Technical Reports of the Ins�tute of Cetacean Research (2023)

pp. 64–68

Technical Report (not peer reviewed)

U�lity of data logging for the es�ma�on of availability bias in sigh�ng
surveys
Taiki Katsumata*, Tatsuya Isoda and Koji Matsuoka
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan*Contact e-mail: katsumata@cetacean.jp

ABSTRACTThis paper describes the progress of the work by the Ins�tute of Cetacean Research on satellite-based datalogging experiments conducted with the aim of obtaining diving and surfacing dura�on data of the Antarc�cminke whale for es�ma�ng availability bias. The paper is organized to provide informa�on on ﬁeld equipment
for tagging, the data obtained on Antarc�c minke whale and results of preliminary es�ma�on of availability
bias. Tags were successfully a�ached to Antarc�c minke whales, and some diving and surfacing dura�on data
were obtained. Based on these data, es�mates of availability bias are presented. However, such es�matesshould be considered as preliminary and further experiments to obtain addi�onal behavioral data are recommended.

INTRODUCTION

FIELD EQUIPMENT FOR TAGGING EXPERIMENTS

Abundance es�mates of whales based on sigh�ng data
and the distance sampling method are aﬀected by anega�ve bias called ʻavailability biasʼ (McLaren, 1961;
Marsh and Sinclair, 1989). To address this point, Laakeet al. (1997), Okamura et al. (2012) and Borchers et al.
(2013) presented analy�cal methods that used whale diving and surfacing dura�on data to correct for availability
bias. These studies were based on diving and surfacing
dura�on data from visual observa�ons or from archival
tags. However, visual observa�on is not ideal for obtaining data on diving and surfacing behavior par�cularly inelusive species such as the Antarc�c minke whale. Also,
retrieving archival tags over several days while conducting the sigh�ng survey is not a prac�cal approach.
Satellite tagging provides a new and useful alterna�veto in obtaining data on diving and surfacing behavior.
Satellite tags were deployed on Antarc�c minke whales
during the 2021/22 and 2022/23 Japanese Antarc�cSigh�ng and Stock structure Survey (JASS-A) surveys witha par�cular aim to obtain diving and surfacing dura�ondata. Such data could be used to es�mate availability bias
following some of the methods indicated above.
This paper brieﬂy reports the details of ﬁeld equipment
for tagging, the data obtained on the Antarc�c minke
whale and the results of preliminary es�ma�on of availability bias.

The following equipment was used in the tagging experiment:– Satellite tags (SPLASH10-f-333, Wildlife Computers,US) in the Low-Impact Minimally Percutaneous External electronics Tag (LIMPET) with two 6.8 cm darts
and six petals;– Aerial Rocket Transmi�er System (LK-ARTS, Skutvik,Norway); and– Deployment arrows (originally developed by Wildlife
Computers and modiﬁed by the Ins�tute of Cetacean
Research [ICR]) (Figure 1).
The deployment arrows and tag were a�ached using
adhesive (Aron Alpha Jelly, TOAGOSEI Co., LTD., Japan).
The tags were shot from the bow deck (8 m above thesea) using an LK-ARTS, with air pressure set at 14 bar. The
video of the experiment in the Antarc�c Ocean can beseen at the following URL: h�ps://www.youtube.com/
watch?v=_wlSpleQEM8.
The SPLASH 10-f-333 can be conﬁgured to deﬁne speciﬁc ranges of diving and the types of data sought using
the so�ware Mk10 Host (Wildlife Computers, 2023). Datasuch as the maximum depth of each dive and the dura�on of diving and surfacing are received, rather than afull-resolu�on diving behavior.
In this study, the tags were conﬁgured to provide data
for each diving and surfacing event as behavior message.
A whale was considered diving when it penetrated deeper64

Utility of data logging for the estimation of availability bias in sighting surveys

Figure 1.

Equipment for satellite tagging: the satellite tags (SPLASH10-f-333) and the cup of the deployment arrow(a); original arrows developed by Wildlife Computers for a crossbow (b); and aerial rocket transmi�er system (LK-ARTS) (c).

Figure 3. Antarc�c minke whale with a SPLASH10-f-333 tag attached on 2 February 2022, at 71°16ʹS, 132°10ʹW. The
red circle indicates the a�ached posi�on of the tag.

Figure 2.

