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Antarctic krill fishery effects over penguin populations under adverse climate conditions: Implications for the management of fishing practices


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Fast climate changes in the western Antarctic Peninsula are reducing krill density, which along with increased fishing activities in recent decades, may have had synergistic effects on penguin populations. We tested that assumption by crossing data on fishing activities and Southern Annular Mode (an indicator of climate change in Antarctica) with penguin population data. Increases in fishing catch during the nonbreeding period were likely to result in impacts on both chinstrap ( Pygoscelis antarcticus ) and gentoo ( P. papua ) populations. Catches and climate change together elevated the probability of negative population growth rates: very high fishing catch on years with warm winters and low sea ice (associated with negative Southern Annular Mode values) implied a decrease in population size in the following year. The current management of krill fishery in the Southern Ocean takes into account an arbitrary and fixed catch limit that does not reflect the variability of the krill population under effects of climate change, therefore affecting penguin populations when the environmental conditions were not favorable.
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Journal: Ambio
Print ISSN: 0044-7447
Online ISSN: 1654-7209
DOI: 10.1007/s13280-020-01386-w
Antarctic krill fishery effects over penguin populations under adverse climate conditions: implications
for the management of fishing practices
Lucas Krüger
*, Magdalena F. Huerta
, Francisco Santa Cruz
, César A. Cárdenas
Departamento Científico, Instituto Antártico Chileno
Plaza Muñoz Gamero 1055, Punta Arenas, Chile
Centro de Humedales Rio Cruces, Universidad Austral de Chile, Valdivia, Chile.
*Corresponding author:
Fast climate changes in the western Antarctic Peninsula are reducing krill density, which along
with increased fishing activities in recent decades, may have had synergistic effects on penguin
populations. We tested that assumption by crossing data on fishing activities and Southern Annular
Mode (an indicator of climate change in Antarctica) with penguin population data. Increases in fishing
catch during the non-breeding period were likely to result in impacts on both chinstrap (Pygoscelis
antarcticus) and gentoo (P. papua) populations. Catches and climate change together elevated the
probability of negative population growth rates: very high fishing catch on years with warm winters and
low sea ice (associated with negative Southern Annular Mode values) implied a decrease in population
size in the following year. The current management of krill fishery in the Southern Ocean takes into
account an arbitrary and fixed catch limit that does not reflect the variability of the krill population
under effects of climate change, therefore affecting penguin populations when the environmental
conditions were not favorable.
Keywords: Antarctic Peninsula, chinstrap penguin, gentoo penguin, population growth rate,
southern annular mode
The western Antarctic peninsula (WAP) is one of the areas most affected by climate change. Fast
warming in the last decades (Cook et al. 2016; Moffat and Meredith 2018) and the southward input of
warmer waters, are decreasing the seasonal sea-ice extent and duration (Stammerjohn et al. 2008;
Moffat and Meredith 2018). Climate change effects have also been observed in different macro-scale
atmospheric phenomena, such as the Southern Oscillation Index (SOI) and the Southern Annular Mode
(SAM) (Stammerjohn et al. 2008; Moffat and Meredith 2018). Specifically, warming in the WAP has been
related to strengthening a positive trend in the SAM, which describes atmospheric circulation patterns
associated to the belt of westerly wind surrounding Antarctica (Clem et al. 2016). The SAM has a strong
influence in the inter-annual variability around the WAP, driving changes in sea-ice formation and
melting, and the injection of meteoric water (combination of glacial discharge and precipitation) to the
Southern Ocean (Moffat and Meredith 2018).
Current climate change has had significant effects in the Antarctic ecosystem, particularly for
sea-ice dependent species, such as the Antarctic krill Euphausia superba. Several studies have shown
dramatic changes in Antarctic krill populations, including distributional range contraction (Atkinson et al.
2019), size reduction (Tarling et al. 2016), decreased recruitment (Atkinson et al. 2019; Perry et al. 2019)
and decreased density (Atkinson et al. 2009; Flores et al. 2012). Variability in regional sea-ice has been
identified as an important limitation for krill abundance (Flores et al. 2012). Sea ice cover can affect the
survival of krill larvae, due to their reliance on sea ice to feed and for shelter during winter (Meyer
2012). Predicted future environmental changes are expected to produce further changes associated
with seawater warming and reduced sea-ice cover having an impact on krill distribution and biomass
(Piñones and Fedorov 2016; Atkinson et al. 2019).
Krill is a keystone species in the Antarctic marine food web (Hofmann et al. 2011; Ballerini et al.
2014) and hence, it is expected that any negative effects on krill will not only affect its direct predators
but also will produce a cascade effect on the entire ecosystem. Whether climate-based reductions in
krill density continue at the predicted rate (Atkinson et al. 2009), it is expected that krill predator
populations will follow a steep decline (Trathan and Reid 2009). There have been widespread decreases
of penguin populations over the Antarctic Peninsula with climate change recognized as the main driver
(Lynch et al. 2012; Casanovas et al. 2015). The population trends in these species seems to be related to
a reduction in sea-ice cover and krill abundance (Forcada et al. 2006; Trivelpiece et al. 2011). Some
authors have supported the hypothesis that there is a direct relationship between the sea ice variations
and the penguin abundance, including contrasting trends for ice-loving” and “ice-avoiding” species
(Forcada et al. 2006). In this sense, it would be expected that sea-ice retreat and the resulting access to
ice-free foraging areas should benefit both chinstrap (Pygoscelis antarcticus) and gentoo (P. papua)
penguins, which have been identified as “ice-avoiding” species. However, although this is consistent
with the Gentoo penguin global population trends (yet local decreases of Gentoo Penguin abundance
exist in the South Shetland Islands; i.e. Petry et al. 2016; Petry et al. 2018) the evidence pointing to a
decline of chinstrap penguin populations throughout the WAP suggests that reduction in krill availability
could be playing a critical role to explain the population dynamics of this species (Trivelpiece et al. 2011;
Lima and Estay 2013).
The Antarctic krill is target of an important fishery in the Southern Ocean, occurring mainly in
the Atlantic sector (FAO statistical subareas 48.1, 48.2 and 48.3). The Commission for the Conservation
of Marine Living Resources (CCAMLR) is the international organization responsible for the management
of the krill fishery and has successfully managed fishery based on a precautionary approach since its
creation in the early 1980s (Constable 2011). In recent years, there has been increasing concerns on how
climate-based changes and the current concentrated behavior of the krill fishery (Santa Cruz et al. 2018;
Krüger 2019) can affect synergistically the penguin colonies over the WAP. Moreover, krill catches have
been reaching values like those recorded in the 1990s before the adoption of a fixed catch (CCAMLR
2018). Although catches are considered to be low compared to the krill abundance
(catch limit is < 1% of
the total estimated biomass ≈ 60 million tones on Antarctic Peninsula alone, CCAMLR 2019), catch is
expected to keep increasing in the future with the development of new technologies and changes in
both fishing technologies and Antarctic environment. Contrasting to what fisheries did back in the
1990s, now the whole krill catches are concentrated on relatively small spots on the WAP and the South
Orkney Islands (Santa Cruz et al. 2018; Krüger 2019). While CCAMLR performance has been considered a
successfully sustainable managed practice (Nicol et al. 2012), under the current climate changes it is
likely that this may change (Hill et al. 2016) as signs of krill fishery decreasing performance of penguins
are becoming evident (Watters et al. 2020). This study aimed to evaluate the risk of the krill fishery to
populations of Pygoscelid penguins, testing if the population changes are proportional to changes in the
distribution of catches in WAP, and their synergistic relation with climate variability. We used 38 years
of fishing data to evaluate risk for both chinstrap and gentoo penguins and used mixed models to test
how population growth could have responded to the fishing pressure under contrasting Southern
Annular Mode conditions.
