Conservation of habitats and flagship species, such as the Asian small-clawed otter, is one of the most effective ways to conserve aquatic biodiversity. The study was conducted at Karlapat wildlife ...sanctuary, Odisha, India, and aims to determine the habitat and diet preferences of Asian small-clawed otters. Presence-absence of Asian small-clawed otters and associated habitat variables were recorded along 1-km sections of streams and rivers. We used principal component analysis (PCA) and logistic regression to examine habitat variables influencing otter presence along streams and rivers. Diet analysis of Asian small-clawed otters was conducted to calculate the percent frequency of occurrence and score-bulk estimate of each food item in the study area. We found that the presence of Asian small-clawed otters was related to denser canopy, higher shrub cover, and rocky stretches. A logistic regression model showed that Asian small-clawed otters significantly selected for higher canopy cover. Crabs were found to be the most preferred food item (>80%) in the diet of Asian small-clawed otters. These findings shed light on the regional-scale habitat selection and diet of Asian small-clawed otters and indicate important species-habitat relationships, thus providing valuable information for conservation management and land-use planning. La conservation des habitats et des espèces clés, telles que la loutre cendrée, est un des moyens les plus efficaces pour préserver la biodiversité aquatique. L'étude a été menée dans le sanctuaire faunique de Karlapat (Odisha, Inde) et visait à déterminer les préférences d'habitat et de diète de loutres cendrées. La présence-absence de loutres cendrées et les variables d'habitat associées ont été enregistrées le long de sections de 1 km de ruisseaux et de rivières. Nous avons utilisé l'analyse en composantes principales et la régression logistique pour examiner les variables d'habitat influençant la présence de loutres le long de ruisseaux et rivières. L'analyse de la diète des loutres cendrées a permis de calculer la fréquence d'occurrence et l'estimation globale du score de chaque item alimentaire dans l'aire d'étude. Nous avons trouvé que la présence de loutre cendrée est liée aux couverts plus denses, au recouvrement arbustif plus élevé et à la présence d'affleurements rocheux. Un modèle de régression logistique a montré que les loutres cendrées sélectionnent significativement les couverts plus denses. Les crabes sont l'item alimentaire préféré (>80%) dans la diète des loutres cendrées. Ces résultats renseignent sur la sélection d'habitat régionale et sur la diète des loutres cendrées et pointent vers d'importantes relations espèce-habitat, fournissant ainsi de l'information utile à la conservation et à la planification de l'utilisation du territoire.
Numerical simulation is an important method for calculating the hydrodynamic performance of otter boards used in sea floor trawling. Although such simulations have been explored in prior studies, the ...effects of the proximity of the otter boards to the seafloor and the plume of upward-drawn sediment during bottom trawling have largely been ignored. In this study, we assessed these factors. The results show that within the angles of attack used during normal operations, the effect of the seafloor bottom boundary of the flow field on the hydrodynamic performance of an otter board is obvious. We found that when the ratio of the distance between the bottom of an otter board and the surface boundary of the flow field to the chord length of the board exceeds 0.4, the influence of the bottom boundary of the flow field on the hydrodynamic performance of the board is negligible. For values of less than 0.4, the seafloor bottom boundary has an increasingly obvious impact on the hydrodynamic performance as this ratio decreases. We also found that the turbid plume of ocean floor sediment raised during bottom trawling has an obvious effect on the lift and resistance coefficients of an otter board at high angles of attack. At low angles, this effect on the lift-to-drag ratio is reversed and less obvious. The simulation results show that the optimal lift-to-drag ratio decreases with an increase in the sediment concentration; however, beyond a certain threshold, an increasing concentration of sediments was not found to have an obvious impact on the lift-to-drag ratio.
Animal stone-handling behavior (SH) has been recorded in detail only in primates, mainly across macaque species. The purpose(s) of SH are still unknown, yet various hypotheses have been suggested, ...including that it is a misdirected behavior when hungry and/or a play behavior that aids individuals' motor and stone tool-use development. SH has also been observed across both wild and captive otter species, but no overview report of the extent of this behavior across otter species has been published yet. To fill this gap in the literature, we contacted wild and captive otter researchers and keepers to enquire directly on SH in the species they work with. We accepted anecdotal reports in this first review of the behavior. Using the reports and anecdotes thus obtained, we compiled the first list of otter species that show SH. We found that most (10 out of 13) of currently known otter species practice SH. Therefore, similarly to macaques, SH is also common in otters and occurs in the majority of species. Future studies should focus on replicating these findings and further investigating the potential functions and selection pressures of SH in otters and other animal species.
