The Diet Composition and Ingested Plastics of Laysan and Black-Footed Albatrosses Incidentally Captured by the Pelagic Longline Fishery in the Western North Pacific
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The stomach contents (food and ingested plastics) of Laysan Albatross Phoebastria immutabilis and Black-footed Albatross P. nigripes were examined by necropsy analysis of birds caught as bycatch in the pelagic longline fisheries in the Western North Pacific. The contents were classified separately for the proventriculus and gizzard. Undigested fish and cephalopods were found in the proventriculus, while hard objects such as cephalopod beaks, plastics, and pebbles were found in the gizzard. This indicates that the retention time of soft tissues in fish or cephalopods differs from that for hard objects. The main prey of both albatrosses consisted of mesopelagic cephalopods such as Cranchiidae, Gonatidae, Histioteuthidae, and Onychoteuthidae species. Laysan Albatrosses also foraged on small teleosts (Japanese Anchovy Engraulis japonicus and some Myctophidae fishes) as major prey items. The estimated dorsal mantle length of cephalopods preyed upon by the albatrosses was below 200 mm, which was smaller than the mature sizes of those cephalopods and the size class mainly preyed upon by cetaceans. This implies that the albatrosses may forage on immature cephalopods floating in the surface layer. Ingested plastics were found in 71.8% of Laysan and 31.8% of Black-footed Albatrosses and plastic fragments were the most abundant.Keywords:
Albatross
Mesopelagic zone
Engraulis
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Gizzard
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Bycatch
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Boluses: An Effective Method for Assessing the Proportions of Cephalopods in the Diet of Albatrosses
Abstract The method of collecting and analyzing boluses to characterize the cephalopod diet of albatrosses has been used in many diet studies. However, no study has validated this method. We compared boluses and stomach samples from Gray-headed Albatrosses (Thalassarche chrysostoma) and Black-browed Albatrosses (T. melanophris) to (1) study the consumption and diversity of cephalopods in these species, (2) investigate biases associated with each sampling method, and (3) estimate the number of samples needed to characterize these albatross’s cephalopod diet. We found that collection and analysis of boluses is a simple, efficient, and noninvasive method for assessing the cephalopod diet of these albatross species, but it is inadequate for characterizing the more easily digestible dietary components, such as fish and crustaceans. Both boluses and stomach samples showed that the two albatross species fed on cephalopods of similar sizes and from the same families (Ommastrephidae, Onychoteuthidae, and Cranchiidae). Furthermore, the main prey species (Martialia hyadesi, Kondakovia longimana, and Galiteuthis glacialis) and the total number of cephalopod species consumed (18–24 species) were the same for both albatrosses. To include all cephalopod species, using a sample-randomization technique, a minimum of 61 and 43 boluses were needed for Gray-headed and Black- browed albatrosses, respectively; but to adequately describe the diversity and size frequency of the main prey species, 82 and 371 boluses would be needed. Les Pelotes de Réjection: Une Méthode Efficace pour Évaluer la Proportion de Céphalopodes dans le Régime Alimentaire chez les Albatros
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BOLUSES: AN EFFECTIVE METHOD FOR ASSESSING THE PROPORTIONS OF CEPHALOPODS IN THE DIET OF ALBATROSSES
The method of collecting and analyzing boluses to characterize the cephalopod diet of albatrosses has been used in many diet studies. However, no study has validated this method. We compared boluses and stomach samples from Gray-headed Albatrosses (Thalassarche chrysostoma) and Black-browed Albatrosses (T. melanophris) to (1) study the consumption and diversity of cephalopods in these species, (2) investigate biases associated with each sampling method, and (3) estimate the number of samples needed to characterize these albatross's cephalopod diet. We found that collection and analysis of boluses is a simple, efficient, and noninvasive method for assessing the cephalopod diet of these albatross species, but it is inadequate for characterizing the more easily digestible dietary components, such as fish and crustaceans. Both boluses and stomach samples showed that the two albatross species fed on cephalopods of similar sizes and from the same families (Ommastrephidae, Onychoteuthidae, and Cranchiidae). Furthermore, the main prey species (Martialia hyadesi, Kondakovia longimana, and Galiteuthis glacialis) and the total number of cephalopod species consumed (18–24 species) were the same for both albatrosses. To include all cephalopod species, using a sample-randomization technique, a minimum of 61 and 43 boluses were needed for Gray-headed and Black- browed albatrosses, respectively; but to adequately describe the diversity and size frequency of the main prey species, 82 and 371 boluses would be needed.
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伊豆諸島鳥島（北緯30°29′02″東経140°18′11″）で，2000年5月中旬，巣立ち期に近いクロアシアホウドリPhoebastria nigripes（Audubon 1849）のヒナが吐出した胃内容物を採取し同定した．4羽すべてが中深層性の遊泳動物を吐出した．このうちイカ類はアカイカ科トビイカ属トビイカSthenoteuthis oualaniensis，ダイオウイカ科ダイオウイカ属，サメハダホオズキイカ科オオホオズキイカ属，ユウレイイカ科ユウレイイカ属，魚類はクロボウズギス科，エビ類はヒオドシエビ科アタマエビ属アタマエビNotostomus japonicusの成体であった．クロボウズギス科はクロアシアホウドリの胃内容物から初めて出現した．クロアシアホウドリの親鳥自らがこれらの中深層性の遊泳動物を自力で捕獲したとみるより，人間活動により投棄されたり，餌動物自らが潜水遊泳に長けた高次捕食者の採食活動や他の理由で死んで浮上したものを，採食した可能性が高いと考えられた．クロアシアホウドリが本来は採食機会がない中深層性の遊泳動物を採食していたことは，彼らが海洋のスカベンジャー，もしくは人間活動や他の高次捕食者の採食活動などに依存した採食ニッチを持つことを示す．
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Abstract Abralia veranyi and Abraliopsis morisii were the most abundant cephalopods caught during epipelagic and mesopelagic surveys off the Canary Islands and accounted for 26% and 35% of the cephalopod catch, respectively. Diel vertical migration patterns were observed in both species. At night, A. veranyi was recorded at depths as shallow as 38–90 m, whereas Abraliopsis morisii occurred at depths of 98–219 m. As individuals grow in mantle length, their diet changes substantially. Abraliopsis morisii showed ontogenetic shifts at 22.9 mm and 35.3 mm dorsal mantle length (DML), while A. veranyi showed ontogenetic shifts at 20.5 mm and 30.9 mm DML. Prior to the first ontogenic shift, both species fed mainly on copepods and mysids. After this shift they fed on larger prey, such as decapods and fish; the diets of larger individuals also contained cephalopods.