Penguin population data
All data on populations of chinstrap (Pygoscelis antarcticus) and gentoo (P. papua) penguins
breeding in the WAP area available at the Mapping Application for Penguin Populations and Projected
Dynamics MAPPPD (, Humphries et al. 2017) between 1980 and 2017 were
downloaded (Fig. 1, Chinstrap = 197 colonies, Gentoo = 78 colonies). MAPPPD is a penguin population
databank, which puts together all available information about population counts of penguins on their
breeding colonies. Counts include different type of data: breeding pairs, adults and chicks. Only pair
counts made in November and December, matching the early breeding season and providing a better
picture of actual population size, were used. Temporal variation in colony-level population growth rate
was expressed as:
= ((n
where n is the number of breeding pairs counted in November or December of a given year (b)
and the number of breeding pairs counted in a previous year (a), divided by the number of years in
between b and a. This procedure allowed us to deal with differences in sampling size by smoothing any
too steep value resulting from a too large temporal gap in data, at the same time, providing population-
level temporal variability of each penguin colony. From this value then was subtracted 1, so that the
result varied from -1 (population extinction) to ∞, with posiQve values represenQng populaQon increase.
Each colony was classified based on CCAMLR Small-Scale Management Units: Elephant Island, Drake
East, Drake West, Bransfield East, Bransfield West and Antarctic Peninsula West, which we will refer as
Gerlache Strait because fishing in this area concentrated within the strait (Fig. 1). Small-Scale
Management Units are zones proposed in order to be a spatial tool for local monitoring of the krill
fishery and krill predators, and devised for spatially subdividing the krill catch limits (Constable and Nicol
2002). Most penguin colonies did not have data on the whole 38 years considered; majority of colonies
had less than 10 counts while 38 chinstrap and 45 gentoo colonies had at least two counts (enough for
calculating the λ
) (Fig. S1).
Krill fishery data
Haul-by-haul data of the fleet operations was obtained from the CCAMLR Secretariat database
for the period between 1980 and 2017 (38 years). The accumulated catch within a 30-km radius of each
colony was used to evaluate the risk of exposition of each colony to the changes in catch distribution.
During breeding season (when counts were made) foraging of pygoscelid penguins is more probable
within 30kms of the colonies (Warwick-Evans et al. 2018). We therefore assumed this to be the distance
where krill availability would be more important during key periods of the year cycle and competition
with fisheries would be more impacting. Each fishing event was classified based on important period of
the penguin intra-annual life cycle: chick-rearing (January to March), non-breeding (April to September)
and early breeding (October to December). Catch was accumulated within those periods for each year
(Fig. S2, Table S1) in order to better describe the periods when penguin are more at risk to experience
impacts from fishery, but catch was accumulated throughout the whole year to test statistically the
response of populations (below)
Climate data
The Southern Annular Mode SAM is the main large-scale pressure system driving climate in
Antarctica (Kwok and Comiso 2002; Doddridge and Marshall 2017). SAM is defined as the difference of
the normalized zonally mean sea level pressure of 40°S and 65°S (see Gong and Wang 1999 for details).
As SAM indicates differences, it can have negative and positive values: negative values mean air
pressure in Antarctic (65°S) is higher than in the subantarctic (40°S); positive values mean air pressure is
higher in subantarctic (40°S) than in Antarctic (65°S). Pressure differences reflects the large-scale
movements of air masses. By examining SAM values is possible to infer whether warmer currents from
the north intruded areas further south, therefore, SAM can accurately indicate trends of sea ice and
temperature anomalies in Antarctica (Marshall and Bracegirdle 2014; Doddridge and Marshall 2017).
Penguins (Forcada et al. 2006) and Antarctic krill (Flores et al. 2012; Meyer 2012) are knowingly
responsive to abrupt changes on temperature and ice conditions during winter. SAM monthly data was
downloaded from NOAA Earth System Research Laboratory ESRL ( Data on Fractional Sea
Ice Cover, Surface Level Temperature and Open Water Sensible Heat Flux were downloaded from NASA
Giovanni data browser ( per month.
Figure 1. Distribution of chinstrap Pygoscelis antarcticus (a) and gentoo P. papua (b) penguins breeding
colonies (white crosses) along the western Antarctic Peninsula, overlapped with the Antarctic krill
accumulated fishing catch. Data on fishing catch represents all the catch in the area accumulated
between 1980 and 2017, it is, all the krill that was extracted from a given spatial cell in 38 years. Penguin
data from MAPPPD (; Humphries et al. 2017).
Penguins, fishery, and climate
Considering the high correlation of the climate variables in WAP (Fig. S3), and correlation of
climate variables with SAM variability with a temporal lag from zero to three months (Fig 2), we used
SAM during the non-breeding period
together with accumulated catch within each year in a binomial
Generalized Linear Mixed Model using the ‘lmerTest’ R package (Kuznetsova et al. 2018) and the ‘sjPlot’
R package (Lüdecke et al. 2019) to plot models:
* SAM + (1| colony id)
where binλ
is a binary estimate of the standardized growth rate λ
(positive values=0,
negative values =1) understood as the probability of population decreasing in a given year. Catch
is the
accumulated year krill catch, SAM is the southern annular mode during winter (non-breeding season).
We used mixed models which allows to control for the effects of lack of independence and sample size
differences within the structure of the data. We used the colony ID as a random term in the formula
accounting for the colony-level differences on the intercept of the response to the explanatory
variables. The effect of the random term was tested with a Likelihood Ratio Test using the function
‘ranova’. All data processing and analysis were done in R environment (R Development Core Team 2014)
using ‘raster’ (Hijmans 2013), ‘plyr’ (Wickham 2020) and ‘ggplot2’ (Wickham and Chang 2015) packages.
Maps were produced using ArcGis 10.4.
Figure 2. Lagged regression model (cross correlation function CCF) testing the temporal response of
Fractional Sea Ice Cover (FSIC), Open Water Sensible Heat Flux (HFLUX) and Sea Level Air Temperature
(TLML) at the Western Antarctic Peninsula to the variation of the Southern Annular Mode (SAM). Lag
interval is in months. Dashed blue line indicates where the correlation is significant at the P<0.05 level.
Analysis was done in the ‘astsa’ R package (Stoffer 2008).
Changes of spatial catches distribution
Krill catches within the 30 km radius from colonies of both species occurred predominantly
during chick-rearing and non-breeding periods (Fig. 3). Although, catches after the mid-1990s decreased
or remained stable in Elephant Island and Drake Passage sectors, respectively (Fig. 2); catches in the
Bransfield Strait increased near colonies of both penguin species (Fig. 3). During the last decade, fleets
started to operate more intensively in the Gerlache Strait, increasing catches during both chick-rearing
and non-breeding periods near chinstrap colonies (Fig. 3).
