Department Fish Ecology and Evolution

Cyprinid partial and differential migration

Of all the great spectacles of nature, animal migration is without doubt one of the most remarkable. It has fascinated mankind for thousands of years, with reports of migratory fishes seasonally moving in and out of the Black Sea being documented over twenty centuries ago. The study of migration continues to be a major focus of contemporary biological research, and we now know that migration is a ubiquitous feature in the life cycle of an extremely diverse range of animals, from microscopic crustaceans to large, sea-dwelling mammals.

When living in an environment where alternative habitats change their relative profitability either during the season, e.g. due to temperature changes or during an animal’s ontogeny, habitat shifts carried out through migration will often be an evolutionary superior strategy over residency. However, although analyses of changes in relative costs and benefits of different habitats may well predict the timing of migration of the average individual, it has rarely been applied to individual organisms, explaining why often only a part of a population migrates (partial migration), why individuals migrate at different times or to different locations (differential migration) or maybe most interestingly, why populations differ in their migration patterns (both partial- and differential migration).

Cyprinid fish often migrates from shallower lakes into streams during winter to escape predation risk during winter, where their growth rates are low due to low temperatures and where they therefore cannot profit from the higher food abundance in the lakes. However, most often only a part of the fish populations are migrating (i.e. partial migration) and among the migrants, timing, duration and destination of migration are different (i.e. differential migration). Since the cyprinid fish are often dominant species in the lake ecosystems with high ecological impact, their temporary absence from the lakes are affecting both lower trophic levels of the lake and resident top-predators. Hence, the study system offers a novel opportunity to study the interactions between differentiation in individual life history and ecosystem structure and dynamics.

Contact

Dr. Jakob Brodersen Tel. +41 58 765 2204 Send Mail

Funding and duration

Funding:         Swedish Research Council (VR), Formas; Danish National Fishing License Funds

Duration:       2003 - ongoing

Collaboration

The studies on partial migration of cyprinid fish are carried out in shallow lakes in Denmark and Southern Sweden in collaboration with the Danish Technical University (DTU-Aqua) and Lund University in Sweden.

Selected publications

Biomanipulating streams: a supplementary tool in lake restoration

Removal of cyprinid fish is a widely used biomanipulation tool to transform turbid shallow eutrophic lakes in north temperate regions into a clear water state. We here evaluate the removal of cyprinids from streams as a supplement to lake fishing. Since cyprinids often aggregate in high densities in lake inlet/outlet streams during winter migration, removal of fish in this space-confined habitat may be cost-efficient as compared to fish removal in the lake habitat. In two consecutive years, we annually removed up to 35% of the dominant cyprinids from an inlet stream to a lake and argue that this could easily be increased with a more targeted fishing effort. Concurrently, we monitored species- and length-specific variation in migration propensity, to explore how this relates to efficient fish removal. Smaller planktivores generally had a much higher migratory propensity than larger benthivores. Hence, stream fishing specifically targets species and size groups that are less efficiently controlled with traditional lake fishing methods. As a rule of thumb, stream fishing is most efficient when water temperature is 2–6°C. Prior to implementing fish removals from streams, the potential evolutionary consequences of the targeted removal of migratory phenotypes should be considered.
Skov, C.; Hansen, J. H.; Baktoft, H.; Brodersen, J.; Brönmark, C.; Hansson, L.-A.; Hulthén, K.; Chapman, B. B.; Nilsson, P. A. (2019) Biomanipulating streams: a supplementary tool in lake restoration, Hydrobiologia, 829(1), 205-216, doi:10.1007/s10750-018-3832-4, Institutional Repository

