Shedding light on the migratory patterns of the Amazonian goliath catfish,Brachyplatystoma platynemum,using otolith 87Sr/86Sr analyses

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Individual movements,home ranges and habitat use by native rheophilic cyprinids and non‐native catfish in a large regulated river

The mobility patterns of two native species, barbel, Barbus barbus (L.) and chub, Squalius cephalus (L.), and of one non‐native fish species, the catfish Silurus glanis (L.), were assessed on a 35.5‐km reach of the Upper Rhône River, a strong flowing river with notable thermal regime alterations. An active acoustic tracking technique adapted to large rivers allowed (1) the identification of longitudinal home ranges, movements and preferred habitat at large scale, and (2) the analysis of the influence of discharge and water temperature on the movement patterns of the fish. The active fish‐tracking system recorded 1,572 fish localisations over 7 months on a weekly basis for 80% of the tagged fish (37 barbel, 23 chub and 13 catfish). Compared with the catfish, barbel and chub showed wider longitudinal home ranges, more movements >1 km and higher interindividual variability. The catfish preferred artificially heated habitats with less morphological diversity. The three species were more often localised in river sections with high density of woody debris. The results suggest that habitat degradation is more damaging for cyprinids in large modified rivers, while the catfish seemed less, impacted.     

十年禁渔初期金沙江下游向家坝水库鱼类资源变化的水声学研究

为科学评价长江十年禁渔政策在金沙江下游水库的初步实施效果,实验于2020年11月和2022年5月在金沙江下游向家坝水库开展了渔获物调查和水声学调查,并分析了鱼类资源的变化情况。渔获物调查结果显示,2020年11月共采集到鱼类2科9种,其中?、瓦氏黄颡鱼占优势地位;2022年5月共采集到鱼类5科14种,其中蛇、瓦氏黄颡鱼占优势地位。水声学调查结果显示,不同年间、不同区域、不同水层间的鱼类目标强度分布存在显著性差异;2022年5月的鱼类密度(0.60尾/1 000 m³)高于2020年11月(0.46尾/1 000 m³),鱼类资源在时空分布上呈现不均匀性;不同调查时期的鱼群密集区域存在一定的差异,2020年11月大部分区域之间差异不显著,2022年5月则差异显著;2022年5月的上层鱼类密度(0.44±0.83尾/1 000 m³)显著大于2020年11月(0.06±0.15尾/1 000 m³);不同水层的鱼类分布差异显著,2次调查均表现为下层大于中、上层;估算得到向家坝水库鱼类资源尾数分别为3.2...     

A riverscape perspective of Pacific salmonids and aquatic habitats prior to large‐scale dam removal in the Elwha River,Washington, USA

Abstract Dam removal has been increasingly proposed as a river restoration technique. In 2011, two large hydroelectric dams will be removed from Washington State’s Elwha River. Ten anadromous fish populations are expected to recolonise historical habitats after dam removal. A key to understanding watershed recolonisation is the collection of spatially continuous information on fish and aquatic habitats. A riverscape approach with an emphasis on biological data has rarely been applied in mid‐sized, wilderness rivers, particularly in consecutive years prior to dam removal. Concurrent snorkel and habitat surveys were conducted from the headwaters to the mouth (rkm 65–0) of the Elwha River in 2007 and 2008. This riverscape approach characterised the spatial extent, assemblage structure and patterns of relative density of Pacific salmonids. The presence of dams influenced the longitudinal patterns of fish assemblages, and species richness was the highest downstream of the dams, where anadromous salmonids still have access. The percent composition of salmonids was similar in both years for rainbow trout, Oncorhynchus mykiss (Walbaum), coastal cutthroat trout, Oncorhynchus clarkii clarkii (Richardson) (89%; 88%), Chinook salmon, Oncorhynchus tshawytscha (Walbaum) (8%; 9%), and bull trout, Salvelinus confluentus (Suckley) (3% in both years). Spatial patterns of abundance for rainbow and cutthroat trout (r = 0.76) and bull trout (r = 0.70) were also consistent between years. Multivariate and univariate methods detected differences in habitat structure along the river profile caused by natural and anthropogenic factors. The riverscape view highlighted species‐specific biological hotspots and revealed that 60–69% of federally threatened bull trout occurred near or below the dams. Spatially continuous surveys will be vital in evaluating the effectiveness of upcoming dam removal projects at restoring anadromous salmonids.     