Mote Enclosure mounted on the upper bridge(upper le�), and Yagi and omnidirec�onal antenna
mounted on the top barrel of the research vessel(upper right). By connec�ng an USB memory s�ck
to the Mote Enclosure, the data received by theantenna can be retrieved (the retrieved data must
be decoded by Wildlife Computers portal).

than 4 m. The start and end of the recording were basedon a depth of 1 m, and the sampling interval was one
second. The percentages of �me spent in arbitrary depthbins (0; 1; 3; 5; 10; 30; 50; 100; 150; 200; 250; 300; 400;
>400 m) were obtained, and the diving dura�on bins (10;20; 30; 40; 50 sec; 1; 2; 3; 4; 5; 10; 15; 20; >20 min) wererecorded 12 �mes a day at two-hour intervals star�ng at
00:00 UTC. Tags were programmed to transmit 24 hours aday and were limited to 3,000 transmissions per day.

Mote (Wildlife Computers, US) is a sta�onary listening sta�on and can con�nuously log telemetry datafrom satellite tags on animals within the recep�on range(Jeanniard-du-Dot et al., 2017). Mote was installed on
the research vessel (Yushin-Maru No. 2, YS2), and Yagi
and omnidirec�onal antenna were equipped on thetop barrel (approximately 20 m above the sea level)(Figure 2). The Yagi antenna has direc�vity and about a60° beamwidth within which distant signals (about 8.5
nau�cal miles when placed at 20 meters) were received.
The omnidirec�onal antenna can receive signals from all
direc�ons, but the distance will be shorter.

DATA OBTAINEDIn the 2021/22 JASS-A survey, two Antarc�c minke
whales were tagged. Figure 3 shows the tag a�ached tothe whaleʼs body (PTT 207827). The vessel tracked this65

Technical Reports of the Ins�tute of Cetacean Research (2023)
Table 1
Details of diving and surfacing dura�on data of an Antarc�c minke whale tagged in the 2021/22 JASS-A survey. Data obtained from 6
February 00:01:00 (UTC) to 17 February 13:33:24 (UTC) 2022.
PTT ID

Number of days withdata obtained

Typendura�on mean
(sec)

SD

Dura�on min(sec)Dura�on max(sec)Dura�on range(sec)

207827

11.6DiveSurfacing

5050

196.5239.12

145.9165.55

62680
348674346Figure 4.

Percentage of behavioral data recorded by satelliteand Mote from an Antarc�c minke whale tagged in
the 2022/23 JASS-A survey.

was tracked on 18 January 2023, from 11:13 to 13:40(UTC+ 14 hours) and data were received via Mote. There
were 35 dives recorded during the tracking. Of these, 30
dives were recorded by the Mote, indica�ng its usefulness (Figure 4). The �me dura�on of the a�ached tag on
the water surface may be too short to transmit behavior
messages to a satellite.
The Mote is suited for acquiring a large amount of dataand can obtain each diving and surfacing dura�on of awhale, which is challenging to collect by satellite alone.
Figure 5 shows the diving behavior of the same whale
recorded for 60 minutes a�er the tag was a�ached. The
�me period during which data could not be received,
even when the Mote was running, suggests that it is par�cularly diﬃcult to receive data from this species.

ESTIMATION OF AVAILABILITY BIAS

Figure 5.

The diving behavior of an Antarc�c minke whale(PTT 224705) tagged during the 2022/23, and recorded for 60 min a�er tag a�achment. This whale
repeatedly dived at depths shallower than 15 m.
There were periods when data was not received
even while the Mote was tracking the individual.

individual and stayed more than 0.5 n.miles away fromthe whale during the tracking. During the tracking diving and surfacing dura�on data were received via Mote
consecu�vely for 26 min, but no data were received via
satellite. The diving and surfacing dura�on of this whale
are summarized in Table 1. Although the tag was a�achedto the whale for more than 10 days, only 50 dives wererecorded in total. This is possibly because the tag was not
suﬃciently out of the water and the signal was weak.
In the 2022/23 survey, two Antarc�c minke whales weresuccessfully tagged. Antarc�c minke whale (PTT 224705)
66

Table 2 summarizes the Antarc�c minke whaleʼs diving
and surfacing dura�on data (PTT 224705) obtained during the 2022/23 JASS-A survey. Using the values of surfacing dura�on of 4.54 s and diving dura�on of 60.03 s, apreliminary es�ma�on of availability bias was conductedbased on the rela�vely simple method of Laake et al.
(1997) under the following two survey cases: the ﬁrst
case is the ICR's vessel-based visual survey (see Isodaet al., 2020), and the second is the ICR's planned UAVbased aerial survey (see Matsuoka and Yoshida, 2021;
Katsumata and Yoshida, 2023).
Laake et al. (1997)ʼs formula to es�mate availability
bias is: t ( ymax ) E (d ) 1 − exp −E (s) E (d ) +a=E ( s ) + E (d )E ( s) + E (d )where a is the probability of a single whale being available on the transect line, E(s) is the mean dura�on ofsurfacing, E(d) is the mean dura�on of diving, and t(ymax)
is the amount of �me the ocean is in the observerʼs viewon the transect line.

