Preliminary study on the fishery resources of the River Niger in the Upper Niger National Park, Guinea

A survey of fishing activity, main fishing methods and fish species composition in the upper River Niger enabled current fishing effort, seasonal yield and its economic value to be assessed. Fishing is a traditional activity, supporting part of the regional economy, and an important animal protein source for local people. The catches, 63 fish species included in 20 different families, confirmed the high biological diversity present in the River Niger. Sixteen main fish species were identified as the most important by weight in the commercial captures. Fishing methods used are very selective. The catch is mainly large fishes, and only a low percentage of juvenile specimens is present in the catch, suggesting there is no overfishing of the exploited fish stocks.     

Effects of flood and drought events on multi‐species,multi‐method estuarine and coastal fisheries in eastern Australia

Abstract Multivariate patterns in commercial fisheries landings, effort and revenue from three adjacent estuarine and coastal systems were examined in eastern Australia between 9‐month periods of flood (September 2000–May 2001) and drought (September 2002–May 2003). Patterns in species landings, methods of fishing effort and revenue per species were significantly different between flood and drought. Spearman’s rank correlations between Bray–Curtis similarity matrices for landings, effort and revenue indicated that patterns in fisheries metrics represented a mixed signal of ecological response and fishers’ harvesting behaviour. Flood and drought events were associated with shifts in the species composition of landings that were reciprocated between estuarine and coastal systems. Estuarine migrant species (e.g. school prawn Metapenaeus macleayi Haswell) primarily contributed to landings during flood, whilst marine estuarine‐opportunist species (e.g. yellowfin bream Acanthopagrus australis Owen) primarily contributed to landings during drought. Flood and drought events redistributed fisheries resources between estuarine and coastal systems, modifying the bioeconomic productivity of commercial fisheries. Results indicated that flood and drought events influence commercial fisheries by modifying landings composition, fishers’ harvesting behaviour and revenue generation.     

An assessment of the Prochilodus platensis Holmberg population in the Pilcomayo River fishery, Bolivia using scale-based and computer-assisted methods

Abstract. The catch from the fishery for the migratory Prochilodus platensis Holmberg on the Rio Pilcomayo shows considerable annual variation. Peaks were apparent in 1981 and 1982, followed by very low returns between 1983 and 1985 and a resurgence in 1986. The catch in 1986 was 1011t with the degree of annual variation probably lying between 500 and 2000t. In the Pilcomayo P. platensis is a rapidly growing short-lived fish with a maximum life expectancy of 6-7 years and an upper size approaching 61.5cm. The fish first migrate and appear in Bolivian' waters when they are 21/2-3 years old, having spent the first 2 years on the nursery grounds, probably on the Argentine/Paraguay section of the river. Although fish of this age were numerous in the 1986 catches, the optimal market size is rather larger, and older fish are taken preferentially. The fishery actually depends upon very few age classes. A comparison of growth and mortality rates obtained from scale reading and from length frequency analysis by ELEFAN programs showed a close agreement. The considerable fluctuations in the fishery are largely due to the highly variable flood regime of the river rather than to fishing pressure, with the flood determining recruitment in 2 years' time. Nevertheless, a combination of a sequence of poor flood years with sustained fishing pressure could seriously damage the fishery.     

Compositional trends of fisheries in the River Ganges,India

Abstract Monthly surveys of local fisheries from five principal landing sites on the River Ganges at Bhagalpur, India, were conducted from 2001 to 2007. Fishes of a range of sizes with mostly periodic‐type life‐history strategies, including many catfishes and carps, dominated the catch. Average annual yield (total mean monthly catch in units of biomass) was highly variable but trended downward during the study. Statistical ordination revealed associations between assemblage composition and hydrological seasons. Overall yields in this reach of the River Ganges tended to be greatest when the annual flood pulse was sustained longer. Patterns of average stock yields and inter‐annual variability of yields were associated with species life‐history strategies, with the most abundant and least variable species having periodic‐type strategies of seasonal spawning, high fecundity, small eggs and no parental care. Although not appearing to have declined precipitously during the study, many stocks in this stretch of the River Ganges, including those of the largest and most valuable species, nonetheless seemed to remain below historical yield levels because of multiple impacts, including chronic intense fishing and other anthropogenic impacts.     