Figure 3. Seasonal accumulated catch within 30-km radius around each breeding colony of chinstrap
(Pygoscelis antarcticus) and gentoo (P. papua) penguins during Chick Rearing CR (January-March), Non-
breeding NBR (April-September) and Early Breeding EBR (October-December) periods classified
according to Small Scale Management Unities SSMUs: Elephant Island, Drake Passage East and West,
Bransfield Strait East and West ; Gerlache Strait. See also Figure 1.
Trend of the penguin populations
Most of the λ
values for chinstrap penguins were negative (58.78% of cases) in the WAP (Fig.
S4). Gentoo penguins presented a mean growth trend bordering the stability (Fig. S4) with 50.72% of
negative cases of λ
Probability of chinstrap population decrease was related to catch
=2.96, z=2.65, P=0.008)
and to the interaction catch
* SAM (F
=1.72, z=-1.63, P=0.055) , but not to SAM alone (F
z=1.50, P=0.133). Random factor was not significant for chinstrap penguins (LRT=0.15, P=0.910),
meaning population-level response was homogeneous throughout the WAP. For Gentoo populations,
the probability of decrease was marginally related to catch
=0.76, z=1.47, P=0.090) and catch
SAM interaction (F
=1.70, z=-1.75, P=0.085), but not to SAM alone (F
=0.11, z=0.74, P=0.461), and
random effects were significant (LRT=5.95, P=0.014), therefore population-level variability was
important in the response of Gentoo penguins to fishing catches (Fig. S5). For both chinstrap (Fig. 4a)
and Gentoo (Fig. 4b) probability of decrease in a given year
) was constant with increasing fishing
catch during years of positive SAM, but increased with increasing catch during years of negative SAM. In
extreme negative SAM, fishing catches above ≈5 thousand tonnes meant a mean estimated probability
of decrease above 75% for both species (Fig. 4).
Figure 4. Estimated probability (trend lines) ±
standard deviation (shaded area) of chinstrap
Pygoscelis antarcticus (a) and gentoo P. papua (b)
penguins having a negative standardized
population growth rate as a response to fishing
catch within 30-km radius around colonies during
years of contrasting Southern Annular Mode SAM
values: negative (solid red line) and positive
(dashed blue line). The ‘sjPlot’ R package through
the function ‘plot_model’ allows visualizing the
estimated mean response to the extreme values of
the interacting variable, in this case maximum and
minimum SAM values.
In the last two decades, krill catches have increased consistently near penguin colonies in the
Bransfield and Gerlache straits during chick-rearing and non-breeding periods, whereas in the Drake
Passage and Elephant Islands catches have remained stable or mostly decreasing. These patterns reflect
the southward expansion experienced by the fleet during the last decade, mentioned by previous works
(Nicol et al. 2012; Santa Cruz et al. 2018; Krüger 2019). Our findings also indicated that the relation
between the standardized penguin growth rate and cumulative fishing catch was contrasting depending
on SAM conditions. In this manner, in positive SAM values, the range of the probability of decreasing
varied largely, while in negative SAM values, there was a consistent rise in the probability of decreasing
for both chinstrap and gentoo penguins when fishing catches near colonies was very high (>≈5000 t).
Moreover, the additional effect over krill recruitment caused by the decrease in sea ice coverage, due to
the key role played by this factor for the development of krill larvae, coupled with the increase in krill
catches in the areas near penguin colonies could generate a much more vulnerable scenario for these
species during the breeding season (i.e. Trivelpiece et al. 2011). Recovery of baleen whale populations
also have been suggested out as a potential explanation for current observed trends in penguin
populations, as whaling in the last century would have allowed for an increase in krill availability, the
krill surplus hypothesis, but so far, studies dealing with that hypothesis did not find solid evidences and
suggested environmental variability as more important to changes in krill biomass (Fraser et al. 1992;
Surma et al. 2014). Previous studies mentioned potential impacts of krill fishery on penguin populations
(i.e. Trivelpiece et al. 2011), and a recent paper (Watters et al. 2020) reached conclusions similar to ours
by applying a different method and evaluating population data at two sites. Our study, to our best
knowledge, is the first to reveal the effect of climate change and krill fishery on penguin population
declines looking explicitly at multi-population trends on the scale of the whole Antarctic Peninsula. It is
worth mentioning that a previous work by Che-Castaldo et al. (2017) tested whether krill fishery could
have an effect on Adelie penguin population dynamics; however, the spatial scale of the fishing data
used was too coarse to allow detecting strong local effects.
Considering what it is mentioned above, the next step from now on would be to move towards
the implementation of a new krill fishery management strategy (see further below), which could
consider new elements that are not currently included. Elements such as regular biomass estimations
and identification of the spatial scales of the impact of krill fishery on penguins, thus, identifying where
higher catches would have higher impact on penguins and other predators, and distributing catches
Risk of competition with krill fishery
Recent changes of the spatial distribution of the krill fishing fleet in the WAP (Santa Cruz et al.
2018; Trathan et al. 2018; Krüger 2019) can be linked to the general trend of decreasing winter sea-ice
extent and duration that has been reported for the area (Parkinson 2019). Increased ice-free conditions
allowing trawlers to continue their activities after the end of the Austral summer (Nicol et al. 2012)
explains the increasing catches near penguin colonies during the non-breeding season. While sensibility
of penguins to climate change is well known (Casanovas et al. 2015; Che-Castaldo et al. 2017), the
interaction of climate change with increasing catches may have a synergistic detrimental effect on
penguins. According to Doddridge and Marshall (2017), negative SAM anomalies precede higher
temperatures, low sea-ice and low krill productivity in the Southern Ocean, particularly in Antarctic
Peninsula, with effects being cascaded throughout the whole food web (Dahood et al. 2019).
Carry-over effects of the potential competition of penguins with the krill fishery during the non-
breeding season are still unknown, but given our results, cumulative catches within 30 km from colonies
seemed to impact negatively both Pygoscelis species in years when sea-ice was low. Although chinstrap
penguins tend to disperse from breeding grounds, it is evident that there is a large variability and part of
the population may remain nearby the breeding area (Trivelpiece et al. 2007; Hinke et al. 2015; Hinke et
al. 2017). On the other hand, Gentoo penguins tend to remain closer to the breeding grounds during
winter (Wilson et al. 1998; Thiebot et al. 2011; Hinke et al. 2017).
Winter distribution of fledgling and
immature stages of both penguin species is still unknown for most populations, but evidence suggests
penguin recruitment is an important population parameter explaining penguin population decrease in
the WAP, which has been also linked to decreased recruitment of krill (Hinke et al. 2007; Trivelpiece et
al. 2011; Atkinson et al. 2019). Penguin populations have been potentially affected by the krill fishery
(this study, Watters et al. 2020) in zones where intense fishing occurred in recent years (i.e. Santa Cruz
et al. 2018) which overlapped with important krill nursery and krill recruitment areas (Perry et al. 2019)
in the Bransfield and Gerlache straits.
