Image: Mostphotos/Lars Kastilan
Image: Mostphotos/Lars Kastilan
FEATURE Coastal dwelling pike are affected by changes in salinity, but appear to have an inherent ability to adapt. Different conditions during spawning engenders variation in populations, which can be crucial for the survival of coastal pike in the Baltic Sea.
What happens when salinity changes in the Baltic Sea, and the salinity gradient shifts southward? Will species living in one area disappear or move to other areas? …or can they live in changing environmental conditions? These issues are important for management of the future Baltic Sea, and are perhaps even more vital when concerning fish. Fish, in addition to being an important part of the ecosystem, are often sensitive to salinity concentrations. Salinity is one of the most important factors constraining the distribution of fish populations.
A stable environment generally leads to higher specialization among organisms, while changing conditions lead to greater genetic variation. This variation can be the key to survival in changing habitats. It is therefore crucial to consider the genetic variation that exists within populations in the management of species.
Pike have a natural inclination to swim back to the area where they hatch when they spawn. This means that populations that spawn in nearby waters can still be genetically distinct. It also gives rise to fish adapting to their local environments. For example, there may be differences in growth rate, body length and number of vertebrae. Not previously known was the question if they can differ even in terms of salinity tolerance, or if they have an inherent ability to cope with different salinity levels.
The pike has an ability to adapt to changing salinity conditions. Pike populations are studied in the Kalmar area in the southern parts of the Baltic.
ImageKristofer BergströmIn the Kalmar region in the southern Baltic Sea, a group of researchers studied coastal pike populations. Their research clearly shows that there is not one pike population but many local populations. Half of the pikes live in the coastal area’s brackish water, while about half of them seek freshwater to spawn. Of the pikes spawning in freshwater, some experience stable freshwater conditions, while others spawned in locations where salinity fluctuates.
By examining the ability of these populations to handle different salinity levels, the researchers were able to demonstrate an inherent ability of the pike to adapt to different conditions. The adaptation seems to take place at a very local level, so that pike that spawn in a stream differ genetically from the pike that spawn in a nearby stream along the coast. When the freshwater juveniles are about a month old, they migrate back to the coastal waters The adaptation thus occurs despite the fact that the fish live together in the same area for the rest of the time.
The pike in Kalmar Sound seem to have a sufficiently wide genetic variation regarding salinity tolerance to be able to withstand future changes in salinity, provided that this variation may remain in the future and form the basis for decisions on the management of the coastal area and its population of coastal pike.
The article has earlier been published in the EcoChange annual report 2018. The text is based on: