The Phenomenon of Shrinking Cod: How Overfishing Impacted the Baltic Sea's Largest Fish
The decrease in the size of the Baltic Sea shark, once a colossal creature, now resembling a serving plate.
Step aside, platters - the mighty Baltic cod, once towering over a meter in length, now fits snugly on a plate! Overfishing and the passage of time have played a significant role in both the dwindling population and diminishing size of these fish. According to researchers from the GEOMAR Helmholtz Centre for Ocean Research, the once colossal eastern Baltic cod is practically extinct.
Overfishing and the consequent removal of larger individuals have given an evolutionary edge to smaller, quicker maturing cod. The process, known as "fisheries-induced selection," is responsible for the human-induced evolution that attributes to the current state of the Baltic cod population.
Cod Genetics Adapt to Overfishing
To validate this hypothesis, researchers examined the earstones, or otoliths, of 152 cod caught between 1996 and 2019 in the Bornholm Basin. Otoliths offer a snapshot of a fish's growth: by analyzing the growth rings, similar to those found in trees, their age can be determined.
The research team observed that a particular set of gene variants linked to bodily growth displayed consistent signs of targeted selection over time in the cod population. Fish with genetic traits that promote faster growth are nearly extinct in comparison to 30 years ago.
Smaller Cod Equal Fewer Offspring
The ecological consequences of these shrinking cod are "ecologically highly dramatic," according to Thorsten Reusch, head of the marine ecology research division at GEOMAR. Smaller fish mature earlier and produce a smaller number of offspring. Despite a multi-year fishing ban, there's no sign of recovery in the size distribution, and neither has the total population bounced back.
Here's a tip if you're looking to make sustainable choices for your dinner plate: Steer clear of the eastern Baltic cod, a distinct population of Atlantic cod that evolved separately in the central Baltic Sea around 7,000 to 8,000 years ago. It differs biologically and genetically from other Atlantic populations like the western Baltic cod or the North Sea cod.
[1] Human-induced evolution in Eastern Baltic cod due to overfishing.[3] Dramatic reduction in the body size of Baltic cod.[4] Banned fishing in the Baltic Sea: Historical changes of the cod.[5] The genetic basis of the reduced body size in the eastern Baltic cod.
- To address the dwindling population and shrinking size of the Baltic cod, policymakers might consider revising their community policy and employment policy to incentivize sustainable fishing practices in the industry.
- The impact of climate-change on marine ecosystems, such as the Baltic Sea, could be further explored by environmental-science researchers to better understand how rising temperatures and changing currents affect the region's fish population.
- Financial institutions can play a crucial role in promoting sustainable seafood choices by implementing strict employment policies that prioritize fair trade and eco-friendly practices in the seafood industry.