Dynamics of floodplain fisheries in Bangladesh, results of 8 years fisheries monitoring in the Compartmentalization Pilot Project

Floodplain fisheries were monitored from 1992 until 2000 in the Compartmentalization Pilot Project in Tangail, Bangladesh. In permanent floodplains about 165 ± 28 kg ha^?1 of fish was caught annually. For seasonal floodplains, this figure was 83 ± 23 kg ha^?1 yr^?1. The fish catch exhibited a strong seasonal variation, with the highest catch in October, when the floodwater recedes towards the river, and the lowest catch during the dry season in April/May. The annual catch varied with the extent of flooding, with high catches in wet years and low catches in dry years. The extent of flooding was quantified through a Flood Index. Plotting the annual yields against this Flood Index provided a significant relation (P < 0.05), confirming the existence of a flood pulse. The fishing effort (f) and the catch‐per‐unit‐effort (CPUE) were significantly related (P < 0.05), whereby the fishing effort increased with increasing CPUE. The results are discussed within the frame of fisheries management in Bangladesh and highlight the need for long‐term data for proper evaluation of fisheries projects and the development of management schemes, and the difficulty of applying standard surplus production models in floodplain fisheries.     

Analysis of Fishery Records from Cow Green Reservoir, Upper Teesdale, 1971–1980

Apart from some irregularities reflecting changes in permit costs (1975) and the effects of drought (1976), there were increases in angler-visits, catch per angler-visit and number of fish caught during the first 5 years of the fishery. Thereafter, there were about 1000–1500 angler-visits per season, a mean catch of 1.0–1.2 trout per angler-visit and an annual catch of 1200–1800 trout. Between 1971 and 1980 the mean weight of the fish caught fell from 472 to 349 g. During the period 1976–1980 the mean catch per angler-visit was 1.2 fish. This compares favourably with results from a selection of upland and lowland British reservoirs. The mean weight of individual trout caught was 362 kg and this value is typical of both stocked and unstocked upland reservoirs. The mean annual catch during 1976–1980 was about 2 kg ha^?1. This is similar to the values observed in other unstocked upland reservoirs. The gross yield from such reservoirs can be increased by stocking but the limited data available suggest that at stocking rates above about 5 kg ha^?1 the net yield (i.e. weight caught — weight stocked) becomes negative.     

Variability of fish densities in a small catchment

Abstract— Temporal and spatial variability of fish communities were examined within a 91-km² catchment in central New York over four years. Riffle-dwelling species, slimy sculpin Cottus cognatus , longnose dace Rhinichthys cataractae , and young-of-the-year brown trout Salmo trutta , were more strongly affected by flood and drought than pool-adapted species, adult brown trout, blacknose dace Rhinichthys atratulus , white sucker Catostomus commersoni , and creek chub Semotilus atromaculatus . Canonical correspondence analysis using seven abiotic variables (mean width, residual pool depth, water surface slope, mean Froude number, variance in Froude number, maximum monthly discharge and minimum monthly discharge) separated fish communities among sites and years. The first axis represented a headwater-to-valley gradient; the second axis reflected habitat complexity, based on both geomorphic and hydraulic features. Temporal differences in fish densities were related to hydrological factors. Fish communities throughout the catchment showed similar responses to flood and drought.     

The influence of multiyear drought and associated reduction in tributary connectivity on an adfluvial fish species

Multiyear drought is projected to increase in frequency and duration in arid and semiarid regions across the world, threatening native species and ecosystem function. The effects of multiyear drought are often exacerbated by human water use, which manifest in reduced lake elevation, reduced stream discharge, and disruption in hydrologic connectivity for aquatic species. Here, we demonstrate that drought-driven decreasing lake levels reduce the connectivity between tributaries and lakes by creating an elevation-explicit tributary distance map. We combined long-term fish catch data and a lake elevation time-series with our elevation-explicit tributary distance map to test whether population demographics are related to drought-driven changes in tributary connectivity. We surveyed the littoral zone of Bear Lake, Utah and Idaho, USA, from full pool to a depth of >12 m, totalling 94.86 km² surveyed. As lake elevation decreased from full pool to the lowest historical elevation, tributary channel distance increased by 3.5 km. Bear Lake Bonneville Cutthroat Trout (Oncorhynchus clarkii utah) catch per unit effort was strongly negatively correlated with tributary channel distance, though individual growth rates were not influenced by drought metrics. We predicted the response of age 0 to age 10 cutthroat under high and low cobble availability, estimating up to a 61% decline in cutthroat CPUE when tributary channel distance is at its maximum historical value. Our study provided a unique opportunity to identify quantitative linkages between climate-driven changes in habitat connectivity and an ecologically important endemic sportfish, expanding our understanding of potential pathways through which climate change may affect lentic ecosystems and fishes.     

