Sustainable harvest of two large predatory catfish in the Cuiabá river basin, northern Pantanal, Brazil.

Fishery is an important economic activity in the Pantanal. Among the regions species, the Pimelodidae catfish stands out as an important part of the annual catch. This study assesses the structure, exploitation and stock management of Hemisorubim platyrhynchos and Sorubim cf. lima, the sixth and seventh largest Pimelodidae of the Pantanal. The analysis is based on fish caught by commercial fishing in the Cuiabá river and landed at the "Ant?nio Moysés Nadaf" Market in the Cuiabá city, Mato Grosso state, Brazil. The findings indicate that commercial fishing activities target several fish cohorts and that usually only individuals above mean length at first maturation are caught. Estimates of the instantaneous mortality coefficient show that the current fishing mortality is low. Simulations of relative yield-per-recruit model demonstrate that the current yield of two species could be greater if the fishery effort were increased, indicating that the stocks are underexploited. However, an increase in current fishery efforts should be viewed with caution, since the stock-recruitment relationship for the species is unknown. The results indicate that the current harvest of two species in the Cuiabá River Basin is sustainable.     

Fishing at Rio Grande (Brazil): Ecological niche and competition

This study is an ecological analysis of the use of resources by two potentially competitive groups, the commercial and recreational fishermen of Rio Grande, located on the border of the States of SÃo Paulo and Minas Gerais. Tourism at Rio Grande was intensified after the construction of the hydroeletric plant of Marimbondo in 1974, and local fishermen have complained about its interference. Values of niche dimensions, such as fishing periods, grounds, and prey caught were obtained through data gathered at landing points. Local and recreational fishermen usually fish in different parts of the river and catch different fish, because they use different gear. However, in transition months between the wet and dry seasons, when fish are less abundant, there is conflict or competition related to fishing grounds, reinforced by the territorial fishing rights of local longline fishermen in this period. We show how ecological concepts, such as niche and competition, may help to understand strategies of exploitation by human groups, fundamental information for the management of tropical areas.     

Using a side‐selective fyke net barrier to research fish assemblages in the transitional and transboundary waters of the Vistula Lagoon,southern Baltic

The natural and territorial conditions of the Vistula Lagoon render it difficult to perform repeatable and representative investigations of fish assemblages. The changeability of hydro‐meteorological conditions (wind strength and direction), hydrological conditions (shallowness, the thickness of bottom sediments, submerged barriers, wavy motion) and the social and transboundary conditions mean that most standard monitoring methods and fish migration studies are either impossible to apply or produce unsatisfactory results. This current work presents the results of long‐term observations of fisheries deploying a side‐selective fyke‐net barrier. The fishing gear was deployed parallel to the border in the Vistula Lagoon in order to determine the difference in the movement of fish from the Polish and Russian sides of the lagoon. Thanks to the co‐operation with fishermen, data was collected from catches during the 1995–2002 period; this permitted the identification of variations in relative abundance and the dominant direction of fish migrations during the fishing season. The highest statistically significant differences between the fishing results on either side of the barrier were noted in the autumn months of September and October.     

The paraty artisanal fishery (southeastern Brazilian coast): ethnoecology and management of a social-ecological system (SES)

ABSTRACT: This study intends to give recommendations to the management of Paraty fishery in Brazil through an interplay of local and scientific knowledge. In particular, the objectives are the following: 1) to describe the Paraty fishery; 2) to compare the fishermen's local ecological knowledge with recorded fish landings and previous studies in Paraty; 3) to combine the data on local fishing and on local/Caicara livelihoods with the SES (social-ecological systems) Model. The methods include a systematic survey of fishing in Tarituba and Praia Grande, which are located in the northern end and the central part of the Paraty municipality, respectively. For four days each month, systematic data on catches at landing points were collected, as well as macroscopic gonad analysis data for the fishes Centropomus parallelus and C. undecimalis (snook, robalo), Epinephelus marginatus (grouper, garoupa), Scomberomorus cavalla (King mackerel, cavala), and Lutjanus synagris (Lane snapper, vermelho). Spring and summer are important seasons during which some species reproduce, and the integration of fishing periods for some target species could assist in fishing management through the use of closed seasons. Fishermen could obtain complementary earnings from tourism and from the "defeso system" (closed season including a salary payment) to conserve fishing stocks. The SES model facilitates an understanding of the historical context of fishing, its economic importance for local livelihoods, the constraints from conservation measures that affect fishermen, and the management processes that already exist, such as the defeso. If used to integrate fishing with complementary activities (tourism), such a system could improve the responsibility of fishermen regarding the conservation of fish stocks.     