Diversity in reproductive traits of arapaima (Arapaima spp., Müller, 1843) in Amazonian várzea floodplains: Conservation implications

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Population dynamics and stock assessment of Colossoma macropomum caught in the Manacapuru Lake system (Amazon Basin,Brazil)

Colossoma macropomum is the second largest scaled fish in the Amazon basin. Reduced harvests in recent decades suggest that populations of this species are already overexploited in some areas. In this study, the population dynamics of C. macropomum was investigated using length and weight data for fish caught in the Manacapuru Lake system, a large ria lake located along the lower reach of the Solimões River. A total of 1270 individuals of C. macropomum with standard lengths varying from 17 to 62 cm and mean length of 31.0 ± 6.7 cm were sampled. Weights varied from 165 to 8195 g, and mean weight was 1148.3 ± 883.8 g. Maximum sustainable yield was estimated at 285.8 g recruit⁻¹, corresponding to a fishing mortality of 0.51 year⁻¹. A scenario analysis based on changes in fishing mortality and age at first capture, two parameters potentially addressed by fishing management strategies, suggested that any improvement in fishing yield depends on increases in age at first capture.     

Temporal changes in ascendance and in‐season exploitation of Atlantic salmon,Salmo salar,inferred by a video camera array

Abstract Weekly exploitation rates of Atlantic salmon, Salmo salar L., in the River Utsjoki, Finland, were estimated from catch reports during the 2003, 2004, 2006 and 2007 seasons, and recordings of all Atlantic salmon ascending the river using a submerged video camera array. In all years, mean weekly fishing mortality rates were significantly higher in June than July to August, with a falling trend throughout the fishing season. Owing to overlap in size between one‐sea‐winter (1SW) and multi‐sea‐winter (MSW) salmon, the estimated fishing mortality rates were based on all sea‐age categories combined. By the second week in June, 18.3–34.7% of large salmon (only MSW) had ascended, compared with 2.2–6.4% of small salmon (1SW and some MSW). Indirectly, the earlier start of ascent of large salmon to River Utsjoki indicated that in‐river fishing mortality of MSW salmon is higher than for 1SW salmon. A later opening of the fishing season may be used to reduce the in‐river fishing mortality, especially for the MSW component.     

Long‐term impacts of introduced flathead catfish on native ictalurids in a north Florida,USA, river

Introduction of flathead catfish, Pylodictis olivaris (Rafinesque), in waters of the USA has been widespread and often with negative impacts. Flathead catfish have been collected in Florida waters since the 1980s, and this study documents their impact on native fishes shortly after establishment. Four sites in the Choctawhatchee River, Florida, were sampled from 1997 to 2011, a time period spanning several years before and after the presence of flathead catfish at all sites. Flathead catfish expanded more than 91 river km in 2 years. The population increased rapidly and became the numerically dominant ictalurid at each site within 3 years of first detection at the site. Concurrent with the increases in flathead catfish was the precipitous decline of the native spotted bullhead, Ameiurus serracanthus (Yerger & Relyea). Electric fishing catch rates of flathead catfish significantly increased (P < 0.03) over time at all sites, while spotted bullhead catch rates significantly declined (P < 0.03) at three of four sites. Catch rates of flathead catfish and spotted bullhead were negatively correlated at all but the last site to be colonised by flathead catfish. This study provides evidence that introduced flathead catfish can quickly and significantly impact native ictalurids.     