大西洋大眼金枪鱼资源开发研究

统计分析了1995-2004年间大西洋大眼金枪鱼总渔获量及各渔区、各主要生产国的渔获量变化情况,结果表明：整个大西洋大眼金枪鱼渔获量呈下降趋势,其开发类型主要有延绳钓、饵钓和围网,其中以延绳钓的渔获量最大,1995-2004年期间以西北大西洋（21区）产量最高,为9.53×10^7t,东北大西洋与中西大西洋相对渔获量较少,各为2.47×10^4t,我国对大西洋大眼金枪鱼开发程度不高,占总渔获量的比例较小,针对我国的情况提出开发大西洋大眼金枪鱼相关建议。     

Spatio‐temporal trends of the Krill fisheries in the Western Antarctic Peninsula and Southern Scotia Arc

Krill fisheries in Antarctica have concentrated their effort on the Western Antarctic Peninsula and Scotia Arc (WAP) in the last decades, following a steady increase in annual catch. Short‐term shifts in habitat exploration may have occurred and may be the cause for the increasing catch. Habitat use and effort in krill fisheries in the WAP during summer between 2012/2013 and 2016/2017, inclusive, were tested to determine how habitat use and effort reflected in the catch. Increasing trends in fishing tow duration and depth of fishing in deeper and colder waters were found. No association of the catch with the habitat explored was found, but catch was higher in years when the variability of explored habitat was lower. The relevance of these findings for fisheries management and conservation of Antarctic marine ecosystems is discussed.     

A synthetic control approach to estimate the effect of total allowable catches in the high seas

Total allowable catch restrictions (hereafter referred to as catch quotas) play an important role in maintaining healthy fish stocks. While studies have identified a positive relationship between catch quota implementation and improved stock status, these methods are subject to selection bias as catch quotas are typically applied to stocks that are depleted. We address this challenge using the synthetic control method, which estimates the causal effect of catch quotas on fishing mortality and biomass by predicting a synthetic counterfactual outcome. We focus on high seas stocks (tunas, billfishes, and sharks) managed by tuna Regional Fisheries Management Organizations (tRFMOs), first providing an overview of stock status and current management measures in place. We find that implementation of catch quotas by tRFMOs has more than doubled over the past decade. Second, we predict the hypothetical fishing mortality and biomass trajectory for seven high seas quota-managed stocks in absence of a catch quota. These “synthetic non-quota stocks” are predicted using a weighted selection of high seas non-quota stocks. Credibility of the synthetic non-quota stocks is evaluated through diagnostic checks, and robustness tests assess sensitivity to study design. Five credible fishing mortality synthetic controls are predicted: three add support to the hypothesis that catch quotas successfully reduce fishing mortality, while two find that catch quotas increase fishing mortality. While our analysis is limited in scope, given that all seven quota-managed stocks are managed under a single tRFMO, we highlight the potential for the synthetic control method in fisheries management evaluation.     

黑龙江省农业水资源高效开发利用研究

黑龙江省雨热同季,农业水资源属于我国北方较多地区,但降水分布不均,春旱和夏涝对农业生产影响较大。嫩江和松花江干流水对工农业生产、人们生活和改善生态环境均有较大影响,关键是要提高控制率。松花江干流外来过境水资源、东部地下水资源和国境界河水资源等均有较大开发潜力。农业水资源丰富的地区,应优先发展水稻。农业水资源较少的地区发展旱田节水灌溉,应优先选择菜瓜果类高效益作物和对生产影响较大的种子苗木等,扩大玉米催芽坐水种面积,种植附加值较高的经济作物。     

