In Erimo, Hokkaido, There is fishery damage called “Tokkari gui”※1caused by Harbor seals(Phoca vitulina) where only the body or head of Yellowtail(Seriola quinqueradiata)or Salmon(Oncorhynchus keta) is eaten by them1,2,3(Figure 1).However, Harbor seals are Near Threatened species on the red list of the Ministry of the Environment2,3. In response to this, Ministry of the Environment has enforced the Erimo Area Kuril Harbor Seal Specified Rare Wildlife Management Plan to promote the coexistence of fishery and seals3.

As one of the way to prevent seals from getting into set nets and eating fish like salmon, trials to set grate net has been carried out(Figure 2) and some good effects are being seen. For example, through the survey conducted from 2016 to 2021, while the control area(no grate net set) had more damaged fish than clean fish, the experimental area with 18cm×18cm grate net had only 0.6% of the fish damaged.

In addition, in another experiment using a 20cm×20cm grate net, all seals were prevented during the survey. However, the aversion rate of salmon from the grate nets(20x20, 40x20, 25x25) had also increased. Nevertheless, considering the lowered damage rate of fish with grate net, the catch amount of fish significantly increased5.

This experiment also indicates that the presence of seals prevents salmon from coming to the set net. So, it can be referred that by reducing the number of seals coming to the set net, the amount of salmon coming to the set nets can be increased5. Additionally, the frequency of seals coming to the set nets decreases as they learn they can be prevented from entering the set nets5.

This kind of fishery damage is being seen with other marine mammals as well. For instance, fishery damages caused by Killer whale(Orcinus orca) in Kushiro is also well known6.

References

1.熊谷文絵. 漁業とアザラシの関係. 環境省 https://hokkaido.env.go.jp/blog/2021/09/post-671.html (2021).

2.服部薫. 日本の鰭脚類ー海に生きるアシカとアザラシ. (東京大学出版会, 2020).

3.環境省. えりも地域ゼニガタアザラシ特定希少鳥獣管理計画（第２期）. (2020).

4. 北海道地方環境事務所. 令和５年度（2023年度）  環境省えりも地域ゼニガタアザラシ管理事業実施計画. (2023).

5.藤森康澄. 定置網の改良によるアザラシの侵入防止（混獲防止）対策. 北海道大学のLASBOS https://repun-app.fish.hokudai.ac.jp/mod/page/view.php?id=11730&lang=ja (2017).

6.三谷曜子. シャチとヒトが共に生きる未来のために。知床・釧路の調査を拡充 - クラウドファンディング READYFOR. https://readyfor.jp/projects/ku_wrc_kw (2022).

※1“Tokkari”means seals in Ainu language. “Gui(食い）”is to eat in Japanese

Ship strikes, in which cetaceans collide with vessels, are considered a problem because of the risk of injury or death of the cetaceans and damage to the vessels. In Hokkaido, a fin whale (Balaenoptera physalus) was discovered in March 2024, caught in the bow of a ferry-type cargo ship that entered Tomakomai Port (Figure 1)1.According to the IWC (International Whaling Commission), most of the reports of collisions are related to large cetaceans, but all species are considered to be potentially affected, especially collisions with large vessels, which often go unnoticed and unreported. The committee is working with various organizations to reduce the risk of ship strikes by identifying “hot spots” where cetaceans and busy shipping lanes overlap.2

As an example of this effort, an attempt was made to reduce ship strikes by regulating vessel speed. In order to reduce the number of right whale (Eubalaena japonica) deaths due to ship strikes along the East Coast of the United States, a rule requiring vessels over about 20 meters to navigate at 18.5 km/h or less in the seasonal management area (SMA) was implemented, and its effectiveness was evaluated by To evaluate the effectiveness of this rule, the locations of right whale and humpback whale (Megaptera novaeangliae) carcasses in U.S. waters since December 1990 were plotted and their proximity to the SMA was investigated (Figure 2). As a result, 13 out of 15 right whales and 12 out of 26 humpback whales were killed by ship strikes in the 18 years before the rule was applied, but no ship strikes of right whales were observed in or near the SMA in the 5 years after the rule was applied. This was a statistically significant reduction, suggesting that the rules implemented in the SMA were effective in reducing ship strike mortality of right whales. It is also proposed that the SMA include right whale migration routes.3In 2023, the World Shipping Council (WSC) will produce a “Whale Chart” and publish it free of charge as a compilation of measures against ship strikes, including areas subject to static speed limits, based on information provided by the IWC and other organizations.

