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1.
Sérgio Amorim Miguel N. Santos Rui Coelho Joana Fernandez‐Carvalho 《水产资源保护:海洋与淡水生态系统》2015,25(4):518-533
- This paper reports the results of using different hook style and bait type combinations on the catches of targeted, bycatch and discarded fishes in the Portuguese commercial longline fishery targeting swordfish (Xiphias gladius) in the South Atlantic Ocean.
- In total, 310 longline experimental sets (446 400 hooks) were deployed between October 2008 and February 2012. Three different hook styles were tested; the traditional J‐hook (9/0) 10o offset was compared with two 17/0 circle hooks (a non‐offset and a 10o offset), and squid (Illex spp.) bait was compared with mackerel (Scomber spp.).
- Catch per unit effort (CPUE) was calculated for each fish species per fishing set and compared between the different hook style and bait type combinations. Results indicated that the effects of hook style and bait on the CPUEs were species‐specific. For example, swordfish (target species, Xiphias gladius) CPUEs were higher with J‐hooks baited with squid, while for the blue shark (most important bycatch species, Prionace glauca) the highest CPUEs were obtained with circle hooks baited with mackerel. For tuna (Thunnus spp.) and marlin (blue, Makaira nigricans and white, Kajikia albida) only the bait effect was significant, with higher catches with squid.
- For the discarded species, the proportions of alive vs dead specimens at the time of fishing gear retrieval were also species‐specific.
- The total retained catch value per unit of effort (VPUE) did not changed between the different hook and bait combinations, but these VPUEs are highly dependent on market fluctuations.
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Caroline S. Andrews L. E. Miranda Daniel B. Goetz Robert Kröger 《水产资源保护:海洋与淡水生态系统》2014,24(5):634-644
- In the alluvial valley of the lower Mississippi River, floodplain lakes form isolated aquatic fragments that retain differing degrees of connectivity to neighbouring rivers. Within these floodplain lakes it was hypothesized that fish species composition, relative abundance, and biodiversity metrics would be shaped largely by aquatic connectivity within a catchment.
- Fish assemblages in 13 floodplain lakes (five on‐channel; eight off‐channel) were assessed with electrofishing in 2006–2012 in the Bear Creek catchment, Mississippi, USA. Bear Creek spans approximately 80 km before draining into the Yazoo River, a tributary of the Mississippi River.
- Fish assemblages in on‐channel and off‐channel lakes were different, and fish assemblages in on‐channel lakes were as a group more homogeneous than off‐channel lakes. Moreover, a longitudinal gradient in fish assemblages occurred in on‐channel lakes. The observed patterns in fish assemblages are linked largely to differing intensities in connectivity among lakes within the catchment. Lakes with irregular connections have greater individuality, whereas lakes with continuous or chronic connection are more similar. The wide variation in connectivity could be a key to the distinctive biodiversity of catchments and the focus of fish conservation programmes.
- Off‐channel floodplain lakes are among the first landscape elements to vanish as a consequence of agricultural development. These habitats tend to accumulate sediments at fast rates and are converted to agricultural land as soon as suitable drainage can be attained. Considering that off‐channel lakes with limited connectivity contribute greatly to the heterogeneity of fish assemblages, such losses pose great concerns to conservation of biodiversity.
3.
Jonathan D. Midwood Nicholas A. Cairns Lauren J. Stoot Steven J. Cooke Gabriel Blouin‐Demers 《水产资源保护:海洋与淡水生态系统》2015,25(1):71-80
- Bycatch of non‐target species in commercial fishing nets can have adverse impacts on their populations. Freshwater turtle populations are particularly susceptible to increases in adult mortality, and freshwater turtles are among the most threatened vertebrates.
- As a case study, the population‐level impacts of bycatch mortality on freshwater turtles were evaluated in Lake Opinicon, Ontario, Canada, a lake that supports a small‐scale commercial fishery. Using population viability analyses, the impacts of bycatch on common snapping turtles (Chelydra serpentina), eastern musk turtles (Sternotherus odoratus), northern map turtles (Graptemys geographica), and painted turtles (Chrysemys picta) were evaluated.