Species integrity enhanced by a predation cost to hybrids in the wild

Species integrity can be challenged, and even eroded, if closely related species can hybridize and produce fertile offspring of comparable fitness to that of parental species. The maintenance of newly diverged or closely related species therefore hinges on the establishment and effectiveness of pre- and/or post-zygotic reproductive barriers. Ecological selection, including predation, is often presumed to contribute to reduced hybrid fitness, but field evidence for a predation cost to hybridization remains elusive. Here we provide proof-of-concept for predation on hybrids being a postzygotic barrier to gene flow in the wild. Cyprinid fishes commonly produce fertile, viable hybrid offspring and therefore make excellent study organisms to investigate ecological costs to hybrids. We electronically tagged two freshwater cyprinid fish species (roach Rutilus rutilus and bream Abramis brama) and their hybrids in 2005. Tagged fish were returned to their lake of origin, exposing them to natural predation risk from apex avian predators (great cormorant, Phalacrocorax carbo). Scanning for regurgitated tags under cormorant roosts 3–4 years later identified cormorant-killed individual fish and allowed us to directly test for a predation cost to hybrids in the wild. Hybrid individuals were found significantly more susceptible to cormorant predation than individuals from either parental species. Such ecological selection against hybrids contributes to species integrity, and can enhance species diversification.
Nilsson, P. A.; Hulthén, K.; Chapman, B. B.; Hansson, L.-A.; Brodersen, J.; Baktoft, H.; Vinterstare, J.; Brönmark, C.; Skov, C. (2017) Species integrity enhanced by a predation cost to hybrids in the wild, Biology Letters, 13(7), 20170208 (4 pp.), doi:10.1098/rsbl.2017.0208, Institutional Repository

A predation cost to bold fish in the wild

Studies of predator-mediated selection on behaviour are critical for our understanding of the evolution and maintenance of behavioural diversity in natural populations. Consistent individual differences in prey behaviour, especially in the propensity to take risks ("boldness"), are widespread in the animal kingdom. Theory predicts that individual behavioural types differ in a cost-benefit trade-off where bolder individuals benefit from greater access to resources while paying higher predation-risk costs. However, explicitly linking predation events to individual behaviour under natural conditions is challenging and there is currently little data from the wild. We assayed individual behaviour and electronically tagged hundreds of fish (roach, Rutilus rutilus) before releasing them into their lake of origin, thereby exposing them to predation risk from avian apex predators (cormorants, Phalacrocorax carbo). Scanning for regurgitated tags at the cormorant roosting site provided data on individual predation events. We found that fish with higher boldness have a greater susceptibility to cormorant predation compared to relatively shy, risk-averse individuals. Our findings hereby provide unique and direct evidence of behavioural type-dependent predation vulnerability in the wild, i.e. that there is a predation cost to boldness, which is critical for our understanding of the evolution and maintenance of behavioural diversity in natural populations.
Hulthén, K.; Chapman, B. B.; Nilsson, P. A.; Hansson, L.-A.; Skov, C.; Brodersen, J.; Vinterstare, J.; Brönmark, C. (2017) A predation cost to bold fish in the wild, Scientific Reports, 7(1), 1239 (5 pp.), doi:10.1038/s41598-017-01270-w, Institutional Repository

Shape up or ship out: migratory behaviour predicts morphology across spatial scale in a freshwater fish

1. Migration is a widespread phenomenon, with powerful ecological and evolutionary consequences. Morphological adaptations to reduce the energetic costs associated with migratory transport are commonly documented for migratory species. However, few studies have investigated whether variation in body morphology can be explained by variation in migratory strategy within a species.
2. We address this question in roach Rutilus rutilus, a partially migratory freshwater fish that migrates from lakes into streams during winter. We both compare body shape between populations that differ in migratory opportunity (open vs. closed lakes), and between individuals from a single population that vary in migratory propensity (migrants and residents from a partially migratory population). Following hydrodynamic theory, we posit that migrants should have a more shallow body depth, to reduce the costs associated with migrating into streams with higher flow conditions than the lakes the residents occupy all year round.
3. We find evidence both across and within populations to support our prediction, with individuals from open lakes and migrants from the partially migratory population having a more slender, shallow-bodied morphology than fish from closed lakes and all-year residents.
4. Our data suggest that a shallow body morphology is beneficial to migratory individuals and our study is one of the first to link migratory strategy and intraspecific variation in body shape.
Chapman, B. B.; Hulthén, K.; Brönmark, C.; Nilsson, P. A.; Skov, C.; Hansson, L.-A.; Brodersen, J. (2015) Shape up or ship out: migratory behaviour predicts morphology across spatial scale in a freshwater fish, Journal of Animal Ecology, 84(5), 1187-1193, doi:10.1111/1365-2656.12374, Institutional Repository

