Diet of the Eurasian otter (Lutra lutra) on the River Gradac,Serbia: Predation in a brown trout‐dominated stream

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Range and diet of Eurasian otters Lutra lutra (L.) in the catchment of the River Lee (south‐east England) since re‐introduction

• 1. After re‐introduction in 1991 of Eurasian otters Lutra lutra (L.) to the River Lee catchment (England), changes in range were assessed from spraint collections in the periods 1991–1994, 1995–1997 and 1998–2000. Diet, assessed from concerted spraint sampling within the first two periods, was compared between 1992–1994 and 1996–1997, with dietary preferences assessed for the initial phase using available fish stock data for that period.
• 2. In 1991–1994, range encompassed much of the catchment, but reduced in 1995–1997 to a small area around the initial release site, when the otters were joined/replaced by natural immigrants presumed to come from a contiguous catchment. Range expanded in 1998–2000 to upper reaches of the catchment's major tributaries.
• 3. Fish, mainly cyprinids, were the major prey taken in 1992–1994 and 1996–1997. In 1996–1997, fish abundant near the initial release site became more prominent, in particular chub Leuciscus cephalus, and (upstream) species characteristic of the initial range decreased in importance.
• 4. Despite confirmed and unconfirmed sightings of females with cubs, it remains unclear whether the presence and apparent expansion of otters in the Lee catchment is the result of the re‐introduction or of natural immigration/recolonization.

Copyright © 2003 John Wiley & Sons, Ltd.     

Changes in the diet of a recovering Eurasian otter population between the 1970s and 2010

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Diet and fish choice of Eurasian otters (<Emphasis Type="Italic">Lutra lutra</Emphasis> L.) in fish wintering ponds in Hungary

The diet composition and fish preference of piscivorous Eurasian otters (Lutra lutra) were studied in two fish farm systems in Hungary using spraint (otter faeces) analysis during two wintering periods. The primary food source of otters in both fish farms was fish (97–99% of biomass). The main fish prey was small-sized, below 100 g in weight (96% in both areas), while fish prey above 500 g comprised only 0.1–0.4% of the diet. The bulk of the otters’ diet consisted of less-valued species, especially non-native Prussian carp (Carassius auratus gibelio). Consumption of commercial fish species ranged between 15 and 31% of the total diet. Otters preferred fish below 100 g in weight (Ivlev’s electivity index, E _i = 0.65–0.70), and showed a lesser preference for (or avoided) fish above 100 g in weight (E _i = −0.37–1.00). With regard to species distribution, otters preferred small (below 100 g) grass carp (Ctenopharyngodon idella), zander (Sander lucioperca), pike (Esox lucius), Prussian carp, topmouth gudgeon (Pseudorasbora parva), while they consumed common carp (Cyprinus carpio), the most important commercial species, proportionally to its abundance in the environment (E _i = −0.18–0.29).     

Impacts of otter (Lutra lutra L.) predation on fishponds: A study of fish remains at ponds in the Czech Republic

The increasing numbers of otters (Lutralutra L.), which are protected by the CzechAct of Nature and Landscape Protection, arecausing serious problems for fishpondmanagement. The diet of otters on pond farmsconsists predominantly (80%) of common carp,Cyprinus carpio, and to a lesser extentother pond fish species (perch, Percafluviatilis, zander, Stizostedionlucioperca and grass carp, Ctenopharyngodon idella). The size of carpcaptured by otters ranged between 376–683 mmTL (500 ± 88 mm) and 1,049–11,768 g(3,478 ± 2,867 g). Reconstructed originalweight and length of captured grass carp andperch were 599 and 182 mm TL, and 2,665 and163 g, respectively. In most of prey fishcorpses left by otters, only viscera andassociated parts were consumed. The weight ofindividual common carp corpses was estimated as73.0 ± 24.6 (26.3–95.9)% of theoriginal reconstructed weight, which means thatonly 27.0 ± 17.2 (4.1–73.7)% of fishbody mass was consumed by otters. In perch,62.8% of fish body mass was left unconsumed.Heavy losses have been reported also on fishstocks in ice-covered ponds during the winterperiod, when shoals of resting fish have beendisturbed and stressed due to otter hunting.     

