I was reminded this week of the importance considering historical events when trying to understand long-term ecological changes. One of the surprising results from our analysis of the amazing long-term Baikal data set has been that many zooplankton species are shifting to shallower positions in the water column through time (see my previous post). There could be many explanations for this, but we think that changes in fish predation could be particularly important. Zooplankton typically migrate to deeper water during the daylight hours to avoid predation by planktivorous (plankton-eating) fish. If fish populations have changed through time then perhaps zooplankton have altered their vertical migration behaviour? Although we do not have long-term data on fish populations in Lake Baikal, we might be able to gain some insight into changes in the abundance of fish by looking at the history of fishing and fisheries management in Lake Baikal. Over the past week we have contacted a historian that has worked on this issue (Dr. Nicholas Breyfogle) and have done some of our own reading on the subject.
In general, it seems that fish populations dropped dramatically in the 1940s with the demands of World War II and the rapidly expanding use of drift nets in the lake. The most precipitous decline occurred after the building of the Irkutsk Dam in the 1950s and the rise of the water levels in Baikal that reduced spawning grounds. Since the 1960s and 1970s there have been efforts to reduce the amount of fishing in the lake, with a ban being imposed on omul (Coregonus migratorius) fishing between 1969 and 1977. It also seems that most commercial fishing on Baikal was halted when the Soviet Union collapsed in 1991.
While we might not be able to directly link these events to changes in the plankton, it is important to consider them as we try to understand the long-term changes occurring in Baikal plankton communities. Over the last few decades historical ecology has grown into an exciting, dynamic field and our study of plankton depth changes in Baikal provides one more example of why ecologists should know their history!