Pacific Cod Hatch Earlier and Grow Less Due to Ocean Warming, Study

Pacific cod are one of the most important commercial fish species in Alaska, but they are also facing unprecedented challenges due to climate change.

Marine heat waves, which are periods of unusually high ocean temperatures, have been occurring more frequently and intensely in recent years, affecting the biology and ecology of Pacific cod and other marine organisms.

In this article, we will explore how Pacific cod are adapting to these changing conditions, and what implications this has for their future.

Adapting to the Heat

One of the most striking effects of marine heat waves on Pacific cod is that they trigger earlier reproduction and faster growth.

A new study from Oregon State University shows that Pacific cod in the Gulf of Alaska were hatching two to three weeks earlier during and after the 2014-2016 marine heat wave, and that this shift persisted even when ocean temperatures cooled in 2017 and 2018.

The researchers also found that the fish grew faster in their first year of life, reaching larger sizes than normal.

These changes are likely a result of the fish's ability to adjust their biological rhythms to match the environmental cues, such as temperature and day length, that signal the optimal time for spawning and feeding.

Jessica Miller, a professor at OSU's Coastal Oregon Marine Experiment Station and the senior author of the study, explains: "Pacific cod have a very flexible life history.

They can spawn over a wide range of temperatures and seasons, and they can grow very fast or very slow depending on the conditions they encounter."

However, this flexibility also comes with trade-offs. While early hatching and rapid growth may seem beneficial for increasing fish populations, they also entail higher risks of mortality and lower reproductive success.

For instance, early-hatched larvae may face a mismatch between their food requirements and the availability of plankton, their main prey. Faster-growing juveniles may also be more vulnerable to predators, diseases, and parasites.

Moreover, the long-term effects of these changes on the fish's survival and reproduction remain uncertain, as they may depend on how the fish cope with the stress of living in warmer waters.

A Delicate Balance Disturbed

Another consequence of marine heat waves on Pacific cod is that they disrupt the delicate balance of the marine ecosystem.

Pacific cod are not only prey for larger predators, such as halibut, salmon, and marine mammals, but also predators themselves, feeding on smaller fish, crustaceans, and mollusks.

Any changes in their abundance, distribution, and behavior can have cascading effects on the food web and the biodiversity of the ocean.

For example, a previous study by NOAA Fisheries found that the 2014-2016 marine heat wave caused a dramatic decline in the abundance of adult Pacific cod in the Gulf of Alaska, leading to the closure of the fishery in 2020 and a federal disaster declaration in 2022.

The researchers attributed this decline to several factors, including reduced food quality, increased metabolic demands, and increased predation.

They also suggested that the early hatching and faster growth of Pacific cod may have contributed to their poor condition and survival, as they may have exhausted their energy reserves and become more susceptible to stress.

On the other hand, the early hatching and faster growth of Pacific cod may also have positive effects on some aspects of the ecosystem.

For instance, they may provide more food for their predators, enhancing their growth and reproduction. They may also reduce the competition and predation pressure on other fish species, allowing them to thrive.

Furthermore, they may facilitate the adaptation and evolution of the Pacific cod population, as they may increase the genetic diversity and the selection pressure for traits that are favorable in a warming ocean.

Also Read: Cod in Arctic Have Multiple Predators; Will Climate Change Alter Food Chain?

A Future in Flux

The future of Pacific cod in a changing climate is uncertain, as it depends on many factors, such as the frequency and intensity of marine heat waves, the availability and quality of food, the interactions with other species, and the management and conservation measures.

While Pacific cod have shown remarkable resilience and adaptability in the face of marine heat waves, they may also face limits and thresholds that could compromise their survival and reproduction.

Therefore, it is crucial to monitor and understand how Pacific cod and other marine organisms respond to these environmental changes, and to develop strategies to mitigate and adapt to their impacts.

Pacific cod are not only a valuable resource for the economy and the culture of Alaska, but also a key component of the marine ecosystem.

By learning more about how they are adapting to a warming ocean, we can also learn more about the health and functioning of the ocean as a whole, and how we can protect and sustain it for the benefit of all.

Related article: Amazing Fish Ear Stones That Act Like Tree Rings and Record Their History