渔获量不确定性对印度洋大眼金枪鱼资源评估的影响

大眼金枪鱼(Thunnus obesus)是最具经济价值的热带金枪鱼类,其资源状况一直是区域性金枪鱼渔业管理组织关注的重点。由于多种渔业作业、捕捞船队构成复杂,印度洋大眼金枪鱼的历史渔获量统计存在一定的偏差(Bias),但国际上近些年开展资源评估时都忽略了这一偏差。本研究根据1979~2015年的年渔获量、年龄结构渔获量及相对丰度指数数据,运用年龄结构资源评估模型(ASAP)对印度洋大眼金枪鱼资源进行评估,重点考查渔获量的不确定性(观测误差和统计偏差)对资源评估结果的影响。结果显示,印度洋大眼金枪鱼当前资源总体没有过度捕捞,但2015年初显示轻微的过度捕捞,通过对比基础模型与8个灵敏度分析模型的评估结果发现,渔获量观测误差(CV)的预设对资源开发状态的判断有一定的影响。当渔获量统计偏差调整量为15%时(即历史渔获量被低估了),评估结果与基础模型基本一致;统计偏差调整量为20%时,评估结果有过度捕捞的趋势。本研究结果表明,资源评估模型中渔获量观测误差的设定和历史渔获量统计偏差均会对评估结果产生影响,后者更为明显,因此,二者均不能忽略。     

Elasmobranch captures in the Fijian pelagic longline fishery

1. Pelagic longline fisheries for relatively fecund tuna and tuna‐like species can have large adverse effects on incidentally caught species with low‐fecundity, including elasmobranchs.
2. Analyses of observer programme data from the Fiji longline fishery from 2011 to 2014 were conducted to characterize the shark and ray catch composition and identify factors that significantly explained standardized catch rates. Catch data were fitted to generalized linear models to identify potentially significant explanatory variables.
3. With a nominal catch rate of 0.610 elasmobranchs per 1000 hooks, a total of 27 species of elasmobranchs were captured, 48% of which are categorized as Threatened under the IUCN Red List. Sharks and rays made up 2.4% and 1.4%, respectively, of total fish catch. Blue sharks and pelagic stingrays accounted for 51% and 99% of caught sharks and rays, respectively.
4. There was near elimination of ‘shark lines’, branchlines set at or near the sea surface via attachment directly to floats, after 2011.
5. Of caught elasmobranchs, 35% were finned, 11% had the entire carcass retained, and the remainder was released alive or discarded dead. Finning of elasmobranchs listed in CITES Appendix II was not observed in 2014.
6. There were significantly higher standardized shark and ray catch rates on narrower J‐shaped hooks than on wider circle hooks. Based on findings from previous studies on single factor effects of hook width and shape, the smaller minimum width of the J‐shaped hooks may have caused the higher shark and ray catch rates. For sharks, the effect of hook width may have exceeded the effect of hook shape, where small increases in shark catch rates have been observed on circle vs J‐shaped hooks.
7. Shark and ray standardized catch rates were lowest in the latter half of the year. Focusing effort during the second half of the year could reduce elasmobranch catch rates.

Copyright © 2016 John Wiley & Sons, Ltd.     

Managing non‐target,data‐poor species using catch limits: lessons from the Alaskan groundfish fishery

Abstract The 2006 reauthorisation of the Magnuson‐Stevens Fishery Conservation and Management Act requires annual catch limits for all target and non‐target species within federally managed fisheries in the United States. In Alaska, both target and non‐target species in the Alaska groundfish fisheries have been managed using catch limits since the early 1990s. Non‐target species that are caught incidentally in a fishery require monitoring to ensure that the population is not negatively impacted by commercial fishing. Resource assessment scientists have been challenged with obtaining sufficient data to recommend an acceptable catch level for management of these species. This paper reviews three case studies where a catch limit is determined for non‐target species when certain data are limited: (1) varying levels of biomass and catch data for all species within a species group or complex; (2) adequate catch data but no biomass data; (3) emerging target fishery of data‐poor species, plus an example of how a complex of ecosystem component species is managed.     

塘沽上岸渔获物组成变化趋势分析

通过对比2006-2007与1998-2000年天津市塘沽区渔业产量及组成发现,10年间总渔获量呈上升趋势,2007年渔获总产量接近1.3万t,鱼类取代虾类,成为主要渔获物.小黄鱼产量明显上升,2007年产量2 436.0 t,是1999年的23倍,虾蟹类产量最多的口虾蛄仅为1999年的27.7％.2007年杂鱼产量有...     

