Bottom trawl fishing has widespread impacts on benthic habitats and communities. The benthic response to trawling seems to be smaller or absent in areas exposed to high natural disturbance, leading ...to the hypothesis that natural and trawl disturbance affect benthic communities in a similar way. However, systematic tests of this hypothesis at large spatial scales and with data from sites spanning a large range of natural disturbance do not exist. Here, we examine the effects of trawl and natural (tidal-bed shear stress) disturbance on benthic communities over gradients of commercial bottom trawling effort in 8 areas in the North and Irish Seas. Using a trait-based approach, that classified species by life-history strategies or by characteristics that provide a proxy for their role in community function, we found support for the hypothesis that trawl and natural disturbance affect benthic communities in similar ways. Both sources of disturbance caused declines in long-living, hard-bodied (exoskeleton) and suspension-feeding organisms. Given these similar impacts, there was no detectable trawling effect on communities exposed to high natural disturbance. Conversely, in 3 out of 5 areas with low bed shear stress, responses to trawling were detected and resulted in community compositions comparable with those in areas subject to high natural disturbance, with communities being composed of either small-sized, deposit-feeding animals or mobile scavengers and predators. The findings highlight that knowledge of the interacting effects of trawl and natural disturbance will help to identify areas that are more or less resilient to trawling and support the development of management plans that account for the environmental effects of fishing.
•The Neotropical otter has previously been recorded in the Yucatan Peninsula.•Flagship species promote ecosystem conservation actions.•We investigate the perception of local people through ...semi-structured interviews.•Local people provided information on the distribution of the Neotropical otter.•The Neotropical otter does not negatively impact local human communities.
There are historical reports of the Neotropical otter (Lontra longicaudis) in water bodies of the Yucatan Peninsula, and some efforts have been made to understand villagers’ perceptions of this threatened species. However, these studies vary in terms of season and location, and the data are limited and outdated. To help fill these gaps, our objective was to determine the current local knowledge on the conservation status of this species in the southern Yucatan Peninsula, Mexico, and the northeastern part of Petén, Guatemala. In 2021 and 2022, we conducted 90 semi-structured interviews with users of local water bodies in Mexico, including Río Hondo (n = 52), Laguna Bacalar (n = 17), and Laguna Guerrero (n = 6), and two natural protected areas (n = 15) in Petén, Guatemala. We tested whether associations existed between the characteristics of the interviewees (e.g., schooling level and activity in the water body) and their responses. We obtained information on 122 otter sightings, most of which involved single individuals (80 %). We found associations among the schooling level (e.g., elementary, high school), the activities of the interviewees (e.g., fishing, tourism services, technical activities), the water bodies and the perceived threats and values given to the otter. Our study provides updated information on the local perception of the species in a transboundary region and suggests that this species does not pose a competitive threat to local human fishing interests. Therefore, this species could be considered a flagship species for promoting regional conservation awareness in unprotected areas.
THE EFFECTS OF TRAY DENSITY AND CARE REGIMES ON GROWTH AND SURVIVAL RATE OF SNOUT OTTER CLAM Cao Truong Giang, Tran The Muu, Tran Thi Thuy, Le Van Khoi, Nguyen Thi Bien Thuy, Nguyen Duc Tuan, Tran Thi Nguyet Minh, Dang Thi Lua, Cao Van Hanh, Hoang Nhat Son, Nguyen Thi Dieu Phuong, Nguyen Manh Cuong; Le Thi Linh; Vu Van In ...
Tạp chí Khoa học,
03/2024, Letnik:
53, Številka:
1A
Journal Article
Recenzirano
Odprti dostop
This study aims to identify suitable density of suspended trays and care regime, which was conducted from February to November 2022 at Tay Van Boi, Lan Ha Bay, Cat Ba, Cat Hai - Hai Phong to improve ...growth, survival rates and helping to shorten the time for snout otter clam grow-out culture. The experiment was carried out with 3 treatments: Densities of 4, 8 and 12 trays/4 m2 combined with 3 care regimes during grow-out culture. The results showed that densities of 4 and 8 trays/4 m2 were higher growth than the remaining treatment, specifically length was from 32.9 - 36.8 mm and survival rate was over 84%, with a significant difference, compared to a density of 12 trays/4 m2 with 3 different care regimes. The results show that to increase productivity and reduce production costs and care time, a density of 8 trays/4 m2 with 3 care regimes/a culturing period should be chosen. The study has also propounded disease prevention and treatment measures for the Snout otter clam to help control the disease well and proposed solutions on farming techniques that contribute to high and sustainable economic efficiency.