We propose two hypotheses to explain our findings. Firstly, krill densities are declining and their
distributions are contracting southward (Atkinson et al. 2019), therefore, increased fishing activities in
areas with reduced krill availability increase competition between penguins and fishery, particularly in
periods of low productivity. Secondly, increased catches on years with low krill productivity decrease
availability of krill to penguin populations. Krill population rises and falls from year to year, with
potential recruitment cycles lasting five to six years (Reiss et al. 2008), mostly driven by food
competition (Ryabov et al. 2017; Walsh et al. 2020). Summer melting of sea ice accumulated during
winter can boost local productivity in the WAP (Eveleth et al. 2017b; Eveleth et al. 2017a), therefore,
during years of negative SAM (when winter sea ice cover is lower) krill could experience population
limitation due to low availability of food, and consequently low recruitment (i.e. Flores et al. 2012;
Meyer 2012). Under this scenario, increased fishing catches could mean a krill shortage for penguins in
the next breeding season if the krill caught is not recovered. The fishery would be extracting biomass
cumulatively from the same population before new adults arrive, temporarily depleting resources for
Management consequences
CCAMLR manages the krill fishery following the principle of rational use of the marine living
resources, which implies both the precautionary and ecosystem-based approach. Since 1991 CCAMLR
has established catch limits for area 48 (WAP and Southern Scotia Arc), oftentimes updated depending
on the availability of new biomass estimations. So far, the current catch limit for area 48 is 620,000
tonnes (known as the trigger level, a value adopted entirely based on the previous highest catches).
Thereafter, trying to avoid potential concentration of the catches in small areas, and based on the
biomass distribution, the trigger level was split proportionally among the subareas, setting 155,000
tones for area 48.1 and 279,000 tones for subarea 48.2 (further details of this process see Nicol and
Foster 2016). Unfortunately, the catch limit is fixed and does not vary according to the variability of the
krill population, being particularly problematic in years of low productivity (i.e. environmentally-
impacted krill recruitment, Thorpe et al. 2019). Catch limits should be established based on seasonal krill
abundance estimates that also must include predator demands. For instance, CCAMLR is pursuing a
feedback management of krill fishery that would be achieved through an ecological risk assessment (i.e.
Trathan et al. 2018; Warwick-Evans et al. 2018. Lowther et al. in review) quantifying the amount of krill
required from top-predators on a spatial grid; fisheries would use that information plus continuously
updated information on krill density to guide when, where, and how much they should fish. Our results
support the need for implementing such kind of management approach, meaning that in years when
krill density is lower, catch limit should be lower than the currently being used. In addition, an increasing
concern is that precautionary catch limit was calculated for a regional scale, but our results as many
others (Hill et al. 2016; CCAMLR 2018; Santa Cruz et al. 2018; Krüger 2019) demonstrated that the
fishery is not a randomly distributed activity, rather catches occurs in a highly concentrated manner,
especially in Bransfield and Gerlache straits. This, coupled with the new evidences of the impacts
produced by climate change and krill fishery on penguin populations (Watters et al. 2020, this study),
creates concerns about whether the precautionary catch limit is still precautionary under the current
CCAMLR is pursuing the implementation of a Marine Protected Area network as a tool to
protect Antarctic marine ecosystems and manage human activities, including fisheries (Brooks et al.
2016; Coetzee et al. 2017). In this regard, a large MPA in the Domain 1 (WAP) was proposed recently by
Argentina and Chile parties (,
aiming to provide extra
protection for several conservation objectives, including krill; however, despite many countries have
strongly supported the proposal, a few have expressed their concerns voting against its adoption:
decision-making in the Commission is based on consensus, the proposal has not been adopted. The
current proposal includes general protection zones that precisely encompass the major locations of the
synergistically climate and fishery affected penguin colonies (and other krill-predators). Particularly,
around SOI, South Shetland Islands and the Gerlache strait, where evidences support that closures to
krill fishing would be beneficial for krill predators if fishing pressure increases (Klein and Watters 2020).
Examples of MPAs that allowed for increases in stocks of harvested species are abundant (Duffy et al.
2016; Chirico et al. 2017; Sala and Giakoumi 2018), even producing better fishing yields (Lynham et al.
2020). Therefore, it is a strategy with potential to not only protect top-predators and its resources, but
also to allow for a long-term fishery in the WAP.
CCAMLR has recognized the need for a more precautionary and dynamic approach taking into
account contemporary changes in the WAP, and its currently working on the development of a new
approach of the management of the krill fishery (CCAMLR 2019). Evidence such as the presented here
along with other new research and new monitoring plans will be crucial for implementation of a more
dynamic management strategy of the krill fishery that ensures the protection of krill dependent
predator under a changing environment in this unique ecosystem.
The authors would like to thank the CCAMLR Secretariat and co-originators/owners for
providing data access on krill fishery. The authors acknowledge the important contribution of the
MAPPPD resources towards the increasing knowledge of penguin species ecology. This study benefited
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Figure S1. Summary of number of breeding pair counts for chinstrap (Pygoscelis antarctius) and
gentoo (P. papua) penguins breeding along the western Antarctic Peninsula.
Figure S2. Example of variability of Antarctic Krill (
Euphausia superba
) fishing catch and sea
ice cover overlapped by the 30km radius around penguin breeding colonies in the Western
Antarctic Peninsula during the year 2010. Data accumulated by period of Pygoscelid penguins
breeding cycle, approximately as: Chick-Rearing (January to March), Non-breeding (April to
September) and Early Breeding (October to December).
Figure S3. Seasonal frequency distribution of Fractional Sea Ice Cover (FRSIC), Open Water
Sensible Heat Flux (HFLUX) and Sea Level Air Temperature (TLML) in the Western Antarctic
Peninsula, and Pearson Correlation (Cor) for each pair of variables.
Figure S4. Temporal variation of the standardized population growth rate for chinstrap
Pygoscelis antarctius
) and gentoo (
P. papua
) penguins breeding along the western Antarctic
Peninsula. Data is for several populations in time, therefore populations are repeated in time, and
this image does not reflect global trends of the species in the Western Antarctic Peninsula. The
black solid line is a linear trend and the dashed grey is a loess fit line.
Figure S5. Random effect of a Generalized Linear Mixed Model testing the probability of gentoo
penguin population decrease between years as a response to Antarctic Krill (
Euphausia superba
fishing and winter Southern Annular Mode SAM in the Western Antarctic Peninsula. Colony
level intercept ± standard deviation. Likelihood ratio test LRT=5.96, P=0.015. For colony names
check the MAPPPD application (, and colony geographical
positions on Supp. Table 1.
... During recent years, around 70% of the allocated catch limit for subarea 48.1 has been caught on the Bransfield strata alone [39]. Although, in recent fishing seasons the fleet has moved to a more autumn-winter operation in the area, if similar levels of catch occur in the future, in conditions like those in years 2001,2002,2004 and 2010 (see results) the catch could represent a substantial amount of the local standing krill stock (meaning eventually that a substantial amount of spawning population could be caught [40]), periods when competition with krill-predators can occur [15,16,19]. In addition, the rapid recovery of baleen whales after reaching critical levels due to whaling [41,42], could potentially increase competition for krill [43], as baleen whales are important krill consumers in the area [44,45]. ...
