The emphasis in TIEE Issues is use of figures and tables for discussion and other types of student-active teaching and learning. These notes will give you ideas about using the figures in this paper in your ecology class. The Student-Active Teaching table will introduce you to a variety of approaches you can use in your class to actively engage your students. To see an essay on leading good discussions, go to Guided Class Discussions.
Focus on some aspect of this Issue (inter-decadal changes) and select a figure or discussion question dealing with this point. Then select a teaching approach. The table of Student-Active Approaches includes suggestions for all class sizes.
Although population change on different time scales, from interannual to interdecadal and longer, is an important aspect of ecology, it is often difficult to interest students in this topic. Barange discusses such variations in marine species in the context of sustainable fisheries. This practical focus may be an effective way to engage students in discussion about long term scale population shifts and their possible causes.
Barange presents remarkable data on temporal changes in marine species composition. Fig. 1 on anchovy abundance from the years 280-2000 off California shows very dramatic changes with time. One of the questions below prompts discussion about the nature of this evidence: why is it available and how do scientists collect it. One problem with this figure for students is that calculation of “abundance index” is not described (see note below).
Fig. 2 shows catch of some major commercial fisheries in the 20th century, again demonstrating dramatic (in this case inter-decadal) species shifts. Students may assume that over-fishing causes fluctuations like these; the idea that changes in atmospheric circulation (wind) can also result in large population shifts will bring home the idea that informed management of fisheries requires much better understanding of natural cycles.
Fig. 4 is even more dramatic. The species composition of catches in bottom trawls off the Alaskan coast shifted from largely invertebrates in the 1970s to finfish (salmon) in the 1980s. Barange calls this a “regime shift” and attributes it to inter-decadal changes in water temperature. Again, it is clear that we cannot manage our fisheries unless we better understand these ecosystem-level interactions.
The focus of Fig. 6 is overfishing. It is intriguing that both the Gulf of Thailand and Georges Bank show the same pattern: fish diversity increases during early years of the fishery and then dramatically decreases several decades later. Students from the northeast may be familiar with the crash of the cod (and other) fisheries off the coasts of Maine, Nova Scotia, and Newfoundland. (However, as a marine ecologist I am surprised how few students know anything about the cod crash, which is on the scale of the buffalo decimation in the American west). Barange also makes the point that the Gulf of Thailand and Georges Bank has not returned to prior high diversity values, despite lower catches in the early 1990s.
Presentations and PDFs by Manuel Barange