NOTES TO FACULTY

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.

Tips on How to Use This Issue

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 20^th 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.

Discussion questions:

Barange’s main point is that development of sustainable fishing practices requires a better understanding of the causes for long-term scale changes in marine species. However, it appears to be quite difficult for people involved in fisheries (both fishermen and managers) to think about fisheries over the long term. What are some reasons for this?
Figure 1 shows changes in anchovy abundance off the coast of California from the years 280-2000. Recent fisheries data are from reported fish catches; that is clearly not the case here. What is the basis for the data in Figure 1? How are these data collected? How reliable would you think these data are? How might you assess their reliability?
Both Figures 2 and 4 show dramatic changes in fisheries catches over the scale of decades throughout the world. The author of this paper cites evidence that these marine population shifts are due to changes in atmospheric circulation (wind) and consequently in coastal water temperature. What does this mean in regard to our ability to effectively regulate marine fisheries?
In Figure 6, fish diversity in very different places in the world (the Gulf of Thailand and Georges Bank off the northeast U.S. coast) responded similarly to over-fishing. In both cases, fish diversity increased during early years of the fishery and then dramatically decreased several decades later (H is an index of diversity). Why might the diversity of fish caught at first increase as more fish were caught in the 1960s-1970s? Why did the diversity of caught fish then decrease?
The diversity data in Figure 6 are evidence of a phenomenon called “fishing down the food chain.” Explain.

Additional activities:

As homework assignment students could figure out what “Abundance Index” means by finding and reading the referenced article by Baumgartner et al. This would help them recognize the value of references and learn that they can work through uncertainties like this on their own.
Students could go to a local seafood market, get lists of fish for sale, and investigate where they were likely caught and their trophic status. In locations with local fisheries, students could investigate the fishery directly. Both activities would make more real the idea of trophic levels.

RESOURCES

http://www.habitatmedia.org/EOEN/index.html
(Habitat Media: includes 2 minute trailer for the video “Empty Oceans, Empty Nets.”)
http://oceanworld.tamu.edu/students/fisheries/salmon_weather/Annsdoc.html
(Paper by Ann Gargett, Institute of Ocean Sciences, BC, called “Why would salmon care about the weather?” Includes 7 high quality figures you can use in class.)
http://msnbc.msn.com/id/3077415/
(Review of Aug. 14, 2003 Science article documenting long term human effects on coral reefs.)
http://www.fisheries.ubc.ca/members/dpauly/
(Includes downloads of articles on overfishing by D. Pauly.)

Presentations and PDFs by Manuel Barange

<top>