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Assessing the consumption of prey by predators in the marine environment is key to fisheries assessment and management. Although environmental and ecological variations can affect the consumption of certain prey by albatrosses interannually, this issue has not been addressed to date. In the present study, the interannual consumption of cephalopods by grey-headed and black-browed albatrosses was assessed while breeding at South Georgia between 1996 and 2000, by comparing consumption estimates from a reparameterised version of the South Georgia Seabird Impact Assessment (SGSIA) model. The reparameterised model showed that there are considerable interannual variations in cephalopod consumption in both albatross species, with the highest consumption occurring in 1996 (5787 tonnes; for black-browed albatrosses) and 1997 (11 627 tonnes; for grey-headed albatrosses), and the lowest in 2000 (2309 tonnes and 772 tonnes for grey-headed and black-browed albatrosses respectively). These interannual variations were linked to oceanographic conditions and changes in cephalopod abundance/availability to predators. The cephalopod species with the most commercial potential (Martialia hyadesi, Kondakovia longimana, Moroteuthis knipovitchi and Gonatus antarcticus) also showed considerable differences in their consumption by predators. Owing to the importance of these squid species in the diet of albatrosses, precautionary measures for future commercial exploitation are suggested.
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MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 168:13-19 (1998) - doi:10.3354/meps168013 Cephalopod predation by the king penguin Aptenodytes patagonicus from South Georgia P. G. Rodhouse1,*, O. Olsson1,2, P. Anker-Nilssen3, A. W. A. Murray1 1British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, United Kingdom 2Department of Zoology, Villavägen 9, Uppsala University, S-752 36 Uppsala, Sweden 3Department of Marine Zoology, University of Oslo, PO Box 1050, N-0316 Blindern, Norway *E-mail: p.rodhouse@bas.ac.uk ABSTRACT: The king penguin Aptenodytes patagonicus is a sub-Antarctic species that feeds primarily on mesopelagic fish and cephalopods in the vicinity of the Antarctic Polar Front (APF). We examined the cephalopod prey of adult penguins at a breeding colony on South Georgia during 4 austral summers, 1990 to 1994. The most important prey (~97% by mass) of the king penguins was found, in a related study, to be mesopelagic fish, mainly myctophids. The penguins¹ cephalopod prey, which constituted the remaining 3%, was shown in this study to be dominated by the ommastrephid squid Martialia hyadesi, both in terms of numbers and biomass. Other squid species were typical of the South Georgia/Antarctic Polar Front (APF) area but only relatively small specimens were present and, apart from Gonatus antarcticus, the presence of flesh indicated that they were probably mostly caught close to the island. M. hyadesi generally fell in the same size range as M. hyadesi exploited by commercial fisheries in the South Atlantic. In the 1992/93 summer, when krill was abundant at South Georgia, the amount of squid consumed, especially M. hyadesi, was substantially less than in the other years. This coincided with a reduction in the amount of the myctophid Krefftichthys anderssoni, which is the major prey of M. hyadesi, in the penguin diet. The total consumption of cephalopods by the king penguin at South Georgia is estimated to be about 75000 t yr-1. Of this, some 3600 to 6000 t yr-1 is estimated to be M. hyadesi. This might underestimate consumption if the penguins consume a greater proportion of squid in the winter, as they do in other sectors of the Southern Ocean. KEY WORDS: Cephalopods · King penguins · Oceanography · South Georgia Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 168. Publication date: July 09, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.
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Study of the ecology of mesopelagic fishes is central for assessing the active biological pump in the ocean, especially in the mesopelagic layers. The use of δ13C and fatty acid analysis can help to analysis the ecology of mesopelagic fishes. Here, we analysed the fatty acid composition of mesopelagic fishes from the continental northern slope of the South China Sea (NSSCS) and compared with nearshore SCS fishes and mesopelagic fishes collected from the Southern Ocean. The mesopelagic fishes had unusually high lipids, which resulted in Δδ13C values exceeding 1‰, more than the enrichment factor in the food web. The mesopelagic fishes had higher C18:1n-9/C18:1n-7 and C20:1n-9/ C18:1n-7 ratios compared with other fishes in the SCS, which confirmed that plankton were their main dietary source. The mesopelagic fishes from SCS and Southern Ocean had different ratios of C20:5n-3/C22:6n-3 (EPA/DHA), suggesting geographical locations and diet sources had obvious influence on their fatty acid composition. The SCS mesopelagic fishes had higher C20:4n-6/C22:6n-3 (ARA/DHA) and C20:4n-6/C20:5n-3 (ARA/EPA) ratios than mesopelagic fishes in the Southern Ocean, indicating the influence of physical factors on fatty acid composition. Thus, future studies of the fatty acids in mesopelagic fishes should consider both dietary sources and physical environments.
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