
FISHERIES, MARINE MAMMALS: PRECAUTIONARY MANAGEMENT 3
of Phocarctos hookeri were used in the analyses) taken
within the coastal area included in the foraging area of
sea lions were used for calculation. These numbers pro-
vided a value for the annual amount of sh in mass
taken by recreational shers based on the most common
length and weight of a sh of each species found in
FishBase (2011). The combined amount of sh taken
annually by commercial and recreational sheries within
the foraging area of sea lions was used to compare
against the amount taken by sea lions and assess the
potential for competition.
Results
Spatial overlap: bycatch risk
Commercial shing activities that have the potential to
catch Phocarctos hookeri incidentally comprised on
average 76% of trawling operations. Cells of 5-km
resolution included in the foraging area of female Phoc-
arctos hookeri annually experienced up to 244 h of sh-
ing activities susceptible to bycatch. Each year, shing
activities were similarly distributed during each season
as shown in the example for distribution of shing acti-
vities during three autumns (Fig. 1).
Fishing activities were unequally distributed around
the Otago Peninsula. The area north of the Otago Penin-
sula, where shing activities were concentrated, was the
area with the highest level of spatial overlap between
sheries and sea lions (Fig. 2). Smaller areas of overlap
also existed in the south and east of the Otago Peninsula
(Fig. 2).
Resource overlap: competition risk
Main prey species of Phocarctos hookeri around the
Otago Peninsula and their energy contents are presented
in Table 1. The average energy content of Phocarctos
hookeri diet, weighted by the percentage in the diet of
the main species, is 6.2 kJ g
1
for males and 7.3 kJ g
1
for females. Values of energetic requirements for the
Otago sea lion population are summarised in Table 2.
The current population of Phocarctos hookeri based
year-round around the Otago Peninsula is approximately
75 males and 22 females and their annual estimated food
requirement is 246 t (Table 3). For a population of 1000
individuals, this value rises to 2588 t yr
1
(Table 3).
Fisheries exploiting the zone corresponding to the Otag-
o sea lion foraging area caught annually 377 t of sh
(76.7% commercially) that are known to be in the diet of
Phocarctos hookeri (Table 4). This component of the
commercial catch represented only 28.2% of the total
1022 t of sh caught commercially each year. Some sh
species are almost exclusively caught by recreational sh-
ers, in amounts close to that of commercial sheries, for
example, blue cod, Parapercis colias Forster (Table 4).
Discussion
The potential for bycatch, depredation and competition
risks between sheries and Phocarctos hookeri around
the Otago Peninsula that may become critical within a
1020 years timeframe was identied. There has been
no reported Phocarctos hookeri death as bycatch in sh-
ing activities around the New Zealand mainland because
the number of sea lions is currently very low. However,
considerable potential overlap exists between shing
activities and areas where female Phocarctos hookeri
forage. As sea lion numbers increase around the Otago
Peninsula, bycatch may become an issue similar to that
of recolonising New Zealand fur seals (Gibson 1995).
Depredation has not been reported around Otago,
although some recreational shers have complained in
the local media about sea lions interacting with their
shing gear and taking their sh. As more sea lions
inhabit the Otago coast, depredation issues with the
commercial shery may also arise. Regarding competi-
tion, the shing quota system in New Zealand is set to
harvest sh stocks to 40% of their estimated unshed
biomass (Ministry of Fisheries 2011). Assuming that the
catches reported in this study corresponded to only half
of the 60% allowed to be caught (owing to the small
Figure 2. Spatial overlap between foraging areas of female New
Zealand sea lions (n=13) and commercial shing activities with
potential bycatch of sea lions (trawling, seining and long-lining) around
the Otago Peninsula, represented by the number of hours of shing in
595 km cells (period January 2008 to June 2010).
© 2012 Blackwell Publishing Ltd.
A. A. AUGE
´ET AL.