Profits and social performance of small-scale fishing in the Upper Paraná River floodplain (Brazil).

Small scale fishing profits in two communities in the Upper Paraná River floodplain (Porto Rico - PRI and Porto S?o José - PSJ villages) are assessed based on interviews carried out with professional fishermen. There is a high illiteracy level in both PRI (50%) and PSJ (44.5%). The main contributions to income are "vessel costs" and "fish consumption" by the family. Specific tackle (such as cevadeira) and gear used for fishing close to dams make the gear costs higher at PSJ, emphasising the heterogeneity of the activity. The majority of fishermen in both villages have income complementation activities associated with tourism, because floodplain fishing is not a profitable occupation with any poverty alleviation capacity. Since the ecosystem is seriously disrupted, nowadays fishers are vulnerable to high oscillations in costs and income due to uncertainty in catches aggravated by flood control of the dams.     

Big Fish are the Best: Seed Dispersal of Bactris glaucescens by the Pacu Fish (Piaractus mesopotamicus) in the Pantanal, Brazil

We studied the potential role as seed disperser of the pacu fish (Piaractus mesopotamicus, Characidae) in the Pantanal of Brazil. The most important food item in the diet of the pacu in the wet season was fruits of the palm Bactris glaucescens found in the guts of 73 percent of all fishes collected (N= 70). We found a positive relationship between fish length, weight, and gape size and the number of intact seeds in their gut. Therefore, large pacus are especially important in dispersing B. glaucescens seeds within the studied system. Since the best seed dispersers are the largest fishes, which are preferred by commercial fisheries, we predict that the ongoing over fishing in freshwater ecosystems will have major impacts on the dispersal system of fish‐dependent plants. We suggest that it is paramount to change the attitudes in fisheries management of fruit‐eating fishes and urgent to evaluate the impact of fishing on forest regeneration.     

The use of optimal foraging theory in the understanding of fishing strategies: A case from Sepetiba Bay (Rio de Janeiro State,Brazil)

The community of Gamboa is located on Itacuruçá Island, Sepetiba Bay (State of Rio de Janeiro, Brazil) and includes 26 families, mostly of artisanal fishermen who use paddled or motor canoes, and encircling nets for fishing. In this study, predictions from optimal foraging theory (patch model), in particular of patch residence time, are compared to the observed behavior of fishermen on fishing trips. Fishermen's strategies differ depending on their intended prey. They spend more time in patches and use fewer patches for shrimp than for fish. Gamboa's fishermen tend to leave a patch later than predicted by the model. The difficulty in evaluating stock availability, the comparatively few patches available for shrimp, and the competitive aspects of fishing contribute to the explanation of this behavior.     

Species composition,abundance and diversity of Ichthyofauna of Ikere-Gorge,Oyo State,Nigeria

Anthropogenic activities in inland water can cause species loss and displacement. Therefore, there is a need to regularly examine species composition, abundance and diversity of freshwater ecosystem as a means to monitor its health. Ichthyofauna of Ikere-gorge, Iseyin, Oyo State was studied for a period of 24 month, from January 2017 to December 2018. Ikere-gorge was divided into four strata, each comprises three fishing villages. One village in each stratum was randomly selected as sampling site. The catches were sorted into taxonomic groups (species and families) using standard fish identification keys. Forty-one fish species from 13 families were identified in which species richness varied among the sampling villages. Asamu had 34, Agatu had 30, Spillway had 39 and Irawote had 29 species. The freshwater fish species of Nigeria is the richest in West Africa and more than 15% of these fish species are found in Ikere-gorge. Mormyridae family was the most represented with 10 species. Cichlidae was the most abundant by catch and by weight. Sarotherodon galilaeus has the highest abundance by catch and by weight. Gnathonemus brucii was identified as a vulnerable species. The result obtained from this study show that conservation program should be urgently put in place to prevent some fish from extinction. There should be introduction of closed season to allow for proper recruitment of fish population. Likewise, minimum mesh size should be set to allow juvenile and immature fish to escape and allow them to spawn at least once before being vulnerable to gear. There should regulation to set maximum number of fishermen to be allowed to fish at a particular day, this is to reduce fishing pressure.     

