Secor Explains Marine Fish Migration

Continuing the Natural Science and Mathematics (NS&M) Colloquium series this semester, David Secor came to St. Mary’s to discuss “Migration Ecology of Marine Fishes,” on Wednesday, Nov. 9 in Schaefer Hall.

Secor is a University of Maryland Regents Professor at the Chesapeake Biological Laboratory in Solomons, where he teaches graduate courses on fisheries ecology, science and management and serves on advisory panels to the Chesapeake Bay Program and various national fisheries commissions. However, Secor is currently on sabbatical at St. Mary’s to write a book about his research. The book, “Migration Ecology of Marine Fishes,” will be published by Johns Hopkins University Press, and is expected to be available some time in 2012.

Secor opened his lecture by talking about general migration patterns of marine fish. He explained that fish are very aligned with one another during migration. Within perception range, depending on range of other fish, fish will take various routes. A close range will avoid, a medium range will align, and fairly distant will attract, and a fish with no other route around will take a random route. He also explained the types of migration schools of fish travel in and compared them to that of humans and birds. The four types include the stationary school, swarm, mobile school, and torus.

He then explained that what drew him so much to the subject was his curiosity of what goes on under water. “The lives of marine fishes are so hidden,” he said. “We still don’t know a lot about the ocean’s ecology.”

Though research is difficult, one major discovery of the past decade has been about eels. Japanese scientists have discovered spawning locations of eels in the North Pacific Gyre, a discovery Secor described as “a lunar landing.”

Findings revealed that eels found way out near Samoa, in the middle of the Pacific Ocean, returned to Japan to spawn. This brought up the phenomenon of Philopatry, or natal homing. Philopatry is when species return to their own birthplace to breed, which can help maintain the adaptation of a population of fish to a specific area. Scientists found that spawning locations were restricted to a small geographical scale relative to the distribution of juveniles and adults due to migration.

The same findings apply to both the Bluefin Tuna in the North Atlantic Ocean and the Pacific Salmon in the North Pacific Ocean, in which more than 95 percent of both species demonstrate natal homing.

Scientists were able to discover this by examining fishes’ otoliths, or ear stones. These are structures in the inner ear of fish and all other vertebrates that can be used to find the origins of the fish and also the age of the fish.

The last part of the lecture focused on a more relevant topic to St. Mary’s: white perch, one of the most abundant fish in the Chesapeake Bay. He explained that many different populations of white perch are located in different areas of the bay, whether it be freshwater or brackish water, and they partially migrate annually to spawn. But is any one population of the fish more important than others? Why is it important to have life cycle diversity of these fish? The answer is that they are all important and that the diversity minimizes risk for the fish as a species.

Secor closed the discussion by elaborating on ways to minimize risk with species and protecting them, mainly by sustaining the environment and creating and maintaining fisheries.

Senior Evan Heck attended and enjoyed the lecture. “I’m especially interested in ecology with marine life. There’s a lot of new things, and we just don’t know a lot about it,” he said. “I thought it was a very interesting report. The speaker did a very good job.”

The next NS&M of the semester will be held on Wednesday, Nov. 16 in Schaefer Hall 106 at 4:40 p.m. The Colloquium will feature Cynthia Down from George Washington University, who will discuss “Novel Therapies against Mycobacterium Tuberculosis.” It is the final NS&M Colloquium of the series for the semester.

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