Installing artificial lights on fishing gear is increasingly being explored to alter the behaviour of fish during the capture process and modify selectivity. We investigated the effect of introducing ...artificial light on a commercial trawler operating in the English southwest mixed demersal fishery. Total catch and species vertical separation were compared and analysed in two identical separator trawls towed simultaneously. One trawl was equipped with blue LEDs along its headline, the other trawl served as a control to allow for pairwise catch comparison. Fishing trials were conducted at night and during the day. In the presence of lights, catches-at-length of haddock (Melanogrammus aeglefinus) were lower during the night and marginally higher during the day. Catches of grey gurnard (Eutrigla gurnardus), megrim (Lepidorhombus whiffiagonis) and whiting (Merlangius merlangus) were unaffected by lights. In terms of vertical separation, in the presence of lights, more haddock were retained in the lower codend during the day and night. Lights also increased the proportion of catches in the lower codend for grey gurnard, whiting and Northern squid (Loligo forbesii), but only during the day. This study shows there are species-specific reactions to artificial light during the trawl capture process and these reactions can be different between day and night. When reviewed with other studies, some common observations are identified, indicating that lights can change the behaviour of some species which normally rise inside the trawl during the capture process, such as haddock. The use of artificial lights offers an alternative method to modify trawl selectivity, by utilising species-specific reactions to light, and the ability to change the position and characteristics of the light, offers many avenues to investigate.
In addition to forecasting population growth, basic demographic data combined with movement data provide a means for predicting rates of range expansion. Quantitative models of range expansion have ...rarely been applied to large vertebrates, although such tools could be useful for restoration and management of many threatened but recovering populations. Using the southern sea otter (Enhydra lutris nereis) as a case study, we utilized integro-difference equations in combination with a stage-structured projection matrix that incorporated spatial variation in dispersal and demography to make forecasts of population recovery and range recolonization. In addition to these basic predictions, we emphasize how to make these modeling predictions useful in a management context through the inclusion of parameter uncertainty and sensitivity analysis. Our models resulted in hind-cast (1989-2003) predictions of net population growth and range expansion that closely matched observed patterns. We next made projections of future range expansion and population growth, incorporating uncertainty in all model parameters, and explored the sensitivity of model predictions to variation in spatially explicit survival and dispersal rates. The predicted rate of southward range expansion (median = 5.2 km/yr) was sensitive to both dispersal and survival rates; elasticity analysis indicated that changes in adult survival would have the greatest potential effect on the rate of range expansion, while perturbation analysis showed that variation in subadult dispersal contributed most to variance in model predictions. Variation in survival and dispersal of females at the south end of the range contributed most of the variance in predicted southward range expansion. Our approach provides guidance for the acquisition of further data and a means of forecasting the consequence of specific management actions. Similar methods could aid in the management of other recovering populations.
Over the past century, the southern sea otter (SSO; Enhydra lutris nereis) population has been slowly recovering from near extinction due to overharvest. The SSO is a threatened subspecies under ...federal law and a fully protected species under California law, US. Through a multiagency collaborative program, stranded animals are rehabilitated and released, while deceased animals are necropsied and tissues are cryopreserved to facilitate scientific study. Here, we processed archival tissues to enrich particle-associated viral nucleic acids, which we randomly amplified and deeply sequenced to identify viral genomes through sequence similarities. Anelloviruses and endogenous retroviral sequences made up over 50% of observed viral sequences. Polyomavirus, parvovirus, and adenovirus sequences made up most of the remaining reads. We characterized and phylogenetically analyzed the full genome of sea otter polyomavirus 1 and the complete coding sequence of sea otter parvovirus 1 and found that the closest known viruses infect primates and domestic pigs (Sus scrofa domesticus), respectively. We tested archived tissues from 69 stranded SSO necropsied over 14 yr (2000–13) by PCR. Polyomavirus, parvovirus, and adenovirus infections were detected in 51, 61, and 29% of examined animals, respectively, with no significant increase in frequency over time, suggesting endemic infection. We found that 80% of tested SSO were infected with at least one of the three DNA viruses, whose tissue distribution we determined in 261 tissue samples. Parvovirus DNA was most frequently detected in mesenteric lymph node, polyomavirus DNA in spleen, and adenovirus DNA in multiple tissues (spleen, retropharyngeal and mesenteric lymph node, lung, and liver). This study describes the virome in tissues of a threatened species and shows that stranded SSO are frequently infected with multiple viruses, warranting future research to investigate associations between these infections and observed lesions.