Many Vulnerable or a Few Resilient Specimens? Finding the Optimal for Reintroduction/Restocking Programs

Most reintroduction and restocking programs consist of releasing captive-raised juveniles. The usefulness of these programs has been questioned, and therefore, quality control is advisable. However, evaluating restocking effectiveness is challenging because mortality estimation is required. Most methods for estimating mortality are based on tag recovery. In the case of fish, juveniles are tagged before release, and fishermen typically recover tags when fish are captured. The statistical models currently available for analyzing these data assume either constant mortality rates, fixed tag non-reporting rates, or both. Here, instead, we proposed a method that considers the mortality rate variability as a function of age/size of the released juveniles. Furthermore, the proposed method can disentangle natural from fishing mortality, analyzing the temporal distribution of the captures reported by fishermen from multiple release events. This method is demonstrated with a restocking program of a top-predator marine fish, the meagre (Argyrosomus regius), in the Balearic Islands. The estimated natural mortality just after release was very high for young fish (m ₀ = 0.126 day^-1 for fish 180 days old), but it was close to zero for large/old fish. These large/old fish were more resilient to wild conditions, although a long time was needed to achieve a relevant reduction in natural mortality. Conversely, these large/old fish were more vulnerable to fishing, creating a trade-off in survival. The release age that maximizes the number of survivors after, for example, one year at liberty was estimated to be 1,173 days. However, the production cost of relatively old fish is high, and only a few fish can be produced and released within a realistic budget. Therefore, in the case of the meagre, increasing the number of released fish will have no or scarce effects on restocking success. Conversely, it is advisable implement measures to reduce the high natural mortality of young juveniles and/or the length of time needed to improve fish resilience.     

Biological, technical and socioeconomic aspects of the fishing activity in a Brazilian estuary

Technical, biological and socioeconomic factors act as obstacles in the development of fishing activity in the Guaratuba Bay, southern Brazil. Amongst the difficulties registered, the following stand out: there was little variety of fishing gear; the purchasing power of the fishermen was low; there was a lack of regularity in the presence of the target species in the estuary; legislation restricted the use of certain gear at particular times; the size of the individual fish was small when compared to those from the continental shelf. Aquaculture could offer an alternative to the revenue of the fishermen, but cultural tradition and the lack of financial resources make it difficult to introduce aquaculture as an activity for the fishermen. The pessimism encountered in the community indicates that the future of artisanal fishing in this estuary is uncertain.     

Barí spear fishing: Advantages to group formation?

A study of spear fishing by the Barí of the Maracaibo Basin provides data demonstrating a benefit accruing to individual fishermen fishing in groups. An analysis of counts of successful and unsuccessful spear thrusts shows that fish are made more vulnerable to spear thrusts by companion fishermen who wear down and confuse the fish. Fish vulnerability is seen to depend on the number of encounters a fish has already survived. This Encounter History effect may be operative in other predator and prey relationships.     

Fish composition and abundance in the wetlands of Cross River, Nigeria

Environmental parameters and ichthyofauna were investigated over a 2 years period in three regions along the 200 km length of Cross River. The objective of the study was to quantify the relative importance of local environmental conditions prevailing within sampling sites and the composition and abundance of the principal fish species in the upper, middle and lower reaches of the river. Vegetation cover, size of river, flow velocity, water level, temperature, transparency, and food availability explained the observed seasonal and spatial changes in fish abundance. Forty-six species and 28 genera of fish belonging to 16 families were recorded among the 14,466 fish caught. Three fish families (Cichlidae, Bagridae, and Clariidae) yielded highest number (41.3%) of species while Denticeptidae, Protopteridae, and Osteoglossidae had the least. Oreochromis niloticus, Chrysichthys nigrodigitatus, and Clarias anguillaris numerically dominated (46.4%) catch composition. Species richness was higher for the river stretch in forest area than in savanna, and it was correlated significantly with width of the reach, water transparency, depth, and flow velocity (P < 0.001) of the river. Wet season samples were more diverse (>0.6) and had higher richness (>9.7) than those for dry season. Wet season and forest regions were therefore critical in maintaining fish stock of Cross River.     

Conflict between spotted-necked otters and fishermen in Hlan River,Benin

The spotted-necked otter (Lutra maculicollis) is believed to be declining across its range and, in Benin, has recently been listed as endangered. In Benin, the spotted-necked otter is largely restricted to the south of the country, where it is threatened by a number of factors, including conflict with fishermen. Understanding the nature and extent of this conflict, and the impact that it has on local fishermen, as well as identifying feasible mitigation strategies, represents a critical challenge for conservation managers.This study documents otter damage experienced by 30 fishermen in the Hlan River, in the Southern Benin wetlands. We performed hierarchical classification analysis using Ward distances to categorize fish species according to the level of otter damage suffered, and used generalized linear models to identify predictors that best explained otter damage. Our results suggest that of the 16 fish species commonly caught by fishermen in the Hlan River, otters favored the most valuable species (but these were also the most abundant in the catch). However, although otter damage was extensive, monthly total income loss attributable to spotted-necked otter damage (including fish loss and damage to equipment) was estimated at only 9% per fishermen (considerably lower than the 30% reported by a preliminary survey of 163 fishermen in the same area). Our model showed that otter damage increased significantly with the number of adult fish captured by fisherman while the cost of otter damage increased with the length of time that the fishing equipment was left unattended. We suggest that otter damage could be reduced if fishing equipment were checked at least twice a day by fishermen, and recommend a maximum interval between checks of 700 min (12 h). Long-term sustainable management of these conflicts will require an integrated approach taking into account socio-economic, political and environmental dimensions.     