4
spatial scale at which sea lions forage, it is not possible
to determine this value as quotas are given for much
larger areas), combined catch by sheries and a popula-
tion of 1000 sea lions may reduce sh stocks to only
approximately 10% of their unshed biomass by 2040
at the latest. At this level, a sh stock is designated as
collapsed(Ministry of Fisheries 2011). Consequently,
competition will arise in that scenario.
The situation of Phocarctos hookeri around Otago can
be compared with that of grey seal, Halichoerus grypus
(Linnaeus), in the Baltic Sea in the late 1960s (Varjopuro
2011). These seals were then considered at risk of
extinction and all conservation funds and actions were
concentrated on their recovery without anticipation of
the consequences for sheries. The population of Phoc-
arctos hookeri around Otago is currently small and vul-
nerable. However, if the recolonisation process is
successful (i.e. a breeding colony establishes), the popu-
lation will exponentially increase within the next few
decades as with the grey seal. In the Baltic Sea, Halic-
hoerus grypus are now engendering large economic
losses to coastal sheries through depredation and man-
agement plans are only currently being developed by the
Finnish government (Varjopuro 2011). However, these
Table 1. Main prey species of New Zealand sea lions around the Otago Peninsula and corresponding energy contents
% in male diet % in female diet Energy content (kJ g
1
) References
Thyrsites atun (Cuvier) 25 26 6.9 Vlieg (1984)
Trachurus sp. 14 31 7.6 Pickston et al. (1982)
Macroctopus maorum (Hutton) 13 - 3.8 Meynier et al. (2008)
Table 2. Values used to calculate the food requirement by mass of Otago New Zealand sea lions. GER: Gross Energy Requirement (from Winship
et al. 2002)
Average
mass (kg)
GER
(MJ day
1
)
Estimated amount of food
required (kg day
1
)
Current number in
recolonising population
§
Estimated percentage in an
established population
Adult male 279 65.8 10.6 30 30.0
Non-lactating
adult female
125 36.1 4.9 8 12.3
Lactating adult
female
125 61.3 8.4 6 17.7
Juvenile male (1
3 year)*
110 32.8 5.3 45 20.0
Juvenile female (1
3 year)*
87 27.5 3.8 8 20.0
*
Pups (<1 year) are considered as fully dependant on lactating females for food.
From Geschke and Chilvers (2009) for males and Augé et al. (2011c) for all others except for juvenile males (estimated).
Based on average prey energy content of 6.2 kJ g
1
for males and 7.3 kJ g
1
for females.
§
From Augé (2010).
On the basis of reproduction rate of 0.67 pup yr
1
(Childerhouse et al. 2010) and 12.2% pup death rate at 3 months (Chilvers et al. 2007) for
adult females, and estimated from Holmes et al. (2007) for juveniles.
Table 3. Estimated amount of food required by New Zealand sea lions at Otago for the current population size and for a population size of 1000
animals, given per day and per year
Current population Population size of 1000
No. animals Food per day (in kg) Food per year (in t) No. animals Food per day (in kg) Food per year (in t)
Adult male 30 318 116 300 3183 1162
Non-lactating adult female 8 40 14 123 608 222
Lactating adult female 6 50 18 177 1486 543
Juvenile male 45 238 87 200 1058 386
Juvenile female 8 30 11 200 753 275
Total 246 2588
© 2012 Blackwell Publishing Ltd.
FISHERIES, MARINE MAMMALS: PRECAUTIONARY MANAGEMENT 5
plans could have been discussed and researched before
the problem started to avoid current associated costs to
sheries. Around Otago, precautionary sheries manage-
ment strategies should be designed and introduced to
avoid the development of situations such as that of the
Baltic Sea Halichoerus grypus.
The further recolonisation of the Otago coast by
Phocarctos hookeri and the related exponential increase
in their numbers will likely onset considerable issues
for sheries in potentially as little as 1020 years.
