Putting Gillnet Bycatch of Seabirds on the Map in Japan

Hotspot Map Report
Yasuko Suzuki1, Yutaka Yamamoto2, Hiroko Okamoto2, Nobuhiko Sato3,
Yann Rouxel4, and Ana Carneiro1
1

BirdLife International; 2Wild Bird Society of Japan;
3
Atmosphere and Ocean Research Institute, University of Tokyo;
4
The Royal Society for the Protection of Birds

Introduction
Bycatch in fisheries has been identified as one of the biggest threats to seabird populations
globally, with up to 400,000 seabirds killed each year in gillnet fisheries alone. However, noeffective mitigation measures have yet been identified for gillnet fisheries. A bycatch mitigation
trial in collaboration with a local fisher from Teuri Island, Hokkaido in 2016 confirmed thatseabird bycatch occurs in this fishery, but data on seabird bycatch at a nationwide scale areseverely limited. The objective of this project was to build on that first step to address seabird
bycatch issue in gillnet fisheries in Japan, by developing a nation-wide map to identify wherebycatch is likely to happen. This is a crucial step to identify priority ports from which to conduct
more detailed data collection and mitigation testing, and will also highlight critical knowledge
gaps. Based on a global review of seabird bycatch in gillnet fisheries by Žydelis et al (2013), 10
diving seabird species breeding in Japan are considered susceptible to gillnet were selected forJapan-wide scale hotspot analysis and mapping.

Methods
Japan-wide scale hotspots were identified by using the datasets and information below.
1) Seabird colony locations, colony sizes, and foraging areas
Ten diving seabird species breeding in Japan that are susceptible to gillnet bycatch wereconsidered in the nation-wide hotspot map (Table 1). Using the Seabird Breeding Colony
Database maintained by the Ministry of Environment (MoE) in Japan, with additional information
identified through literature review, we compiled breeding colony information (location andcolony size) for nine out of the 10 diving species from a 20-year long dataset (1998-2017). The
majority of data (94%) were from 2010-2017. Colony data from 2015-2018 on great cormorants
was compiled from datasets managed by prefectural governments because of data gaps in theaforementioned database. The original data matrix for colony sizes was a mixture of estimatednumbers of individuals and nests. We took the simplest approach to estimate numbers ofindividuals from numbers of nests (multiplied by 2) because other approaches applicable to1

certain species were not appropriate for others. In order to estimate the foraging areas for eachspecies, foraging distances were identified in the BirdLife International Seabird Foraging Area
Database (based on published literature and databases not open to the public). The mean of
maximum foraging distances (as radii) from multiple breeding colonies of each species were used
if this information was available (Table 1). Maximum foraging distance, unpublished data, orexpert opinion was used for other species.
Table 1. Species, conservation status, and foraging distance of diving seabirds breeding in Japanand considered particularly susceptible to bycatch in gillnet fisheries.
Species

Conservation status inForaging distance (used as radius in km
Japan’s Red Data Book
from center of each breeding colony)
Great cormorant
Least concern
15 2,4
Japanese cormorant Least concern
34 2
Red-faced cormorant Critically endangered
53
Pelagic cormorant
Endangered
10 3Common murre
Critically endangered
84 3
Spectacled guillemot Vulnerable
53
Ancient murrelet
Critically endangered
67 3Japanese murrelet
Vulnerable
36 3
Rhinoceros auklet
Least concern
100 1,3
Tufted puffin
Critically endangered
30 3123
Mean of maximum distances, maximum distance, unpublished data, 4 expert opinion

