It would probably come as a surprise to most Nagoya residents to learn that a sizable population of finless porpoises resides in the dark, extremely polluted waters of Nagoya Port -- even in its busy heart near Kinjofuto, the Meijo Bridge, the shipbuilding dock and among the enormous ships that carry Japanese automobiles to foreign ports. Nagoya, of course, is one of the busiest ports in the world.
Though in February and March these sunameri can be seen right in the northern limits of the port near the Nagoya Aquarium, even these hardy marine mammals have difficulty living entirely within the port during the hot summer months. Then, when the water turns a disgusting reddish-brown and its foul smell is nearly overpowering, they move into Ise Bay in the vicinity of the port entrance, although individuals are occasionally still seen in the port itself.
Why on earth do these animals -- of which Masamichi Hayashi, leader of a local environmental group, estimates there are "perhaps as many as 100" -- choose to live in such an inhospitable environment?
There are, surprisingly, certain advantages to living in these filthy waters. One important one is that commercial fishermen are banned from the port, thus allowing fish populations to increase and the port to serve as a sort of sanctuary. Mullet, for example, a favorite food of many dolphin species, is abundant in the port, resulting in immense feeding flocks of cormorants. In fact, the best way to locate small groups of finless porpoises is to look for feeding cormorants and various gulls.
Another advantage is that orca (killer whales) only very rarely enter the port, although one made news last year by swimming up one of Nagoya's rivers, where it needed human help to return to the bay. Fisherman also report that both orca and great white sharks are annual visitors to the northern portions of Ise Bay in winter and spring. Both these species also dine on small cetaceans, and the finless porpoise is one of the smallest, with large males reaching only about 1.8 meters in length.
Hence, the diminutive porpoises are safe from these dangerous predators while within the port.
The disadvantages of life in the crowded port are far more obvious. Poor visibility, however, poses no serious problem for finless porpoises. These western Pacific/Indian Ocean dolphins live in coastal bays and estuaries, often going far up rivers in China and Southeast Asia, where murky waters have always been its normal habitat. Their heads are large, supporting the "melon," a remarkable organ that enables dolphins to distinguish food and enemies and to navigate in total darkness by echolocation.
Rather than the lack of visibility, the port's underwater noise level must pose a serious problem. In our attempts to record the porpoises' acoustic communication, we were amazed by the roar of the engines and noise of the churning screws of ships. This may or may not interfere with echolocation, but it certainly limits the range of social communication within the group.
Each mother knows her calf's whistles, and the calf can easily identify its mother's chirps and whistles. Acoustic signals related to parental care, group feeding opportunities and danger are certainly greatly hampered by ships' engine noise. Obviously, too, industrial chemicals (especially mimic hormones) are a threat to this population, and it would be remarkable if the porpoises' fertility had not decreased dramatically in recent years.
In addition, individuals often eat plastic garbage. Numerous finless porpoises have been found dead on the beach at Mikawa Bay in southern Aichi Prefecture with plastic jamming their stomachs. Porpoises regularly eat squid and evidence suggests that they also dine on jellyfish, so it's quite likely that they occasionally confuse plastic as their prey.
To me, the important message to be learned from Nagoya's porpoises is that valuable and endangered species still exist in some areas with immense human interference and habitat destruction -- and it doesn't get much worse than Nagoya Port, where the entire shoreline is concrete!
But why don't they just decamp to a more favorable location? Some populations of finless porpoises seem to make fairly long migrations, but the Nagoya Port population does not, other than making those minor movements in summer. A calf is born in the port, grows up in that environment and knows no other life. As long as it can manage to survive at "home," it "knows" no reason to go elsewhere, especially as it faces obvious dangers lurking out in Ise Bay and, of course, knows nothing about mimic hormones, dioxins, etc. Indeed, this population has probably resided in the port area since ancient times, and those animals there today are probably the remnants of a much greater population in preindustrial times.
Notwithstanding such vestigial survivors, one of the biggest environmental threats of the 21st century, on a par with climate change and ozone holes, is the dramatic loss of biological diversity. Scientists predict that by the end of the century, 50 percent of all species of organisms on our planet will be extinct. We humans may well be among them -- in large part due to environmental destruction caused by our own kind.
Efforts must be made immediately to minimize negative impacts on species diversity. The finless porpoise is one species most likely to disappear in this century, due to the unfortunate fact that it evolved to utilize the same habitat as coastal populations of early humans. Nowadays, with greatly increased human populations, they and other animals with similar lifestyles (such as the dugongs and the river dolphins of China, Pakistan and the Amazon) are now on a fast track to extinction. As much as possible, this must be avoided.
But, Nagoya Port is necessary for the survival of the people of the Chubu region and is important to human society worldwide. In light of this, can we do anything to help preserve this porpoise population? Should we? The answer to both questions is "definitely yes!"
Although not directly related to the Nagoya porpoise problem, the Kyoto Protocol was a good start, but the United States has effectively (and foolishly) damaged it, while at the same time giving the war on terrorism priority over eliminating environmental destruction. My hope is that an emphasis on fighting terrorism (a hopefully temporary condition) will not result in a decrease in our efforts to protect what remains of our environment for future, post-terrorism generations.
As for the Nagoya Port porpoises, it is encouraging to note that the problem of ocean noise has been recognized and engineers are working to produce much more quiet marine engines, with the long-range goal of building truly silent ones.