Vertical movements of coastal pike (Esox lucius)—On the role of sun basking

Abstract

Knowledge of patterns and drivers of the spatiotemporal distribution of top predatory fish is key to understand ecological dynamics and to successful management. Here, we integrated field and laboratory approaches to study vertical movements of pike (Esox lucius) in relation to season, light regimes and body temperature. We tagged pike from the Baltic Sea with data storage tags during spawning migration and retrieved them during migration the following years to obtain high‐resolution data from full year of movements. The results showed seasonal and diel patterns of activity and body temperature that conformed to distinct patterns of crepuscular activity and diel vertical migrations. The latter manifested as two different patterns, either a stationary phase in the surface water during day followed by night‐time in deeper water or vice versa. The occurrence of these two behaviours varied among individuals and within individuals among seasons. Diel vertical migration has previously not been described for this shallow‐dwelling species, but was a common and consistent behaviour among individuals in this study. We suggest that the function of the daytime surface behaviour in pike is to increase body temperature through sun basking. This thermoregulatory role of surfacing was supported by the laboratory study where individuals sought the surface layer, exposed themselves to infrared light and thereby attained body temperatures in excess of ambient water. These results support sun basking as a mechanism for heat gain and further suggest that access to sunlight in the surface layer could be an important driver of vertical migrations.

Ecological and Evolutionary Consequences of Environmental Change and Management Actions for Migrating Fish

“…Some species instead utilize the near surface waters during the daytime and return to bottom layers in the evenings to feed. Other proximate triggers of vertical migrations include light intensity and water temperature, and ultimate drivers encompass bioenergetics efficiency, foraging opportunities and predator avoidance (Mehner, 2012;Nordahl et al, 2019). Horizontal fish migrations include movements between shallow, inshore littoral areas and offshore pelagic areas performed by fishes in larger lakes.…”

“…Migrating between water bodies also offers a means to buffer against changing external physicochemical conditions, maintain internal homeostasis and regulate body temperature to conserve energy expenditure or to maximize aspects of performance (Reynolds and Casterlin, 1980;Nakamura et al, 2015;Pépino et al, 2015;Nordahl et al, 2018Nordahl et al, , 2019. Observations of diel horizontal migrations in juvenile coho salmon (Oncorhynchus kisutch) indicate that individuals that moved to warmer habitats after feeding processed their food more quickly and grew faster compared with individuals that adopted other behaviors (Armstrong et al, 2013).…”

“…Observations of diel horizontal migrations in juvenile coho salmon (Oncorhynchus kisutch) indicate that individuals that moved to warmer habitats after feeding processed their food more quickly and grew faster compared with individuals that adopted other behaviors (Armstrong et al, 2013). A behavioral study of pike has shown that individuals surface during daytime and seek out deeper waters during night in the summer, whereas the direction is reversed during winter, thus pointing to a possible role of sun basking (Nordahl, 2018;Nordahl et al, 2019).…”

“…A recent study of carp (Cyprinus carpio) demonstrates that sun basking close to the surface during sunny conditions enables fish to increase their body temperature above that of the ambient water, and further indicates that the temperature excess gained by basking enabled the fish to grow faster , thereby putting the individual in a favorable situation compared to those not expressing this behavior. The discovery that sun basking can offer thermoregulatory benefits even in aquatic environments (Nordahl et al, , 2019 is likely to spur future research and may ultimately change the way we think about fish ecology and evolution, in particular with regards to behaviors and migrations.…”

“…Some species of fish [such as tunas (Scombroidei) and sharks (Lamniformes) (Dickson and Graham, 2004), and the opah (Lampris guttatus) (Wegner et al, 2015)] can evade the temperature boundaries of ambient water by generating and conserving metabolic heat internally, but this capacity is restricted to about 0.1% of the known fish species (Dickson and Graham, 2004). Most fish instead rely on external heat from the environment and on behavioral thermoregulation, including both larger scale migrations between colder and warmer environments and smaller scale vertical movements involved in sun basking and when fish take advantage of temperature differences among strata in stratified lakes and oceans, to regulate their internal temperature (May, 1979;Reynolds and Casterlin, 1980;Hertz et al, 1993;Gillooly et al, 2002;Mehner, 2012;Ma et al, 2018;Nordahl et al, 2018Nordahl et al, , 2019.…”