The Neotropical otter Lontra longicaudis is a top predator in aquatic ecosystems from North, Central, and South America and is subjected to substantial environmental distress due to historic and ...contemporary anthropogenic disturbance. Currently, L. longicaudis is considered 'near threatened' by the International Union for Conservation of Nature Red List of Threatened Species. This study renders the first genomic resource for L. longicaudis; its mitochondrial genome was assembled and characterised in detail. The AT-rich mitochondrial genome of L. longicaudis was 16,436 bp in length and encoded 13 protein coding genes (PCGs), 22 transfer RNA genes, two ribosomal RNA genes, and a 994 bp long putative control region (CR). The heavy use of CTA (Leu), ATA (Met), and ATC (Ile) codons in PCGs contributes to the AT-rich nature of this genome. Out of 22 tRNAs, tRNA-Ser (AGY) (trnS1) lacked a typical 'cloverleaf' secondary structure. In the CR, numerous microsatellites and two tandem repeats were detected as well as multiple 'hairpin' structures. Ka/Ks values estimated for all but one PCG were < 1, indicating purifying selection in most PCGs. atp8 experienced neutral selection. A phylogenomic analysis based on PCGs confirms the monophyly of the family Mustelidae and also supports the monophyletic status of the subfamilies Guloinae, Helictidinae, Melinae, Mustelinae and Lutrinae; Ictonychinae was found to be polyphyletic. In the Lutrinae, L. longicaudis had an early branching position. The characterisation of a complete mitochondrial genome in the Neotropical otter L. longicaudis constitutes the first step towards supporting conservation efforts using genomic tools in this and other mustelids inhabiting aquatic neotropical environments under considerable contemporary anthropogenic disturbance.
Opportunistic records of animal occurrence may be problematic for inferring species distribution and habitat requirements because of unknown and uncontrolled sources of sampling variance. In this ...study, we used occurrence records for river otters (Lontra canadensis) derived from sign surveys, road kills, trapper bycatch, and opportunistic sightings (n=185 records collected 2001–2012) to assess the potential distribution and habitat relationships of otters across central and western New York, USA. To mitigate for obvious observation biases, we standardized observation intensity across regions a priori and restricted inference to readily accessible areas (i.e., ≤700m from the nearest road). Model selection, and the direction of covariate effects, proved robust to these sampling biases although effect sizes varied −7.1% to +48.0% after bias correction, with the coefficient for the proportion of available shoreline being the most unstable. Ultimately, the top bias-corrected model proved a reliable index for otter probability of occurrence given a strong, positive, and linear relationship with a withheld set of standardized survey records for otters collected in winter 2016–2017 (n=57; R²=0.90). This model indicated that approximately 20% of the study area represented high probability of otter occurrence. We demonstrated that reliable inference on wildlife habitat requirements can be obtained from disparate records of animal occurrence provided that data biases are known and effectively mitigated.
The shape optimization approach of the cambered otter board has been performed by the integration of the neural network model and the multi-objective genetic algorithm (MOGA). Because the excellent ...performance of an otter board is expressed by great lift and less drag force, in this study the lift and drag coefficients were chosen as objective functions to obtain the optimal otter board. The Bézier curve represented the cambered otter board as a simple structure with five control points resulting in the six coordinates, which were adopted as the design variables. The hydrodynamic characteristics of twenty-five otter board models were calculated in a two-dimension computational fluid dynamics (CFD) analysis at an attack angle of 20°. The implicit fitness function in the MOGA algorithm was then obtained by the backpropagation neural network model based on the estimated results of CFD calculation. A set of thirty optimal otter board models were extracted in the optimal solutions of the MOGA, and two optimal models were selected to verify the feasibility of the approach by hydrodynamic and visualization experiments with a comparative hyper-lift trawl door (HLTD). The model 1 showed greatest lift-to-drag ratio before the attack angle of 30° as a high lift-to-drag ratio otter board, and the model 2 showed a large lift coefficient and lift-to-drag ratio than the HLTD before the attack angle of 25° as a large lift force otter board. Through the flow distribution around the model 2, it is observed that the flow separation on the suction side is prevented as a result of less drag owing to the modified shape. In summary, the shape optimization approach is efficient in designing optimal otter board to satisfy supposed needs in otter trawling.