- In all four species, even low levels of additional annual female mortality as a result of bycatch were sufficient either to reduce population size or to cause extirpation of the local population within 500 years. Bycatch reduction programmes, such as seasonal closures and implementation of bycatch reduction devices, can help alleviate the risk of extirpation. Changes to fishing season length could help reduce the number of snapping turtles and musk turtles captured. Installation of simple bycatch reduction devices can exclude between 95% and 100% of snapping turtles and between 0% and 97% of the other three species, depending on the width of the exclusion device. If combined, these two bycatch reduction methods would help prevent adult female mortality and help maintain turtle populations in Lake Opinicon.
- Although these findings are specific to the study area, the same principles apply to other areas where similar simple bycatch reduction strategies can be employed to prevent the extirpation of other freshwater turtle species. Considering the consequences of bycatch and of bycatch reduction programmes on populations provides managers with important information to support development of risk‐averse conservation strategies.
4.
Renato A.M. Silvano Gustavo Hallwass Anastácio A. Juras Priscila F.M. Lopes 《水产资源保护:海洋与淡水生态系统》2017,27(2):521-533
- Gillnets are commonly used in tropical multi‐species fisheries and there is a need to investigate the comparative efficiency and impacts of this gear on fish populations and diversity. The efficiency and the impact of gillnets of distinct mesh sizes were compared in the Lower Tocantins River (Brazilian Amazon).
- Fish sampling was conducted in 12 floodplain lakes using gillnets of distinct mesh sizes and 345 fish landings were recorded. Indicators of gillnet efficiency were: (1) catch per unit of effort (CPUE) of total fish sampled; (2) CPUE of fish caught by fishers; (3) CPUE of commercial fish sampled; and (4) proportion of biomass of commercial fish sampled. Indicators of impact were: (1) the number of non‐commercial fish (by‐catch); (2) the proportion of fish above the length at first maturity; (3) mean fish size (length); (4) total number of fish species and of rare fish species caught.
- Gillnets of 8 cm mesh size showed a higher CPUE in fish samples and fish landings. This mesh size also showed reduced impacts (lower numbers of non‐commercial fish caught and higher proportion of adult fish).
- Gillnets of 6 cm mesh size caught a smaller proportion of adult fish, smaller fish, more species and more rare species. Therefore, intensive use of these gillnets could increase the risk of regional species extinctions and impair the provision of ecosystem services by target fish.
- Gillnets of 8 cm mesh size could improve fish catches while minimizing adverse effects of gillnet fishing. The practical management recommendation would be to replace the more damaging small mesh gillnets by gillnets with intermediate mesh size. This recommendation could simultaneously protect small‐sized rare species and larger fish, being broadly applicable to other small‐scale and multi‐species fisheries that use gillnets intensively in tropical countries with high fish diversity.
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Catherine Seytre Mathew A. Vanderklift Pascaline Bodilis Jean‐Michel Cottalorda Julien Gratiot Patrice Francour 《水产资源保护:海洋与淡水生态系统》2013,23(2):189-201
- Assessing both direct and indirect effects of fishing, i.e. effects extending to two or more trophic levels, is becoming a key issue in restoration ecology. The present study compared the Cap Roux no‐take area (NW Mediterranean) with the surrounding non‐protected areas.
- Direct effects of fishing were investigated using experimental net fishing and underwater visual census (UVC) specifically to survey species targeted by commercial fishing and angling. Indirect effects of fishing were deduced from predation and density of sea urchins.
- Observations showed higher biomass and abundance (from catch rates) inside the MPA and differences in size composition (from UVC). The effect of protection from fishing was rapid, with differences apparent within 5 years of protection, and was most evident for highly targeted fish.
- Rates of predation on two species of sea urchin (Paracentrotus lividus and Arbacia lixula) were dependent on protection level and season. This pattern was consistent with the presence of large Diplodus spp., known sea urchin predators, observed inside the reserve only in winter. However, the density of the sea urchins did not differ between the MPA and adjacent fished areas.
