Using the stomach content of penguins to study the ecology of squids and octopuses

Penguins, one of the most abundant groups of seabirds in the Southern Ocean, feed mainly on cephalopods (e.g., squids and octopus). A recent study, led by our Hugo Guímaro, studied the diet of Snares penguins, Eudyptesrobustus, an endemic penguin species from Snares Islands, New Zealand. to assess the importance of cephalopods in their diet and to assess the trophic levels and habitats that cephalopods occupy. This penguin may be threatened due to their reduced foraging capacity and restricted habitat and susceptibility to anthropogenic activities.

The cephalopods found in the diet of this penguin species are identified, in most cases, through the presence of beaks. These hard, chitinous and digestion-resistant structures can provide information on the species, distribution, relative abundance, size, life-stage and trophic ecology of cephalopods.

In the first instance, measurement and determination of the mass of the beaks and the analysis of the darkening of the beaks were used in order to identify cephalopod species and their maturity stage, respectively. The results showed that Snares penguin feeds on three different cephalopod species: Nototodarussloanii, Onykiaingens (two squid species) and Octopuscampbelli (an octopus), and all individuals of the three species were juveniles.

Then, carbon (δ13C) and nitrogen (δ15N) indicators were measured on cephalopod beaks to infer the cephalopod habitat and the trophic level, respectively, throughout their life cycle (i.e., adults vs juveniles).

The researchers found that:

· The squid species, N.sloanii and O.ingens, occupied a similar habitat on the continental shelf of the Snares Islands. The δ13C values of these species are consistent with the values of sub-Antarctic / sub-tropical waters, indicating that these squid live in these waters;

· The octopod species O.campbelli,had a lower value of δ13C, suggesting that this octopod has a more southern habitat than squid species;

· O.campbelli showed δ15N values higher than those of N.sloaniiand O.Ingens,suggesting that the octopod consumes prey at a higher trophic level compared to the squid species.

Climate change, more specifically the increase in the temperature of the oceans, can influence the availability and diversity of cephalopods on the islands of Snares. This and other threats, such as extensive fishing, bycatch, and depletion of fish stocks, may affect the access of the penguins to their prey and thus increase the threat to this endemic species of Snares Penguins.


Source: Guímaro, H., D. Thompson, V. Paiva, F. Ceia, D. Cunningham, P. Moors, and J. Xavier. Cephalopods habitat and trophic ecology: historical data using snares penguin as biological sampler. Polar Biology:1-12.

Author: Joana Fragão


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