Using DNA metabarcoding to investigate diet and niche partitioning in the native European otter (Lutra lutra) and invasive American mink (Neovison vison)

In the UK, the native European otter (Lutra lutra) and invasive American mink (Neovison vison) have experienced concurrent declines and expansions. Currently, the otter is recovering from persecution and waterway pollution, whereas the mink is in decline due to population control and probable interspecific interaction with the otter. We explored the potential of DNA metabarcoding for investigating diet and niche partitioning between these mustelids. Otter spraints (n = 171) and mink scats (n = 19) collected from three sites (Malham Tarn, River Hull and River Glaven) in northern and eastern England were screened for vertebrates using high-throughput sequencing. Otter diet mainly comprised aquatic fishes (81.0%) and amphibians (12.7%), whereas mink diet predominantly consisted of terrestrial birds (55.9%) and mammals (39.6%). The mink used a lower proportion (20%) of available prey (n = 40 taxa) than the otter and low niche overlap (0.267) was observed between these mustelids. Prey taxon richness of mink scats was lower than otter spraints and beta diversity of prey communities was driven by taxon turnover (i.e. the otter and mink consumed different prey taxa). Considering otter diet only, prey taxon richness was higher in spraints from the River Hull catchment and beta diversity of prey communities was driven by taxon turnover (i.e. the otter consumed different prey taxa at each site). Studies using morphological faecal analysis may misidentify the predator as well as prey items. Faecal DNA metabarcoding can resolve these issues and provide more accurate and detailed dietary information. When scaled up across multiple habitat types, DNA metabarcoding should greatly improve future understanding of resource use and niche overlap between the otter and mink.

Using DNA metabarcoding to investigate diet and niche partitioning in the native European otter (Lutra lutra) and invasive American mink (Neovison vison)

In the UK, the native European otter (Lutra lutra) and invasive American mink (Neovison vison) have experienced concurrent declines and expansions. Currently, the otter is recovering from persecution and waterway pollution, whereas the mink is in decline due to population control and probable interspecific interaction with the otter. We explored the potential of DNA metabarcoding for investigating diet and niche partitioning between these mustelids. Otter spraints (n = 171) and mink scats (n = 19) collected from three sites (Malham Tarn, River Hull, and River Glaven) in northern and eastern England were screened for vertebrates using high-throughput sequencing. Otter diet mainly comprised aquatic fishes (81.0%) and amphibians (12.7%), whereas mink diet predominantly consisted of terrestrial birds (55.9%) and mammals (39.6%). The mink used a lower proportion (20%) of available prey (n = 40 taxa) than the otter, and low niche overlap (0.267) was observed between these mustelids. Prey taxon richness of mink scats was lower than otter spraints, and beta diversity of prey communities was driven by taxon turnover (i.e. the otter and mink consumed different prey taxa). Considering otter diet only, prey taxon richness was higher in spraints from the River Hull catchment, and beta diversity of prey communities was driven by taxon turnover (i.e. the otter consumed different prey taxa at each site). Studies using morphological faecal analysis may misidentify the predator as well as prey items. Faecal DNA metabarcoding can resolve these issues and provide more accurate and detailed dietary information. When upscaled across multiple habitat types, DNA metabarcoding should greatly improve future understanding of resource use and niche overlap between the otter and mink.

Update on the Geographic Distribution of Lutra lutra at the Romanian Black Sea Coast

We report the occurrence of the European otter (Lutra lutra Linnaeus, 1758) along the entire Romanian Black Sea coast, for the first time. Several sightings were within the harbor and the city of Constanţa, indicating that the otter can accommodate to and tolerate high human impact. The report is based on observations made between 2012 and 2015. The species has been previously reported from all Romanian regions but not from the Black Sea coast. The occurrences reported within this article confirm an extension of the range of this Near Threatened species on the Romanian Black Sea coast, most probably due to the increasing of population size from other sources such as the Danube floodplain.

Dietary specifications reflect the feeding behaviour of the European otter (Lutra lutra) in “Strandzha” Natural Park (Bulgaria)

Within the scope of the present study a field survey in the area of “Strandzha” Natural Park in south-east Bulgaria was carried out. The main goal of the investigation was to gain more detailed information on the diet of the European otters (Lutra lutra) that inhabit the park. As indicators for the presence of the mustelids a set of standard procedures, such as footprints tracking and inspecting the terrain for otter spraints were used. A total of 204 excrements were found, measured, documented and then disintegrated in water. The food rests in the faeces were investigated and the diet of the local population was documented. On the base of the results we separated the excrements into six groups and analysed the relations between the contents of the spraints and the characteristics of the habitat where they were found. We discovered a clear tendency toward piscivory in the middle and down streams of the studied rivers in the Natural Park. In the upper streams, otters relied almost exclusively on invertebrates like bivalves and crayfish as food source. The fact, that even suboptimal habitats, which offered invariable menu, were exploited by the otters is an indication for the stability of the local population.