The response of otters to environmental changes imposed by the construction of large dams

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Factors affecting the occurrence of smooth‐coated otter in aquatic systems of the Upper Gangetic Plains,India

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PCBs and organochlorine pesticide residues in otter (Lutra lutra) spraints from Welsh catchments and their significance to otter conservation strategies

• 1. A survey is presented of PCB and organochlorine pesticide concentrations in otter (Lutra lutra) spraints (faeces) from 18 catchments/sub-catchments in Wales and adjacent English counties.
• 2. There were wide differences in concentrations of lindane, dieldrin, DDE and PCBs between catchments and at sites within catchments. Only PCBs were considered likely to be of significance in influencing otter populations. Mean PCB concentrations (but not those of dieldrin and DDE) were inversely related to otter population performance (as measured by both catchment distribution and sprainting intensity) between catchments.
• 3. It is suggested that PCB contamination is exerting a negative impact on otter populations in four catchments, while there is concern over four others. A study of food chain contamination should be an essential component of otter conservation strategies at both the national and local level.

     

Common dolphins,common in neritic waters off southern Israel,demonstrate uncommon dietary habits

1. During the last decade, the common dolphin (Delphinus delphis) has become the second most sighted species in Israeli coastal waters, after the common bottlenose dolphin. Documentation mostly relies on opportunistic, photo and/or video-backed second-party reports, delimited within a 10 km near-shore strip.
2. Sightings occur year round, are confined to the southern part of the Israeli coast and typically comprise relatively large groups (mean ± SD: 21.5 ± 13.3), often with young calves.
3. Strandings are relatively scarce, typically one per year, and have so far yielded five upper digestive tract contents for diet analysis.
4. Cephalopods comprised 1.2% of the estimated number of prey items in the combined content. Surprisingly, by far the most abundant and prevalent prey item found (57% of pooled prey items; present and dominant in four out of five tracts) was the Balearic eel (Ariosoma balearicum), a sand burrower which is also a major dietary component of the common bottlenose dolphins.
5. Bottlenose dolphins in Israel are known to forage in association with bottom trawlers, leading to the notion that common dolphins also make use of this foraging mode. Indeed, in addition to their association with purse seiners, they have been documented accompanying bottom trawlers, by both day and night. The slender Balearic eels are frequently found protruding from the net's eyes, presumably making easy prey for both dolphin species.
6. Information gaps on common dolphins include range extension to the south/south-west, abundance estimation and genetic flow/isolation. Even so, its unusual diet and the fact that the closest known populations to the north/north-west are from the Aegean Sea, were major considerations in the recent designation of the ‘Coastal Shelf Waters of the South-east Levantine Sea’ as a Mediterranean Important Marine Mammal Area.

     

Use of diet and body condition assessments as intermediate indicators of translocation success in the Critically Endangered Philippine crocodile (Crocodylus mindorensis)

1. Intermediate metrics of translocation success are useful for long-lived, slow to mature species where survival and reproduction happen over decades.
2. With fewer than 150 individuals in the wild, the Critically Endangered Philippine crocodile (Crocodylus mindorensis) is one of the most threatened species on Earth. This study presents the first analysis of diet and body condition of wild Philippine crocodiles and headstarted (i.e. captive-reared) individuals released into the wild over the last decade, and uses these results to show how diet and body condition can be pertinent intermediate metrics of translocation success.
3. Analyses of stomach contents revealed 17 different aquatic and terrestrial invertebrate and vertebrate prey species. Interestingly, 70% of Philippine crocodiles showed snails to be the predominent prey type, followed by fish (36.7%), birds (33.3%) and reptiles (33.3%). More than 50% of crocodiles consumed the invasive golden apple snail, a leading agricultural pest. Regardless of crocodile history (wild vs. headstarted) or size class (juvenile vs. adult), no evidence was found for dietary differences in percentage occurrence, percentage composition or prey diversity.
4. Body condition was significantly higher in wild compared with headstarted individuals when analysed together in a pooled group, although neither group differed significantly from the standardized expectation, and headstarted individuals were not significantly different when body condition was derived independently for the two groups.
5. This study provides a working example of how assessing the convergence of diet and body condition between translocated and wild individuals can provide complementary monitoring parameters to demonstrate post-release establishment of translocated crocodylians. The congruent dietary composition and comparable body condition observed in this study suggest that headstarted crocodiles adapt well following release.
6. Crocodylus mindorensis survives in an agricultural landscape and is likely to play an ecologically important role by exploiting invasive species, reinforcing the importance of this species to local communities.