... Our results indicated that decreases of breeding success of the three species of Pygoscelis penguins were observable throughout the WAP. A geographical coherence was noted where populations north of 65°S tended to have steeper decreases, which are sectors experiencing faster warming [46,47] with consequent lower sea ice coverage [48,49], increased krill fishing catches [16,50] and spatiotemporal fishery concentration [31]. Localized reductions of penguin populations have been observed by other studies [51][52][53], which might be linked to a reduction in breeding success and recruitment [5] as a response to lower availability of krill under climate change [21]. ...
... The hypothesis that increased fishing catches in periods of low krill availability implied in lower penguin breeding success was supported by the results, therefore indicating that the current strategy management based on a fixed catch limit (trigger level) may not prevent potential effects of the fishery on predators when local krill biomass is low. This mechanism was previously proposed to reductions in the number of breeding pairs and on breeding performance [15,16]. ...
Full-text available
Pygoscelis penguin populations in the Antarctic Peninsula have dropped dramatically in the last 50 years. The main probable cause is the reduction in Krill (Euphausia superba), the most important feeding item for Pygoscelis penguins during breeding. The scientific community has expressed concerns on the potential that competition with the fishery during periods of low krill availability might be exacerbating the effects of climate change. By bringing together data on breeding success of penguin colonies throughout the Antarctic Peninsula with information of krill availability from acoustic survey and krill fishery monitoring data, we were able to show that fishery has had in the past an effect over breeding success. That is a consequence of a management strategy based on a constant catch level enabling the fishery to maintain the same levels of production even when krill availability is low. The total catch limit may have represented a substantial amount of the available krill biomass in some years, and we detected that when the catch goes over 5% of the available biomass during summer, breeding success of penguins decreased by one third. We discuss the implications of our findings to the revised ecosystem-based management strategy of the krill fishery in Antarctica.
... Understanding of ecological mechanisms underpinning chinstrap penguin behaviour and population dynamics in response to fluctuations in krill availability is crucial to develop management and conservation strategies under a scenario of higher environmental variability and increased krill fishing in the Antarctic Peninsula AP [25][26][27] . Hereby, the aims of this study are to quantify and compare foraging metrics of chinstrap penguins from a population in the tip of the AP during two breeding seasons between 2019 and 2022, and investigate the links between foraging behaviour differences and environmental variability. ...
... When coupled to fisheries, climatic events can have even greater local effects on krill availability 13,26 . Hypothesis stated that a year of high fishing catches followed by a warm winter with lower concentrations of sea ice could affect penguin breeding populations by reducing krill availability below what penguin populations require 25 . Our results demonstrated that lower winter sea ice conditions had consequences for krill availability in summer. ...
... Our results demonstrated that lower winter sea ice conditions had consequences for krill availability in summer. Although we did not measure the effects of fishery, in a season when environmental conditions are not favourable, such as 2021/22, high levels of fishing could affect the krill population itself 18 and, therefore, lead to punctual effects over penguin populations 26,65 that have the potential to persist through the following seasons 25 . Of particular concern are the chinstrap penguins whose bulk of the population is located in the AP 12 and whose breeding success (therefore recruitment in the long run) can be directly related to changes in krill distribution and abundance as a direct effect of warming (this study). ...
Full-text available
Dramatic decreases of chinstrap penguin populations across the Antarctic Peninsula (AP) are thought to be influenced by climate-driven changes affecting its main prey, the Antarctic krill, however, empirical evidence supporting such hypotheses are scarce. By coupling data on breeding chinstrap penguins, environmental remote sensing and estimates of krill acoustic density, we were able to demonstrate that penguins substantially increased their foraging effort in a year of low krill availability, with consequent reduction in breeding success. A winter of low sea ice cover followed by a summer/spring with stronger wind and lower marine productivity explained the lower and deeper krill availability. Our results highlight the importance of environmental variability on penguin populations, as variability is expected to increase under climate change, affecting foraging behaviour responses.
... However, prolonged food deprivation will nevertheless lead to starvation (Büßer et al. 2004;Kuepper et al. 2018), negatively affecting chick growth and survival. In addition, food stress may exacerbate oceanographic effects under harsh weather circumstances (Ritz et al. 2005;Krüger et al. 2021). ...
... Here, we explored the link between environmental conditions and breeding population demographics of WSP. Given the reported decreasing trend in the population sizes of various krill-eating Antarctic predators (Croxall et al. 2012;Dias et al. 2019;Krüger et al. 2021), we expected to find lowered breeding output of WSP in more recent years compared to earlier years, and to find evidence for declining population sizes over time. Considering the phenological shifts of WSPs breeding on the coast of Adélie Land (Barbraud and Weimerskirch 2006), we expected that WSP reproductive phenology on KGI has also shifted to later in the year. ...
Full-text available
Numerous seabird species are experiencing population declines, and this trend is expected to continue or even accelerate in the future. To understand the effects of environmental change on seabird populations, long-term studies are vital, but rare. Here, we present over four decades (1978–2020) of population dynamic and reproductive performance data of Wilson’s Storm Petrels (Oceanites oceanicus) from King George Island (Isla 25 de Mayo), Antarctica. We determined temporal trends in population size, breeding output, and chick growth rates, and related interannual variation in these variables to various environmental variables. Our study revealed a decline of 90% in population size of Wilson’s Storm Petrels in two colonies, and considerable changes in breeding output and chick growth rates. Temporal changes in breeding demographics were linked to interannual environmental variation, either causing changes in food availability (particularly Antarctic krill, Euphausia superba) or in nest burrow accessibility due to snow blocking the entrance. With the expected rise in air and sea surface temperatures, the predicted increases in precipitation over the Antarctic Peninsula will likely lead to increased snowstorm prevalence. Additionally, the rising temperatures will likely reduce food availability due to reduced sea ice cover in the wintering grounds of Antarctic krill, or by changing phyto- and zooplankton community compositions. The ongoing environmental changes may thus lead to a further population decline, or at the very least will not allow the population to recover. Monitoring the population dynamics of Antarctic seabirds is vital to increase our understanding of climate change-induced changes in polar food webs.
... Modern monitoring data also show that Adélie penguin breeding is closely linked to temperature (Croxall et al., 2002;Riaz et al., 2020;Watanabe et al., 2020), sea ice extent/concentration (Iles et al., 2020;Smith et al., 1999), and polynya size (Mezgec et al., 2017;Thatje et al., 2008). As crucial atmospheric-oceanic circulation patterns in Antarctica, ENSO and SAM also produce indispensably direct (e.g., winds) or indirect (e.g., polynya, ice cover, and SST) impacts on penguin ecology (i.e., survival rate and breeding; Croxall et al., 2002;Forcada and Trathan, 2009;Krüger et al., 2021;Wilson et al., 2001), especially in the Antarctic Peninsula (Barbraud et al., 2012;Henley et al., 2019;Hinke et al., 2014). Although previous studies have discussed the potential impacts of ENSO and SAM on modern penguin ecology based on observation data in Antarctica Peninsula and east Antarctica, they rarely cover the long-term influences of these circulations on penguin populations using geological proxies from sediments, particularly in the Ross Sea region (Forcada and Trathan, 2009). ...