However, various precautionary management strategies
along with the production of a detailed management
plan, developed in partnership between shers and con-
servationists, could be progressively implemented to
anticipate any onset of bycatch or competition issues.
This should include marine protected areas, local sh-
ing quotas and management of sea lion numbers (cur-
rently illegal under the New Zealand Marine Mammal
Protection Act 1978). The rst option can be put for
consultation and progressively implemented as soon as
deemed necessary by all parties involved, whilst the
other two options will rst require additional data on
marine production, sh stocks and sea lion population
dynamics around the Otago Peninsula.
A marine protected area (MPA) or a network of
MPAs with shing restrictions or no-take zones would
ensure bycatch, depredation and competition issues are
avoided. MPAs would also protect critical benthic habi-
tats from damage or destruction. Shallow rocky reefs
and bryozoans thickets (the two main foraging habitats
of sea lions) have signicant environmental values and
their protection from shing damage could benet the
overall ecosystem of the area. Areas of coral formations
such as bryozoans are often associated with higher levels
of biodiversity and biomass than soft sediments and are
important for juvenile sh (Mortensen et al. 1995).
Rocky reefs are an important habitat for juvenile sh in
New Zealand (Andrew & Francis 2005) and are vulnera-
ble to damage by shing activities (Steneck et al. 2002).
In New Zealand, MPAs are jointly implemented and
administered by the Ministry of Fisheries and Depart-
ment of Conservation. Local shery parties (commercial
and recreational) are also involved in the decision pro-
cess, along with conservation organisations and other
stakeholders. This makes MPAs the best available man-
agement method to ensure that shery and conservation
sides are represented and collaborate to determine the
best options.
On the basis of the areas of overlap between shing
activities and foraging areas of sea lions and on the biolog-
ical importance of bryozoan thickets and coastal shallow
rocky reefs, four different potential areas are proposed for
MPAs (Fig. 3). The area of bryozoan thickets could be
entirely protected from shing under a no-take zone (i.e.
classied as a marine reserve). Proposed Area 1 had the
highest level of potential direct interactions between sea
lions and shing activities and should receive the status of
MPA where only shing gears with no bycatch risk can be
used. As this area supported the highest level of shing
activities, a no-take zone would severely impede shers
and would consequently be inadequate. Proposed Area 2
corresponds to the main coastal area used by sea lions
Table 4. Estimated mass of sh taken annually by commercial and
recreational sheries within the foraging area of the New Zealand sea
lion population around the Otago Peninsula. NS, no signicant amount
(<1 t) (based on data obtained from January 2008 to June 2010)
Fish species
Amount taken by
commercial sheries (t)
Amount taken by
recreational sheries (t)
Raja nasuta 78.0 NS
Genypterus
blacodes
73.8 NS
Pseudophycis
bachus
60.1 11.7
Nototodarus
sloanii
37.3 NS
Thyrsites atun 33.0 22.2
Parapercis
colias
2.8 43.3
Flatsh (soles
and ounders)
2.2 7.4
Colistium
guntheri
1.6 NS
Odax pullus NS 3.1
Trachurus sp. NS NS
Macroctopus
maorum
NS NS
Squalus
acanthias
NS NS
Wrasse Labridae
2 spp.
NS NS
Total 288.8 87.7
Figure 3. Proposed areas for precautionary management of interac-
tions between local sheries and New Zealand sea lions around the
Otago Peninsula, New Zealand.
© 2012 Blackwell Publishing Ltd.
A. A. AUGE
´ET AL.
6
where commercial shing was low but where recreational
shing occurs. Hence, this area could be designated as an
MPA with a series of no-take zones alternating with zones
where recreational shing could still be allowed (with a
ban on gillnetting). This would ensure that the two critical
sea lion foraging habitats are fully protected and decrease
risks of competition as marine reserves that protect habi-
tats important for juvenile sh have been shown to
improve sh stocks in neighbouring unprotected areas
(Roberts et al. 2001). Proposed Area 3 could be the buffer
zone. Some bycatch risk exists but if Area 2 and the bryo-
zoan thickets become MPAs, the inclusion of this area as
a marine reserve would allow easier management of one
entity that protects almost all foraging areas of sea lions.