Abstract
Fisheries using bottom trawls are the most widespread source of anthropogenic physical disturbance to seafloor habitats. To mitigate such disturbances, the development of fisheries-, ...conservation-, and ecosystem-based management strategies requires the assessment of the impact of bottom trawling on the state of benthic biota. We explore a quantitative and mechanistic framework to assess trawling impact. Pressure and impact indicators that provide a continuous pressure–response curve are estimated at a spatial resolution of 1 × 1 min latitude and longitude (∼2 km2) using three methods: L1 estimates the proportion of the community with a life span exceeding the time interval between trawling events; L2 estimates the decrease in median longevity in response to trawling; and population dynamic (PD) estimates the decrease in biomass in response to trawling and the recovery time. Although impact scores are correlated, PD has the best performance over a broad range of trawling intensities. Using the framework in a trawling impact assessment of ten métiers in the North Sea shows that muddy habitats are impacted the most and coarse habitats are impacted the least. Otter trawling for crustaceans has the highest impact, followed by otter trawling for demersal fish and beam trawling for flatfish and flyshooting. Beam trawling for brown shrimps, otter trawling for industrial fish, and dredging for molluscs have the lowest impact. Trawling is highly aggregated in core fishing grounds where the status of the seafloor is low but the catch per unit of effort (CPUE) per unit of impact is high, in contrast to peripheral grounds, where CPUE per unit of impact is low.
Abstract The Eurasian otter, Lutra lutra , faced adversity in Europe in the 1950s and 1960s due to hunting, declining fish populations and the American mink invasion. Slow recovery since the 1970s ...led to a ‘Near Threatened’ in the IUCN Red List status, but recent pollution, fishing pressure and habitat loss caused slight population declines. Otters, known for aquatic habits, are mainly piscivorous and exhibit solitaire or social behaviours. Infanticide with parent‐offspring cannibalism has been previously reported in otter species, but although cannibalism has been suggested, it has not been documented before. This study presents the first documented case of cannibalism among free‐living Eurasian otters observed in northern Norway. Some authors described cannibalism as an opportunistic resource‐efficient behaviour in several mammal species, offering benefits like weight gain and reduced competition, challenging the view of adverse health effects. Factors leading to otter cannibalism include ecological changes, resource competition with other species and global warming and overfishing practices contributing to increased otter competition. Further studies will be vital to answering intriguing questions about the implications of cannibalism for otter conservation.
Keystone predators can impact many prey species, including those that are endangered. A requisite to assess the impact predators have on different prey populations is to identify the species being ...consumed in different types of communities, while accounting for possible seasonal variation in consumption. Here we used analysis of North American river otter (Lontra canadensis) scat to assess the impact river otters have on their prey populations, particularly endangered salmonids and migrating birds. We analyzed the prey composition of 1,411 river otter scats collected from 10 sites in Humboldt County, California, between 2011 and 2012. Analysis of prey items in scat placed study sites into four distinct clusters based on diet. Fish, mostly from the families Gasterosteidae, Cottidae, and Pholidae, formed the primary prey component, and crustaceans, birds, amphibians, and insects, also were important components of river otter diet. Salmonids constituted < 5% of overall diet, but river otters consumed the largest percentage of salmon during salmon spawning season at the inland cluster where salmonids spawn. Scat marking intensity varied between clusters and seasons, with the most scats collected in the autumn and the fewest in the winter/spring, except at the inland cluster where the pattern of marking activity was reversed. River otters may be responding to seasonal migrations of endangered and threatened salmonids. Diet surveys of this type are useful for monitoring resource use by top predators in aquatic ecosystems.
Abstract Assumptions about gear efficiency and catchability influence estimates of abundance, mortality, reference points and catch potential. Despite the need to better quantify fishing effects on ...some target species and on many non-target species taken as bycatch, there are few gear efficiency estimates for some of the most widely deployed towed fishing gears in the northeast Atlantic. Here, we develop a method that applies generalised additive models to catch-at-length data from trawl surveys and a commercial catch and discard monitoring program in the North Sea to estimate catch-ratios. We then rescale these catch-ratios and fit relationships to estimate gear efficiency. When catches of individuals by species were too low to enable species-specific estimates, gear efficiency was estimated for species-groups. Gear efficiency (and associated uncertainty) at length was ultimately estimated for 75 species, seven species-groups and for up to six types of trawl gear per species or species-group. Results are illustrated for dab (Limanda limanda), grey gurnard (Eutrigula gurnardus) and thornback ray (Raja clavata), two common non-target species and a depleted elasmobranch. All estimates of gear efficiency and uncertainty, by length, species, species-group and gear, are made available in a supplementary data file.
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