     

Otter occupancy in the Cape Peninsula: Estimating the probability of river habitat use by Cape clawless otters,Aonyx capensis,across a gradient of human influence

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Quantifying the extent of river fragmentation by hydropower dams in the Sarapiquí River Basin,Costa Rica

• 1. Costa Rica has recently experienced a rapid proliferation of dams for hydropower on rivers draining its northern Caribbean slope. In the Sarapiquí River Basin, eight hydropower plants were built between 1990 and 1999 and more projects are either under construction or proposed. The majority of these dams are small (<15 m tall) and operate as water diversion projects.
• 2. While the potential environmental effects of individual projects are evaluated prior to dam construction, there is a need for consideration of the basin‐scale ecological consequences of hydropower development. This study was a first attempt to quantify the extent of river fragmentation by dams in the Sarapiquí River Basin.
• 3. Using simple spatial analyses, the length of river upstream from dams and the length of de‐watered reaches downstream from dams was measured. Results indicated that there are currently 306.8 km of river (9.4% of the network) upstream from eight existing dams in the Sarapiquí River Basin and 30.6 km of rivers (0.9% of the network) with significantly reduced flow downstream from dams. Rivers upstream from dams primarily drain two life zones: Premontane Rain Forest (107.9 km) and Lower Montane Rain Forest (168.2 km).
• 4. Simple spatial analyses can be used as a predictive or planning tool for considering the effects of future dams in a basin‐scale context. In the Sarapiquí River Basin, we recommend that future dam projects be constructed on already dammed rivers to minimize additional river fragmentation and to protect remaining riverine connectivity.

Copyright © 2007 John Wiley & Sons, Ltd.     

Cumulative impacts of habitat fragmentation and the environmental factors affecting upstream migration in the threatened sea lamprey,Petromyzon marinus

1. River ecosystems are often fragmented by artificial structures, such as weirs. For anadromous species, these structures can impede access to upstream spawning sites and ultimately lead to severe population declines.
2. This study focused on the freshwater spawning migration of the sea lamprey, Petromyzon marinus, an anadromous species threatened by habitat fragmentation across its native range. To quantify the cumulative impacts of multiple weirs on upstream-migrating adults, and to explore the environmental factors affecting migratory movements, passive acoustic telemetry was applied to 56 individuals during their spawning migration in the heavily fragmented River Severn basin, UK.
3. While 89% of tagged sea lamprey passed the first weir upstream of the release site on the main river, only 4% passed the fifth weir. For 85% of migrants, the upstream extent of migration was immediately downstream of a weir. Individuals that passed weirs upstream of the release site (n = 50) took 21.6 ± 2.8 days to reach their most upstream location, experiencing cumulative passage times at weirs of 15.7 ± 2.8 days; these delays constituted a median of 84% of total upstream movement times.
4. Multistate models showed that the weir passage rates of sea lamprey in tidal and non-tidal areas increased significantly when downstream river level and discharge were elevated. Upstream-to-downstream changes in direction were frequent downstream of weirs, but rare in unobstructed river sections.
5. The results provided evidence for a cumulative effect of multiple weirs on sea lamprey movements, substantially delaying upstream migrants and limiting their spawning to atypical habitat. The results also demonstrated the crucial roles of high tides and elevated discharge events in enabling weir passage. Although the Severn Estuary features conservation designations for sea lamprey, this study reveals that barriers are inhibiting their upstream migration, a problem that should be addressed to assist sea lamprey conservation.

