Strange lights in the night: using abnormal peaks of light in geolocator data to infer interaction of seabirds with nocturnal fishing vessels

Abstract

Many seabird species forage at night and potentially interact with nocturnal fishing activities. Jigging fisheries use powerful lights to attract squid, and such high intensity lights can be recorded using global location-sensing loggers (geolocators) attached to seabirds. We use this potential source of information as evidence for interaction of southern giant petrels Macronectes giganteus with night fisheries during the non-breeding season. We compared the number of light spikes at night between sexes and evaluated whether the intensity of the light on those geolocator records matched periods of water immersion (wet–dry) of geolocators, as a measure of foraging activity. Females had more night light spikes than males, and although the activity on water was higher during nights with light spikes than nights without light spikes for both sexes, females had a higher probability to be resting on the water when peaks of light were higher. Females moved further north than males and used areas of higher squid fishery activities within Patagonian waters. This type of information is useful to record potential interactions with night fisheries and proposes that future studies should relate the accurate distribution of individuals (from GPS loggers) with light information (geolocators data) to highlight this undocumented interaction. Southern giant petrels are recognized as interacting intensively with fisheries off Patagonia waters with consequences for population dynamics (e.g. mortality through bycatch events).

Full text

SHORT NOTE
Strange lights in the night: using abnormal peaks of light
in geolocator data to infer interaction of seabirds with nocturnal
fishing vessels
Lucas Kru
¨ger
1,3
•Vitor H. Paiva
1
•Maria V. Petry
2,3
•Jaime A. Ramos
1
Received: 2 December 2015 / Revised: 9 March 2016 / Accepted: 15 March 2016
ÓSpringer-Verlag Berlin Heidelberg 2016
Abstract Many seabird species forage at night and
potentially interact with nocturnal fishing activities. Jigging
fisheries use powerful lights to attract squid, and such high
intensity lights can be recorded using global location-
sensing loggers (geolocators) attached to seabirds. We use
this potential source of information as evidence for inter-
action of southern giant petrels Macronectes giganteus
with night fisheries during the non-breeding season. We
compared the number of light spikes at night between sexes
and evaluated whether the intensity of the light on those
geolocator records matched periods of water immersion
(wet–dry) of geolocators, as a measure of foraging activity.
Females had more night light spikes than males, and
although the activity on water was higher during nights
with light spikes than nights without light spikes for both
sexes, females had a higher probability to be resting on the
water when peaks of light were higher. Females moved
further north than males and used areas of higher squid
fishery activities within Patagonian waters. This type of
information is useful to record potential interactions with
night fisheries and proposes that future studies should relate
the accurate distribution of individuals (from GPS loggers)
with light information (geolocators data) to highlight this
undocumented interaction. Southern giant petrels are
recognized as interacting intensively with fisheries off
Patagonia waters with consequences for population
dynamics (e.g. mortality through bycatch events).
Keywords Antarctica Light sensor data Remote
sensing Seabird ecology Spatial ecology Squid fisheries
Introduction
Fisheries play an important role in seabird ecology because
many seabird species feed on fishery discards (e.g. Ryan
and Moloney 1988), and fishery-induced mortality is one of
the main causes for strong population declines of seabird
species like mollymawk albatrosses Thalassarche spp.
(Weimwerskirch et al. 2000; Rolland et al. 2010; Tew Kai
et al. 2013), Wandering Albatrosses Diomedea exulans
(Barbraud et al. 2013) or Cory’s Shearwater Calonectris
diomedea (Ramos et al. 2012). To quantify the interactions
between seabirds and fisheries, it is important to understand
how much of a population is affected by fishing activities
(Votier et al. 2010). The main studies on the subject have
overlapped fishery areas with the short- to long-term dis-
tribution of seabirds, respectively, by means of satellite
telemetry (e.g. Xavier et al. 2004; Bugoni et al. 2009),
geolocation (e.g. Reid et al. 2013), quantifying interactions
by cameras attached to seabirds (Gre
´millet et al. 2010;
Votier et al. 2013) or by direct onboard sighting (Ryan and
Moloney 1988; Bugoni et al. 2008; Yeh et al. 2013).
Literature has illustrated that the attraction to night
lights from fisheries may have noxious effects to night
foraging seabirds—like colliding against vessels—but
simply reducing the amount of lights to a minimum on the
outside of the vessel is an efficient solution (Black 2005;
Glass and Ryan 2013). However, it is not the case for
&Lucas Kru
¨ger
biokruger@gmail.com
1
MARE—Marine and Environmental Sciences Centre,
Department of Life Sciences, University of Coimbra,
Coimbra, Portugal
2
Laborato
´rio de Ornitologia e Animais Marinhos,
Universidade do Vale do Rio dos Sinos, Sa
˜o Leopoldo, Brazil
3
Instituto Nacional de Cie
ˆncia e Tecnologia Anta
´rtico de
Pesquisas Ambientais INCT-APA, Rio de Janeiro, Brazil
123
Polar Biol
DOI 10.1007/s00300-016-1933-y