References

1.ストランディングネットワーク北海道.漂着情報. https://kujira110.com/?p=6758 (2024/5/30閲覧)

２. IWC | INTERNATIONAL WHALING COMMISSION.SHIP STRIKES https://iwc.int/management-and-conservation/ship-strikes (2024/5/50閲覧)

３. David W.Laist et al.(2014)”Effectiveness of mandatory vessel speed limits for protecting North Atlantic right whales”ENDANGERED SPECIES RESEARCH,23,133-147

 Bycatch is the unintentional taking of species different from the target species in fisheries, and not only fish but also seabirds and cetaceans may be taken by accident. Bycatch of cetaceans was observed between July 2001 and the end of October 2017, including minke whales (Balaenoptera acutorostrata), humpback whales (Megaptera novaeangliae), fin whales (Balaenoptera physalus), sei whales (Balaenoptera omurai), etc.¹, bycatch not only harms cetaceans but also reduces the efficiency of the fishery. In order to avoid bycatch, research has been conducted on the mechanism of bycatch of cetaceans, their behavior around fixed nets, and the mechanism of swimming in and out of the nets.

　 In Hokkaido, it has been reported that small dolphins called harbor porpoises (Phocoena phocoena) were caught as bycatch in fixed nets targeting squid and salmonids in April and May at Usushiri, Hakodate (Figure 1). Because harbor porpoises are known to inhabit shallow coastal waters in the Northern Hemisphere and are found in close proximity to fishing areas, there is concern about the conservation status of the population due to bycatch. In a paper describing the behavior of harbor porpoises around fixed nets, the behavior of harbor porpoises was shown using an acoustic recording device called an A-tag. As a result of this study, harbor porpoises were found 18 days out of 40 in the entrance area of the fixed nets, and 10 days out of 28 in the final trap. However, the study showed that harbor porpoises were actually caught as bycatch on only one day, and that only a small proportion of the harbor porpoises entering the fixed nets were caught as bycatch2. This study also showed that harbor porpoises in the final trap can escape the nets. Another study used an acoustic device called a “pinger” to keep harbor porpoises out of fixed nets. In a study using a different fishing method called gill nets, it was reported that the use of an appropriate number of pingers reduced the amount of bycatch to 1/3 of that in nets without pingers (Figure 2) (it would increase if not used properly)3. It has also been found that bycatch rate increases as the mesh size is increased3. Thus, studies to prevent bycatch using various research methods and behavioral analysis have been conducted. However, bycatch

has not been eliminated to this day. Therefore, various

approaches to prevent bycatch are needed in the future.

References

1. 日本鯨類研究所三十年誌. Accessed June 4, 2024. https://www.icrwhale.org/pdf/30nensi5.pdf

2. Higashisaka H, Matsuishi T, Akamatsu T. Presence and behavior of harbor porpoises (Phocoena phocoena) around set nets revealed using passive acoustic monitoring. Fisheries Research. 2018;204:269-274. doi:10.1016/j.fishres.2018.03.003

3. Palka DL, Rossman MC, VanAtten AS, Orphanides CD. Effect of pingers on harbour porpoise (Phocoena phocoena) bycatch in the US Northeast gillnet fishery. J Cetacean Res Manage. 2008;10(3):217-226. doi:10.47536/jcrm.v10i3.638

Ecotourism is an effort to promote better understandings toward the natural environment, history, culture, and other attractions unique to a region to tourists, while aiming for the sustainable development of tourist destinations. Whale watching has been conducted in many parts of the world as part of this effort, but there are concerns about the negative impact of whale watching on the behavior of whales.

The first example of a study of this effect was conducted on humpback whales. In this experiment, three different volume noise patterns from whale-watching vessels were played against a resting mother and calf from a research vessel. Compared to the lowest volume, the highest volume decreased the mother's resting time by 30%, doubled her breathing rate, and increased her swimming speed by 37%.

The second example, also conducted on humpback whales, investigated the possibility that whale-watching noise interferes the communication between whales. Four types of boats used for whale-watching in the area were used to record the noise and behavior of the whales when the boats approached the whales. It was shown that some of the noise overlapped with the frequency of the calls, which may have negatively affected the behavior of the whales using their hearing.

The third example was conducted on minke whales and observed changes in behavior depending on the presence or absence of whale-watching vessels. Minke whales responded to whale-watching vessels by decreasing their breathing, surfacing to forage, and underwater foraging behavior.

While whale watching is touted as an effort to promote understanding of environmental conservation among tourists, it can be stressful to cetaceans and can lead to the decline of local populations. In Canada, the U.S., Australia, and other countries, there are restrictions and penalties for approaching certain cetaceans, or cetaceans in general, beyond a certain distance. In Japan, Zamami Village (Okinawa Prefecture) and Mikurajima Island (Tokyo) have established their own rules, but most areas have not fully developed regulations for cetaceans.

Unlike fieldwork, aquariums are capable of long-term observation and study of specific individuals, and the following are examples of activities that make use of this property.

Ecological Research

In aquariums that house a wide variety of creatures, long-term observation and research can lead to the discovery of new ecology. For example, the sexual cycle of bottlenose dolphins kept at an aquarium was elucidated through year-round observation and research. In addition, the Otaru Aquarium has been conducting research to prevent the bycatch of Harbor porpoises, and other efforts are being made to return ecological research to conservation activities.

Rescue operation

Aquariums sometimes rescue wild animals using the skills and experience gained through breeding marine creatures. For example, the Otaru Aquarium keeps porpoises that were rescued and treated after being caught as bycatch. The development of various techniques has also contributed to the conservation of wild animals, such as the well-known artificial tailed dolphin, Fuji*.

