Net Mesh Size Research Articles

莱州湾水母种类多样性及群集结构的季节变化

PDF HTML阅读 XML下载 导出引用 引用提醒 莱州湾水母种类多样性及群集结构的季节变化 DOI: 10.5846/stxb201505030902 作者: 作者单位: 中国水产科学研究院黄海水产研究所,中国水产科学研究院黄海水产研究所,中国水产科学研究院黄海水产研究所,中国水产科学研究院黄海水产研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展规划项目（2011CB403604）；国家基金委-山东省联合基金项目（U1406403）；山东省自然科学基金（2009ZRB02317） Annual survey of the species diversity and assemblage dynamics of medusae in Laizhou Bay, Bohai Sea Author: Affiliation: Yellow Sea Fisheries Research Institute,Chinese Academy of Fishery Sciences,Yellow Sea Fisheries Research Institute,Chinese Academy of Fishery Sciences,Yellow Sea Fisheries Research Institute,Chinese Academy of Fishery Sciences,Yellow Sea Fisheries Research Institute,Chinese Academy of Fishery Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于2011年5月至2012年4月（除冰期12月和翌年1-2月外）在渤海莱州湾逐月采集的数据资料，系统地开展水母种类组成、数量分布的周年季节变动，弥补自20世纪90年代以来该区域相关资料的不足，有利于掌握该水域水母（主要是小型水母）主要种类数量时空分布特点，促进莱州湾生物类群对生境改变响应的相关研究。结果显示：所有调查中，共出现水母30种，无全年出现的种类。各月中，莱州湾水母以8月种数最多，5月数量居多。各月水母总数量的80%多由1-2种优势种贡献所致；水母优势种类组成季节更替明显。3-5月优势种为八斑唇腕水母；6月为嵊山秀氏水母和贝氏真囊水母；7月为贝氏真囊水母、9月有细颈和平水母；10月为细颈和平水母和大西洋五角水母，8月和11月无明显的优势种，但8月细颈和平水母和曲膝薮枝螅水母数量较多。莱州湾小型水母聚集结构主要呈现季节性时间格局上的变动。春季有八斑唇腕水母为代表、在湾内分布的聚集组；夏季有以嵊山秀氏水母和贝氏真囊水母为代表、在湾口西侧和湾中部分布的聚集组，以及细颈和平水母为代表、在湾中底部分布的聚集组；秋季有四枝管水母和大西洋五角水母为代表、在湾口和中部分布的聚集组。水温对小型水母聚集结构分布具有较为重要的影响作用。大型水母在本调查出现较少。海蜇和沙海蜇出现于6-8月个别站位；海月水母7-10月均有出现，但高密集区出现在10月紧邻莱州湾的湾底水域。 Abstract:Laizhou Bay, an estuary of the Yellow River, lies to the north of the Shandong Peninsula and is one of the three largest and most important bays of the Bohai Sea. It is characterized by a high level of primary productivity and is an important spawning, nursery, and feeding ground for many fish species in the Yellow Sea and Bohai Sea. Medusae play crucial roles, not only ecologically in the marine ecosystem but also economically, as commercial target species for some large scyphomedusae in Laizhou Bay. In the past few decades, the interacting impacts of climate change and human activities have changed the ecosystem of Laizhou Bay significantly, leading to regime shifts in biological organisms, including medusae. Recently, increasing concern has prompted studies on the ecological impacts of changes in the gelatinous species community of the estuary and coastal area. To explore the temporal and spatial distribution of the composition and abundance of medusa species in the bay, annual surveys were designed and carried out from May 2011 to April 2012 (excluding December 2011 and January and February 2012, because of the presence of sea ice). Based on the data collected from 147 samples collected over the course of 9 cruises, nearly thirty cnidarians including twenty-four hydromedusae, one siphonophore, and three large scyphomedusan jellyfish were identified. The species of hydromedusae and siphonophore were small, and were collected by being vertically hauled from the seafloor to the surface using a mesoplankton net (mesh size 160 μm). Of the smaller medusae, no common species were collected throughout the year. Species richness peaked in August, while the total abundance peaked in May. One or two dominant species contributed over 80% of the total monthly abundance. The dominant species varied among months, with Rathkea octopunctata dominating from March to May, Sugiura chengshanense and Euphysora bigelowi dominating in June, E. bigelowi dominating in July, Eirene menoni dominating in September, and E. menoni and Muggiaea atlantica dominating in October. In August, E. menoni and Obelia geniculata were abundant, but were distributed regionally in the central parts of the bay. Very few medusa species were collected in November. Multiple statistical analyses, including cluster analysis and BVSTEP modules conducted with Primer 6.0 software, were used to identify the best matches for environmental factors that affect the composition of the medusa assemblages. Based on the abundance of small medusae, cluster analysis recognized four seasonal and spatial assemblage groups. The first group, with R. octopunctata as its representative species, was collected at the runoff inlet of the bay in spring. The second group was collected in the western section of the river mouth or the central parts of the bay in summer. The second group's representative species were S. chengshanense and E. bigelowi. The third group also occurred in summer, but its location was very similar to the spring group, and it included E. menoni as its representative species. The fourth group appeared in autumn and was collected in the river mouth or the central part of the bay, and included two indicator species:M. atlantica and Proboscidactyla flavicirrata. According to the results of the BVSTEP modules analysis, the water temperature had a more significant effect on the seasonal and spatial distribution of the hydromedusae than salinity, pH, or dissolved oxygen. The three large scyphomedusan jellyfish were only caught by fishing methods that utilized a net with a 20 mm mesh size. They occurred only at a few inlet sites after June. Aurelia spp. peaked later in October. Rhopilema esculentum and Nemopilema nomurai were collected from June to August at only a few sites. 参考文献 相似文献 引证文献