6.
William M. Twardek Chris K. Elvidge Alexander D.M. Wilson Dirk A. Algera Aaron J. Zolderdo Stephen C. Lougheed Steven J. Cooke 《水产资源保护:海洋与淡水生态系统》2017,27(4):789-796
- While the use of aquatic protected areas that exclude angling might be considered an evolutionarily enlightened management approach to dealing with fisheries‐induced evolution (FIE), there is little empirical data on the effectiveness of this approach at maintaining the diversity of phenotypic traits within protected areas.
- In species with paternal care, including largemouth bass (Micropterus salmoides), active nest‐guarding and aggression towards potential brood predators by males may render these individuals particularly vulnerable to capture by angling because of increased propensity to attack fishing lures/bait near their nests. Relative levels of aggression by these males during the parental care period correlates with their vulnerability to angling year round. Selective removal of more aggressive individuals by anglers should drive population‐average phenotypes towards lower levels of aggression.
- To assess the effectiveness of protected areas at mitigating FIE, the parental care behaviours of wild, free‐swimming male bass were compared during the early nesting period for bass within and outside protected areas in a lake in eastern Ontario. Nesting males within long‐standing aquatic protected areas closed to fishing for >70 years were more aggressive towards bluegill sunfish (Lepomis macrochirus), a potential nest predator, and patrolled larger areas around their nests compared with bass outside of sanctuaries. Males within protected areas were also more likely to strike at artificial fishing lures and were more prone to capture during angling events.
- Collectively, the findings suggest that the establishment of protected areas may promote phenotypic diversity such as more attentive and vigorous parental care, relative to areas open to angling. The extent to which this phenomenon occurs in other species and systems is likely to depend on the reproductive strategies of fish and their spatial ecology compared with protected area boundaries, and habitat quality within protected areas.
7.
Margaret Boothroyd Nicholas E. Mandrak Michael Fox Chris C. Wilson 《水产资源保护:海洋与淡水生态系统》2016,26(6):1107-1119
- Determining the occurrence and site occupancy of rare and endangered species can be challenging, particularly without causing harm or stress to the species of concern.
- Environmental DNA (eDNA) detection was used to assess habitat occupancy by spotted gar (Lepisosteus oculatus), which is federally listed as Threatened in Canada, with known occurrences limited to a small number of locations in southern Ontario.
- Quantitative polymerase chain reaction (qPCR) assays were developed to detect spotted gar eDNA, which was detected in all but one previously recorded location. The eDNA method was shown to be more effective than traditional netting for detecting spotted gar habitat use.
- The use of qPCR allowed for quantification of substantial variation in detection strength (copy number) among replicate eDNA samples, with implications for establishing sampling designs for detection and surveillance.
- The use of eDNA for detection and monitoring of aquatic species of conservation concern shows great potential as a non‐invasive method for assessing species occurrences and habitat occupancy, as well as for informing targeted sampling by conventional capture methods.
8.
Alaric Mccarthy Chris Hepburn Nigel Scott Katja Schweikert Rachel Turner Henrik Moller 《水产资源保护:海洋与淡水生态系统》2014,24(3):369-390
- Overfishing has the potential to adversely affect the ecological stability, economic value, social and spiritual integrity of a given area. Of these contexts, relatively little emphasis in literature is placed on the social and cultural consequences of overfishing and marine biodiversity loss.
- New Zealand's fisheries management system is regarded as one of the best in the world. But is this ‘success’ reflected at the local community scale? This study uses the knowledge of 100 participants from different stakeholder groups including Māori, New Zealand's indigenous peoples, and investigates local perception of the state of inshore fisheries stocks.
- Quantitative methods were used to assess the relative significance of important seafood species among different groups, while qualitative analysis highlighted main stakeholder concerns. A common consensus among all participants emerged; access to important inshore seafood species had become more difficult during the course of their lifetime with marked declines occurring from the 1970s onwards. Even where food species are present, they are typically harder to obtain, take longer to harvest and/or require expensive gear.