     

Genetic analysis of the diet of red-footed boobies (Sula sula) provisioning chicks at Ulupa'u Crater,O'ahu

1. The diet of red-footed boobies (Sula sula) provisioning chicks was quantified using 106 regurgitations collected from 81 adults over two study years with contrasting oceanographic conditions: 2014 and 2015.
2. A total of 1,049 prey items were sorted into three broad categories (fish, squid, and other, consisting of highly-digested ‘mush’ and parasitic isopods) and assigned a categorical freshness value of 1 (perfect condition), 2 (superficial digestion), or 3 (highly digested and incomplete).
3. A total of 492 undigested prey items (freshness 1 and 2) were measured and sampled for genetic identification with 401 (82%) successfully identified. Rarefaction analyses suggested robust diet sampling, with 32 documented species: 29 fishes and three squids.
4. While the prey-specific index of relative importance highlighted that fish dominated the diet in 2014 (32.3% fish, 15.1% squid) and in 2015 (29.9% fish, 22.3% squid), diet composition varied significantly between the two study years.
5. The purpleback flying squid (Stenoteuthis oulaniensis) accounted for 98.7% (232 of 236) of the identified squid specimens. Mantle lengths were significantly longer in 2015 (7.2 ± 1.1 SD cm) than in 2014 (6.3 ± 1.7 SD cm).
6. These results indicate a higher relative abundance and size of the epipelagic squids available to foraging red-footed boobies in 2015, during warm-water conditions associated with the positive phase of the El Niño Southern Oscillation.
7. Due to their diverse diet, red-footed boobies are useful bioindicators of epipelagic nekton assemblages during changing oceanographic conditions. Moreover, their reliance on the purpleback flying squid makes these seabirds ideal samplers of the juveniles of this poorly studied species.
8. Understanding how interannual and longer-term oceanographic variability affects central-place foraging seabirds and the recruitment and abundance of their squid prey is critical for precautionary ecosystem-based fisheries management of oceanic islands and the surrounding marine environment.

     

It is the ambience,not the menu. Prey availability does not drive habitat selection by the endangered Pyrenean desman

1. The Pyrenean desman (Galemys pyrenaicus) is an endangered stream-dwelling insectivore endemic to the Iberian Peninsula and the north of the Pyrenees. It favours riffles over slow habitats such as runs or pools, yet it is still unclear whether habitat preference is based on prey availability or on other factors, such as mechanical constraints on its hunting habits.
2. Desman diet and prey selection were analysed along the pristine Elama Stream and the slightly modified Leitzaran Stream in the Basque Country, Spain.
3. In each stream the prey consumed were identified by metabarcoding 94 desman faeces, and prey availability characterized from 10 Surber samples taken in each habitat type (riffles, runs and pools). Invertebrates were sorted and identified, the biomass of each taxon was calculated, and their DNA was also extracted, amplified using PCR, and sequenced to build a reference database.
4. Prey availability and diet varied between streams. Desmans positively selected shredders and invertebrates that live on the substrate, and selected against taxa that live in fine sediment, taxa with hard shells or those that are highly mobile. The diet of desmans was more selective in the Elama, the stream with better ecological status. Food availability did not differ among habitats, and therefore does not explain the preference of desmans for riffles; rather, mechanical constraints to deal with buoyancy and physical habitat heterogeneity were hypothesized to be the reason behind the habitat preference.
5. The results suggest that promoting the formation of riffles in streams can improve the situation of some desman populations living in degraded habitats.

     

Movement ecology of imperilled fish in a novel ecosystem: River‐reservoir movements by razorback sucker and translocations to aid conservation

