Fishes in the Hawaiian monk seal diet, based on regurgitate samples collected in the Northwestern Hawaiian Islands

Hawaiian monk seals (Neomonachus schauinslandi) began recolonizing the main Hawaiian Islands (MHI) roughly 20 yr ago. The species’ abundance is still declining, but the subpopulation in the MHI is increasing by 6.5% per year. This difference may be due to differences in prey availability or habitat quality between the northwest (NWHI) and main Hawaiian Islands, which could be reflected in the movements and behavior of the seals. For example, foraging trip durations may be shorter in areas with higher forage quality. From 2007 to 2014 we deployed GPS phone tags on the islands of Molokai (n = 7), Kauai (n = 6), and Oahu (n = 6) to study movements and dive behavior. Foraging trips typically lasted 0.57 d (IQR: 0.34–0.83) and seals traveled 18 km (IQR: 10.2–30.5) per trip. Seals began benthic dives shortly after entering the water, with most dives to depths of 12–32 m. The median 95% and 50% kernel density isopleths for seals in the MHI were 149.2 km2 and 23.2 km2, respectively. The duration and distance of foraging trips in the MHI were shorter than that observed in other studies from the NWHI, suggesting that foraging habitat is currently better in the MHI.

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“…, Baechler et al . ) and monk seals are known to be benthic foragers that prefer cryptic prey (Longeneker , Cahoon et al . ).…”

Section: Discussionmentioning

confidence: 99%

Movements and home ranges of monk seals in the main Hawaiian Islands

Wilson

Littnan

Read

2017

Marine Mammal Science

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“…Studies on the Hawaiian monk seal (Monachus schauinslandi) suggest that it is also a generalist predator, although fish appear to be the most important component of its diet (Goodman-Lowe, 1998). Longnecker (2010) reported anguilliform fish species of the families Congridae and Muraenidae to be the most numerous prey of Hawaiian monk seals.…”

Section: Discussionmentioning

confidence: 99%

Diet of the Monk Seal (Monachus monachus) in Greek Waters

Pierce¹,

Hernández-Milian

Santos

et al. 2011

Aquat Mamm

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Stomach contents were collected from 27 monk seal carcasses between 1997 and 2008 from different areas along the Greek coast. This sample included nine animals that had been deliberately killed and five accidental deaths due to fisheries interactions. Stomachs from monk seals of both sexes, including adults and subadults, were analysed. A total of 530 prey items from at least 71 prey species was identified, with approximately 74% of prey identified at least to genus, while 2.8% could be identified only to class level (i.e., fish or cephalopods). We found 266 cephalopods (50%), 253 fish (48%), a few non-cephalopod molluscs (1.5%), and two crustaceans (0.4%). Faecal samples were also collected but contained no identifiable prey remains. Octopuses were the most important prey in terms of numbers eaten and contribution to reconstructed prey biomass. The common octopus (Octopus vulgaris) (33.9% of prey by number) was around three times as numerous in the diet as the lesser octopus (Eledone cirrhosa) (11.1%). Fish of the families Sparidae (28.1%) and, to a lesser extent, Scorpaenidae (2.3%), Congridae (2.5%), and Atherinidae (2.5%) were also frequent in the stomachs. Many of the prey species recorded are of commercial fishery importance. Exploratory multivariate analysis (redundancy analysis [RDA]) indicated weakly significant seasonal, spatial, and interannual variation in diet and also suggested a relationship between diet composition and cause of death. No trends in diet related to sex or age class were identified. Sparids occurred more frequently in animals that had been deliberately killed than those that had died due to other causes, highlighting the interactions taking place between monk seals and fishing activities.

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“…The oldest and most common methods, and still widely used, involve the recovery of prey hard parts ( i.e ., calcified structures) from stomach contents, intestines, and feces that are resistant to digestion (Scott , Fitch and Brownell ). Less commonly, prey hard parts recovered from spewings (regurgitates) are also used ( e.g ., Gales and Pemberton , Longenecker ). More recently, several chemical methods have been developed.…”

Section: Strengths and Limitations Of Methods Used To Estimate The DImentioning

confidence: 99%

Methods of estimating marine mammal diets: A review of validation experiments and sources of bias and uncertainty

Bowen

Iverson

2012

Marine Mammal Science

167

142

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Diet estimation in marine mammals relies on indirect methods including recovery of prey hard parts from stomachs and feces, quantitative fatty acid signature analysis (QFASA), stable isotope mixing models, and identification of prey DNA in stomach contents and feces. Experimental evidence (9 species/13 studies) shows that digestion strongly influences the proportion and size of otoliths that can be recovered in feces. Number correction factors (NCF) and digestion coefficients have been experimentally determined to reduce the biases in fecal analysis. Correction factors and coefficients have not been determined for diet estimated from stomach contents. QFASA estimates which prey species and amounts must have been eaten to account for the fatty acid composition of the predator. Experimental studies on mammals and seabirds (9 species/10 studies) indicate that accurate estimates of diet can be determined using QFASA. Stable isotope mixing models provide rather coarse taxonomic resolution of diet composition. Prey DNA analysis shows promise as a method to estimate the species composition of diet, but further development and testing is needed to validate its use. Obtaining a representative sample from marine mammal populations is a significant challenge. Therefore, the use of complementary methods is recommended to obtain the most informative results.

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Fishes in the Hawaiian monk seal diet, based on regurgitate samples collected in the Northwestern Hawaiian Islands

Cited by 17 publications

References 20 publications

Movements and home ranges of monk seals in the main Hawaiian Islands

Movements and home ranges of monk seals in the main Hawaiian Islands

Diet of the Monk Seal (Monachus monachus) in Greek Waters

Methods of estimating marine mammal diets: A review of validation experiments and sources of bias and uncertainty

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