Netting For Fish

July 27, 2019

By Miles Scheuering

 

It is the peak of the chick-rearing period for rhinoceros auklets on Southeast Farallon Island, which means every night the adults return to their burrows with bill-loads of fish for their chicks. As part of a long-term monitoring study of their diet, we use mist nets to capture adults and collect the fish they carry. Once the netting is complete, we identify the species and measure the size of each prey item to determine energy content. Types of prey generally include juvenile rockfish, anchovies, sablefish, and squid; and this year the chick diet has been almost exclusively anchovy. They have specialized hooks on the backs of their tongues that allow them to carry as many as eight fish at a time. That’s a lot of fish! By handling the birds we are also able to band and measure adults to improve our demographic data, along with deploying geolocators (leg-mounted archival tags used to estimate geographic positions of birds over year-long deployments).

 

We set the net up at sunset and lie in wait on either side for birds to fly in. As soon as a bird makes contact, people run over and begin extracting the bird, while others search for fish that have fallen on the ground. They are feisty birds and are not afraid to nibble on your hand while you are trying to extract them. These diet samples are valuable in determining the foraging success of provisioning parents, as well as a tool for monitoring fish abundance within the Gulf of the Farallones where these birds feed.