2) Gillnet fisheries annual catch and fishing areas
A questionnaire to collect fisheries data, including detailed information on fishing methods, wasdistributed to 39 prefectures with coastal lines, where gillnet fisheries are active. The availabilityof detailed fisheries data greatly varied by prefecture. We could not reflect those data as
consistent data matrix throughout the prefectures was necessary for a nation-wide analysis. We
instead used annual catch data in gillnet fisheries collected at a local scale through marine
fisheries production surveys conducted by the Ministry of Agriculture, Forestry, and Fisheries as
a proxy for gillnet fishing effort. Median annual catch across the three year period from 20152017 for each prefecture was used. Spatial data for areas where gillnet fisheries are authorized
were also collected. Rights to fish using gillnets in Japan can be obtained through two approaches,Class 2 Common Fisheries and governor’s permits. Information on areas where gillnet fishing ispermitted under Class 2 Common Fisheries was obtained from MDA Situational Indication
Linkages (https://www.msil.go.jp/). Information on gillnet fisheries areas permitted under
governor’s permits was not readily available, even through direct conversations with prefecturalgovernments. Fishing areas for drift gillnets were also unidentifiable in most prefectures because
fishing grounds move through vast areas seasonally and annually. Thus, gillnet fishing areas
reported in this document are partial and only based on Class 2 Common Fisheries information(hereafter referred to as “permitted gillnet fishing areas”). This limitation in the current analysis
is not negligible, and filling the knowledge gap will be necessary for more comprehensive spatial
analysis of bycatch risk in gillnet fisheries.

23) Water depth
Set gillnets in Japan are mostly bottom set, thus water depth was considered an important factor
to identify seabird bycatch in gillnets. Bathymetry data for the coastal waters of Japan wereacquired from the Japanese Oceanographic Data Center. The data allowed us to draw contours
at 100m, assuming deep diving seabirds breeding in Japan would not dive deeper based onliterature review. The 100m cut-off for water depth is also supported by information provided byfishers we interviewed in Hokkaido and the northeastern part of Japan; seabird bycatch has notbeen observed in gillnets set deeper than 100m (see #4 below for details).
4) Supporting information through interviews with fishers and local fisheries associations
During an early phase of the hotspot map analysis, we identified four areas where gillnet bycatchrisk was potentially high based on seabird colony concentration and annual fish catch data; thesouthwest, northwest, and eastern regions of a northern island (Hokkaido) as well as thenortheastern region of main island (Honshu). We conducted in-person interviews with fishers
and local fisheries associations in those regions. Seabird bycatch was confirmed in eastern andnorthwestern Hokkaido as well as Miyagi prefecture. In Miyagi, no seabird bycatch was reported
in fisheries targeting olive flounder and cod at water depths of 100m, while bycatch has occurredin fisheries targeting mantis shrimp and flounder at water depths of 10-20m. In southwestern
Hokkaido, where gillnet fisheries target Okhotsk atka mackerel and Japanese rock fish at water
depth at 120-150m, seabird bycatch was reported as very rare. Although not based on scientific
data collection, those interviews provided valuable information, especially as they supported thehypothesis of the importance of water depth in bycatch analysis.
ArcGIS was used to create data layers for breeding seabird distribution, gillnet fishingeffort/areas, and bathymetry, to build a series of maps including a gillnet bycatch hotspot map.

Results
Seabird breeding colony distribution and foraging ranges
Mapping of the 10 diving seabird species identified concentrations of seabird breeding colonies
in Hokkaido and the northeastern region of Honshu (Figure 1). Nine and seven diving species
were confirmed breeding in Hokkaido and NE region of Honshu, respectively. In contrast, 2-4
diving seabird species were breeding in other regions. The total number of individuals of thosespecies were the highest in Hokkaido, an order of magnitude higher than the sum of individuals
in the rest of Japan. The high number of diving seabirds in Hokkaido during the breeding season
is mainly attributed to large colonies of rhinoceros auklets (one site on the northwestern coastis the largest colony of the species in the world with >758,000 individuals, Figure 1). Hokkaido
and the northeastern region of Honshu collectively host colonies of six species of conservation
concern (four critically endangered [red-faced cormorant, common murre, ancient murrelet,tufted puffin], one endangered [pelagic cormorant], and two vulnerable species [spectacledguillemot, Japanese murrelet], Table 1) in Japan’s Red Data Book (Figure 2). Three species withrelatively large foraging areas (radii >50km: common murres, ancient murrelets, and rhinocerosauklets) are also concentrated in these two regions.