Escaping peril: perceived predation risk affects migratory propensity

Although migratory plasticity is increasingly documented, the ecological drivers of plasticity are not well understood. Predation risk can influence migratory dynamics, but whether seasonal migrants can adjust their migratory behaviour according to perceived risk is unknown. We used electronic tags to record the migration of individual roach (Rutilus rutilus), a partially migratory fish, in the wild following exposure to manipulation of direct (predator presence/absence) and indirect (high/low roach density) perceived predation risk in experimental mesocosms. Following exposure, we released fish in their lake summer habitat and monitored individual migration to connected streams over an entire season. Individuals exposed to increased perceived direct predation risk (i.e. a live predator) showed a higher migratory propensity but no change in migratory timing, while indirect risk (i.e. roach density) affected timing but not propensity showing that elevated risk carried over to alter migratory behaviour in the wild. Our key finding demonstrates predator-driven migratory plasticity, highlighting the powerful role of predation risk for migratory decision-making and dynamics.
Hulthén, K.; Chapman, B. B.; Nilsson, P. A.; Vinterstare, J.; Hansson, L.-A.; Skov, C.; Brodersen, J.; Baktoft, H.; Brönmark, C. (2015) Escaping peril: perceived predation risk affects migratory propensity, Biology Letters, 11(8), 20150466 (4 pp.), doi:10.1098/rsbl.2015.0466, Institutional Repository

Fixed and flexible: coexistence of obligate and facultative migratory strategies in a freshwater fish

Migration is an important event in many animal life histories, but the degree to which individual animals participate in seasonal migrations often varies within populations. The powerful ecological and evolutionary consequences of such partial migration are now well documented, but the underlying mechanisms are still heavily debated. One potential mechanism of partial migration is between-individual variation in body condition, where animals in poor condition cannot pay the costs of migration and hence adopt a resident strategy. However, underlying intrinsic traits may overrule such environmental influence, dictating individual consistency in migratory patterns. Unfortunately, field tests of individual consistency compared to the importance of individual condition on migratory propensity are rare. Here we analyse 6 years of field data on roach migration, gathered by tagging almost 3000 individual fish and monitoring their seasonal migrations over extended periods of time. Our aims were to provide a field test of the role of condition in wild fish for migratory decisions, and also to assess individual consistency in migratory tendency. Our analyses reveal that (1) migratory strategy, in terms of migration/residency, is highly consistent within individuals over time and (2) there is a positive relationship between condition and the probability of migration, but only in individuals that adopt a migratory strategy at some point during their lives. However, life-long residents do not differ in condition to migrants, hence body condition is only a good predictor of migratory tendency in fish with migratory phenotypes and not a more general determinant of migratory tendency for the population. As resident individuals can achieve very high body condition and still remain resident, we suggest that our data provides some of the first field evidence to show that both facultative and obligate strategies can co-exist within populations of migratory animals.
Brodersen, J.; Chapman, B. B.; Nilsson, P. A.; Skov, C.; Hansson, L.-A.; Brönmark, C. (2014) Fixed and flexible: coexistence of obligate and facultative migratory strategies in a freshwater fish, PLoS One, 9(3), e90294 (7 pp.), doi:10.1371/journal.pone.0090294, Institutional Repository