Heavy metal concentrations in zooplankton of Sinop coasts of the Black Sea, Turkey

Estimation of level contamination of marine ecosystems with heavy metals is important task in the field of MSFD. Total zooplankton samples were collected using a standard zooplankton net (mesh size = 112 µm, mouth diameter = 50 cm) from Sinop coast of the Black Sea, Turkey in 2011 and 2012. Concentrations of Al, As, Cu, Zn, Hg, Fe, Cd and Pb were determined in the total zooplankton samples. The average concentration of heavy metals followed order: Fe > Al > Zn > Pb > Cu > As > Cd > Hg. Of all the heavy metals estimated Hg was below the detection limit in all the samples. Fe was the most common heavy metal in total zooplankton samples present in all, Al was the other heavy metal commonly present in the samples. Pb showed high value (210 mg·kg-1) in total zooplankton. Similar to Pb, a high average concentration of As (40 mg·kg-1) was observed in total zooplankton. Cd was 1.1 mg·kg-1.

Freshwater ostracods (Crustacea) and environmental variability of polygon ponds in the tundra of the Indigirka Lowland, north-east Siberia

Freshwater ostracods (Crustacea, Ostracoda) are valuable biological indicators. In Arctic environments, their habitat conditions are barely known and the abundance and diversity of ostracods is documented only in scattered records with incomplete ecological characterization. To determine the taxonomic range of ostracod assemblages and their habitat conditions in polygon ponds in the Indigirka Lowland, north-east Siberia, we collected more than 100 living ostracod individuals per site with a plankton net (mesh size 65 µm) and an exhaustor system from 27 water bodies and studied them in the context of substrate and hydrochemical data. During the summer of 2011, a single pond site and its ostracod population was selected for special study. This first record of the ostracod fauna in the Indigirka Lowland comprises eight species and three additional taxa. Fabaeformiscandona krochini and F. groenlandica were documented for the first time in continental Siberia. Repeated sampling of a low-centre polygon pond yielded insights into the population dynamics of F. pedata . We identified air temperature and precipitation as the main external drivers of water temperatures, water levels, ion concentrations and water stable isotope composition on diurnal and seasonal scales. Keywords: Arctic limnology; permafrost; patterned ground; ecological indication; freshwater ostracods. (Published: 1 March 2016) To access the supplementary material for this article, please see the supplementary files in the column to the right (under Article Tools). Citation: Polar Research 2016, 35 , 25225, http://dx.doi.org/10.3402/polar.v35.25225

Mesh size of nets to prevent invasion of Large-billed Crows

Mesh size of nets to prevent invasion of Large-billed Crows

Length-weight and length-length relationships of four native fish species of the Qinghai-Tibet Plateau, China

This study presents the length–weight (LWR) and length–length relationships (LLR) of four fish species (Gymnocypris namensis Wu & Ren, 1982; Herzensteinia microcephalus Herzenstein, 1891; Triplophysa stenura Herzenstein, 1888; and Triplophysa brevicauda Herzenstein, 1888) collected from the Qinghai-Tibet Plateau, China. A total of 291 specimens was collected using electric fishing (12V), gill nets (mesh size: 2 × 2 cm, 3 × 3 cm) and cast nets (mesh size: 2 × 2 cm), in July 1998 and October 2014.

Length-weight relationships of five fish species from the Hongshui River, China

The length–weight relationships (LWRs) of five Chinese endemic fish species caught by cast nets (mesh size 1 cm) and gillnets (mesh size 4 cm) in the Hongshui River in June and July 2011 and October to November 2012 were determined. These are the first LWRs records for the five little-known species.