Full-text available
The atmospheric-oceanic circulation patterns, especially for the Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO), two major atmospheric circulation patterns in the Ross Sea region, have been reported to greatly affect climate and marine ecosystems. However, from a historical perspective, the influence of atmospheric-oceanic circulation patterns on penguin populations remains unclear in this region. Here, we analyzed two lacustrine sediment cores collected from abandoned penguin colonies at Inexpressible Island, Ross Sea, Antarctica, and by applying alternative geochemical indices, successfully reconstructed the populations of the Adélie penguins (Pygoscelis adeliae) over the past ∼1500 years. We found that penguin population peaked during 750–1350 AD at Inexpressible Island, potentially due to habitat expansion in the warmer climate. After comparing with historical records of penguin populations at Cape Bird, Dunlop Island, and Cape Adare, all were found to have a common increase during the 750-1350 AD period in the Ross Sea. The population trend also coincided with extreme activities of El Niño and SAM (+). We inferred that the SAM-ENSO might promote influxes of Circumpolar and Modified Circumpolar Deep Waters into the Ross Sea. The enhanced influx of nutrient-rich deep water, together with a warmer climate may jointly enhance polynya efficiency and population increase of Adélie penguins. Our study indicates the potentially significant roles of ENSO and SAM in the regulation of Antarctic ecosystems.
... Modern monitoring data also show that Adélie penguin breeding is closely linked to temperature (Croxall et al., 2002;Riaz et al., 2020;Watanabe et al., 2020), sea ice extent/concentration (Iles et al., 2020;Smith et al., 1999), and polynya size (Mezgec et al., 2017;Thatje et al., 2008). As crucial atmospheric-oceanic circulation patterns in Antarctica, ENSO and SAM also produce indispensably direct (e.g., winds) or indirect (e.g., polynya, ice cover, and SST) impacts on penguin ecology (i.e., survival rate and breeding; Croxall et al., 2002;Forcada and Trathan, 2009;Krüger et al., 2021;Wilson et al., 2001), especially in the Antarctic Peninsula (Barbraud et al., 2012;Henley et al., 2019;Hinke et al., 2014). Although previous studies have discussed the potential impacts of ENSO and SAM on modern penguin ecology based on observation data in Antarctica Peninsula and east Antarctica, they rarely cover the long-term influences of these circulations on penguin populations using geological proxies from sediments, particularly in the Ross Sea region (Forcada and Trathan, 2009). ...
... These changes are particularly concerning both because of its importance within Southern Ocean food webs Saunders et al., 2019;McCormack et al., 2020), and because it is commercially harvested. Currently, krill fishing occurs only within the Southwest Atlantic, but while landings remain well below the total annual catch limit (8.6 million tons; Nicol et al., 2012) set by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), there are growing concerns over the increasingly localised nature of this fishery and its impacts on dependent ecosystems (Lowther et al., 2020;Krüger et al., 2021). Under these combined pressures there is increasing need for spatiotemporally resolved frameworks that capture the dynamics and environmental underpinnings of the krill population, building capacity for fine-scale management of the species (e.g. ...
Full-text available
Robust prediction of population responses to changing environments requires the integration of factors controlling population dynamics with processes affecting distribution. This is true everywhere but especially in polar pelagic environments. Biological cycles for many polar species are synchronised to extreme seasonality, while their distributions may be influenced by both the prevailing oceanic circulation and sea-ice distribution. Antarctic krill (krill, Euphausia superba) is one such species exhibiting a complex life history that is finely tuned to the extreme seasonality of the Southern Ocean. Dependencies on the timing of optimal seasonal conditions have led to concerns over the effects of future climate on krill’s population status, particularly given the species’ important role within Southern Ocean ecosystems. Under a changing climate, established correlations between environment and species may breakdown. Developing the capacity for predicting krill responses to climate change therefore requires methods that can explicitly consider the interplay between life history, biological conditions, and transport. The Spatial Ecosystem And Population Dynamics Model (SEAPODYM) is one such framework that integrates population and general circulation modelling to simulate the spatial dynamics of key organisms. Here, we describe a modification to SEAPODYM, creating a novel model – KRILLPODYM – that generates spatially resolved estimates of krill biomass and demographics. This new model consists of three major components: (1) an age-structured population consisting of five key life stages, each with multiple age classes, which undergo age-dependent growth and mortality, (2) six key habitats that mediate the production of larvae and life stage survival, and (3) spatial dynamics driven by both the underlying circulation of ocean currents and advection of sea-ice. We present the first results of KRILLPODYM, using published deterministic functions of population processes and habitat suitability rules. Initialising from a non-informative uniform density across the Southern Ocean our model independently develops a circumpolar population distribution of krill that approximates observations. The model framework lends itself to applied experiments aimed at resolving key population parameters, life-stage specific habitat requirements, and dominant transport regimes, ultimately informing sustainable fishery management.
... Using multi-decadal monitoring data and modeling, they showed that expected penguin performance was reduced when local harvest rates where high; an effect comparable in magnitude to the effect of poor environmental conditions. Similar results were obtained by Krüger et al. (2021), who reported that catches in combination with climate change (warm winters and low sea ice associated with negative Southern Annular Mode values) increased the probability of negative population growth rates, implying a decrease in population size of two Antarctic penguin species in the following year. Additional evidence of a reduction in krill CPUE and a higher spatial concentration of fishing (Santa Cruz et al., 2022) further supports the need for improving fisheries management and considering more refined spatial scales. ...
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Abstract The expected increase in global food demand, as a consequence of a rising and wealthier world population, and an awareness of the limits and drawbacks of modern agriculture, has resulted in a growing attention to the potential of the seas and oceans to produce more food. The capture production of presently exploited marine fish stocks and other species has more or less reached its maximum and can only be slightly improved by better management. This leaves four alternative options open to increase marine food production: (1) manipulating the entire food web structure via removal of high trophic level species to allow an increasing exploitation of low trophic level species, (2) harvesting so far unexploited stocks, such as various fish species from the mesopelagic zone of the ocean or the larger zooplankton species from polar regions, (3) low‐trophic mariculture of seaweeds and herbivorous animals, and (4) restoration of impoverished coastal ecosystems or artificially increasing productivity by ecological engineering. In this paper, we discuss these four options and pay attention to missing scientific knowledge needed to assess their sustainability. To assess sustainability, it is a prerequisite to establish robust definitions and assessments of the biological carrying capacity of the systems, but it is also necessary to evaluate broader socio‐economic and governance sustainability.
The southern giant petrel ( Macronectes giganteus ) is a widely distributed top predator of the Southern Ocean. To define the fine-scale foraging areas and habitat use of Antarctic breeding populations, 47 southern giant petrels from Nelson Island were GPS-tracked during the summers of 2019–2020 and 2021–2022. Step-selection analysis was applied to test the effects of environmental variables on habitat selection. Visual overlap with seal haul-out sites and fishing areas was also analysed. Birds primarily used waters to the south of the colony in the Weddell and Bellingshausen seas. Females showed a broader distribution, reaching up to -70°S to the west of Nelson Island, while males were mainly concentrated in waters off the northern Antarctic Peninsula. Habitat selection of both sexes was associated with water depth and proximity to penguin colonies. Both overlapped their foraging areas with fishing sites and females in particular overlapped with toothfish fishery blocks in Antarctica and with fishing areas in the Patagonian Shelf. Due to their habitat associations and overlap with fisheries, when harnessed with tracking devices and animal-borne cameras, giant petrels can act as platforms for monitoring the condition and occurrence of penguin colonies, haul-out sites and unregulated fisheries on various temporal and spatial scales in Antarctica.
