Historical datasets can be true treasures in biological analyses because of providing information about systems that do not exist today, but working with those can also sometimes be frustrating due to a lot of unknowns.
Both these “sides of the coin” were present in our analyses of historical salmon weir catches recorded during 1870-1902. The data originated from rivers Oulujoki, Iijoki and Torniojoki, former two of which no longer sustain natural salmon population due to hydroelectricity. However, one hundred years ago situation was quite opposite: the populations were large and healthy even though the annual salmon catches were also substantial (from hundreds to thousands of salmon per river). Moreover, rivers were running free and populations were free from genetic disturbances such as stocking, so that the catch records provide rarely available information about variation in the timing of river entry in natural Atlantic salmon population.
New analyses of the old data revealed that even though there were some annual variations in the timing of river entry, differences between the rivers were substantial and very consistent. Assigning among year and among river variations to environmental variables was then a harder task due to lack of environmental and hydromorphological data from the old days. However, no matter what the source of the variation is, the message emerging from the analyses is clear: fixed regional opening date for coastal salmon fisheries can lead to uneven exploitation of different salmon populations. Today, in the Finnish coast of the Baltic Sea salmon fisheries are still managed in this manner.
Kuparinen A. & J. Merilä (2009) Variation in the timing of river entry of Atlantic salmon (Salmo salar L.) in the Baltic. Current Zoology 55: 342 – 349
Kuparinen A. & J. Merilä (2009) Sata vuotta tutkimuksia lohien vaelluksesta Pohjanlahden jokiin. Luonnon Tutkija 3: 108-109