CLASSIFYING PREY HARD PART STRUCTURES RECOVERED FROM FECAL REMAINS OF CAPTIVE STELLER SEA LIONS (<i>EUMETOPIAS JUBATUS</i>)

Cottrell, Paul; Trites, Andrew W.

doi:10.1111/j.1748-7692.2002.tb01053.x

Cited by 29 publications

(37 citation statements)

References 19 publications

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“…Steller sea lion scats contain few otoliths, and erosion from partial digestion is high. Identification of all diagnostic skeletal structures in addition to otoliths, as used in our study, increases the detection rate of many species (Olesiuk et al 1990, Cottrell & Trites 2002, Tollit et al 2007). However, more robust bone structures from species such as pollock may have greater recovery rates compared to fragile structures of smaller species such as capelin and sand lance (Tollit et al 2003(Tollit et al , 2007.…”

Section: Potential Biasesmentioning

confidence: 70%

“…The limitations and biases associated with scat analysis have been discussed previously for Steller sea lions (Cottrell & Trites 2002, Tollit et al 2003, 2007, Joy et al 2006) and other pinniped species (Dellinger & Trillmich 1988) and primarily relate to differential rates of digestion and recovery of diagnostic structures between and within prey species. Steller sea lion scats contain few otoliths, and erosion from partial digestion is high.…”

Section: Potential Biasesmentioning

confidence: 97%

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Spatial and temporal variation in the diet of Steller sea lions in the Kodiak Archipelago, 1999 to 2005

McKenzie¹,

Wynne²

2008

Mar. Ecol. Prog. Ser.

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Spatial and temporal variation in the diet of Steller sea lions Eumetopias jubatus was investigated using scat (fecal) samples collected from 4 regions in the Kodiak Archipelago. Over 2700 scats with identifiable prey were collected from the northern, eastern, southern and western sides of Kodiak Island from 1999 to 2005. Of 76 prey types identified using hard remains, the most important species in terms of frequency of occurrence and numerical abundance were Pacific sand lance Ammodytes hexapterus, walleye pollock Theragra chalcogramma, arrowtooth flounder Atheresthes stomias, Pacific cod Gadus macrocephalus, salmon Oncorhynchus spp., and Pacific herring Clupea pallasi. Significant differences in diet composition were found among regions, seasons, and years, suggesting that the diet of sea lions is strongly influenced by local and temporal distributions and abundances of prey. Herring dominated scat collections from the west coast and accounted for most (14 to 30%) of the differences in regional diet in spring and winter. Annual variation in diet was relatively low in winter, whereas spring and fall diets varied from year to year, with regional-specific shifts in dominant prey. Results from our study generally agree with diet studies conducted in the 1990s, but differ markedly in the relative importance of the major prey species.

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Section: Potential Biasesmentioning

confidence: 70%

Section: Potential Biasesmentioning

confidence: 97%

Spatial and temporal variation in the diet of Steller sea lions in the Kodiak Archipelago, 1999 to 2005

McKenzie¹,

Wynne²

2008

Mar. Ecol. Prog. Ser.

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“…As the seasonal sample sizes are small, our findings should be taken as an indication of the harbour seal's diet to be confirmed by subsequent years of study. Problems associated with the complete digestion of bones can be reduced by using all‐structure identification techniques to determine the presence of prey species such as we did in this study (Browne et al., ; Cottrell & Trites, ; Olesiuk, Bigg, & Ellis, ; Olesiuk, Bigg, Ellis, Crockford, & Wigen, ; Tollit et al., ).…”

Section: Discussionmentioning

confidence: 98%

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

et al. 2017

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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 invertebrates. Sculpins and rockfishes remained as important prey items for harbour seals in summer and autumn, in addition to codfishes, snailfishes and blennies. In contrast, the main groups caught by fisheries in summer were other fishes, particularly Japanese amberjack (Seriola quinqueradiata) and various species of sharks and eels, and invertebrates. By autumn, Erimo fisheries had focussed on catching salmon. Salmon were taken by harbour seals as well during this period, but at a relatively lower frequency compared to other prey groups. The results of our study show that although harbour seals consumed several of the prey species targeted by fisheries, the relative importance of these species to seals and fisheries and the seasons in which they were targeted were different.

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“…Seal diets are being determined more commonly now from the hard parts (bones, eye lenses and beaks) found in stomachs or faecal remains collected from sites where animals haul out and rest (e.g. Tollit et al, 1997;Kirkman et al, 2000;Cottrell and Trites, 2002). Stable isotope analysis is yet another recently developed technique for determining diet (e.g.…”

Section: Food Websmentioning

confidence: 99%

Food webs in the ocean: who eats whom and how much?

Trites

2003

Responsible Fisheries in the Marine Ecosystem

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Over 100 food webs have been published for marine ecosystems to describe the transfer of food energy from its source in plants, through herbivores, to carnivores and higher order predators. The webs suggest that the lengths of the chains that form food webs are typically short (3-4 links), and that ecosystems with long food chains may be less stable than those with shorter food chains.Stomach contents have been the primary means for determining what marine organisms eat. More recently developed techniques include faecal analysis and fatty acid signatures from blood or fat samples. Consumption has been estimated from the volume of food found in stomachs, from the feeding rates of captive individuals and from bio-energetic modelling. Consumption of marine organisms, expressed as a percentage of an individual's body weight per day, ranges from about 4-15% for zooplankton, to 1-4% for cephalopods, 1-2% for fish, 3-5% for marine mammals and 15-20% for sea birds. Immature age classes consume about twice as much (per unit of body weight) as do mature individuals. Furthermore, consumption is not constant throughout the year, but varies with seasonal periods of growth and reproduction. Most groups of species consume 3-10 times more than they produce, and export or pass up the food web about 70-95% of their production. Marine organisms tend to be larger at successive trophic levels and are limited in the sizes of food they can consume. Humans are one of the few species that can prey upon almost any level of the food chain and any size of prey.Food web analysis and estimates of consumption are essential for understanding which ecosystems can support additional species, and which may be less stable and susceptible to species loss through the synergistic effects of fishing or culling. They are also critical tools for understanding changes in ecosystem dynamics as highlighted by a case study from the eastern Bering Sea.

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CLASSIFYING PREY HARD PART STRUCTURES RECOVERED FROM FECAL REMAINS OF CAPTIVE STELLER SEA LIONS (EUMETOPIAS JUBATUS)

Cited by 29 publications

References 19 publications

Spatial and temporal variation in the diet of Steller sea lions in the Kodiak Archipelago, 1999 to 2005

Spatial and temporal variation in the diet of Steller sea lions in the Kodiak Archipelago, 1999 to 2005

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

Food webs in the ocean: who eats whom and how much?

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