Fishery yields vary with land cover on the Amazon River floodplain

Inland fisheries underpin food security in many tropical countries. The most productive inland fisheries in tropical and subtropical developing countries occur in large river–floodplain systems that are often impacted by land cover changes. However, few studies to date have assessed the effects of changes in floodplain land cover on fishery yields. Here, we integrated fisheries and satellite‐mapped habitat data to evaluate the effects of floodplain deforestation on fishery yields in 68 floodplain lake systems of the lower Amazon River, representing a wide range in relative amounts of woody, herbaceous and non‐vegetated land cover. We modelled relative fish yields (fish capture per unit effort [CPUE]) in the floodplain lakes as a function of the relative amounts of forest, shrub, aquatic macrophyte and bare/herbaceous habitats surrounding them. We found that forest amount was positively related (p = .0003) to multispecies CPUE. The validity of these findings was supported by rejection of plausible alternative causative mechanisms involving habitat‐related differences in amount of piscivores, fishing effort, lake area, and habitat effects on CPUE of the nine taxa dominating multispecies yields. Our results provide support to the idea that removal of floodplain forests reduces fishery yields per unit effort. Increased protection of floodplain forests is necessary to maintain the food, income and livelihood security services provided by large river–floodplain fisheries.     

Gharial (Gavialis gangeticus) populations and human influences on habitat on the River Chambal,India

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Age‐0 blue catfish habitat use and population demographics in the middle Mississippi River

The demographics (e.g. hatch time, growth and mortality) and habitat (macrohabitat and mesohabitat) use of age‐0 blue catfish Ictalurus furcatus (Lesueur) were evaluated in the un‐impounded reach of the middle Mississippi River during 2003–2010. Each year, island complexes and adjacent main river habitats were trawled, and 7,373 age‐0 blue catfish (10–144 mm total length) were collected. Blue catfish hatch timing varied slightly across years and generally began in June and ended in August. Age‐0 blue catfish growth rates and instantaneous mortality rates differed among years. Catch rates of age‐0 blue catfish were highest in side channels and around islands, whereas main channel habitats were infrequently occupied. Regarding mesohabitat use, age‐0 blue catfish frequently occupied low velocity areas (i.e. 0.3–0.4 m/s) of shallow depth (i.e. 1–4 m) and sand substratum. This study has provided insight into age‐0 blue catfish population dynamics and has highlighted the importance of specific habitat characteristics in large rivers that may aid in recruitment of this species.     

Movement of flathead catfish in the Missouri River: examining opportunities for managing river segments for different fishery goals

The dispersal patterns of 2939 flathead catfish, Pylodictis olivaris (Rafinesque), were determined within a 90‐km section of the Missouri River, USA. Fish were captured by electric fishing and tagged in early June each year from 1999 through 2001. Dispersal was determined via angler tag returns between 1999 and 2001 or by subsequent recapture during sampling 1 or 2 years after initial tagging (June 2000 or 2001). Dispersal was localised for the majority of the 370 flathead catfish recaptured in the Missouri River. Over 80% of recaptures were within 5 km of tagging location, and 94% were within 20 km of tagging location. Maximum displacement was 160 km. To examine differences in movement patterns of various sized fish, flathead catfish were placed into one to three size groups (305–380, 381–507, or ≥508 mm). A significant difference (P < 0.001) was detected in dispersal patterns among the three size groups; the largest size group moved greater distances than either of the smaller size groups. Movements average 4.5, 5.6 and 12.6 km for small, medium, and large size classes, respectively. Dispersal movements of flathead catfish in the Missouri River appeared to be localised, suggesting that different sections of the Missouri River could be managed for different fishery goals for flathead catfish to accommodate a variety of angler types and desires.     

