Fish Decline Means a Trashy Diet for Gulls
An analysis of nearly 150 years of data has revealed that seagulls are eating far more trash than they used to, leading to low fertility and population declines. Now, researchers are suggesting that this may have occurred because fish stocks are not as nearly as plentiful as they once were.
That's at least according to a study recently published in the journal Global Change Biology, which details how researchers used 270 gull feather samples left to museums between 1860 and 2009 to measure fish intake.
Assessing ratios of the heavy isotopes carbon and nitrogen, researchers from the University of British Columbia, Environment Canada, and Queen's University in Canada discovered that the average gull diet has slowly been shifting to more fish and more supplemental garbage scavenging.
All the gull feather samples originated from seabirds that lived near the Salish Sea region off the coast of southwestern Canada and the northwestern United States.
Predictably, the gulls' observed change in diet was found to coincide with overfishing in the region by the early 1900s.
This overfishing drove the common eulachon (Thaleichthys pacificus) - a once staple meal for locals - to dangerously low numbers. That is why, while the overall eulachon population is considered to be stable, the fish in this particular region are considered threatened by Ecological Society of America and the NOAA Fisheries.
Interestingly, records indicate that despite local fish populations dropping, the gull populations actually grew between 1960 and 1986. The feather analysis indicates that this may be when trash became much more readily available, helping to support gulls, even while less nutritious than fish.
Field observations have found that while gull chicks today are being fed sand lance and herring, they are just as likely to be fed discarded food like chicken wings or French fries.
According to New Scientist, study author Louise Blight has also been involved in other research that found that gulls have been producing smaller and fewer eggs over the last few decades. She implies in her latest study that this could be attributed to the decline in gull diet quality.
The worry is that this work could have dire implications as pollution levels and climate change continue to threaten population numbers of fish across the world. The consequence - besides empty oceans - could be that seabirds wind up choking down more of our trash to survive.