American Oceans

The Shocking Phenomenon of Zombie Salmon

a dead salmon in a river

Zombie salmon, a term perhaps as intriguing as it is macabre, encapsulates the remarkable life cycle of Pacific salmon. These fish embark on a one-way journey from the ocean to their natal freshwater rivers to spawn.

Unlike other migratory species, Pacific salmon’s reproductive endeavor doubles as a poignant finale to their lives. After they lay eggs, they begin to decay, which has earned them the moniker of ‘zombie’ given their deteriorated state while still managing to fulfill their biological imperative.

The Phenomenon of Zombie Salmon

closeup of a dead salmon

The concept of “zombie salmon” refers to the transformation of coho salmon during their final life phase, marked by physical deterioration as they approach spawning, which gives them an appearance akin to the living dead.

Understanding Zombie Salmon

Zombie salmon are not creatures of myth but rather a biological reality for species of salmon like the coho when they engage in their last act of life: reproduction. During this period, the fish undergo significant physical changes: their skin breaks down and takes on a pale, at times mold-like appearance, and their teeth may become more fearsome-looking as their bodies are put under extreme stress.

Lifecycle and Reproduction

Lifecycle:

  • Stage 1: Egg
  • Stage 2: Fry
  • Stage 3: Smolt
  • Stage 4: Adult
  • Stage 5: Spawning phase

As salmon enter the spawning phase, they cease eating and invest all their energy into the journey upstream. This migration, driven by an innate biological imperative, takes a heavy toll on their bodies. Muscles deteriorate, the immune system weakens, and internal organs begin to decay, contributing to the zombie-like appearance. Their eyeballs may cloud over, and even their skin rots as they stop feeding and start to decay while still alive.

Environmental Impact

Zombie salmon play a crucial role in their ecosystem. As they migrate upstream and eventually die after spawning, their decaying bodies release nutrients into the water, providing food for bacteria and other organisms.

This process supports the birth of new salmon by fertilizing the water, but it also means that during this stage, salmon are more susceptible to environmental stressors and any chemicals in the water – a subject of concern for scientists investigating stormwater exposure effects on salmon.

Ecosystem Interactions and the Role of Zombie Salmon

Zombie salmon, a term sometimes used to describe Pacific salmon that continue to persist in a state of decay, play a surprisingly integral role in aquatic and terrestrial ecosystems, particularly in regions like the Pacific Northwest and Alaska.

These creatures, spent from the effort of upstream migrations to freshwater spawning grounds, contribute to nutrient cycling, form key components of the food web, and interact with various wildlife and human communities.

Nutrient Cycling and Decomposition

Salmon, after completing their life cycle, bring essential marine nutrients to freshwater and terrestrial ecosystems. As they decay, a process often referred to as salmon graveyards, their bodies release nutrients that enrich the aquatic grazers, such as insects and amphipods, and help sustain the surrounding flora.

During spring floods, the nutrients can spread, reducing nutrient deficit in various parts of the ecosystem. This decomposition underpins the health of both forested areas like the woods and meadows of Alaska and freshwater habitats by providing shade and fallen trees that are critical for the survival of juvenile salmon.

Food Web Contributions

The rotting carcasses of sockeye and chinook salmon are a crucial meal for a broad range of creatures. Bears, including those of Kodiak Island, rely on these fish as a significant energy source, often leaving remnants that support scavengers and fly larvae. Birds and mammals benefit from the salmon directly, while smaller entities like caddisflies and maggots feast on the decomposing remains.

Such interactions demonstrate the salmon’s pivotal role in maintaining the balance of complex food webs extending from the watery depths to the battle-scarred forests and meadows.

Human and Wildlife Interactions

Zombie salmon impact human activities and wildlife in multiple ways. Fisherfolk and organizations like the U.S. Fish and Wildlife Service monitor these salmon to ensure migrations remain sustainable and to assess the health of ecosystems. On social platforms like Facebook, these entities sometimes share information about the conditions of these fish, which have succumbed to infections and immunosuppression after reproduction, provoking discussions on whether they are safe to eat when they appear moldy and spent.

Furthermore, decomposing salmon attract feathered scavengers and provide an environment for flies like the beaked scavengers of the Buskin River and Uganik River to lay eggs, persisting in a cycle that revolves around the salmon’s substantial contribution to the ecosystem.

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