The Amazonian dwarf cichlid Apistogramma agassizii (Steindachner, 1875) is a geographic mosaic of potentially tens of species: Conservation implications

1. Assessing biodiversity and understanding how it works is a prerequisite for species conservation. The Amazon basin is one of the main biodiversity hotspots where fish are heavily exploited for ornamental purposes.
2. The ornamental trade heavily exploits the genus Apistogramma, which is one of the most species‐rich among Neotropical cichlids with 94 formally described species. This number is certainly underestimated owing to the limitations of conventional taxonomy, which is still too often based solely on morphological criteria and sometimes on few individuals.
3. Most species of this genus have a high degree of endemism and are highly prized on the ornamental market, which could put them at risk. A few species are supposed to have extensive distributions, and in particular Apistogramma agassizii, present from the Amazon estuary up to the Ucayali and Marañon rivers in Peru.
4. This study assessed the taxonomic status of 1,151 specimens of A. agassizii collected from 35 sites around Iquitos in the Peruvian Amazon. On the basis of molecular analyses (nuclear and mitochondrial DNA) and mate choice experiments, at least three biological species within the nominal A. agassizii were evidenced in the sampling area, which is extremely small compared with the known distribution of the species as initially described.
5. According to the molecular calibrations, these three species would have diverged during the Plio‐Pleistocene. Two of them seem to be endemic from small sub‐basins, one from the Nanay River and the other from the Apayacu/Ampiyacu systems. A possible scenario that may explain the evolutionary history of these species is proposed.
6. The conservation implications of these results on the estimation of the diversity of A. agassizii, of Apistogramma species in general, and of other Amazonian cichlids are discussed.

     

The large‐scale stocking of young anadromous whitefish (Coregonus lavaretus) and corresponding catches of returning spawners in the River Tornionjoki,northern Baltic Sea

Stocking and fishing effort are two important potentially conflicting factors in fish stock management that require appropriate assessment to ensure a sustainable fishery. In the River Tornionjoki, which discharges into the northern Baltic Sea, a summer‐ascending whitefish, Coregonus lavaretus L., stock has long been a target by traditional dipnet fishing. Enhancement stocking of young whitefish started in the River Tornionjoki in the 1970s after a collapse in catches, with millions of age‐0 whitefish stocked annually in the river, but after about three decades, the stocking rates were considerably reduced. As a result, dipnet catches of whitefish in the Kukkolankoski Rapids rose simultaneously, peaking in the 1980s and 1990s, and then subsequently decreased. There was a significant positive correlation between stocking intensity and catch, both in weight and in numbers, revealing a strong relationship between whitefish releases and dipnet catch. Changes in gillnet fishing effort in the sea affected dipnet catches in weight as well as in mean size of captured whitefish. When the combined effect of stocking and gillnet effort was evaluated, only stocking significantly affected dipnet catches.     

An assessment of catches of shore sport fishing competitions along the coast of the Maltese Islands: Implications for conservation and management

Competitive shore‐based sport fishing is a popular recreational activity in the Maltese Islands. However, prior to this study, no scientific research surveys had been carried out during sport fishing competitions to investigate catches. Collaboration with Maltese sports fishermen was developed to target sustainable management. Recreational fishing catches were recorded between July 2012 and December 2015 by means of 1,633 roving‐access creel surveys, conducted during 79 sport fishing competitions, totalling a fishing effort of 7,548 hr. A total of 29,916 fish belonging to 80 species from 26 different families were caught at a mean catch‐per‐unit‐effort (CPUE) of 4.16 fish angler/hr (SD ± 3.79) and 0.18 kg angler/hr (SD ± 0.17) but with seasonal variation. Catch‐and‐release practices were implemented by all Maltese sport fishing clubs, however, the mean mortality rate stood at 35.5% (SD ± 42.1), indicating that more effort is required to improve survival of fish. The study outcomes provide conservation recommendations.     

The effect of stocking density on yield,growth, and survival of Asian river catfish (<Emphasis Type="Italic">Pangasius</Emphasis><Emphasis Type="Italic">bocourti</Emphasis> Sauvage, 1880) cultured in cages