nocturnal fisheries that use powerful lights to attract catch
(Maxwell et al. 2003; Arkhipkin et al. 2015). They repre-
sent a source of intense artificial light that can even be
caught by satellites (Waluda et al. 2004,2008). Seabirds
are attracted to jigging fisheries due to the potent lights the
vessels use to lure squid; however, it is assumed to have
minimal bycatch for seabirds (Reid et al. 2006) as jigs are
designed to snag squids by the tentacles (Arkhipkin et al.
2015). On the other hand, nocturnal bycatch is significant
in longline fisheries, inclusively the amount of artificial
light used to attract prey is recognized to affect the rate of
seabird bycatches, like white-chinned petrel Procellaria
aequinoctialis (Petersen et al. 2009; Gonza
´lez et al. 2012)
and Wandering Albatross (Gonza
´lez et al. 2012).
We quantified abnormal spikes on light curves regis-
tered by geolocator tags, which are assumed to indicate
potential interaction with nocturnal fishing vessels (Pe
´ron
et al. 2010) during the non-breeding season of southern
giant petrels Macronectes giganteus. We relate those light
peaks with the individual wet/dry activity and overlap of
the Giant Petrels home range and foraging areas with the
spatial distribution of nocturnal lights at sea. We envisage
this should be a useful method to identify and quantify
individual interactions with squid fisheries.
Methods
Twenty-three southern giant petrels (13 females, 10 males)
were tagged with Biotrack MK3 geolocators
(16 914 96 mm, 2.5 g) from January to December 2014
at Stinker Point, Elephant Island, maritime Antarctic
Peninsula (61°13020.500S, 55°2103500 W). All the tagged
birds were active breeders, incubating eggs when tagged.
With the rings (2.2 g), the 3 M Super Weatherstrip
Adhesive (to glue the tag to the ring) plus the plastic belts,
the devices reached a maximum weight of 6.0 g, which is
well below the recommended 3 % of the bird’s body mass
(Phillips et al. 2003), which was 4.27 kg (range
3.00–5.40 kg) for the birds deployed on. We analysed data
from the non-breeding period, which we considered April
to September. All birds were tracked throughout the whole
considered period, so they all have a similar amount of
tracking days during the non-breeding period (183 days).
Geolocators register the intensity of light continuously
every 3 s providing a 10-min cumulative value, measured
in terms of exposure of the light sensor to light flux per unit
of area (lux). Light intensity varies from 0 (night) to 64
(day). It is possible to estimate artificial sources of light
when there are odd peaks of light during the night period
(Fox 2010). We investigated this, considering only peaks of
light intensity above 10, so it would avoid any natural
source of light like bioluminescent organisms or reflection
of a full moon on the water or on ice. Geolocators also
register a salt switch every 3 s, giving a record of when the
bird is sitting on the water. Then, light and wet–dry curves
were merged, and each individual was inspected for
abnormal peaks of light intensity during the night in the
non-breeding season. Wet–dry activity records failed for
two individuals (one female and one male), so we were
able to use only 877 out of the 1137 light peaks when
relating to wet–dry activity. We calculated, for each indi-
vidual, the number of nights with light spikes, the mean
number of spikes per night (considering only nights with
spikes) and the mean wet activity per nights with and
without light spikes.
Geographical data were processed by the BASTrack
Package. We used the BASTrackLocatorAid software to
determine the sun elevation angle (= -1) and set the light
threshold to 8. Thresholds in the light curves are used to
determine sunrise and sunset times, thus allowing an esti-
mation of latitude based on day length and longitude based
on the timing of local midday with respect to universal
time. Daily light curves were cleaned according to inter-
ruptions in the sunrise/sunset sequence. Data from the
7 days before and after the equinoxes (20th March and
22nd September in 2014) were also excluded (around 4 %
of geographic positions). We calculated the 50 % (Forag-
ing Area, FA) and 25 % (Core Area, CA) kernel density for
each individual and for sexes, using the adehabitat R
package (Calenge 2006).
Satellite images from the National Oceanic and Atmo-
spheric Administration (NOAA; http://ngdc.noaa.gov/eog/)
depicting global light at night were used to identify the
activities of squid fisheries vessels following methods
described by Waluda et al. (2004), Paulino and Escudero
(2011) and Elvidge et al. (2015). Global light images
represent the recordings for cloud-free light intensity
(NOAA 2015) presented in a 2.7 km grid image. We cal-
culated a mean value for the last 4 years of satellite data
and filtered the light values through a 3 93 cell grid
median calculation, to detect light spikes (Elvidge et al.
2015).
Mean wet activity was normally distributed (Shapiro–
Wilk W=0.96, p=0.22) and variances were homoge-
neous among nights with and without spikes (Bartlett’s
K
2
=0.81, p=0.37); the same goes for the individual
number of nights with spikes (Shapiro–Wilk W=0.94,
p=0.19; Bartlett’s K
2
=0.44, p=0.51) and number of
spikes per night (Shapiro–Wilk W=0.93, p=0.14; Bar-
tlett’s K
2
=0.42, p=0.52). So we used linear models to
compare the wet activity between sexes on nights with and
without light spikes and to compare number of nights with
spikes and number of spikes per night between sexes.
Generalized linear models (GLMs) with logistic distribu-
tions were used to test the effect of sex and light intensity
Polar Biol
123