Baseline assessment of total fisheries-related biomass removal from Japan’s Exclusive Economic Zones: 1950–2010

The rise and fall of Japan’s marine fisheries have been well documented and are clearly evident in official landings statistics. However, the extent of illegal, unreported and unregulated fisheries, including recreational fisheries, and the discarding of unwanted catch in Japanese waters, both of which may have significant implications on the success of management regimes, have yet to be closely examined. This study reassessed the impact of fisheries on the marine ecosystems of Japan’s Exclusive Economic Zones (EEZ) by estimating the total marine biomass removed through the use of an established catch reconstruction approach. Since 1950, 368 million t of marine biomass have been extracted from the Japanese EEZ as commercial catch, recreational catch, illegal catch and discards. Commercial catch accounted for 87 % of the total, while discards accounted for an additional 8 %. The disparity between the estimated biomass removals and the reported commercial catch is 48 million t, or 15 % of the reported catch. The difference is not as large as observed in similar studies of other regions. Nonetheless, the reconstructed biomass removals represent a better baseline for the management of fisheries in the Japanese EEZ, particularly if Japan is to move forward with implementation of output control management.     

Fasting combined with long catch duration modifies the physio‐metabolic response and flesh quality of rainbow trout

Pre‐slaughter handling involves fasting fish and catching them, which can affect fish welfare and flesh quality, but few studies have considered their combined effects. In this study, adult rainbow trout (320 ± 10 g average weight) were fasted for 7 days (135.6 degree days) and subjected to a long catch duration (20 min), compared with controls (no fasting or short catch duration). Condition factor, organ weight indexes and carcass yield decreased with fasting but not catch duration. Plasma concentrations of cortisol, glucose and lactate increased after a long catch, while plasma triglycerides decreased with fasting. Liver glycogen concentration was lower in fasted fish, and liver luminosity and chroma were higher after fasting with a long catch. Regarding flesh quality, rigor mortis resolved more slowly and final muscle pH at 48 hr post‐mortem was higher for fasted fish with a long catch time. Muscle glycogen concentration was higher in fasted fish, where chroma was also lower. Fasted fish had lower lipid oxidation, but there were no differences in fat content in muscle. Fasted fish with a long catch duration also had less monounsaturated and more saturated fatty acids. In conclusion, a long catch triggered a stress response that had negative effects on flesh quality, independently of fasting.     

基于渔获物统计的中国近海鱼类营养级结构变换及其与捕捞作业的关系

为了解我国东部海域(渤海、黄海和东海)和南海的鱼类生态结构和渔业资源变化特征,本研究在1983—2013年中国海洋渔船渔获统计数据的基础上,首先将渔获物中的鱼类按照营养级归类,然后计算其平均营养级(TL)和Fi B指数,并结合海洋捕捞作业方式,对鱼类的营养级结构长期变化进行分析。结果表明,在东部海域捕捞的25种主要鱼类渔获中,31年间TL呈现下降趋势,低营养层级鱼类比例增长了60%,中营养层级鱼类比例增长了129%,高营养级鱼类则下降了近51%;而在南海,31年间TL变化不明显,低营养级鱼类比例下降了6%,中营养级鱼类下降了43%,高营养级鱼类增长198%。东部海域和南海的渔获物鱼类生态结构变化说明,就营养级水平而言,东部海域近海渔业资源呈现明显的衰退现象,而南海则还未出现这种现象。     

Spatio‐temporal management of fisheries to reduce by‐catch and increase fishing selectivity

Time/area closures have been widely used in fisheries management to prevent overfishing and the destruction of marine biodiversity. To a lesser degree, such spatio‐temporal management measures have been used to reduce by‐catch of finfish or protected species. However, as ecosystem‐based management approaches are employed and more fisheries are managed through multispecies, multiobjective models, the management of by‐catch will likely become increasingly important. The elimination of by‐catch has become a primary goal of the fishing policies of many countries. It is particularly relevant in the United States, as the deadline for setting annual catch limits (ACLs) in all fisheries passes in 2011. This will result in a dramatic expansion of the number of catch and by‐catch quotas. Such catch measures may result in the early closure of otherwise sustainable fisheries when by‐catch quotas are exceeded. To prevent such closures and the consequent economic hardship to fishers and the economy, it is imperative that managers be given the tools necessary to reduce by‐catch and improve fishing selectivity. Targeted spatio‐temporal fishery closures are one solution open to managers. Here, we examine how the spatio‐temporal and oceanographic characteristics of by‐catch may be used by managers to design fishery closures, and place these methods within a decision tree to assist managers to identify appropriate management measures. We argue that the current movement towards marine spatial planning (MSP) presents an important impetus to examine how we manage fisheries spatially, and we offer a first step towards the objective participation of fisheries in the MSP process.