Reconstruction of walleye exploitation based on angler diary records and a model of predicted catches

The walleye population in Canadarago Lake, New York, was 81-95% exploited in the 1988 fishing season, the year in which a previous restriction on the length and number of legally harvestable fish was liberalized. Using diary records from a subset of fishermen, growth estimates, and an estimate of the walleye population in the following year, a method is developed to reconstruct the fish population back to the spring of 1988 and thus determine the exploitation rate. The method is based on a model of diary catches that partitions time and fish length into a set of cells and relates predicted catches and population sizes in these cells. The method's sensitivity to the partitioning scheme, the growth estimates, and the diary data is analyzed. The method could be employed in other fish exploitation analyses and demonstrates the use of inexpensive angler-collected data in fisheries management.     

Farming,fishing, and fire in the history of the upper Río Negro region of Venezuela

Studies of Río Negro subsistence farming and fishing activities are used to estimate the human carrying capacity for the region and the likely pattern of human land-use during prehistory. Ceramic evidence suggests human presence in the region more than 3000 years ago. Traditional farming is labor intensive and relatively unproductive. Nevertheless, farmers achieve an energy return of 15.21, and produce 2600 kcal per work hour. Fish are the major protein source, but fish catch per unit of effort and fish yield per hectare of floodplain are very low; fishermen are probably exploiting local fish resources very close to their limit. The low human population density would suggest that the Río Negro forest has been relatively undisturbed. Nevertheless, charcoal is widespread and abundant in forest soils. This charcoal is probably from anthropogenic or natural wildfires. These results suggest a much more complex history for Amazonia than previously thought.K. Clark is a free-lance biologist residing in Lima, Peru     

When Does this Fish Spawn? Fishermen’s Local Knowledge of Migration and Reproduction of Brazilian Coastal Fishes

Fishermen’s local knowledge of fishing resources may be an important source of information to improve artisanal tropical fisheries management, such as those found in Brazil, where most data on fish biology is lacking. We aim to study the local ecological knowledge that Brazilian coastal fishers have about reproductive aspects (season, places and migration) of 13 coastal fish species of commercial importance. We selected fishermen with more than 30 years of fishing practice and we interviewed a total of 67 fishermen: 29 from the southeastern coast, from the communities of Puruba, Almada, Picinguaba and Bertioga, and 38 from the northeastern coast, from the communities of Valença, Arembepe and Porto Sauípe. In the interviews, we used standardized questionnaires and showed photos of fish species. Our results indicate some general patterns in fishes’ reproduction according to fishermen knowledge: fish species spawn in open ocean, near reefs or in coastal rivers (estuaries); some fishes reproduce during the summer and others in winter, while some have more defined spawning months. The main fish migratory patterns mentioned by interviewees were: long migrations along the coast, usually in the South to North direction, short migrations among reefs, fishes that do not migrate, migrations between the shore and open ocean and migrations between the sea and coastal rivers. Fishermen’s knowledge differed among fish species: most fishermen did not know spawning places or seasons of large pelagic fishes, which raised concerns of their possible depletion. We compared such ethnoichthyological information with available scientific data, indicating promising insights about reproduction and migration of Brazilian coastal fishes. Data gathered from local fishermen may provide inexpensive and prompt information, potentially applicable to fisheries management. Our approach might be useful to several other small-scale fisheries, especially the tropical ones, where there is a high diversity of target species and a low biological and ecological knowledge about these species.     