These different areas could be progressively implemented
over the next decade as the sea lion population increases,
leaving time for local shers to adapt to the changes and,
possibly, make some recommendations for improvements.
Further management options (i.e. local shing quotas,
sea lion control) will rely on data available to model sh
stocks and marine production around the Otago Penin-
sula, and changes in law. A priority for the management
of interactions between sheries and sea lions around the
Otago Peninsula is to increase the amounts of data and
knowledge of the local marine ecosystem, especially sh
stocks.
In conclusion, bycatch, depredation and competition
are expected as the population of Phocarctos hookeri
increases on the Otago Peninsula and no management
measures are implemented. Overall, the main area used
by sea lions is relatively small and management mea-
sures would be easy to achieve with minimum economic
losses or disadvantages to sheries. If this is only imple-
mented after conicts occur, costs to the economy will
be exponentially larger as demonstrated in the Auckland
Islands and other parts of the world. Consequently, the
introduction of precautionary measures, an explicit man-
agement plan and a research programme into marine
production, sheries and sea lion population dynamics
around Otago would likely benet both sheries and sea
lion conservation. This could test the effectiveness of
precautionary management for future recolonisation
events by sea lions at other sites in New Zealand, but
also for the recovery or recolonisation of marine mam-
mals around the world.
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A. A. AUGE
´ET AL.
8
... Predator removal through culling programmes stands as an effective means of reducing predator abundance; nonetheless, such programmes offer a short-term solution that does not always result in an increase in the target species population (see Morissette et al. 2012, Houle et al. 2013), since the effects are difficult to project and measure (Bowen & Lidgard 2013). Thus, the scientific community recommends a precautionary approach to managing marine mammals such as the top predators (which also includes moderate harvesting) to avoid adverse effects on the fish and economic losses for fisheries due to sudden and unregulated predator population increase (see Augé et al. 2012). This occurred in many pinniped populations which, following historical declines, thrived under protection programmes, in some cases leading to increased biological competition with fisheries and commercial fish stock de clines ( Augé et al. 2012, Marshall et al. 2016. ...
... Thus, the scientific community recommends a precautionary approach to managing marine mammals such as the top predators (which also includes moderate harvesting) to avoid adverse effects on the fish and economic losses for fisheries due to sudden and unregulated predator population increase (see Augé et al. 2012). This occurred in many pinniped populations which, following historical declines, thrived under protection programmes, in some cases leading to increased biological competition with fisheries and commercial fish stock de clines ( Augé et al. 2012, Marshall et al. 2016. ...
... In addition to marine mammal removal, which can potentially disrupt the finely tuned trophic connectivity throughout the ecosystem, fewer unexpected outcomes might result from ensuring the survival and viability of marine mammal populations ( Augé et al. 2012, Garcia et al. 2012, Papastavrou et al. 2017. This requires an adequate 'package' of mutually complimentary and synchronised conservation and management measures that could ensure the preservation of the trophic web and long-term, sustainable harvesting. ...
Article
Competitive interactions between marine mammals and fisheries represent some of the most complex challenges in marine resource management worldwide. The development of commercial fisheries and recovering marine mammal populations have contributed to a decrease in fish availability. Whilst ecosystem-based fisheries management (EBFM) can counteract this decrease, achieving the EBFM objectives faces certain major obstacles including insufficient or unreliable data, inapplicable assessment models, as well as inadequate management decisions that do not account for fisheries-induced morphological alterations (FIMA) and marine mammal management. Despite a body of evidence addressing various aspects of marine mammal−fisheries competition, little is known about the effects of marine mammal−fisheries biological interactions affecting the fish viability and food web stability. We review the research on marine mammal−fisheries competitive biological interactions (hereafter biological competition) by focussing on (1) the prerequisites for marine mammal−fisheries biological competition and the relevant methodologies to explore them and (2) recent studies revealing the implications of FIMA and trophic interactions for the biological competition. We also discuss the implications of FIMA, eco-evolutionary feedback and prey−predator dynamics for EBFM implementation in contemporary harvested ecosystems. Our main findings reveal a lack of data about marine mammals’ prey choice and selectivity, the need for better representation of marine mammals in modelling approaches and lastly, the necessity for additional research linking FIMA, trophic interactions and the EBFM objectives. To conclude, interdisciplinary approaches may serve to link all of the efforts needed to effectively and holistically support the implementation of EBFM.