Conserving species inhabiting areas overlapped with human settlements is more challenging than usual as anthropogenic impacts need to be accounted for when management plans are formulated. This study ...aims to identify conservation priority areas for two otter species and evaluate the impact of land-use changes on conservation management in the coastal wetlands of southern Thailand. We conducted camera-trap surveys across 283 grids of 25 km2 each between 2016 and 2020. A single-species occupancy model was applied to estimate the occupancy probability of two otter species in relation to landscape characteristics and human factors. Occupancy probabilities were then correlated with anthropogenic threat levels obtained from Bayesian Belief Network to identify conservation management hotspots and conservation importance areas under various scenarios. The Smooth-coated Otter shows a higher occupancy probability in the Andaman, where a larger proportion of less disturbed wetlands remains compared to the Gulf. The Small-clawed Otter, in contrast, has higher occupancy in the Gulf. In the Andaman, the Smooth-coated Otter appears to occupy areas associated with lower human impacts and a higher proportion of natural habitats, while in the Gulf, both otter species have higher occupancy in areas where modifications of natural habitats are more intensive. In total, 1350 km2 were identified as very high conservation management hotspots, with an additional 750 km2 identified as very high conservation importance. The majority of these areas were located along the Andaman coast. However, land-use changes expanded the management hotspot areas to 2025 km2 while reducing conservation importance areas to just 175 km2. Our results emphasize the importance of protecting natural habitats and the urgency of implementing management interventions for otters on the Andaman coast, for the long-term survival of these threatened species.
The fishery for Patagonian scallop (Zygochlamys patagonica) in Argentinean waters began over 25 years ago. This fishery - utilizing bottom otter trawl gear - was the first scallop fishery in the ...South-West Atlantic certified under the Marine Stewardship Council scheme, firstly in 2006, and recertified in 2012 and 2017. However, there is still no data available on its relationship with non-target species such as seabirds that attend these operations. This is the first study investigating the direct interactions between seabirds and this fishery. Records were obtained by observers tasked onboard two freezer trawlers (representing 50% of the whole fleet) from early October 2019 to mid-March 2020. Procellariiformes dominated the attending seabird assemblages; being the Black-browed albatross (Thalassarche melanophris), White-chinned petrel (Procellaria aequinoctialis), Great shearwater (Ardenna gravis), Atlantic-yellow nosed albatross (T. chlororhynchos), Southern giant petrel (Macronectes giganteus), Royal albatrosses (Diomedea sandfordi/epomophora) and the Cape petrel (Daption capense) the most frequent and abundant species. Seabird abundance decreased with increasing swell height and increased with cloud coverage. Seabird interactions with the vessel or fishing gear were recorded in 4.3% of the surveys (i.e. number of hauls), resulting in an estimated rate of 0.11 seabird contacts with fishing gear per haul, the bulk of which corresponded to Black-browed albatrosses and Great shearwaters. A single individual was bycaught during the study period, meaning a mortality rate of < 0.001 birds per haul. The interactions increased during towing operations compared to shooting and haulback. The information presented in this study contribute to the implementation of actions in the Argentine National Plan of Action - Seabirds as well as monitoring and conservation actions that Argentina undertakes in compliance with international instruments. Moreover, this information is relevant to the current fishery certification process.
•First data on seabird interactions with the Patagonian scallop fishery.•Procellariiform birds dominated the attending assemblages.•Low occurrence of seabird interactions and bycatch were registered.•Information relevant to the implementation of the Argentine NPOA-Seabirds.•Information also pertinent to the current fishery certification process.
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