Utility of data logging for the estimation of availability bias in sighting surveys
Table 2
Details of diving and surfacing dura�on from behavior messages on an Antarc�c minke whale in the 2022/23 JASS-A cruise. Data wereobtained from January 18, 2023, 11:13:24 (UTC+14h) to 13:40:09 (UTC+14h).
PTT IDTypenDura�onmean(sec)

SDDura�onmin(sec)Dura�onmax(sec)

Dura�onrange(sec)224705

DiveSurfacing

35
35

60.03
4.54

37.54
1.79

1
2

162
12161
10

Case 1: Vessel-based visual survey
Here it is assumed that the survey speed is 11.5 knots (approx. 21 km/h) and that an Antarc�c minke whale can besighted up to 2 n.miles ahead. Under these assump�ons,
the value of t (ymax) is 626.1 seconds; that of a is 1.00. Thissuggests that there are no missing Antarc�c minke whalein the vessel-based survey due to diving.
Case2: UAV-based aerial survey
Here it is assumed that the survey speed is 43 knots(approx. 80 km/h), and that the UAV ﬂies at an al�tude
at 100 m above the sea and that the camera captures arange 0.1 n.miles directly below the aircra�. Under theseassump�ons the value of t(ymax) is 8.4 seconds; that of
a is 0.19. This suggests that more than 80% of Antarc�cminke whales are not sighted due to diving.

DISCUSSION
This study presented the results of the ﬁrst tagging experiment using SPLASH10-f-333 on Antarc�c minke whales
during Japanese whale surveys in the Antarc�c. Tags werea�ached and data were obtained. Thus, this ﬁrst a�empt
can be considered successful. This approach proved to be
useful to obtain diving and surfacing dura�on data froman elusive species as is the case with the Antarc�c minke
whale. However, a data gap was observed in the behavior
message even while Mote was ac�ve (Figure 5). In thecase of animals that repeatedly make short diving, it ispossible that too many behavior messages were createdand transmi�ed. Since SPLASH10-f-333 can set the diving
deﬁni�on and types of data produced in a ﬂexible way,
it is important to set it to a conﬁgura�on that maximizes
the data collec�on relevant to the es�ma�on of availability bias.
Laake's method has been applied to vessel-based visual surveys previously (e.g. Weir et al., 2021). However,this method assumes that whales above the sea surface
will always be sighted regardless of forward distance.
However, the Antarc�c minke whale has small blows
and some�mes only the body is visible. Therefore, theassump�on that these whales are always sighted up to

2 n.miles ahead is unlikely to be met. As a consequence,
availability bias could be overes�mated with this method,
leading to an underes�ma�on of abundance es�ma�on.
As for the vessel-based visual survey, the detec�on probability should be considered for the forward distance, aswas described in Borchers et al. (2013).
For the aerial survey, the value a 0.19 is consideredreasonable, because it is similar to Hansen et al. (2018),
which es�mates availability bias on aerial surveys using
Laakeʼs method for common minke whales in the North
Atlan�c Ocean. However, in the case of the aerial survey,
the availability bias changes depending on the depth towhich whales can be detected. The data in this study assumed that it can be detected when shallower than one
meter, but this assump�on also needs to be examined in
the future. In both cases, the sample size of the diving
and surfacing dura�on is s�ll small, so it is necessary toaccumulate more data to accurately correct the availability bias of abundance es�mates using the distancesampling method.
In the 2022/23 JASS-A surveys, one ﬁn whale and two
humpback whales were successfully tagged and data on
diving and surfacing dura�on were obtained. These data
will be used to es�mate the availability bias for these species in the near future.

ACKNOWLEDGEMENTS
We acknowledge Yong Huang (Enfotran Corpora�on) andKevin Lay (Wildlife Computers) for their technical advice
regarding the tagging of the SPLASH10-f-333, Mote, andrelated data processing. We also acknowledge Hiroto Murase (Tokyo University of Marine Science and Technology)
for his advice on opera�ng SPLASH10-f-333 and installing
Mote on the JASS-A cruise. We appreciate Yoshihiro Fujise and Takashi Hakamada (ICR) for suppor�ng the experiments and the preliminary analysis. We thank Captains
Hidenori Kasai and Nobuo Abe, and their crew members,
and the researchers who par�cipated in the 2021/22 and2022/23 JASS-A surveys for their eﬀort in the tagging
experiment. We are grateful to Luis A. Pastene (ICR) for
his assistance in preparing this report and to the Editorial67

Technical Reports of the Ins�tute of Cetacean Research (2023)

Team of TEREP-ICR for editorial work.

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