... She foraged primarily on the coastal rocky reefs and 91% of all marine locations were < 300 m from land. She only foraged offshore (5-7 km from land) during parts of five foraging trips when she exclusively foraged in the area of the bryozoan thickets (see Augé et al., 2012b). Marine locations within 50 m of the rocks that constitute Gull Rocks and Tow Rock and on the shallow rocky reefs between them accounted for 31% of all her marine locations. ...
... In conclusion, as the population of sea lions in The Catlins increases, management issues arising from sea lions with human activities will likely increase if management is not implemented (e.g. in Otago; Augé et al., 2012b). In order to prevent issues from arising, actions must be proactive. ...
Technical Report
Full-text available
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.
... Fisheries and sea mammals often have overlapping ranges because they tend to target similar prey species, particularly in coastal areas (Augé et al. 2012). Interactions between sea mammals and commercial fi sheries have occurred for centuries but are increasing in frequency and intensity (Morissette et al. 2012). ...
... Few countries have any effective reporting system for bycatch of any species, and there is no centralized global data repository that holds information on bycatch of sea mammals (Read et al. 2006). A priority for the management of interactions between fi sheries and sea mammals will be to increase the amount of data and overall knowledge we possess on local marine ecosystems, especially fi sh stocks (Augé et al. 2012). ...
... As the recolonization progresses and sea lion number increases, it is predicted that bycatch and competition issues will arise in the foraging grounds of the Otago female NZ sea lions, and spatial conservation measures (e.g. protected areas such as marine reserves and gear-restricted areas) may be the best options to manage these interactions (Augé, Moore & Chilvers, 2012c). However, it is important to understand if the animals in the Otago sea lion population show annual site fidelity for defined foraging grounds before decisions can be made on the best approach. ...
... Our study shows that female NZ sea lions exhibit foraging site fidelity throughout the year and across years. Consequently a study determining the degree of overlap between the foraging areas of female NZ sea lions and fishing areas should efficiently delineate areas of potential direct interactions between this marine mammal and local fisheries (see Augé et al., 2012c). ...
Article
Full-text available
The efficiency of spatial conservation measures for threatened species depends mostly on the proportion of time that animals spend within the protected areas. We illustrate this with our case study of the population of recolonizing female New Zealand (NZ) sea lions Phocarctos hookeri (n = 13) at Otago Peninsula, South Island, NZ. Human interactions at sea, where sea lions forage, are of concern, and spatial management measures have been proposed. Understanding the level of foraging site fidelity of these animals was consequently essential. We used satellite tracking of individuals across three autumns to assess foraging site fidelity and year-round on-land sighting surveys over 2.5 years as proxy to foraging areas outside autumns. Each individual exhibited a high level of autumnal site fidelity for foraging areas between years (64% overlap between 65% Kernel ranges with a 3-km buffer) while using beaches along a 12-km stretch of coastline during 96 ± 8% (range 79–100%) of their time onshore. As a proxy for foraging areas outside autumns, these animals exhibited a high level of site fidelity to this stretch of coastline throughout the year. Breeding females were sighted there during 86% of months (range = 73–100%) and non-breeding females during 69% of months (range = 58–90%). The site fidelity of these animals indicates that protected areas would be efficient in this case and highlights the importance of studying foraging site fidelity in mobile predators to design efficient conservation measures.