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Antarctic krill (Euphausia superba) are considered a keystone species for higher trophic level predators along the West Antarctic Peninsula (WAP) during the austral summer. The connectivity of krill may play a critical role in predator biogeography, especially for central-place foragers such as the Pygoscelis spp. penguins that breed along the WAP during the austral summer. Antarctic krill are also heavily fished commercially; therefore, understanding population connectivity of krill is critical to effective management. Here, we used a physical ocean model to examine adult krill connectivity in this region using simulated krill with realistic diel vertical migration behaviors across four austral summers. Our results indicate that krill north and south of Low Island and the southern Bransfield Strait are nearly isolated from each other and that persistent current features play a role in this lack of inter-region connectivity. Transit and entrainment times were not correlated with penguin populations at the large spatial scales examined. However, long transit times and reduced entrainment correlate spatially with the areas where krill fishing is most intense, which heightens the risk that krill fishing may lead to limited krill availability for predators.
Climate change and climate variability have been shown to affect a broad range of species worldwide. As seabirds are likely to be affected by changing climate while breeding on-land and foraging at-sea, their population status and ecological changes are monitored as indicators of ecosystem change. This paper reviews the ecological processes and population consequences of climate impacts on penguins. The review shows that climate change and climate variability are important factors driving the changes in the population size and breeding success of various penguin species (up to 13 of 18 extant species) via changes in their breeding and foraging environments. However, these factors affect penguins in a complex way. For example, the effects of a warming climate can vary from negative to positive in different parts of the distribution range of a single species, or in different life-history parameters within a single population (e.g., breeding success vs. adult survival rates). Some simulation studies have produced future population projections for Antarctic and subantarctic penguins based on multiple climate change scenarios, emphasizing the importance of climate mitigation. The results of these simulations should still be interpreted with caution, while appreciating the uncertainties associated with climate projections and penguin responses to future climate. More research on penguin foraging ecology is needed, especially during data-poor non-breeding or juvenile periods, to elucidate fully the processes of climate impacts on penguins. Finally, mitigating existing human impacts is essential to safeguard penguin species, and will help penguin populations become more resilient to existing and future climate impacts.
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Both costs and benefits must be considered when implementing marine protected areas (MPAs), particularly those associated with fishing effort displaced by potential closures. The Southern Ocean offers a case study in understanding such tradeoffs, where MPAs are actively being discussed to achieve a range of protection and sustainable use objectives. Here, we evaluated the possible impacts of two MPA scenarios on the Antarctic krill (Euphausia superba) fishery and krill-dependent predators in the Scotia Sea, explicitly addressing the displacement of fishing from closed areas. For both scenarios, we employed a minimally realistic, spatially explicit ecosystem model and considered three alternative redistributions of displaced fishing. We projected both MPAs to provide positive outcomes for many krill-dependent predators, especially when closed areas included at least 50–75% of their foraging distributions. Further, differences between the scenarios suggest ways to improve seal and penguin protection in the Scotia Sea. MPA scenarios also projected increases in total fishery yields, but alongside risks of fishing in areas where relatively low krill densities could cause the fishery to suspend operations. The three alternatives for redistributing displaced fishing had little effect on benefits to predators, but did matter for the fishery, with greater differences in overall catch and risk of fishing in areas of low krill density when displaced fishing was redistributed evenly among the open areas. Collectively, results suggest a well-designed MPA in the Scotia Sea may protect krill-dependent predators, even with displaced fishing, and preclude further spatial management of the krill fishery outside the MPA. More broadly, outcomes denote the importance of delineating fishing and predator habitat, spatial scales, and the critical trade-offs inherent in MPA development.
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Winter sea-ice conditions are considered important for Antarctic krill Euphausia superba survival and recruitment, yet few broad-scale longitudinal studies have examined the underlying relationships between winter conditions and krill recruitment. We used data from a 4 yr winter study of krill condition (lipid content), diet (stable isotopes and fatty acids), and length distributions around the northern Antarctic Peninsula to examine relationships among environmental variables (annual sea-ice cover, water column chlorophyll a [chl a] , and upper mixed-layer water temperature), the condition and diet of krill, and recruitment success the following year. Diet indicators (lipid content, δ ¹⁵ N, δ ¹³ C, and the fatty acid ratios 16:1n-7/18:4n-3 and 18:1n-9/18:1n-7) in post-larvae were consistent among years regardless of sea-ice cover, suggesting that post-larval krill do not rely on sea-ice resources for overwinter survival. Diet indicators in larvae were more variable and suggest that larvae may feed on sea-ice resources when they are available but can still persist in the water column when they are not. Principal component analysis between environmental variables and diet indicators showed that water-column chl a was the only variable that significantly affected diet, regardless of annual changes in sea-ice cover. Extensive winter ice in one year did not translate into successful recruitment the following year. Krill demonstrate a high degree of flexibility with respect to overwinter habitat and diet, and the degree to which sea ice is important during different times of year and at different life stages may be more complex than previously thought.
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Two of the largest protected areas on earth are U.S. National Monuments in the Pacific Ocean. Numerous claims have been made about the impacts of these protected areas on the fishing industry, but there has been no ex post empirical evaluation of their effects. We use administrative data documenting individual fishing events to evaluate the economic impact of the expansion of these two monuments on the Hawaii longline fishing fleet. Surprisingly, catch and catch-per-unit-effort are higher since the expansions began. To disentangle the causal effect of the expansions from confounding factors, we use unaffected control fisheries to perform a difference-in-differences analysis. We find that the monument expansions had little, if any, negative impacts on the fishing industry, corroborating ecological models that have predicted minimal impacts from closing large parts of the Pacific Ocean to fishing. There are concerns that expansion of marine protected areas could have negative effects on the fishing industry. Here Lynham et al. demonstrate that the expansion of two of the world’s largest protected areas did not have a negative impact on catch rates in the Hawaii longline fishery.
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Low catch limits for forage species are often considered to be precautionary measures that can help conserve marine predators. Difficulties measuring the impacts of fisheries removals on dependent predators maintain this perspective, but consideration of the spatio-temporal scales over which forage species, their predators, and fisheries interact can aid assessment of whether low catch limits are as precautionary as presumed. Antarctic krill are targeted by the largest fishery in the Southern Ocean and are key forage for numerous predators. Current krill removals are considered precautionary and have not been previously observed to affect krill-dependent predators, like penguins. Using a hierarchical model and 30+ years of monitoring data, we show that expected penguin performance was reduced when local harvest rates of krill were ≥0.1, and this effect was similar in magnitude to that of poor environmental conditions. With continued climate warming and high local harvest rates, future observations of penguin performance are predicted to be below the long-term mean with a probability of 0.77. Catch limits that are considered precautionary for forage species simply because the limit is a small proportion of the species’ standing biomass may not be precautionary for their predators.
