For Baltic Sea pike, timing is everything – especially when it comes to assuring reproductive success and even prolonging life. That's the word from researchers at Linnaeus University who spent the last six years studying spawning patterns of over 2,000 marked pike. Since a single pike can live for up to 15 years, researchers were given a rare opportunity to thoroughly observe repeated migratory patterns among individual fish.   

Pike are widely-distributed predatory fish that breed annually after maturing. They generally have long, dark green bodies with yellow spots on their sides. In the Baltic Sea, many individual pike from different home streams coexist for most of their lifetimes. However, when it comes to spawning season, they instinctively migrate back to the streams where they were born. Pike reproduce in shallow waters during spring (March-May) and in water temperatures ranging from 4 to 14 degrees Celsius, according to the study.

Animals often interpret environmental cues to decide when they should start their annual migrations and pike are no different. But researcher noted that body size and gender impact migratory outcomes. Males, for instance, arrive home before females, and larger males arrive sooner than smaller ones, which makes it tougher for the smaller ones to reproduce. Over time – with age and experience – pike are able to fine-tune their journeys and schedule their departure times in accordance with optimal conditions for mating, offspring birth and to ensure their own survival.

"Results show that individual migratory timing is consistent across years and that arriving too early or too late increases mortality. Individuals also continuously fine-tune their timing with increased experience, a behavior that is similar to the trial-and-error method used by many mammals but previously not shown for fish," Dr. Petter Tibblin, lead author of the study, explained in a news release. 

Flexibility among the fish's timing habits and its relation to increased fitness was also observed during the study. 

"We demonstrate that there is variation among individuals in the degree of flexibility (adjustments in migratory timing across years) and further establish that greater flexibility at early reproductive events improves life expectancy," Professor Anders Forsman, co-author of the study, said in a statement.

The study was recently published in the British Ecological Society's Journal of Animal Ecology

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