... The population dynamics of NZ sea lions have been studied at both the Otago coast and Auckland Islands. Demographic characteristics vary significantly between these two populations Augé et al., 2011Augé et al., , 2012. It was considered the Campbell Island population may be demographically more similar to the Auckland Islands than the Otago population, based on foraging ecology data (M.-A. ...
Article
Full-text available
The endangered New Zealand sea lion, Phocarctos hookeri is killed as incidental bycatch in a trawl fishery operating near their second largest population on Campbell Island in New Zealand’s sub-Antarctic. Using the Potential Biological Removal (PBR) procedure to assess the sustainability of this bycatch for the sea lion population on Campbell Island indicated that annual bycatch estimates, particularly following the implementation of bycatch mitigation measures, are below the PBR threshold of 25 (derived using a precautionary approach). Preliminary Population Viability Analysis (PVA) modelling supported the finding that current bycatch levels, especially given a strong male bias (98%) in bycatch, are sustainable for this population. Models showed that reducing pup mortality through management actions, such as installing ramps in wallows where large numbers of pups drown, would lead to increased population growth. While obtaining more accurate data on population status and demographic parameters for the Campbell Island population should be a priority, this will take many years of research. The PBR and PVA tools demonstrate that contemporary conservation management should continue to focus on increasing pup survival while maintaining mitigation approaches that have reduced bycatch to low levels, together with high observer coverage to sustain confidence in annual bycatch estimates.
... The persistence of hunting protected animals is an indicator of a lack of understanding of the species conservation importance (Coll et al 2014). The economic condition of the community is thought to be one of the factors triggering such fishing activities (Augé et al 2012). ...
Article
Dugong (Dugong dugon) population continues to decline due to the high pressure coming from the environment and hunting by humans. Bintan Island is one of the D. dugon habitats in Indonesia. This study aims to confirm the existence of dugongs and identify threats to the survival of dugongs through interviews with local communities based on local ecological knowledge. The study was conducted at five locations on Bintan Island which included Berakit, Pengudang, Teluk Bakau, Kelam Pagi and Kelong. The results obtained indicate that the majority of respondents of Berakit (100%) and Kelong (78%) have seen the presence of D. dugon in nature with a fairly frequent level of intensity. The threat to the survival of D. dugon on Bintan Island originates from the existence of fishing gear such as nets and fishing traps. Besides, at several locations it is still in the habit of the communities to hunt D. dugon and this is one of the biggest threats to the D. dugon species conservation.
... In the marine environment, the global expansion of fisheries over the last fifty years has led to the overexploitation of many fish stocks and major changes in fishing techniques. It also has resulted to changes in food-search behavior of some predators such as marine mammals that has resulted in the emergence of direct marine predators-fisheries interactions, including depredation on fishing gears (Augé et al., 2012;Fertl, 2008;Kaschner and Pauly, 2004;Plagányi and Butterworth, 2002;Read, 2008). Depredation on fisheries is defined as the partial or total removal of captured fish from fishing equipment by marine predators (Donogue et al., 2002;Fertl, 2008;Read, 2005) and has received growing attention over the past five decades (Northridge, 1991). ...
... In the marine environment, the global expansion of fisheries over the last fifty years has led to the overexploitation of many fish stocks and major changes in fishing techniques. It also has resulted to changes in food-search behavior of some predators such as marine mammals that has resulted in the emergence of direct marine predators-fisheries interactions, including depredation on fishing gears (Augé et al., 2012;Fertl, 2008;Kaschner and Pauly, 2004;Plagányi and Butterworth, 2002;Read, 2008). Depredation on fisheries is defined as the partial or total removal of captured fish from fishing equipment by marine predators (Donogue et al., 2002;Fertl, 2008;Read, 2005) and has received growing attention over the past five decades (Northridge, 1991). ...