- Five species of marine invertebrates, three finfish species and one seabird were identified as having considerable worth to stakeholders. Of these, quantitative analysis revealed that pāua (abalone), tuna (eel) and tītī (muttonbird) were of particular significance to Māori stakeholders. Māori discussed pāua almost twice as much as non‐Māori, despite pāua ranking as the most significant species among both ethnic groups. Furthermore, Māori associated the depletion of pāua with a loss of cultural identity, hospitality, tradition, practices, emotional and spiritual connection to their environment. As such, in this paper pāua is defined as a ‘cultural keystone species’, whereby the removal of such a species jeopardizes cultural integrity.
- This paper serves as a case study bringing to light the disparity between an internationally acclaimed fisheries management strategy and the concerns of local stakeholders.
9.
- The purpose of this study was to investigate the effects of a circle hook ring on catch rates of target fish species and bycatch rates of sea turtles, elasmobranchs, and non‐commercial fish in a shallow‐set Italian swordfish longline fishery.
- Results were compared from 65 sets from six commercial fishing vessels totalling 50 800 hooks in which ringed and non‐ringed 16/0 circle hooks with a 10° offset were alternated along the length of the longline. In total, 464 individuals were caught in the 4 years of experiment, with swordfish (Xiphias gladius) comprising 83% of the total number of animals captured. Catch rates of targeted swordfish were significantly higher on ringed hooks (CPUEringed hooks = 8.465, CPUEnon‐ringed hooks = 6.654).
- Results indicate that ringed circle hooks captured significantly more small‐sized swordfish than non‐ringed circle hooks (27.7% vs. 19.5%, respectively).
- For species with sufficient sample sizes, the odds ratio (OR) of a capture was in favour of ringed hooks; significantly for swordfish (OR = 1.27 95%CI 1.04–1.57), and not significantly for bluefin tuna (Thunnus thynnus) (OR = 1.50, 95%CI 0.68–3.42) nor for pelagic stingray (Pteroplatytrigon violacea) (OR = 1.13, 95%CI 0.54–2.36). All six loggerhead turtles (Caretta caretta) and three of the four blue sharks (Prionace glauca) were captured on ringed hooks, however, the small sample sizes prevented meaningful statistical analysis.
- In summary, results from this study suggest that the addition of a ring to 16/0 circle hooks confers higher catchability for small‐sized commercial swordfish, and does not significantly reduce catch rate of bycatch species and protected species in a Mediterranean shallow pelagic longline fishery.
- These findings should motivate fisheries managers to consider factors in addition to hook shape when aiming to promote sustainable fishing practices. The presence of a ring has the potential to negate some conservation benefits.
10.
Marília Hauser Carolina R.C. Doria Roberto V. Santos Aurea García‐Vasquez Marc Pouilly Christophe Pcheyran Emmanuel Ponzevera Gislene Torrente‐Vilara Sylvain Brail Jacques Panfili Audrey Darnaude Jean‐Franois Renno Carmen García‐Dvila Jesus Nuez Franck Ferraton Gladys Vargas Fabrice Duponchelle 《水产资源保护:海洋与淡水生态系统》2019,29(3):397-408
- In the Amazon, migratory catfishes of the genus Brachyplatystoma are apex predators that are important for fisheries and conservation. The life cycle of Brachyplatystoma platynemum Boulenger, 1898 is poorly known, although it has been hypothesized to be very similar to that of Brachyplatystoma rousseauxii Castelnau, 1855, which uses the entire length of the Amazon basin to complete its life cycle (from the Andes to the estuary). This study provides the first data on the migratory patterns of B. platynemum at the individual level using otolith microchemistry.
- In total, 94 individuals were sampled close to major breeding areas in the Amazon basin (78 fish from the middle and upper Madeira River and 14 fish from the upper Amazon), and their lifetime movements were assessed by measuring variations in 87Sr/86Sr along transverse sections of their otoliths (ear stones), using laser ablation multi‐collector mass spectrometry (LA‐MC‐ICP‐MS).