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Figure 1. Foraging areas around breeding colonies of 10 diving seabird species. Color codesof foraging areas are based on numbers of individuals at the breeding colonies.

Figure 2. Foraging areas around breeding colonies of 10 diving seabird species. Color codes offoraging areas represent conservation status in Japan’s Red Data Book (RDB). Areas with water
depth of <100m are also indicated for reference.

4Gillnet fisheries annual catch and fishing areas
Annual catch in gillnet fisheries in Hokkaido prefecture was by far the largest compared to otherprefectures (Figure 3). The second largest annual catch was observed in Miyagi prefecture (4,094t) in the northeastern region of Honshu, but it was an order of magnitude lower than that of
Hokkaido (78,720 t). Permitted gillnet fishing areas were observed in most prefectures withcoastlines. The permitted areas for gillnetting are larger in Hokkaido prefecture than otherprefectures. Areas with a water depth of <100m extend further offshore from the permitted
gillnet fishing areas in some regions (e.g. eastern Hokkaido).

Figure 3. Annual fish catch in gillnet fisheries by prefecture and permitted areas forgillnet fishing (only Class 2 Common Fisheries areas are shown). Areas with water
depth of <100m are also indicated.

Potential seabird bycatch hotspots in gillnet fisheries
By layering seabird colony and foraging range information with areas with water depth of <100mon a map, we identified areas where diving seabirds and gillnet fisheries overlap in Japanesewaters (Figure 4). We used water depth information instead of permitted areas for gillnet
fisheries because the aforementioned governor’s permit (for which we do not have data) allows
gillnet fisheries beyond the permitted areas shown in Figure 3 – this is therefore a slightly
precautionary approach to considering potential bycatch hotspots.
Based on the gillnet bycatch hotspot map (Figure 4) and annual fish catch information (Figure 3),
four areas where bycatch risk is expected to be high were identified:51) Eastern Hokkaido
There are many breeding colonies of species threatened with local extinction, including redfaced cormorants, pelagic cormorants, spectacled guillemots, and tufted puffins in this area.
Water depth is <100m in the vast area from Nemuro Bay to Nemuro Strait. Annual fish catch ingillnet fisheries in this area is quite high even within Hokkaido prefecture.
2) Northwestern Hokkaido
There are breeding colonies of pelagic cormorants, common murres, spectacled guillemots, andancient murrelets, and a very large colony of rhinoceros auklets in this area. Water depth is<100m between Teuri Island and the coastline of mainland Hokkaido.
3) Coastal area of Miyagi prefecture in northeastern region of Honshu
There are breeding colonies of ancient murrelets and rhinoceros auklets in this area. Water
depth is relatively shallow (<100m) in Sendai Bay. Annual fish catch in gillnet fisheries is alsosignificant in this area.
4) Northwestern Kyushu (most southwestern island among the main islands)
There are breeding colonies of Japanese murrelets on islands in Fukuoka prefecture (e.g.
Tsukuejima, Okinoshima, Koyajima). Water depth around those islands are relatively shallow(<100m). Annual fish catch in gillnet fisheries in this area is significant.

Figure 4. Hotspot map of seabird bycatch risk areas in gillnet fisheries. Overlap between
foraging areas of diving seabirds during breeding season and areas with water depth of<100m is shown. The numerical identifications correspond with the descriptions above of thefour areas.

