How overfishing of Herring in Norway dramatically changed migration behavior when too many old fish are caught

Amazing stuff!

"Herring had a spawning ‘culture.’ Overfishing obliterated it

For more than a century, the world’s biggest stock of the oily, nutritious herring has migrated annually to spawn in the same waters off southern Norway. But in 2021 only a few fish arrived, leaving boat crews with empty nets and pressing questions. ...

Excessive harvests in prior years eliminated “cultural” knowledge passed down from older generations of herring, so that younger fish didn’t find their way to the traditional spawning grounds.

Adult herring spend the winter in Norway’s uppermost fjords, then swim as far as 1300 kilometers down the coast to Møre to reproduce. The researchers noticed that after 2020 most young herring were no longer spawning near Møre. Instead, they had stopped short on their southbound journey, near Lofoten, which is 800 kilometers away. ...

Without older fish as guides, the younger ones stopped halfway down the coast to spawn in Lofoten. And now, with these fish returning there year after year, the new pattern seems established. ..."

From the abstract:

"Entrainment is a process in schooling migratory fish whereby routes to suitable habitats are transferred from repeat spawners to recruits over generations through social learning.

Selective fisheries targeting older fish may therefore result in collective memory loss and disrupted migration culture.

The world’s largest herring (Clupea harengus) population has traditionally migrated up to 1,300 km southward from wintering areas in northern Norwegian waters to spawn at the west coast. This conservative strategy is proposed to be a trade-off between high energetic swimming costs and enhanced larval survival under improved growth conditions. 

Here an analysis of extensive data from fisheries, scientific surveys and tagging experiments demonstrates an abrupt approximately 800-km poleward shift in main spawning.

The new migration was established by a large cohort recruiting when the abundance of older fish was critically low due to age-selective fisheries. 

The threshold of memory required for cultural transfer was probably not met—a situation that was further exacerbated by reduced spatiotemporal overlap between older fish and recruits driven by migration constraints and climate change.

Finally, a minority of survivors from older generations adopted the migration culture from the recruits instead of the historically opposite.

This may have profound consequences for production and coastal ecology, challenging the management of migratory schooling fish."

ScienceAdviser

Herring spawned poleward following fishery-induced collective memory loss (open access)

Fig. 1: Migration strategies of herring in a dynamic environment.

Dancing sea turtles reveal how animals navigate magnetic fields for migration over thousands of kilometers and to find food

Amazing stuff!

"... But a new study has presented the first evidence that loggerhead turtles (Caretta caretta) use magnetic fields as a compass to determine direction and also use it to determine their geographical location.

There’s a little dance involved, too.

Sea turtles are extraordinary navigators, able to trace unseen pathways across thousands of kilometres of the ocean and return to the same feeding sites migration after migration. ..."

"...  sea turtles returning to the same feeding sites again and again throughout their lifetimes — despite traveling up to 10,000 miles across the planet. ... hypothesized that these turtles used Earth’s magnetic field to memorize specific geographic areas that they associated with food ...

team conditioned loggerhead turtles to magnetic fields replicating those that exist in various oceanic locations, repeatedly feeding the turtles in some magnetic fields while not feeding them in others. When later exposed to the fields in which they were fed, the turtles exhibited “turtle dancing behavior,” indicating that they associated that specific magnetic signature with food. ..."

From the abstract:

"Growing evidence indicates that migratory animals exploit the magnetic field of the Earth for navigation, both as a compass to determine direction and as a map to determine geographical position. It has long been proposed that, to navigate using a magnetic map, animals must learn the magnetic coordinates of the destination, yet the pivotal hypothesis that animals can learn magnetic signatures of geographical areas has, to our knowledge, yet to be tested.

Here we report that an iconic navigating species, the loggerhead turtle (Caretta caretta), can learn such information. When fed repeatedly in magnetic fields replicating those that exist in particular oceanic locations, juvenile turtles learned to distinguish magnetic fields in which they encountered food from magnetic fields that exist elsewhere, an ability that might underlie foraging site fidelity. Conditioned responses in this new magnetic map assay were unaffected by radiofrequency oscillating magnetic fields, a treatment expected to disrupt radical-pair-based chemical magnetoreception, suggesting that the magnetic map sense of the turtle does not rely on this mechanism.

By contrast, orientation behaviour that required use of the magnetic compass was disrupted by radiofrequency oscillating magnetic fields. The findings provide evidence that two different mechanisms of magnetoreception underlie the magnetic map and magnetic compass in sea turtles."

Dancing turtles reveal how animals navigate magnetic fields

Dancing turtles unlock scientific discovery (original news release)

Learned magnetic map cues and two mechanisms of magnetoreception in turtles (no public access)

Songbirds may 'talk' to other bird species of similar kind as they migrate during the night

Amazing stuff!

"A study of thousands of hours of flight calls suggests that songbirds may be forming social connections with other species as they migrate, possibly even exchanging information about the journey. ...

Last year, the co-authors found that birds across northeastern North America “buddy up” with other species at stopover sites during migration. Their new findings suggest that social relationships between songbird species are also important during migratory flights. ..."

"Songbirds, such as warblers, thrushes, orioles and sparrows, tend to migrate at night when the air is calmer, cooler and there are fewer predators lurking about. But the songbird flight paths may not be entirely instinctive, according to new research. Evidence from over 18,300 hours of recorded flight calls suggests songbirds may 'talk' to other species as they migrate, forming social connections and, perhaps, exchanging information about the journey. ..."

From the highlights and abstract:

"Highlights

• Migrating songbirds associate socially with other species during nighttime flights

• Associations are stronger among species with similar calls and flight speeds

• Social information could play an underrecognized role in nocturnal bird migration

Summary

An emerging frontier in ecology explores how organisms integrate social information into movement behavior and the extent to which information exchange occurs across species boundaries.

Most migratory landbirds are thought to undertake nocturnal migratory flights independently, guided by endogenous programs and individual experience.

Little research has addressed the potential for social information exchange aloft during nocturnal migration, but social influences that aid navigation, orientation, or survival could be valuable during high-risk migration periods.

We captured audio of >18,000 h of nocturnal bird migration and used deep learning to extract >175,000 in-flight vocalizations of 27 species of North American landbirds. We used vocalizations to test whether migrating birds distribute non-randomly relative to other species in flight, accounting for migration phenology, geography, and other non-social factors.

We found that migrants engaged in distinct associations with an average of 2.7 ± 1.9 SD other species. Social associations were stronger among species with similar wing morphologies and vocalizations. These results suggest that vocal signals maintain in-flight associations that are structured by flight speed and behavior.

For small-bodied and short-lived bird species, transient social associations could play an important role in migratory decision-making by supplementing endogenous or experiential information sources.

This research provides the first quantitative evidence of interspecific social associations during nocturnal bird migration, supporting recent calls to rethink songbird migration with a social lens. Substantial recent declines in bird populations may diminish the frequency and strength of social associations during migration, with currently unknown consequences for populations."

Songbirds may 'talk' to other species as they migrate

Songbirds socialize on the wing during migration, new study says (original news release)

Social associations across species during nocturnal bird migration (no public access)

Why going 'lights out' in Texas could help migrating birds as cold front passes by. Really!

What a silly idea from single minded do gooders! 

Birds are not stupid! Birds have lived with city lights for many decades now!

"Texas plays an important role along the migratory path for birds. Going “lights out” could help birds on their long journey, especially during cold fronts. ..."

Texans asked to go 'lights out' as bird migration season peaks