- The migrations of B. platynemum are not as extensive as those of B. rousseauxii, and do not involve natal homing. Furthermore, the estuary is not a nursery area, at least for fish hatched in the Madeira. Nevertheless, B. platynemum migrates several thousand kilometres within the Amazon basin, with transboundary displacements between at least Bolivia, Brazil, and Peru.
- Current and planned hydroelectric development in the Amazon basin will severely disrupt both migration and access to breeding grounds, ultimately affecting the recruitment and population dynamics of these apex predators.
- The conservation of B. platynemum is crucial for the stability of the Amazonian aquatic food webs. This requires building effective fish passage on the two existing Madeira dams and considering alternative options to the large‐scale hydropower development in the Amazon basin.
11.
Robert Nikolaus Malwina Schafft Andreas Maday Thomas Klefoth Christian Wolter Robert Arlinghaus 《水产资源保护:海洋与淡水生态系统》2021,31(1):153-172
- Humanity is facing a biodiversity crisis, with freshwater-associated biodiversity in a particularly dire state. Novel ecosystems created through human use of mineral resources, such as gravel pit lakes, can provide substitute habitats for the conservation of freshwater and riparian biodiversity. Many of these artificial ecosystems are subject to a high intensity of recreational use, however, which may limit their biodiversity potential.
- The species richness of several taxa (plants, amphibians, dragonflies, damselflies, waterfowl, and songbirds) was assessed and a range of taxonomic biodiversity metrics were compared between gravel pit lakes managed for recreational fisheries (n = 16) and unmanaged reference lakes (n = 10), controlling for non-fishing-related environmental variation.
- The average species richness of all the taxa examined was similar among lakes in both lake types and no substantial differences in species composition were found when examining the pooled species inventory. Similarly, there were no differences between lake types in the presence of rare species and in the Simpson diversity index across all of the taxa assessed.
- Variation in species richness among lakes was correlated with woody habitat, lake morphology (surface area and steepness), and land use, but was not correlated with the presence of recreational fisheries. Thus, non-fishing-related environmental variables had stronger effects on local species presence than recreational fisheries management or the presence of recreational anglers.
- Collectively, no evidence was found that anglers and recreational fisheries management constrain the development of aquatic and riparian biodiversity in gravel pit lakes in the study region; however, the conservation of species diversity in gravel pit lakes could benefit from an increasing reliance on habitat enhancement activities.
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- In comparison with other habitats, the littoral zone can be disproportionately important to lentic fishes, especially for species that rely on it for reproduction. Impoundment of lentic waters can alter hydrological regimes, littoral inundation patterns and hydrodynamic processes, which can affect the quantity and quality of littoral habitats.
- This study examined the effects of water‐level fluctuations on the quantity and quality of rocky littoral spawning habitat for the threatened Galaxias auratus in the Crescent–Sorell lake system, Tasmania (Australia) using GIS analyses, sediment measurements and observations of the composition and condition of littoral substrates under varying hydrological conditions.
- The extent of littoral rocky substrate was found to be limited in Lake Crescent (<1.3% of the lake's bed). The relationship between water levels and G. auratus spawning habitat (littoral rocky substrates at depths of 0.2–0.6 m) was non‐linear with spawning habitat quantity and quality declining markedly at water levels <802.20 m Australian Height Datum (AHD). Hydrological impacts of global climate change on the Crescent–Sorell lake system are likely to increase the occurrence of water levels below this threshold in Lake Crescent in the future, thereby limiting the ability of G. auratus to sustain its population in this lake.
- The structure of littoral areas of rocky substrate in Lake Crescent and Lake Sorell, and influential processes acting on these areas under varying hydrological conditions, were conceptualized to assist transferability of this knowledge to other lentic waters and species with similar habitat requirements.
