Clarifying some factors contributing to decreasing catches of the sand lance—food shortage during the growth period causes declines in their growth rate and egg production
 
  Most fish and shellfish that we use as food are wildlife, and there have been fluctuations in catches of these marine resources. The major research objective of Associate Professor Takeshi Tomiyama is to clarify the fluctuation mechanism, thereby enabling us to use marine resources in a sustainable manner. To this end, it is necessary to fully understand what kind of organisms they are, and what kind of environments they need. According to him, however, many marine organisms are unfortunately still shrouded in numerous mysteries.

“Recently, the catches of sand lance, hairtail, flatfish and other kinds of fish have significantly decreased in the Seto Inland Sea. In actuality, however, we don’t understand much about the reasons for this. We are therefore striving to identify the characteristics of fish species living in the Seto Inland Sea and the factors affecting the decline in catches, by conducting fieldwork and rearing experiments, in cooperation with related local and national research institutes located in areas around the Seto Inland Sea.
 
One example of these collaborative activities is the Study into the Mechanisms of Declining Catches of the Sand Lance Ammodytes japonicus in the Seto Inland Sea, a joint project carried out with the National Research Institute of Fisheries and Environment of Inland Sea (FEIS), Japan Fisheries Research and Education Agency (FRA).

In recent years, catches of the sand lance from the Seto Inland Sea have declined to extremely low levels. Meanwhile, a decrease has also been observed in volumes of zooplankton, on which the sand lance feed. As such, his research team studied their correlations, and the research results suggested some potential factors.
Associate Professor Tomiyama explains: “We have found that if juvenile sand lance are amply fed, in the following year all the individuals can mature and spawn many eggs. Conversely, when they are grown under a limited food condition, some individuals will remain immature, and even if matured, these individuals spawn a smaller number of eggs. To examine other conceivable hypotheses, we are continuing our research.” These research findings were published in the U.S. scientific journal PLOS ONE in 2019. 		 
 
Seeking new discoveries through a broad range of initiatives, with a particular interest in inter-latitudinal variations
 
  Associate Professor Tomiyama says that recently he has been particularly interested in latitudinal variations in biological characteristics.

He comments: “Even the same species of fish may exhibit growth characteristics that vary according to the place where they live. For example, fish living in the north tend to be larger in size, but grow slowly and live long, due to the low seawater temperature. However, it is known that northern fish populations grow faster than others when all are reared under the same temperature conditions. This is thought to be a characteristic that the fish species has acquired as it has expanded its distribution to the north (i.e., in the direction of higher latitudes).”

How about the inverse case—that of a fish species which has expanded its distribution in the direction of lower latitudes? This question has remained unanswered. So, Associate Professor Tomiyama’s research team carried out an investigation to clarify whether or not a fish population living in low latitudes can grow faster than others under the same environmental conditions, during the process in which a fish species inhabiting high latitudes, i.e., a cold-water fish species, expands its distribution. He says that as a result, his team succeeded in discovering a possibility of faster growth. In the future, his team plans to continue working to verify this possibility and to study how fish species adapt to changes in the environment, including global warming.
 
When asked about the pleasures of research, Associate Professor Tomiyama answers, “Research stimulates my imagination.” He adds, “To understand what is happening in the ocean, needless to say, conducting many surveys and experiments is vital. However, it is also extremely important to imagine various things and formulate hypotheses in the course of these activities. The results are rarely as I have imagined, and I always experience unexpected discoveries and surprises. Each time I make new findings, I feel the joy of research.”

Ever since he was very young, he has been fascinated by living organisms, particularly fish. “There are a wide variety of fish species, and their appearances and existences are very diverse. Even in the same species, fish may have quite different life histories according to their habitat.” For these reasons, fish have inexhaustible appeal to Associate Professor Tomiyama. While continuing his investigations, he can make a lot of small but surprising discoveries. He remarks with a smile, “I hope to eventually make a great discovery.” 		 
 
Hoping to share understanding about living organisms for the benefit of people engaged in the fisheries industry
 

  Associate Professor Tomiyama pursues truly extensive areas of research. He has not only studied diverse fish species, but also carried out fieldwork in various locations, ranging from the Seto Inland Sea, the waters off the Tohoku District where he started his research, to the Bungo Channel located between Oita and Ehime Prefectures.

Originally, as a student at Tohoku University, he studied on flatfish ecology. After graduation, he worked as a staff member of the Fukushima Prefectural Fisheries Experimental Station, where he conducted survey research from a standpoint different from that of a university researcher. With this background, Associate Professor Tomiyama is now eager to promote research projects in the form of collaboration with external partners.
“Since there are many researchers in the Seto Inland Sea area, which is home to Hiroshima University, we have many opportunities for information exchange. By working together successfully with outside researchers, we can substantially broaden the scope of research,” he says.

On the other hand, Associate Professor Tomiyama points out that he can learn a lot from fishery workers. “For example, people generally cannot tell the sex of flatfish by their external appearance. However, when I was a staff member of Fukushima Prefecture, a fishery worker taught me that we can tell the sex of a marbled flounder by touching it with our hand.”

His wealth of accumulated experience also changed his attitude toward research. He became aware of the importance of utilizing his research outcomes for the benefit of fishery workers. Furthermore, he subsequently experienced the Great East Japan Earthquake. After joining the School of Hiroshima University, he has undertaken his research activities from a broader perspective, in order to provide support for fishery workers and Fukushima Prefecture.

Associate Professor Tomiyama says, “Previously, my basic research policy was solely to understand living organisms. However, now I want to pursue my research focusing on the impact of and measures against global warming and other environmental changes, which have become increasingly accelerated. Notably, I feel that cold-water fish species in the Seto Inland Sea are decreasing significantly, probably because of the rising seawater temperature. While paying attention to these changes occurring in fish, fishing and the ocean environment, I will consider the potential of the fisheries industry.”

In closing, he offered words of encouragement to high school students who are interested in the afore-mentioned research activities.

“I hope that you will take on many challenges and build up various experiences to broaden your perspective and develop your imagination. I also expect that you will be tenacious and not give up easily, even when you face difficulty. I myself have undergone countless failures and regrettable errors in experiments and surveys. However, from these bitter experiences I have learned valuable lessons, which helped me get to where I am now. Please be constructive and make your best efforts towards anything you want to achieve.”
 
Takeshi Tomiyama
Associate Professor
Laboratory of Fish Biology and Fisheries

April 2001 – May 2011　Researcher, Fukushima Prefectural Fisheries Experimental Station Researcher, Fukushima Prefectural Fisheries Experimental Station　Staff member, Fisheries Division, Fukushima Prefectural Government
October 2012 – March 2019　Associate Professor of School of Applied Biological Science, Hiroshima University
April 2019 –　Associate Professor, Graduate School of Integrated Sciences for Life, Hiroshima University

Posted on Sep 15, 2020