Lake Pátzcuaro fishery management plan

Lake Pátzcuaro, a97.5 km² lake in central México, has animportant artisanal multi-species fishery thatis currently overexploited. Twelve fishes andone amphibian are important in the fishery,which is conducted largely from small woodenboats using seines, gill nets, and thetraditional butterfly net. Fishery yields fromthe lake peaked in 1988, but have declined tonear record lows since then. We propose amanagement plan to restore the fishery. Keycomponents of the plan include: 1) licensingand restricting the number of fishermen; 2)continuing a recent ban on seines andimplementing limits on the number and meshsizes of gill nets to allow fish to complete atleast one spawning before they are vulnerableto harvest; 3) establishing a closed season andareas closed to fishing to protect spawningfish; 4) increased education for fishermen inbasic skills, fishing technology, andalternative jobs; 5) continued monitoring andresearch to assess trends in the fishery and todevelop culture techniques to help restore fishpopulations; and 6) compliance and enforcementmechanisms to make the plan effective,including perhaps establishment of propertyrights for particular areas of the lake forspecific groups of fishermen and more generallyan equitable assignment of lake ecosystem usesbetween fishery and non-fishery users. Werecommend the plan be implemented in anadaptive fashion with provisions for adjustingregulations as conditions warrant. If at leastsome elements of this plan are not adopted thenthe Lake Pátzcuaro fishery is likely tocollapse.     

Species composition and dynamics of larval and juvenile fishes in the surf zone of Mauritius

The importance of the surf zone as a nursery ground for larval and juvenile fishes has been widely recognized, however the zone has yet to be studied in Mauritius. Recently, the coastal area of the island has been increasingly affected by human activities, especially by tourism. We collected fish samples with a hand pulled seine net during the period of August 2001 to March 2003 to clarify the fish fauna and the dynamics of fishes in the surf zone. Two sampling sites adjacent to river mouth areas and one sampling site adjacent to a mangrove area were selected for comparison of fish fauna in relation to environmental conditions. A total of 9,429 fish larvae and juveniles, representing at least 112 species from 48 families were collected. The abundant species were hardyhead silverside, Atherinomorus lacunosus, bluespot mullet, Valamugil seheli, and Ambassis spp., each contributing 16.2, 12.4, and 11.8% of the total number of individuals, respectively. Estuarine species dominated in the surf zone adjacent to the river mouth areas. Species composition and diversity changed seasonally. The number of fish increased during the rainy season. Species diversity increased at the turn of the seasons from the dry season to the rainy season. We conclude that species composition in each site was affected by environmental factors, such as the scale of the flux from the rivers, which is related to the precipitation. The results indicated that freshwater from the river is a trigger to aggregate larvae and juveniles in the surf zone.     

广西合浦儒艮国家级自然保护区及邻近水域鱼类种数及保护对策

2003年6月至2004年5月,通过底拖网作业收集鱼类标本对广西合浦儒艮国家级自然保护区及其邻近水域鱼类种数进行了调查,并走访当地鱼市进行实地调查.共记录到保护区及其邻近水域的鱼类14目41科57种,其中55种为硬骨鱼类,占总数的96.49%,另有2种软骨鱼类,占总数的3.51%.有41种为暖水性鱼类,占总数的71.93%.生态类型中底层鱼类共37种,占总数64.91%.区系特征以北太平洋和印度太平洋区系为主.掠夺性获取和开发以及环境污染是目前这一水域鱼类资源面临的最大威胁,针对以上威胁提出了相应的保护对策.     

长江流域生态退捕渔民生计脆弱性评价及生计风险预测

渔民作为长江十年禁渔的参与主体,其后续生计发展将直接决定此生态保护政策的实施成效。在重构非自愿生态移民生计脆弱性评价体系的基础上,结合长江流域重点禁渔水域典型退捕渔民的抽样数据,测度渔民生计脆弱性指数(LVI)并找出影响后续生计恢复的主要障碍因子,最后跨领域的引入支持向量回归(SVR)预测模型动态分析了不同区域渔户生计脆弱性的演变趋势。结果表明:(1)渔民弃船上岸后呈现出生计脆弱性的比例较高,但不同类型区域间存在明显差异,其中内湖保护区最高,干流非保护区次之而干流保护区最低;(2)敏感性维度在诱发渔民生计脆弱性上起着主导作用,即个体禀赋比安置区条件更为重要,特别是成员年龄大但无基本社保兜底,受教育程度低且"双转"难的渔民家庭更易陷入生计困境;(3)自然和金融资本是推动渔民生计恢复的主要生计资本,而阻碍渔民生计脆弱性降低的共性因子主要有上岸后的收支失衡,社会支持不足及过分依赖原有生计方式等,同时各区域在脆弱性各维度上还有特殊的障碍因子;(4)推动安置区经济社会发展和家庭转产增收后,并不一定能确保缓解未来五年中的渔户生计脆弱性程度,上岸后完成社会融入并有效降低生产生活成本也至关重要,而干流保护区则还需加强人力资本建设,否则后续将面临极高的返贫风险;(5)长江临近区域的同类渔民生计脆弱性现状、面临的生计风险、后续生计恢复的进程具有一定的相似性和规律性,生计监测和帮扶政策可进行协同统筹。