- Global climate change is predicted to alter lacustrine hydrological regimes and shoreline environments. This is likely to have significant ramifications for fishes that use littoral habitats during their life cycles, especially crucial reproductive phases. We believe the influence of alterations to hydrological regimes on the availability of these habitats to lacustrine fishes requires further investigation globally.
14.
Anthony Maire Laëtitia Buisson Julie Canal Benoit Rigault Julien Boucault Pascal Laffaille 《水产资源保护:海洋与淡水生态系统》2015,25(6):839-854
- Although ecosystems are increasingly threatened worldwide, the resources available to set up management actions, such as conservation or restoration, remain severely limited. Methods designed to spatially allocate conservation and restoration actions while maximizing their ecological benefits are urgently needed. Whereas conservation planning methods have been extensively developed in past decades, improvements in restoration planning are still needed to build efficient management tools. This methodological gap may be explained by the difficulties encountered when estimating non‐disturbed ecological conditions (i.e. reference conditions) which are usually required to compare past and present ecosystem states.
- Here, the species composition of stream fish assemblages in 607 river stretches of the Pas‐de‐Calais department in the north of France was predicted using species distribution models. Present occurrence was predicted according to four environmental variables, including two related to human‐induced disturbances (i.e. proportion of river stretch length affected by hydraulic works and local geomorphological alterations). The fish assemblages potentially present in the absence of such disturbances were then predicted using hindcasting modelling which involves artificially setting to zero the values of the disturbance variables in the models.
- A framework based on a multi‐faceted approach of diversity was applied to the present‐day fish assemblages and those predicted under the two non‐disturbed scenarios (i.e. restoration scenarios) to assess their suitability for management.
- While the theoretical restoration of the natural flow regimes was likely to result in few changes in fish assemblage composition and consequently in their multi‐faceted diversity, the restoration of natural geomorphological characteristics was predicted to reduce the taxonomic diversity but increase the functional diversity, the natural heritage importance and the socio‐economic value of the fish assemblages.
- This study provides environmental decision‐makers with a tool to identify precisely and simultaneously the conservation and restoration actions that have to be undertaken as a priority, by comparing the present and non‐disturbed multi‐faceted diversity indices.
15.
Rita Cannas Flavio Sacco Alessandro Cau Danila Cuccu Maria Cristina Follesa Angelo Cau 《水产资源保护:海洋与淡水生态系统》2016,26(2):236-250
- The precious coral Corallium rubrum is one of the most vulnerable resources in the Mediterranean Sea because of the high levels of human‐related and natural mortality rates. The aim of the present study was to document the diversity and connectivity patterns among Sardinian Corallium rubrum populations focusing, in particular, on deep populations (>80 m depth) where the commercial exploitation is concentrated.
- Microsatellite markers revealed high levels of inbreeding, heterozygote deficits, and significant genetic differentiation between and within areas at different depths, with an associated ‘isolation by distance’ pattern.
- These results indicated that for precious coral populations in Sardinia the ‘deep reef refugia hypothesis’, that envisages the capacity for deep corals to act as seed banks for the shallower impaired (over‐harvested) populations, is not supported.
- The highest genetic diversity recorded in Sardinia for all areas and depths with respect to other Mediterranean areas indicates that the strict local management has been effective, since harvesting has not yet led to a substantial erosion of the genetic pool.
- Possible causes for the high levels of observed diversity in Sardinia are discussed in relation to hydrological conditions, its geographical position and its proximity to some putative glacial refugia.
- Thus, given the occurrence in Sardinia of highly diverse and differentiated deep‐water populations of C. rubrum whose genetic diversity are important for the long‐term resilience of the species, the results of the present study strongly support the close monitoring of harvesting, along with the maintenance or even strengthening of the current management and conservation measures (no‐take protected areas) already in place in the area.
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- Few conservation studies have examined fish communities in entire drainage basins, especially in developing regions such as Southeast Asia, one of the most diverse biomes globally. The aim of this study was to establish conservation projections for the whole of the Irrawaddy River system, based on fish diversity patterns, human impact, and environmental change.