Asian river catfish (Pangasius bocourti Sauvage, 1880) were cultured at five different stocking densities in cages (submerged volume 1 m³) suspended in a dugout pond from August to November 2009. Pangasius bocourti fingerlings (mean weight 27.09 ± 0.54 g) were stocked at densities of 12, 25, 50, 100, and 200 fish m⁻³. At the end of 3 months, the harvest weights (gross yields) were, respectively, 2.05 ± 0.30, 5.20 ± 0.31, 10.60 ± 0.42, 19.98 ± 0.78, and 42.37 ± 0.41 kg m⁻³. The mean fish weights among the stocking densities of 25, 50, 100, and 200 fish m⁻³ were not significantly different, but were significantly higher than that of the 12 fish m⁻³ density. The specific growth rates among high stocking densities of 50, 100, and 200 fish m⁻³ were not significantly different; however, they were significantly higher than those of the low stocking densities of 12 and 25 fish m⁻³. Asian river catfish performed poorly at the lowest density. The results indicate an initial lower stocking threshold for Asian river catfish of above 5.20 kg m⁻³. The Asian river catfish cultured in small cages placed in a pond reached the desirable market size (>200 g) within a 90-day grow-out period. The results show that the maximum yield for Asian river catfish during a 3-month production cycle was not reached.     

Ecosystem‐based management of Amazon fisheries and wetlands

Infrastructure development and overfishing in the Amazon make it imperative to define adequate scales for the ecosystem‐based management of commercial fisheries and the wetlands on which they depend. We mapped fisheries and fish ecology data from Brazil, Peru, Bolivia and Colombia to an explicit GIS framework of river basins and mainstems. Migratory species account for more than 80% of the known maximum catches of commercial fisheries across the Amazon. Of these migratory species, we nominated six long‐distance migratory fish taxa as flagship species to define the two main commercial fishery regions. The migrations of at least one goliath catfish species define a large‐scale longitudinal link joining the Andes, Amazon Lowlands and Amazon River estuary. Migratory Characiforms demonstrate interbasin wetland connectivity between nutrient‐rich and nutrient‐poor rivers over at least 2 million km², or about one‐third of the Amazon Basin. We show that flooded forest area is the most important wetland variable explaining regional variations in migratory characiforme biomass as indicated by maximum annual fishery catches. The sustainable management of Amazon fisheries will require transnational cooperation and a paradigm shift from local community management alone to a more integrated approach that considers both rural and urban consumers and challenges, and the realistic life histories of migratory species.     

Impacts of fishing,river flow and connectivity loss on the conservation of a migratory fish population

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A preliminary appraisal of the contribution of recreational fishing to the fisheries sector in north-west Trinidad

Abstract An assessment of the recreational fishery in north-west Trinidad was made by questioning participants about the principal fishing methods used, location of activities, catches, effort and cost of fishing. Surface handline methods (live baiting [à la vive] and trolling) and rod and line (banking) were the most common methods used and were pursued mainly in the summer months (April to August). Total fish landings from the fishery were estimated at 1000 t year^-1, equivalent to about 10% of commercial catches for Trinidad. The principal species caught were kingfish, Scomberomorus cavalla (Cuv.), carite, Scomberomorus brasiliensis (Cuv.), cavalli, Caranx hippos (L.), snappers, Lutjanus spp., and groupers, Epinephelus spp. Many of the fishermen sold their catch to offset the costs of the fishing trip and thus competed with commercial fishermen. Recommendations for monitoring and possibly regulating the fishery through a licensing scheme are made.     

A size-based stock assessment model for invasive blue catfish in a Chesapeake Bay sub-estuary during 2001–2016

Stock assessment modeling provides a means to estimate the population dynamics of invasive fishes and may do so despite data limitations. Blue catfish (Ictalurus furcatus) were introduced to the Chesapeake Bay watershed to support recreational fisheries but also consume species of conservation need and economic importance. To assess management tradeoffs, managers need to understand the current status of the population and anticipate future population abundance and trends. A Bayesian size-based stock assessment model was used to estimate blue catfish abundance, fishing mortality, and size structure over time (2001–2016) in the tidal James River. The model estimated population size increases until around 2006, with declines in total abundance after 2011 and large blue catfish (≥80 cm total length) after 2001. These first estimates of blue catfish population dynamics in the Chesapeake Bay region provide inputs for projection models to evaluate prospective management actions and identify monitoring needs.