Dietary analysis of harbour seals ( Phoca vitulina) from faecal samples and overlap with fisheries in Erimo, Japan

• Published in: Marine Ecology
• Main Authors: Hui, Tabitha C. Y., Morita, Yuka, Kobayashi, Yumi, Mitani, Yoko, Miyashita, Kazushi
• Other Authors: Sasakawa Scientific Research Grant, Explorers Club Exploration Fund, Sigma Xi, Japanese Ministry of Education, Culture, Sports, Science and Technology (Monbukagakusho), Graduate Student Scholarship, Japan Asian Youth Fellowship Program
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2017
• Subjects: harbour seal; Phoca vitulina; Theragra chalcogramma
• Online Access: http://dx.doi.org/10.1111/maec.12431; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fmaec.12431; https://onlinelibrary.wiley.com/doi/pdf/10.1111/maec.12431

Abstract The number of harbour seals in Japan has been rebounding since protection began in the mid‐1980s. With the increase in seal numbers, increased conflict with fisheries has occurred through depredation and the belief that seals compete with fisheries for prey. However, competition can only be determined if the prey species and quantities seals consume over time are known. We studied the diet of harbour seals in Erimo, site of the largest population of harbour seals in Japan, from 2011 to 2012 and assessed the degree of prey overlap with local fisheries. We used both hard parts and DNA techniques to identify prey items in seal scats, and compared these results to local fisheries data. A total of 46 prey occurrences was detected by both methods, of which 17 matched between techniques at least to the family level. Hard parts methods identified five incidences of prey undetected by DNA methods in five scats (one incidence per scat). DNA methods identified 24 additional prey occurrences in 13 scats, for which no hard part evidence for that prey had been found. This more than doubled the total number of prey occurrences across the 15 scats compared. Overall, the most frequently occurring harbour seal prey were walleye pollock ( Theragra chalcogramma ), sculpins and snailfishes. In contrast, the top three groups targeted by fisheries were codfishes, salmon and invertebrates. Many species common in the harbour seal's diet such as snailfishes and blennies were not targeted by fisheries. Fishes such as greenlings, sculpins, rockfishes and Japanese anchovy ( Engraulis japonicus ) were common in the diet of harbour seals, but made up a very small proportion of fisheries catches in Erimo. The importance of other prey species varied between seasons. Sculpins, greenlings and forage fishes were the top three prey groups for harbour seals in spring by percent modified frequency of occurrence, whereas the most important target groups by percentage mass caught by fisheries were codfishes, cephalopods and other ...