- The Irrawaddy River is one of the five largest rivers in Southeast Asia. Although it has very high diversity of fish species and species endemism, our understanding of resident fish status remains poor.
- Based on 1,726 field survey and 1,056 database records, 470 fish species and their distribution patterns (i.e. alpha, beta, threatened species, and endemic species diversities) in sub-basins of the Irrawaddy drainage were identified. Canonical correspondence analysis of diversity and environmental patterns indicated that climatic factors had the largest effect on diversity, compatible with the species–energy theory.
- Fish conservation priorities of sub-basins were evaluated based on diversity patterns and human impact. The delta and Manipur basin regions were highlighted as areas of focus for future fish diversity conservation, and the importance of connectivity in the Irrawaddy main stem was demonstrated.
- The results of this study will be valuable for future management of the Irrawaddy basin and as a reference for other river basins when implementing protection strategies for fish diversity. This study also advocates the need for systematic investigations across entire drainage basins and further detailed studies on the ecological conditions of poorly studied river systems.
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This study aimed to assess the relationship between basic metrics in recreational fishing and the size of the fishing ground. Data were obtained from individual angling logbooks collected by the Czech Fishing Union over 12 years on 212 fishing grounds located in the regions of Prague and Central Bohemia in the Czech Republic. Small fishing grounds had the highest catch, yield, numbers of fishing visits and numbers of angling guard controls per hectare. Medium‐sized fishing grounds had the highest catch, yield, and numbers of both fishing visits and angling guard controls per fishing ground. Anglers returned to medium‐sized fishing grounds most frequently. The percentage of anglers who caught and took home at least one fish decreased with increasing size of the fishing ground. In conclusion, basic metrics in recreational fishing are related to the size of the fishing ground, which thus plays an important role in fisheries management. 相似文献
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本文根据对台湾北部渔场中上层鱼类为期三年的生产性探捕试验结果,着重分析了莆田市现有灯光围网作业渔船采用的渔具渔法在该渔场的适应情况和生产性探捕试验的经济效益。指出了该渔场中上层鱼类的渔期、中心渔场位置和渔获组成。 相似文献
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L. Cynthia Watson Donald J. Stewart Kean Clifford Leandro Castello Deirdre Jafferally Samantha James Zacharias Norman Graham G. Watkins 《水产资源保护:海洋与淡水生态系统》2021,31(9):2533-2546
- Using population estimates that were made regularly between 2001 and 2013, the state of recovery of arapaima populations and their IUCN conservation status were assessed after they were almost extirpated from the upper Essequibo basin, Guyana. Recovery rates were compared across multiple areas with different degrees of access by fishers to evaluate effectiveness of conservation efforts.
- Population estimates were also used to investigate the influence of environmental factors on arapaima abundance in lakes with different morphometries, vegetation, and water types and to determine the relationship between the numbers of spawning individuals and subsequent recruits (at about age 2 years).
- The most recent census conducted in November–December of 2013 indicated a 5.6-fold increase in overall abundance compared with 2001, with 4,591 individuals, of which 1,932 were juveniles (1.0–1.5 m total length) and 2,659 adults.
- Assessment of conservation status following IUCN criteria indicated that arapaima populations in the upper Essequibo basin in 2001 would have been considered borderline Critically Endangered, but in 2013 after conservation interventions, status would be categorized as Near Threatened.
- Arapaima in the Essequibo basin appear to favour larger but shallow lakes with low conductivity, clear water, and abundant aquatic macrophytes. Stock–recruitment relationships suggest that the entire upper Essequibo basin population may still be growing and that there is approximately a 1:1 juvenile to adult ratio. This ratio of juveniles to adults across all areas suggests a paucity of young fishes to sustain overall population growth, which might reflect widespread illegal removals of young fishes in the basin.
- Comparisons of arapaima densities in the upper Essequibo basin with those at four localities across the Amazon Basin, suggest that with enhanced conservation efforts in the Essequibo, populations could potentially increase two-fold or more.