Article
Marine mammal depredation on fisheries (animals removing fish caught on fishing gear) is a worldwide issue involving socioeconomic and ecological consequences. Longline fisheries are the most impacted by odontocete (toothed whales) depredation. While technological means have provided limited efficacy in reducing depreda-tion, this study examined the fishing practices influencing both the proportion of depredated longline sets and the amount of fish removed by whales. We used an 8-year dataset from the Patagonian toothfish (Dissostichus eleginoides) longline fisheries operating in Crozet and Kerguelen Economic Exclusive Zones (EEZs) (South Indian Ocean) and GLMMs to investigate sperm whale (Physeter macrocephalus) depredation. Sperm whale depredation occurred on 61% of 5260 sets in Crozet and 41% of 16,902 sets in Kerguelen, and resulted in minimum estimated toothfish losses of 702 tons and 2649 tons, respectively, in the two areas. The probability of depredation decreased in winter months, increased with depth fished and decreased when vessels travelled over distances of > 60 km from fishing grounds with encountering depredation. These findings suggest the natural spatio-temporal distribution of sperm whales and their ability to follow vessels over limited ranges influence the number of captured fish removals. The amount of depredated toothfish decreased with the speed at which longline sets were hauled and increased with the soaking time of sets suggesting that whales may depredate sets during both hauling and soaking operations. Together, these observations indicate that rates of depredation may be influenced by the conditions of fishing operations and could therefore be employed to implement strategies of avoidance in all fisheries facing similar depredation impacts.
... Direct interactions between marine mammals and fishery operations pose a threat to the sustainability of many marine mammal populations and could be detrimental to fisheries. These interactions may result in the injury or death of marine mammals, damage to the fishing gear, reduced catches and increased time spent in fishing operations [1][2][3]. ...
Article
Full-text available
Common dolphins (Delphinus delphis) are responsible for the large majority of interactions with the pole-and-line tuna fishery in the Azores but the underlying drivers remain poorly understood. In this study we investigate the influence of various environmental and fisheries-related factors in promoting the interaction of common dolphins with this fishery and estimate the resultant catch losses. We analysed 15 years of fishery and cetacean interaction data (1998–2012) collected by observers placed aboard tuna fishing vessels. Dolphins interacted in less than 3% of the fishing events observed during the study period. The probability of dolphin interaction varied significantly between years with no evident trend over time. Generalized additive modeling results suggest that fishing duration, sea surface temperature and prey abundance in the region were the most important factors explaining common dolphin interaction. Dolphin interaction had no impact on the catches of albacore, skipjack and yellowfin tuna but resulted in significantly lower catches of bigeye tuna, with a predicted median annual loss of 13.5% in the number of fish captured. However, impact on bigeye catches varied considerably both by year and fishing area. Our work shows that rates of common dolphin interaction with the pole-and-line tuna fishery in the Azores are low and showed no signs of increase over the study period. Although overall economic impact was low, the interaction may lead to significant losses in some years. These findings emphasize the need for continued monitoring and for further research into the consequences and economic viability of potential mitigation measures.
... It will be important for future development not to impede the recovery of these species, as it has been shown that precautionary management could ensure the cohabitation of maritime activities and marine mammals (e.g. Augé et al., 2012). However, at this point in time, there is no cetacean monitoring program in place. ...
Article
Full-text available
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.
Article
Full-text available
There are two types of interactions between seals and commercial fisheries in South Africa: biological (potential competition for shared resources between the two "predators") and operational (conflicts during fishing operations). Using data for the 1980s, a comparison is made of relative consumption by different predators in South African waters. Seals and fisheries are not the major consumers in the system, but they do take comparable amounts. This has resulted in calls for a reduction in the seal population, but to date, no studies have shown that reducing seal predation of commercial species will make more fish available for the fisheries. Most fisheries are subject to some form of operational interaction with seals. These interactions include consumption of catches (operational consumption), disturbance of fishing operations (operational disturbance) and damage to fishing gear (operational gear damage); they vary in degree of severity, both seasonally and regionally. Estimates of the consumption by seals from fishing operations in South Africa show it to be a minimal percentage of fishery catches and a small proportion of the total predation by seals. Preliminary calculations of overall economic losses resulting from seal interference show this to be small in comparison with the wholesale value of the catches. Seals die as a result of fishing operations, and estimates of the potential mortality through entanglement, drowning and deliberate killing indicate this mortality to be of a magnitude that should be monitored.