1. Reservoirs and associated river fragments are novel ecosystems not experienced by fishes in their evolutionary history, yet they are now commonplace across the globe. Understanding how fishes use these novel habitats is vital to conservation efforts in contemporary riverscapes.
2. Movement patterns of the endangered razorback sucker (Xyrauchen texanus) synthesized from tagging efforts in the upper Colorado River basin, USA, illustrate the applications of tagging technology and data sharing by multiple agencies to better understand the spatial ecology of large river fishes.
3. Tagging studies between 2014 and 2018 in Lake Powell and its two main tributary rivers, the Colorado (unfragmented) and San Juan (waterfall‐fragmented), were used to quantify movement of razorback sucker within this river–reservoir habitat complex. In addition, facilitated translocations of fish upstream of a waterfall barrier in the San Juan River were assessed in 2016–2017.
4. Extensive movement of fish occurred within and across river and reservoir habitats. Of 722 fish captured in the Colorado River arm of Lake Powell, 36% of re‐encounters occurred upstream in the Colorado or Green rivers, or fish dispersed through the reservoir and were detected in the San Juan River arm. Fourteen fish moved more than 600 km. In the San Juan arm of the reservoir, 29% and 20% of fish in 2017 and 2018, respectively, had moved ~30–40 km upstream below the waterfall in the San Juan River within a year. In 2016–2017, 303 fish were translocated upstream of the waterfall into the San Juan River, but 80% were re‐encountered downstream of the waterfall within a year.
5. Long‐distance movements by razorback sucker were common within and among rivers and reservoirs illustrating how large river fish, in general, might maintain population connectivity in highly altered ecosystems.

     

Characterizing tourism benefits associated with top‐predator conservation in coastal British Columbia

1. Facing public concern over costs related to top‐predator reintroductions and conservation, ecosystem services such as ecotourism are often used to evoke benefits that outweigh or offset those costs. Quantifying these benefits using rigorous scientific methods can provide confidence to policymakers and other stakeholders that predators can in fact deliver positive outcomes to people living alongside them. The evaluation of these benefits is often anecdotal or qualitative, however, and empirical quantifications are rare.
2. In coastal marine ecosystems, sea otter reintroduction is seen as a conservation success to some but a bane to others. The contribution of sea otters (Enyhdra lutris) to tourism revenue is touted as a crucial ecosystem service benefit to offset the loss of shellfish harvesting and associated revenue, but remains unquantified, weakening the favourable reception of conservation action.
3. The potential economic benefits of sea otters associated with tourism and the extent to which benefits are realized were evaluated based on: (i) choice‐experiment surveys of tourists; and (ii) interviews with tourism operators in British Columbia.
4. Sea otters were a strong factor in people's choices regarding wildlife viewing, and sea otters could have large benefits for local economies. Alongside socio‐economic characteristics, tourism experience influences tourists’ preferences. Tourism operators did not perceive sea otters as strongly influencing tourist choice, highlighting the gap that can occur between the perception and the reality of tourist preferences, leading to missed opportunities for the alignment of economic development with conservation actions.

     

Prey C:P ratio and phosphorus recycling by a planktivorous fish: advantages of fish selection towards pelagic cladocerans

Prey selection by the small planktivore Galaxias maculatus and phosphorus gain depending on diet has been examined related to predator–prey daily distribution. Prey elemental composition (C:P ratio) was analysed as a factor of selectivity. Field experiments were carried out to evaluate the effect of prey on phosphorus recycling. Results revealed that the pelagic cladoceran Ceriodaphnia dubia was a highly selected prey by all fish sizes at dawn and dusk, despite its low abundances in comparison with other zooplankters, while the littoral were ingested only during day. The high selectivity for C. dubia showed that G. maculatus moved to pelagic zone during night to consume this prey but returned to littoral areas during day due to the increase in predation risk. Analysis of elemental composition revealed that P content of C. dubia was significantly higher than other planktonic or littoral prey (Bosmina longirostris, Boeckella gracilipes and chironomids). Phosphorus recycling experiments showed that G. maculatus would transport and supply P in available forms for primary producers. Fish size was observed to influence P recycling as YOY had significant higher mass‐specific P release in the morning and mid‐day when they preyed mainly upon C. dubia. Low prey C:P ratio appears as a factor that would add benefits to the classical visual fish selection towards cladocerans, as this preference would imply a net phosphorus gain for fish.     

Intensive fishing has not forced dietary change in the South American fur seal Arctophoca (=Arctocephalus) australis off Río de la Plata and adjoining areas

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Movement patterns and habitat use of smalltooth sawfish,Pristis pectinata,determined using pop‐up satellite archival tags

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