Guillermo Duque, Diego Esteban Gamboa-García, Andrés Molina, and Pilar Cogua (2025) Effects of consecutive dredging on the fish community of a tropical estuary, Continental Reef Research. 286, Jan. 15. https://doi.org/10.1016/j.csr.2025.105402
Dredging Activity
Buenaventura Bay, Colombia is one of South America’s major ports and accounts for nearly 60% of Colombia’s imports and exports. Sediment is regularly deposited in the bay by two major river systems, making it difficult for large ships to navigate without running aground. As a result, this sediment is regularly removed from the bay in a process called dredging, to deepen the channel. This makes it easier for ships to navigate, and allows for more traffic to enter and exit the bay at one time.
However, dredging is an intense human activity that can upset the environmental balance on the seafloor. Namely, when sediment is excavated, particles that aren’t removed from the water will stay suspended, lowering visibility and water quality. This can have major impacts on fish. Dredging also changes the configuration of the bottom, altering fish habitat that can force them to find new places to shelter or feed.
Not only is Buenaventura Bay a busy port, it also supports many local fisheries. There is concern that dredging is changing the fish communities present, driving them away from the area, reducing the quality of catches for local fishers. A new study from Duque et al. (2025) investigated how consecutive dredging events impacted fish presence and diversity in the bay.
Sensitive or Tolerant?
Three dredging events were monitored from 2015 to 2021 in the bay. Water variables including salinity, transparency, and amount of oxygen in the water all significantly decreased over time. Organic matter within the sediment, which is an important food source for fish, also experienced significant reductions after the first two dredging events. These variables are important indicators of water quality, indicating dredging had a negative impact on the quality of the environment for fish. However, the fish themselves had more variable responses.
The pygmy pufferfish (Sphoeroides trichocephalus) was the most abundant fish before the first dredging event. But their numbers decreased afterwards, indicating a negative interaction with the activity. This was concerning because the species is a key link in the food web here. They weren’t the only species to leave with sole and ray numbers significantly decreasing as well. On the flipside, box sea catfish (Cathorops multiradiatus) numbers increased after the first event.
Feast or Famine
The different reactions to dredging is believed to be caused by the type of food available before and after the activity. Before the activity, primary producers like plankton and algae that photosynthesize are widely available to fish like the pygmy pufferfish. When dredging kicks up sediment into the water column, it clouds the water, blocking out the sun. Unable to photosynthesize, the plankton and algae die and decompose. This is the primary food of the box sea catfish, bringing more into the area to feast.
Future Activity?
Dredging is an important activity to maintain rivers and seabeds, but can have a range of impacts on the environment. Water properties like transparency and dissolved oxygen concentration can decrease, degrading conditions for fish. Sensitive species like the pygmy pufferfish will leave the area, while more tolerant species like the box sea catfish will take its place. This change of fish diversity can influence local fisheries, leading to less desirable catches. Future dredging activity should be assessed for environmental impacts to understand how it will influence fish presence. This will help identify sensitive species and how we can mitigate negative impacts on them.
I am a recent MSc graduate in marine biology from Bangor University, where I studied population dynamics of elasmobranchs off the coast of Wales. My interests lie in ecological data analysis to understand environmental processes and identify natural patterns. However, nothing beats being in the field and interacting directly with the marine life.