Thesis
Full-text available
The New Zealand (NZ) sea lion, Phocarctos hookeri, is endemic to NZ and listed as threatened and nationally critical. It was extirpated from mainland NZ by the 1800s and it has only started recolonising part of its historical breeding range, the Otago Peninsula (OP), since the 1990s. This recolonisation has opened two areas of research: 1) data were needed for the management of interactions between humans and sea lions at sea and for marine habitat protection around the OP, and 2) comparison of data between the only three remnant breeding areas in the sub-Antarctic islands (hypothesised as marginal habitat) and the recolonising population. This thesis presents the results of the first study into the foraging ecology of the small recolonising population of female NZ sea lions inhabiting the OP. Up to 2010, 45 pups had been born at the OP, all descendants from a unique matriarch that emigrated from the sub-Antarctic North Auckland Islands (AI) breeding colony. During autumns 2008 to 2010, the foraging ecology, diet and condition of 13 female NZ sea lions born on the OP (all known-to-be alive ≥ 2 years old, including six during two different years) were investigated. They foraged within a small area around the OP (mean shore distance 4km), predominantly on shallow rocky reefs (<30m depth) and in the area of bryozoan thickets in deeper waters (50-100m depth). Their diving behaviour qualified them as some of the shallowest diving otariids (mean dive depth 20m). Two prey of medium-to-high-energy content (barracouta, Thyrsites atun, and jack mackerel, Trachurus sp.) made up approximately 60% of the diet of female NZ sea lions, although individual specialisations were identified. Pup growth and mass, body mass index and milk fat content all had values in the highest ranges reported for otariids and there was no indication of serious disease or parasite infection. From 2008 to 2010, weekly surveys of female NZ sea lions presence on the OP showed that they are likely permanent residents on the OP. Combined with calculated inter-annual foraging site fidelity, it enabled the descriptions of areas of potential by-catch risk in fisheries around the OP. A technique using decoys was developed to possibly orientate immigrating females to join the existing group and limit areas of interactions, at least during the start of this recolonisation. The recolonising population of female NZ sea lions on the OP exploits what appear to be abundant, easily accessible and high-energy food resources. Age was not a significant factor in explaining any foraging parameters, and foraging effort did not correlate to energy content of prey. This accentuated the suitability of the habitat around the OP for NZ sea lions. This is in contrast with results for the females in the AI that are the deepest and longest diving otariids, feed on lower energy prey and have lower condition than OP females. The results of this thesis corroborate the hypothesis that the AI are marginal marine habitat for this species. Current large-scale fisheries there may be depleting the already limited food resources and reducing the carrying capacity of the marine habitat. Management needs to address the marginality of the habitat to ensure the survival of the remnant populations. Management of the recolonisation of NZ sea lions onto mainland NZ needs to focus on public education, marine habitat protection, monitoring potential competition and determining if by-catch has been unreported. Given the importance of this population for the recovery of the NZ sea lion, a protected area covering the main foraging habitats of female NZ sea lions appears to be the best option to ensure its establishment. Regular monitoring of pup mass, diet and population numbers of sea lions and other large marine predators should increase our understanding of the impact of recolonisation to the habitat, and potential issues that need to be managed. The results presented in this thesis constitute the baseline of foraging ecology and condition for this population and are available to help manage and document the recolonsiation for future management needs in other areas where the NZ sea lion may return.
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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 references 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.