Literature
- Härkönen T. and Heide-Jørgensen M.-P. 1991. The Harbour Seal Phoca vitulina as a predator in the Skagerrak. Ophelia 34: 193-207.
- Reinhold A.-B. 1996. Nahrungsökologie des Kormorans (Phalacrocorax carbo) auf Helgoland. Msc thesis Humbolt University, Berlin and Vogelwarte Helgoland, Helgoland, 72p.
- Van Damme C. 1994. Poep en kots: dieetstudies van Zeehonden en Aalscholvers. Ongepubl. rapport, NIOZ, Texel, 32pp, bijlagen I-XLIII.