Competition in the form of industrial fishing activities have caused North Pacific seabirds to consume more squid and less fish, thereby bringing about a downward shift of their place in the food web.
Over the past 125 years, North Pacific seabirds have shifted their prey preferences, consuming more squid and less fish. This trend has become more accentuated since 1950 due to the advent of industrial fishing.
With the seabirds' dietary shift to squid, their position in the food web (their trophic position) has correspondingly shifted lower. At first glance, this may not appear to be much of a big deal. However, it gives us a glimpse into the marine ecosystem, and may have extensive ecological and economic impact.
Research has also uncovered some details into this trend, which have been outlined in a paper recently published in the Science Advances journal.
In the study, the researchers looked into the diet of eight species of central North Pacific seabirds from 1891 to 2016 by analysing the isotopic composition of their tissues. They discovered that the seabirds' consumption of four families of fishes declined in proportion to their marked increased in squid consumption. They attribute the change in dietary preferences to commercial fishing, climate change and the seabirds' adaptation to their changing environment.