on the wet–dry activity of the giant petrels. Analyses were
conducted in R (R Core Team 2015), and data are pre-
sented as mean ±SD.
Results
We can clearly see that females overlapped most of their
FA with zones of high squid fishing activities off the
Argentina and Falklands waters, while males concentrated
their foraging areas in southern waters where these types of
fisheries occurred less frequently (Fig. 1). However, both
sexes used at some extent the pelagic waters towards the
north of Antarctic Peninsula, the South America shelf and
Falkland Islands (Fig. 1).
The number of nights with light spikes was marginally
different between sexes (F
1,21
=4.0, R
2
=0.17,
b=-10.1, p=0.059) with females (33.1 ±10.6 nights)
having more nights with light spikes than males
(23.1 ±13.1 nights). On the other hand, the number of
spikes per night was not different between sexes
(F
1,21
=1.4, R
2
=0.06, b=-0.74, p=0.257). Individ-
ual mean number of spikes per night varied from 1.68 to
6.7, with a mean value of 4.03 ±1.5. As each spike cor-
responds to a 10-min interval, the mean time spent around
the squid fisheries was around 40 min per night. The wet
activity (F
3,40
=10.3, R
2
=0.44, p\0.0001) was sig-
nificantly higher in nights with light spikes than in nights
without light spikes (T
3,40
=4.73, b=52.17, p\
0.0001), but the effect of sex was marginally significant
(T
3,40
=-1.74, b=-28.47, p=0.07). Females and
males had similar wet activity during nights without light
spikes [females: 21.95 ±12.00 % (2.41–40.45 %), males:
20.20 ±14.54 % (2.06–41.9 %)] and both increased wet
activity during nights with light spikes [females:
48.03 ±11.61 % (26.45–64.45 %), males: 32.04 ±
16.10 % (4.87–56.3 %); Fig. 2]. There was a positive and
significant effect of night light intensity on the probability
of landing on water (Z
1,875
=5.62, b=0.021, odds
ratio =1.02, p\0.0001), with females having a higher
probability to land on water than males (Z
2,874
=2.91,
b=-0.025, odds ratio =0.97, p=0.003).
Discussion
As proposed by Pe
´ron et al. (2010), we were able to
quantify the number of night light spikes, and this repre-
sents a potential source of information on interaction with
squid fisheries, as giant petrels’ wet activity behaviour
Fig. 1 Core areas (thick lines) and foraging areas (thin lines)of
female (a) and male (b) southern giant petrels Macronectes giganteus,
overlapped with the intensity of lights (lux) at night. Light data
extracted from NOAA satellites (http://ngdc.noaa.gov/eog/). White
cross locates the breeding colony, Elephant Island, light grey areas are
zones of 50 % probability for sea-ice occurrence, calculated based on
10-year mean data from NOAA CoastWatch (coastwatch.pfeg.noaa.
gov)
Polar Biol
123

