Is Climate Change Interfering With Migration? Scientists Warn Of Grim Future

Migration is one of nature's best strategies for survival. Countless species depend on precise timing to align their journey with food availability, breeding options, and perfect weather to raise their young. This timing is known as phenology, and it took millennia to evolve. It was shaped by seasonal cues such as temperatures, rainfall, and the length of the day. Today, climate change is disrupting the signals various species have followed for centuries. Global temperatures rise and weather patterns shift. Many plants flower earlier, insects emerge sooner, and habitats transform in ways that no longer match the migratory schedule of various species. Many birds, for example, rely on synchronizing their migration with peak insect abundance. Even a small mismatch can mean food shortages during the critical breeding period. These disruptions ripple through ecosystems, affecting not only the migratory species but also the communities depending on them.

Understanding how climate change interferes with migration phenology is essential for predicting ecological outcomes. Recent studies, such as Murphy Jr. et al, show that fish and marine mammals face similar problems. Increasing temperatures of the oceans alter the currents and prey distribution. Marine migration is also being studied, and it raises questions of future ocean biodiversity.

Phenological mismatch is continuously being observed and documented in terrestrial systems, but its marine counterpart remains poorly understood. The signs of disruption are evident. In the U.S. Mid-Atlantic, scientists have begun observing how striped bass and its key prey, the Atlantic menhaden, are behaving differently as oceans warm. Historically, striped bass spawn in estuaries such as Chesapeake Bay and the Hudson River. The successful growth of their young depends on prey such as menhaden being plentiful at the predictable time. The warming of the waters is influencing when and where this prey will show up. In some cases, their abundance is significantly reduced. As a result, the striped bass is now relying on aggregated baitfish off the coasts of New Jersey and New York during the fall. The traditional mix of species the striped bass used to feed on is no longer available to them.

The spawning, migration, feeding, and growth cycle of this predator fish and its prey are out of sync. The striped bass was forced to change its diet, and the lower recruitment (fewer juveniles surviving) has already been observed in spawning estuaries such as Chesapeake Bay, despite the apparent abundance of adult bass offshore.

The primary issue lies in understanding the multispecies phenological mismatches in marine systems. It received far less attention than the single-species timing shifts. While we concentrate on observing how one species shifts its spawning and migration, we fail to understand the relation that's shifting between prey and predator. On a larger scale, this might lead to the disruption of fishing networks and the collapse of marine food sources.

Phenological mismatches strike at the foundation of marine ecosystems. When predators and prey fall out of sync, the entire food chain is destroyed. For striped bass, reduced access to energy-rich prey means weaker spawning success and a declining population. This effect reaches out to recreational fisheries, coastal economies, and cultural traditions tied to these species. Similar mismatch threatens seabirds, marine mammals, and commercial fish stocks worldwide.

New tracking technologies and satellite monitoring are helping scientists track fish movement in greater detail. Climate models are being refined to anticipate where and when the mismatches are most likely to occur. Even the long-term data programs, such as the Northeast Fisheries Science Center surveys in the U.S., build a clearer picture of shifting ocean phenology. Yet all this is not enough to tackle the challenge. Unlike on land, the oceans hide much greater complexity. Changes are harder to detect and observe, let alone predict.

Acknowledging that the problem exists is the first step forward. Investing in research, adaptive fisheries management, and international collaboration will help us understand, and maybe even mitigate, the cascading impact of warming, out-of-sync oceans.