Overfishing is one of the biggest threats our oceans are facing. With fish stocks quickly depleting, some marine ecosystems are greatly struggling. Each animal has a specific role to play in the food web. Some fish live longer than others; some reproduce earlier or later in the life cycle than others. What happens when the natural food web is disrupted due to overfishing? Researchers from the Vancouver Aquarium and Florida International University teamed up to study how predators interact with their prey when the food web is forced to change due to overfishing and disruption of the natural life cycle of certain species.
Interspecific variation in life history relates to antipredator decisions by marine mesopredators on temperate reefs, by Alejandro Frid and Jeff Marliave of the Vancouver Aquarium, and Michael R. Heithaus of Florida International University, is an experimental study published June 29 in the open access journal PLoS ONE.
The study explains how the overfishing of upper-level predatory fishes such as adult lingcod has impacted the population and feeding patterns of mid-sized fishes that, as a result, are becoming the new ‘top’ predators of over-exploited marine communities.
The group hypothesized that the level of risk taken by each fish species to acquire food resources would interspecifically vary based on the lifespan of each fish.
During field experiments on natural reefs in the Northeast Pacific, the team presented kelp greenling, juvenile lingcod and rockfishes with live shrimps, as well as with a fiberglass model of their common predator, a large adult lingcod. With the help of a fixed camera, they witnessed that kelp greenling, which live the “fastest” (shortest) life style, took the highest level of risk and was the only species to attack shrimps adjacent to the model adult lingcod (see video below).
Juvenile lingcod, with the second “fastest” life cycle, attacked shrimp only when they were far from the model adult lingcod, and copper rockfish attacked shrimps only when the model adult lingcod was absent from the reef. Quillback rockfish, which live the “slowest” (longest) life style, took the least risk, never leaving rocky sheltered areas to attack the shrimps.
In other words, despite occupying similar positions in the food web, mid-sized fishes with long life spans have stronger antipredator responses and therefore are less likely to feed in the presence of large predators than mid-sized fishes with shorter life spans.
This could mean that fisheries that deplete the largest predators could potentially allow midsized fishes with long life spans to feed at rates similar to those of shorter-lived fishes. These behavioural changes, in turn, might affect populations of shrimps or other small species of prey, or the competitive balance between the mid-sized fishes.
To read the complete study, please click here.