changes coincide with the occurrence of night light spikes.
Many species of seabirds feed at night (i.e. Ballance and
Pitman 1999; Dias et al. 2012; Ramı
´rez et al. 2013), and
even species considered mostly diurnal (Weimerskirch and
Wilson 1992; Regular et al. 2011) forage at night when
abiotic conditions are favourable or take advantage of the
diel vertical migration of their prey (e.g. Elliot and Gaston
2015). This behaviour, associated with the attraction
towards light (as an adaptation to find bioluminescent
organisms), may lead seabirds to interact with night light
sources in the ocean. Such attraction to artificial at-sea
lights can also impact on survival, with birds colliding with
oil platforms (Wiese et al. 2001; Black 2005), fishing
vessels (Black 2005; Glass and Ryan 2013) or being
bycaught on fishing gear (Ryan 1991; Gonza
´lez et al.
2012). For instance, nocturnal bycatch of white-chinned
petrels and wandering albatrosses has been positively
correlated with the amount of light used in longliners
(Petersen et al. 2009; Gonza
´lez et al. 2012). The bycatch on
jigging vessels is assumed to be very low (Arkhipkin et al.
2015), but the jigs’ crew has been recorded to target sea-
birds as a food source when they approach the vessel, and
this could represent a substantial impact for threatened
seabirds (Reid et al. 2006).
Southern giant petrels are known to interact with fish-
eries (Gonza
´lez-Zevallos and Yorio 2006; Copello and
Quintana 2009; Yeh et al. 2013), feed on waste from
trawlers and jiggers (Quintana et al. 2006) and have been
registered as bycatch at low rates in nocturnal (Petersen
et al. 2009; Gonza
´lez et al. 2012) and diurnal longliners
(Yeh et al. 2013). For instance, catch rates of giant petrels
reported for night longlining varied around one to five per
cent of total catch (Petersen et al. 2009; Gonza
´lez et al.
2012) and is similar to the amount of catch rates for diurnal
longlining (Favero et al. 2003; Yeh et al. 2013). Despite
that, interactions with night fisheries for this species are
insufficiently documented. Southern giant petrels in South
America feed on squid species targeted by those night
fisheries (Copello et al. 2008). For instance, squid Ilex
argentines was an important food item for chicks of a
population of southern giant petrels in Argentina during
four consecutive years (Copello et al. 2008) and is also the
main target for the Argentine squid fisheries (Waluda et al.
2008). Jigging fisheries off the Patagonia shelf are quite
intensive—landings were reported to represent 40 % of
world total catch for squids in 14 years (Arkhipkin et al.
2015).
On the other hand, we also found a sexual effect for
interactions with night fisheries. Giant petrels are highly
dimorphic, and sexes have different foraging strategies
(Hunter 1987; de Bruyn et al. 2007). While males rely
more on scavenging and preying upon other seabirds,
females feed more on fish and squid (Hunter 1984; Gon-
za
´lez-Solı
´s et al. 2000; Rey et al. 2012), which likely
explains the spatial differences we detected. Such sex-bi-
ased interaction with night fisheries might translate into
females interacting more with jigging fisheries than males.
Despite the associated mortality of seabirds with jigging
for squids is assumedly low (Reid et al. 2006; Arkhipkin
et al. 2015), as already discussed, there is the issue of
jiggers’ crew using seabirds for food (Reid et al. 2006).
Furthermore, similar methods of fishing proved to have
substantial bycatch of large seabirds (Gonza
´lez et al. 2012),
and the use of jigging discards as a food source may have
demographic consequences for giant petrels (Quintana
et al. 2006; Copello et al. 2008).
Finally, we propose that future investigations should use
the light sensor data (provided by the geolocator device)
with the accurate geographical locations of the bird (cap-
tured by a GPS logger), both deployed on the same birds, to
precisely map seabird interactions with fisheries at the
individual level. Furthermore, tracking effort should be
coupled with onboard observations of seabirds attending
fishing vessels during night. It would provide valuable
information to help with the at-sea conservation of seabird
species, through mitigation of the light-induced seabird
mortality.
Acknowledgments LK acknowledges the National Council of
Technological and Scientific Development CNPq for his Ph.D.
scholarship (Programa Cie
ˆncia sem Fronteiras processo 245540/2012-
1). VHP acknowledges the postdoctoral grant given by ‘Fundac¸a
˜o
para a Cie
ˆncia e Tecnologia’ (SFRH/BPD/85024/2012). We
acknowledge the Brazilian Navy for field research support in
Fig. 2 Mean ±SD individual percentage of time on water (wet
activity) for southern giant petrel (Macronectes giganteus) females
and males during nights without (dark grey bars) and with (light grey
bars) night light spikes
Polar Biol
123

Antarctica. The project received funding from the National Institute
of Science and Technology Antarctic Environmental Research
(INCT-APA) that receives scientific and financial support from the
National Council for Research and Development (CNPq Process: No.
574018/2008-5) and Carlos Chagas Research Support Foundation of
the State of Rio de Janeiro (FAPERJ No. E-16/170.023/2008). The
authors also acknowledge the support of the Brazilian Ministries of
Science, Technology and Innovation (MCTI), of Environment
(MMA) and Inter-Ministry Commission for Sea Resources (CIRM).
This study benefited from the strategic program of MARE, financed
by FCT (MARE—UID/MAR/04292/2013). LK thanks Julia Finger,
Elisa Petersen and colleagues for field work support. Authors
acknowledge Naomi Tremble for English review.
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