As we tuck into our Superbowl snacks this weekend, let's be grateful we're not seabirds. In fact, please chew whatever you have in your mouth before you read further.
For some seabirds, fishing waste is a blessing. Fish parts and other refuse discarded by fishing boats help certain birds sustain much larger populations than could otherwise survive in their area. Gulls usually benefit near shore, and albatrosses, skuas, petrels, and frigatebirds will follow commercial fishing vessels to scavenge easy snacks. However, this stuff is actually a mixed blessing for the Cape Gannet...rather like nachos are for us.
Cape Gannets breed on islands off the western coast of South Africa and Namibia. The waters are a prime location for small fish such as sardines and anchovies and the larger fish that prey upon them. Fleets of commercial fishing vessels have joined the flocks of gannets to reap the bounty, and adult gannets have learned to follow fishing boats to feed on discarded fish parts. Often, the fish would have been too large for the gannets to capture themselves, which means the gannets have access to food they otherwise wouldn't. (Think of your neighbor's seven-layer bean dip, which you can never make because you're always missing an ingredient.) In fact, sometimes fishing waste makes up more than 80 percent of the diet of adult gannets, contributing to their very high survival rate. Burp.
High survival rate? "So what's the problem?" you ask. The answer: feeding the kids. Fishing waste is a good food resource for adult gannets, but it is much lower in calories than the small, oily fish that their babies should be eating. Gannet chicks don't grow well when they eat mostly fishing waste. In fact, their parents seem to know this: parents with chicks make many more dives seeking live fish than do non-breeding adult gannets. Unfortunately, depletion of the anchovy and sardine stocks by overfishing has made it harder for Cape Gannets to find the food their young need to thrive. They often have to feed their babies on fishing waste because there's not enough of anything else. Sadly, in some years nearly all of the chicks in such colonies have died. Researchers refer to this problem as the “junk-food” phenomenon.
Want to find out more after the game? Read this: Gremillet et al. A junk-food hypothesis for gannets feeding on fishery discards. Proceedings of the Royal Society of London B 275:1149-1156 (2008). Thanks to The Cornell Lab of Ornithology for reporting on this research.