Performance Characteristics of AOAC Method 2005.06 for the Determination of Paralytic Shellfish Toxins in Manila Clams, European Otter Clams, Grooved Carpet Shell Clams, Surf Clams, and Processed King Scallops

An approach was developed for the verification of method performance of the AOAC 2005.06 LC-fluorescence detector (FLD) method for determination of paralytic shellfish poisoning (PSP) toxins in bivalve shellfish. This was developed following advice published by the Analytical Laboratory Accreditation Criteria Committee and applied to shellfish species that had not been previously subjected to a full single-laboratory validation scheme. The refined approach was developed following the need to assess performance in a number of shellfish species infrequently monitored through the UK statutory monitoring program, while reducing the impact and cost of the studies, most notably in terms of the use of valuable reference standards. The species assessed were manila clams (Ruditapes philippinarum), European otter clams (Lutraria lutraria), grooved carpet shell clams (R. decussatus), surf clams (Spisula solida), and king scallops (Pecten maximus) presented as adductor only or adductor plus roe. The method was assessed for sensitivity in terms of LOD and LOQ, toxin recovery, and method precision in each species. It incorporated the PSP toxins deemed toxic and/or prevalent in UK samples and commercially available as certified reference standards. The toxins studied included GTX1-5, dcSTX, STX, C1&2, and NEO. The toxins dcGTX2&3 were included for surf clams due to the prevalence of these toxins in this species as a result of toxin decarbamoylation. Method performance targets were met for each of the characteristics investigated. Consequently, the method was deemed fit for purpose for the screening and quantification of these clam and scallop species for PSP toxins by AOAC Method 2005.06 LC-FLD.

The mechanisms of intertidal fish coexistence: a model

Research into the ecology of intertidal fishes of the U.K. appears to be lacking, reportedly due to the mobility and cryptic nature of the more common species. However, some intertidal fishes contribute to the diets of commercially important species such as cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and near-threatened European otter (Lutra lutra). The current study contains the first comprehensive research into the ecology of intertidal fishes from the English, Yorkshire coast and Welsh, Anglesey coast, identifying and addressing the mechanisms which allow for their coexistence. Seven mechanisms were identified which promote interspecific fish coexistence. It was found that coexistence can occur when: (I) fish diversity on a shore is low, thus minimising high degrees of co-occurrence within pools, (II) co-occurrence on shores (at tidal height level) is minimal and when fishes do co-occur, they are of similar sizes thus reducing size-dominated hierarchies, (III) the significant variables which predict fish presences differ, (IV) there is an abundance of shelter/protection readily available, which reduces the competition to access such features, (V) morphology is such, that for the majority of the year, it is more profitable for the piscivorous fishes to predate on food items other than fish, (VI) competition for prey items is reduced, when variability of resources is high, and (VII) there is a difference in the most targeted prey items between fish species, despite some overlap in targeted prey items.

The mechanisms of intertidal fish coexistence: a model

Research into the ecology of intertidal fishes of the U.K. appears to be lacking, reportedly due to the mobility and cryptic nature of the more common species. However, some intertidal fishes contribute to the diets of commercially important species such as cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and near-threatened European otter (Lutra lutra). The current study contains the first comprehensive research into the ecology of intertidal fishes from the English, Yorkshire coast and Welsh, Anglesey coast, identifying and addressing the mechanisms which allow for their coexistence. Seven mechanisms were identified which promote interspecific fish coexistence. It was found that coexistence can occur when: (I) fish diversity on a shore is low, thus minimising high degrees of co-occurrence within pools, (II) co-occurrence on shores (at tidal height level) is minimal and when fishes do co-occur, they are of similar sizes thus reducing size-dominated hierarchies, (III) the significant variables which predict fish presences differ, (IV) there is an abundance of shelter/protection readily available, which reduces the competition to access such features, (V) morphology is such, that for the majority of the year, it is more profitable for the piscivorous fishes to predate on food items other than fish, (VI) competition for prey items is reduced, when variability of resources is high, and (VII) there is a difference in the most targeted prey items between fish species, despite some overlap in targeted prey items.