＊Fuji

She was bred at Churaumi Aquarium. As treatment for an illness, her tail fin was amputated. Later, in cooperation with a private company, an artificial tail fin was created. It made it possible for her to jump again.

Discovery of a new population

Aquariums also exhibit creatures from wild environments. Some of these species and other distinctions are incomplete. For example, in 2022, a study and survey of the Pacific white-sided dolphins kept in aquariums throughout Japan revealed that there are two groups of genetic distinctions among the Pacific white-sided dolphins. Thus, the nature of aquariums can lead to new distinctions!

Pregnancy and childbirth

It is extremely difficult to continuously observe pregnancy and childbirth in nature. In aquariums, on the other hand, continuous observation of pregnant animals is easy, and assistance and research on births is conducted. In the vicinity of Hokkaido University, Merry, a bottlenose dolphin at the Otaru Aquarium, is currently pregnant, and if the pregnancy leads to delivery, it will be the first case in Hokkaido.

Column: Recommended Animals

Commerson's dolphin

Length: 1.25~1.75m

Distribution：Coast of South Africa, Fuego Island, etc.

Characteristics: The black and white coloration of its body is distinct. They are smaller than other dolphins. In Japan, they are kept at Sendai Uminomori Aquarium and Toba Aquarium.

References

１.Mtoi Yoshiokaら.Annual Changes in Serum Reproductive Hormone Levels in the Captive Female Bottle-nosed Dolphins.1986年

２.鈴木美和.日本沿岸域に形態が違う２タイプのカマイルカ集団が生息していることを遺伝学的に立証.2022年

3.アンソニー・マーティン.クジラ・イルカ大図鑑.平凡社.1994年

　In accordance with the IWC Scientific Committee, Japan conducted research whaling in the Antarctic Ocean from 1987, and in the Northwest Pacific Ocean from 1994, to investigate the abundance, stock, role in the ecosystem, and effects of marine pollution against each whale species.

　The term “stock assessment” does not simply mean determining the number of individuals. In addition to population size, age composition, sex composition, feeding ecology, and sexual maturity characteristics can be obtained to understand the actual status of the resource and to simulate more accurate behavioral population dynamics.

　In the late 1900s, there were many unclear area in the Antarctic whale stocks, and it was essential to clarify the actual status of the stocks in order for Japan to resume commercial whaling. As shown in Table 1: Content and validity of lethal and non-lethal methods for each research item, some data such as stomach contents can only be obtained by lethal methods. In the Japan's Research Whaling in the Antarctic (JARPAII), Antarctic minke, fin and humpback whales (humpback whales were excluded from the sample surveys) were the research targets.

　As a result of the research, long-term changes in the distribution of whale species, age of sexual maturity of Antarctic minke whales, and stock structure were analyzed, which obtained certain scientific results. For example, the age of sexual maturity of Antarctic minke whales was found to have increased from around 14 years before the whaling era of the 1940s to around 7 years in recent years, on average, based on the annual rings in the cerumen of individual research whales. Possible reasons for the downward trend in age of sexual maturity include the effects of reduced population density due to whaling and earlier maturation due to increased food availability. In addition, genetic analysis of DNA sequences and other data revealed changes in the boundary position of the area where the stock of Antarctic minke whales in the research area migrates, and the possibility that the boundaries of the stock distribution may differ depending on the sexes. Other data were also obtained on stock increase of humpback and other species, and the status of segregation by whale species and growth stages.

　Other research whaling in the Northwest Pacific also revealed feeding conditions of fishery resources such as mackerel, sei and saury as well as stock relations of minke whales. This has been pointed out by overseas researchers as a top-down effect (i.e., higher-order predators affecting bottom-dwelling organisms through a cascade effect), with increased cetaceans having a significant impact on the abundance of herring and big-eyed mackerel (Szymon Surma et al, 2015).

While these scientific results were achieved, JARPAII lost the ICJ (International Court of Justice) case against Australia and New Zealand, and the court concluded in its decision that the research results were limited. In the midst of political disputes, it has also become difficult to determine whether research whaling was purely “scientific research.”

References

1.令和5年度　国際漁業資源の現況　大型鯨類（総説）. 水産庁・国立研究開発法人　水産研究・教育機構

https://kokushi.fra.go.jp/R05/R05_47_whalesL-R.pdf

2.森下丈二. IWC脱退と国際交渉. (成山堂書店, 2019).

3.竹内俊郎ら編..水産海洋ハンドブック (生物研究者.2015).

4.捕鯨問題の真実 .水産庁・一般財団法人鯨類研究所
https://www.icrwhale.org/pdf/04-B-k.pdf.

5. Szymon Surma et al. Predicting the effects of whale population recovery on Northeast Pacific food webs and fisheries: An ecosystem modelling approach.2015

https://www.researchgate.net/publication/277336750_Predicting_the_effects_of_whale_population_recovery_on_Northeast_Pacific_food_webs_and_fisheries_An_ecosystem_modelling_approach.