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Antarctic krill, Euphausia superba, have a circumpolar distribution but are concentrated within the south-west Atlantic sector, where they support a unique food web and a commercial fishery. Within this sector, our first goal was to produce quantitative distribution maps of all six ontogenetic life stages of krill (eggs, nauplii plus metanauplii, calyptopes, furcilia, juveniles, and adults), based on a compilation of all available post 1970s data. Using these maps, we then examined firstly whether “hotspots” of egg production and early stage nursery occurred, and secondly whether the available habitat was partitioned between the successive life stages during the austral summer and autumn, when krill densities can be high. To address these questions, we compiled larval krill density records and extracted data spanning 41 years (1976–2016) from the existing KRILLBASE-abundance and KRILLBASE-length-frequency databases. Although adult males and females of spawning age were widely distributed, the distribution of eggs, nauplii and metanauplii indicates that spawning is most intense over the shelf and shelf slope. This contrasts with the distributions of calyptope and furcilia larvae, which were concentrated further offshore, mainly in the Southern Scotia Sea. Juveniles, however, were strongly concentrated over shelves along the Scotia Arc. Simple environmental analyses based on water depth and mean water temperature suggest that krill associate with different habitats over the course of their life cycle. From the early to late part of the austral season, juvenile distribution moves from ocean to shelf, opposite in direction to that for adults. Such habitat partitioning may reduce intraspecific competition for food, which has been suggested to occur when densities are exceptionally high during years of strong recruitment. It also prevents any potential cannibalism by adults on younger stages. Understanding the location of krill spawning and juvenile development in relation to potentially overlapping fishing activities is needed to protect the health of the south-west Atlantic sector ecosystem.
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Significance A newly completed 40-y record of satellite observations is used to quantify changes in Antarctic sea ice coverage since the late 1970s. Sea ice spreads over vast areas and has major impacts on the rest of the climate system, reflecting solar radiation and restricting ocean/atmosphere exchanges. The satellite record reveals that a gradual, decades-long overall increase in Antarctic sea ice extents reversed in 2014, with subsequent rates of decrease in 2014–2017 far exceeding the more widely publicized decay rates experienced in the Arctic. The rapid decreases reduced the Antarctic sea ice extents to their lowest values in the 40-y record, both on a yearly average basis (record low in 2017) and on a monthly basis (record low in February 2017).
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The pelagic ecosystems of the Western Antarctic Peninsula are dynamic and changing rapidly in the face of sustained warming. There is already evidence that warming may be impacting the food web. Antarctic krill, Euphausia superba, is an ice-associated species that is both an important prey item and the target of the only commercial fishery operating in the region. The goal of this study is to develop a dynamic trophic model for the region that includes the impact of the sea-ice regime on krill and krill predators. Such a model may be helpful to fisheries managers as they develop new management strategies in the face of continued sea-ice loss. A mass balanced food-web model (Ecopath) and time dynamic simulations (Ecosim) were created. The Ecopath model includes eight currently monitored species as single species to facilitate its future development into a model that could be used for marine protected area planning in the region. The Ecosim model is calibrated for the years 1996–2012. The successful calibration represents an improvement over existing Ecopath models for the region. Simulations indicate that the role of sea ice is both central and complex. The simulations are only able to recreate observed biomass trends for the monitored species when metrics describing the sea-ice regime are used to force key predator-prey interactions, and to drive the biomasses of Antarctic krill and the fish species Gobionotothen gibberifrons. This model is ready to be used for exploring results from sea-ice scenarios or to be developed into a spatial model that informs discussions regarding the design of marine protected areas in the region.
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High-latitude ecosystems are among the fastest warming on the planet¹. Polar species may be sensitive to warming and ice loss, but data are scarce and evidence is conflicting2–4. Here, we show that, within their main population centre in the southwest Atlantic sector, the distribution of Euphausia superba (hereafter, ‘krill’) has contracted southward over the past 90 years. Near their northern limit, numerical densities have declined sharply and the population has become more concentrated towards the Antarctic shelves. A concomitant increase in mean body length reflects reduced recruitment of juvenile krill. We found evidence for environmental controls on recruitment, including a reduced density of juveniles following positive anomalies of the Southern Annular Mode. Such anomalies are associated with warm, windy and cloudy weather and reduced sea ice, all of which may hinder egg production and the survival of larval krill⁵. However, the total post-larval density has declined less steeply than the density of recruits, suggesting that survival rates of older krill have increased. The changing distribution is already perturbing the krill-centred food web⁶ and may affect biogeochemical cycling7,8. Rapid climate change, with associated nonlinear adjustments in the roles of keystone species, poses challenges for the management of valuable polar ecosystems³.
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In the Southern Ocean, the at-sea distributions of most predators of Antarctic krill are poorly known, primarily because tracking studies have only been undertaken on a restricted set of species, and then only at a limited number of sites. For chinstrap penguins, one of the most abundant krill predators breeding across the Antarctic Peninsula, we show that habitat models developed utilizing the distance from the colony and the bearing to the shelf-edge, adjusting for the at-sea density of Pygoscelis penguins from other colonies, can be used to predict, with a high level of confidence, the at-sea distribution of chinstrap penguins from untracked colonies during the breeding season. Comparison of predicted penguin distributions with outputs from a high-resolution oceanographic model shows that chinstrap penguins prefer nearshore habitats, over shallow bathymetry, with slow-flowing waters, but that they sometimes also travel to areas beyond the edge of the continental shelf where the faster-flowing waters of the Coastal Current or the fronts of the Antarctic Circumpolar Current occur. In the slow-moving shelf waters, large penguin colonies may lead to krill depletion during incubation and chick-rearing periods when penguins are acting as central place foragers. The habitats used by chinstrap penguins are also locations preferentially used by the commercial krill fishery, one of the last under-developed marine capture fisheries any- where on the planet. As it develops, this fishery has the potential to compete with chinstrap penguins and other natural krill predators. Scaling our habitat models by chinstrap penguin population data demonstrates where overlap with the fishery is likely to be most important. Our results suggest that a better understanding of krill retention and krill depletion in areas used by natural predators and by the krill fishery are needed, and that risk management strategies for the fishery should include assessment of how krill movement can satisfy the demands of both natural predators and the fishery across a range of spatial and temporal scales. Such information will help regional management authorities better understand how plausible ecosystem-based management frameworks could be developed to ensure sustainable co-existence of the fishery and competing natural predators.
Krill fisheries at Antarctica have concentrated their effort on the Western Antarctic Peninsula and Scotia Arc (WAP) in the last decades, following a steady increase in annual catch. Short-term shifts in habitat exploration may have occurred and may be the cause for the increasing catch. I compared habitat use and effort of Krill fisheries at the WAP during summer in the last five years and tested how habitat use and effort reflected in the catch. I detected a trend for an increase in fishing tow duration and depth of fishing, and also fish in deeper and colder waters. On the other hand, I found no association of the catch with the habitat explored, but catch was higher in years when the variability of explored habitat was lower. Finally, I discuss the relevance of these findings under the perspective of fisheries management and conservation of Antarctic Marine ecosystems.