• Guðbjörg Ásta Ólafsdóttir

Movement patterns and environmental preferences of migratory and resident Atlantic cod juveniles

Recently the Icelandic Centre for Research funded a three-year research project at the University of Iceland Research Centre of the Westfjords to examine movement patterns and environmental preferences of migratory and resident Atlantic cod juveniles.

The Atlantic cod consists of divergent migratory ecotypes and populations of varying levels of migratory propensity. Although this variation is highly correlated with functional genes it is nevertheless to some extent plastic. In fact, current theory predicts that migratory propensity is likely to be correlated to a number of behavioral traits that effect ecology and resource use through smaller scale movement decisions and that the development of adult migratory tendencies may be either hindered or facilitated by early experiences.

There is currently very limited research on the behavior, environmental preferences and migratory propensity of Atlantic cod migratory ecotypes at early life stages. However, research on these factors is important to predict resource and habitat use of different migratory ecotypes of the Atlantic cod at the juvenile stage, thereby facilitating management and conservation and examine the phenotypic plasticity present in the Atlantic cod migratory system, which will for example influence how Atlantic cod respond to climate change.

Should I stay or should I go? When and why do juvenile cod leave near-shore waters to join feeding migrations?

The aim of the funded project is to test if juvenile cod of different migratory genotypes differ in behavior, environmental preferences, habitat use and distribution. We specifically will ask if juveniles of the migratory cod genotype share some of the same traits as adult cod of the same type, that is, forage more broadly, move more quickly, show bolder behavior and have preferences for cooler, high salinity waters. We then ask if juvenile behavior, environmental and habitat preferences diverge across ontogeny, that is, whether the migratory genotypes become more similar to their adult counterparts, and less similar to juveniles with resident genotypes, as they age. Finally, we intend to test if the correlation of migratory genotypes and migratory phenotypes is plastic, specifically, if behavior, movement, environmental preferences and migratory propensity changes for either genotype depending on early environmental temperature.

The project will involve following individually identifiable juvenile cod across development.

The high correlation of specific genes to migratory life-strategy in Atlantic cod make them an ideal species to examine partial migration at the juvenile stage, including how behavioral and movement variation diverges and how plastic these traits are. This may answer fundamental questions on the determinants and developmental canalization of partial migration.

However, as there is increasing anthropogenic pressure on near–shore environments it is crucial to understand and map ecological or behavioral divergence of Atlantic cod migratory genotypes at nursery grounds as this may allow conservation of the total genetic diversity in the Atlantic cod populations. This has relevance outside Iceland as Atlantic cod is of high economic importance across sub-arctic and temperate waters and among the most pressing current question in Atlantic cod management is how between group variation, importantly variation in migratory propensity, is partitioned geographically.

We are excited about getting started on this important project and hope that the work will contribute to Atlantic cod conservation and management.

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