Fish are getting smaller and that may be a problem. Why?

In oceans worldwide, a puzzling trend is emerging: fish are getting smaller in size, posing significant concerns for ecosystems and human populations reliant on seafood. Despite this observable phenomenon, the exact reasons behind this shrinkage remain elusive, stirring debates among scientists and fisheries experts alike.

Recent analyses indicate a widespread reduction in the average body size of marine fish populations sampled from 1960 to 2020, reported Washington Post. This trend extends from salmon populations near the Arctic Circle to skate in the Atlantic Ocean.

Nearly three-fourths of marine fish populations studied have experienced a decrease in size, raising alarms about the sustainability of seafood as a vital protein source for over 3 billion people globally.

Who is to blame?

Two primary culprits emerge as potential drivers behind the shrinking fish phenomenon: overfishing and human-induced climate change. The relentless pursuit of large fish by recreational and commercial fisheries leaves smaller individuals behind.

Additionally, rising ocean temperatures due to climate change pose a threat to marine life, impacting their size and, consequently, the global food supply chain.

One prevalent theory attributes the size reduction in fish to the temperature-size rule. According to this theory, warmer waters lead to increased oxygen demand in fish, potentially limiting their growth. However, recent experiments challenge this notion, suggesting that factors beyond gill capacity may contribute to fish shrinkage.

What do the experts have to say?

Scientists are striving to unravel the intricate mechanisms underlying fish shrinkage in response to environmental stressors. Lisa Komoroske, a conservation biologist at the University of Massachusetts, emphasises the urgency of this inquiry, noting the fundamental question remains unanswered despite years of research.

Daniel Pauly, a prominent marine biologist, stands by the gill oxygen limitation theory, arguing that gill capacity restricts fish growth in warmer waters. Despite conflicting interpretations, researchers like Komoroske emphasise the collaborative nature of scientific inquiry, aiming to refine theories through rigorous experimentation.

“We’re blinded to fixing problems if we don’t understand what’s causing them in the first place,” Timothy Clark, a professor at Deakin University in Australia who has conducted similar experiments on fish and temperature told Washington Post.

What will the impact be?

The shrinking fish phenomenon has far-reaching consequences for ecosystems and economies. Smaller fish sizes could disrupt predator-prey dynamics, alter reproductive strategies, and impact market prices for seafood products.

Understanding the drivers of fish shrinkage is crucial for effective fisheries management and aquaculture practices. Without addressing the root causes, efforts to mitigate overfishing and sustainably harvest marine resources may fall short, exacerbating food security challenges.

“It’s a problem for the fishery,” Art Bloom, a salmon fisherman in Alaska’s Bristol Bay with more than three decades of experience told Washington Post. “They don’t present as well in the supermarket.” During his career, he has had to switch from using nets with 5¼ inch openings to ones with 4¾ inch openings as the salmon he caught got smaller.

Smaller fish produce less offspring than larger fish and therefore less productive fish populations. Fishermen will catch smaller fish. This will in turn reduce the global fish supply. This adds to the problems fisheries face from overfishing, pollution, and habitat degradation. In addition to warming, climate change makes the oceans more acidic.

Despite these challenges, some species demonstrate resilience, highlighting the complex nature of ecosystem responses to environmental changes.

Inês Martins, an ecologist at the University of York in England, observed that nearly three-fourths of marine fish were diminishing in size. However, she noted that despite this trend, many of the same species are experiencing an increase in abundance, even as their average body sizes decrease.

With inputs from agencies