(Apologies for the long delay between posts)
Summer is turning to autumn here in Chignik Lake. The air is taking on a chill and the berries are starting to ripen. This also means that the rivers are low, the salmon are spawning, and the bears are feeding on the salmon in the shallow water.
The combination of salmon dying after spawning and being preyed upon by bears results in the banks of the rivers and streams in the area to be covered in dead salmon carcasses. These carcasses, while pungent, can actually provide us with an incredible amount of data.
One research project we are working on is examining the otoliths (ear bones) of adult salmon to determine their habitat use as juveniles. This may sound like a strange way to look at juvenile habitat use. A more common approach to studying juvenile habitat use is to study, well, juvenile salmon and observe their behaviors. However, one limitation of this approach is that is nearly impossible to follow the ultimate fate of individual juveniles, particularly for organisms with low survival rates such as fish. When we sample otoliths from spawning salmon carcasses, we know their ultimate fate – they survived to reach the spawning grounds.
A cross-section of an otolith looks similar to a cross-section of a tree. Material is laid down as a fish grows, with periods of slow growth making dark rings (usually in winter, an annual marker). The otoliths also incorporate the chemistry of the water in which the fish resides. Thus, the otolith contains a record of the water chemistry throughout its life. If the water chemistry of different habitats varies in a consistent manner, we can determine what habitat an individual used throughout its life. For the Chignik system, Black Lake, Chignik Lake, and the marine environment have significantly different water chemistry and we can determine which habitat an individual was located in at any point during its life. From this, we can determine which habitats contribute most to the growth of individual fish.
We are currently drafting a manuscript describing the first round of results, which demonstrate that, even within a single population, there are a diversity of viable juvenile behavioral strategies that contribute to the spawning population.