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The hotspot map also identified areas where species of conservation concerns forage and water
depth is <100m, but gillnet fishing effort is relatively low. Gathering information from local
communities would be ideal to assess if gillnet bycatch is a risk to seabirds in those areas.
Seabird conservation using nation-wide hotspot map
Through compilation of the hotspot map and interviews with fishers conducted under thisproject, we have identified areas where the potential for bycatch of diving seabirds in gillnet
fisheries is high. Future work should be focused on these high priority geographical areas totackle this important conservation issue for seabirds.
Although this project has been the first important step in increasing our knowledge of seabird
bycatch in gillnet fisheries at a nation-wide scale, data to evaluate the extent of bycatch in gillnet
fisheries in Japan remains severely limited. A critical next step, focused initially on the highpriority areas identified in this project, is to collaborate with fishing communities and authorities
to collect further data on seabird bycatch and gillnet effort, to define more accurately the scaleof the issue for particular species and to refine the areas of greatest risk. This will help target
future mitigation efforts.
Effective technical gillnet bycatch mitigation measures are yet to be established. Developing
practical and effective technical measures, together with fishing communities, is urgentlyneeded, particularly in the Japanese context. We have initiated collaborative work with fishers
in the town of Haboro in northwestern Hokkaido to conduct at-sea trials of potential mitigation
measures (see details in Mitigation Measure Trial Report). This is the obvious place to start theprocess of more systematic data collection and mitigation testing.
The hotspot map presented in this document was based on bycatch risks during the seabird
breeding season because systematically collected data outside the breeding season is limited inJapan. However, gillnet bycatch of diving seabirds during winter months has been confirmed insome areas. Thus, including seabird distribution during the non-breeding season in future
potential hotspot mapping will provide a more comprehensive understanding of gillnet bycatchin Japan.

Through the hotspot map analyses of seabird bycatch in gillnet fisheries at Japan-wide scale, wewere able to identify high priority geographical areas where targeted data collection and focused
engagement with fishing communities should be conducted. Raising awareness and finding
solutions tailored towards each community through collaboration with local fishers and local
authorities will be essential to tackle this important conservation issue. We propose next steps
as outlined below.
Systemic data collection at local scale: Through collaboration with fishers, collecting
baseline data (target species, location, depth, catch and seabird bycatch) throughout
fishing seasons to evaluate geographical and temporal patterns of bycatch is an
important next step to better refine the scale of the issue.

Trials of potential mitigation measures in controlled environment: Considering the lackof mitigation measures to tackle seabird bycatch in gillnets despite previous trials

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conducted in multiple countries, developing effective and practical methods throughexperiments is urgently needed, especially in a controlled setting such as an aquarium
that holds seabird species of interest (e.g. alcids).


Full at-sea trials of the most promising mitigation measures: Informed by outcomes ofthe experiments in a controlled setting, conducting full-scale at-sea trials with sufficientscale for statistical analysis would be an essential step to evaluate effectiveness andpracticality of the mitigation.

Community-based engagement: Strengthen our collaboration with northwestern
Hokkaido fishers, and engage in further grassroots activities with new fishingcommunities identified in the bycatch hotspots analysis are much needed steps to tackle
the bycatch issue.

Acknowledgements
This project was made possible by support from the Kingfisher Foundation, to whom we arevery grateful. We would like to thank prefectural governments for providing gillnet fisheries
information through the questionnaire and direct correspondence. We very much appreciate
fishers and local fisheries associations for their generosity to share knowledge of gillnet
fisheries. We also thank Japan Coast Guard for providing data on areas permitted for gillnet
fisheries under Common Fisheries Rights. We would like to extend our appreciation to thefollowing organizations and individuals for sharing information on seabird colonies and foraging
distances as well as providing technical support to develop the hotspot map: Ministry ofEnvironment, prefectural governments (Regional Councils of Tohoku, Kanto, Chubu Kinki, andChugoku Shikoku), Bird Research, Kyle Elliott, Scott Hatch, Seiji Hayama, Kentaro Kazama,Mami Kazama, Tagaki Kentaro, Jumpei Okado, Kuniko Otsuki, Akiko Shoji and Yutaka Watanuki.

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