Selective predators or choosy fishermen? Relation between fish harvest, prey availability and great cormorant (Phalacrocorax carbo sinensis) diet

The increase in numbers and range of the continental subspecies of great cormorant Phalacrocorax carbo sinensis in Europe has led to a growing number of conflicts with commercial fisheries and recreational angling. We investigated the dietary preferences (fish species and size classes) of wintering cormorants in two freshwater basins in Northern Italy, using pellet analysis and data on fish community composition. First, we compared cormorant diet (biomass of fish species consumed) with the annual harvest by professional fishing (biomass/year). Second, we compared diet with a measure of prey availability: direct fish sampling with nets of different mesh size. Cormorants preyed mainly on cyprinid fish. A comparison of pellet analysis and commercial fishing data showed that some fish species consumed by cormorants did not occur in the commercial harvest. Using only species that occurred in the diet and in the commercial harvest, there was no relationship between the amount of fish of different species taken. A positive correlation between pellet analysis data (consumed) and data from scientific fish sampling (available) showed that cormorants exploited fish resources on the basis of prey availability. Comparing the size of fish collected from nets and fish consumed by cormorants also showed that birds were selective with respect to prey size, picking mostly small individuals (< 110 g). We conclude that potential effects of cormorants on commercially important fish will mainly depend on habitat type (fish ponds, natural deep lakes, others), and that in the natural lakes in Lombardy cormorants mainly concentrate on species which are of limited value for commercial fishing.

Length-weight relationships of five fish species from the Hongshui River, China

The length-weight relationships (LWRs) were determined for five Chinese endemic fish species caught by electrofishing, cast nets (mesh size 1 cm) and gillnets (mesh size 4 cm) in the Hongshui River during June and July 2011 and October to November 2012. These are the first LWRs records for these five little-known species.

Age, growth and population dynamics of two congeneric and invasive gobies, Rhinogobius giurinus and R. cliffordpopei (Actinopterygii, Gobiidae) in a plateau lake, southwestern China

Although many goby species have become widely established outside of their native ranges, little is known yet about invasive population biology. The age, growth and population dynamics of two introduced goby species (Rhinogobius giurinus and Rhinogobius cliffordpopei) were quantified in Lake Erhai (southwest China) with the general aim to improve empirical knowledge and management strategies. The results revealed that their lifespan ranges 2 years. The size and time at sexual maturity for R. cliffordpopei was lower than for R. giurinus. R. cliffordpopei displayed higher total mortality, fishing mortality and exploitation rates than R. giurinus, whereas the natural mortality of R. cliffordpopei was lower than that of R. giurinus. The catch per unit effort of benthic fyke nets was low from April to June in R. cliffordpopei and from July to September in R. giurinus, whereas it was high from July to September in R. cliffordpopei and from April to June in R. giurinus. Thus, several specific strategies are suggested to improve the cost-efficiency of the current management practices related to the mesh size of benthic fyke nets used for physical removals, the timing of deployment of control actions and the use of synergic control methods.

Comparison of the effects of two bongo net mesh sizes on the estimation of abundance and size of Engraulidae eggs

Abstract Studies of ichthyoplankton retention by nets of different mesh sizes are important because they help in choosing a sampler when planning collection and the establishment of correction factors. These factors make it possible to compare studies performed with nets of different mesh sizes. In most studies of mesh retention of fish eggs, the taxonomic identification is done at the family level, resulting in the loss of detailed information. We separated Engraulidae eggs, obtained with 0.333 mm and 0.505 mm mesh bongo nets at 172 oceanographic stations in the southeastern Brazilian Bight, into four groups based on their morphometric characteristics. The difference in the abundance of eggs caught by the two nets was not significant for those groups with highest volume, types A and B, but in type C (Engraulis anchoita), the most eccentric, and in type D, of the smallest volume, the difference was significant. However, no significant difference was observed in the egg size sampled with each net for E. anchoita and type D, which exhibited higher abundance in the 0.333 mm mesh net and minor axis varying from 0.45-0.71 mm, smaller than the 0.505 mm mesh aperture and the mesh diagonal.

Analysis of body size selectivity of by-catch using the cover net method for a shrimp beam trawl

Selectivity and by-catch are the main features used to define fish catch for fisheries management or to determine fishing gear efficiency. A fish girth distribution analysis was carried out to determine the retention rate of juveniles discarded and to establish common selectivity for a multispecies catch. Total body length, body weight, and girth of juvenile fish retained in the cod-end and cover net separately were collected using an 18-mm mesh cover net during 12 fishing trials with a 41-mm cod-end beam trawl. The by-catch weight ratio in the cod-end was twice that of the by-catch ratio in number. The 50% selectivity of body length and 50% girth of redfin velvet fish were not significantly different between the cod-end and cover net, whereas those of other fish species were significantly different between the cod-end and cover net. The difference in 50% selectivity girth of other fish between the cod-end and cover net was similar between cod-end mesh size and cover net mesh size. Furthermore, the difference in 50% body length selectivity of other fish between the cod-end and cover net was almost double the difference in girth. Girth selectivity in a multispecies catch using towed fishing gear was effectively used to determine fish and net mesh size.

New insights on the biological parameters of the exploited cuttlefish Sepia officinalis L. (Mollusca: Cephalopoda) in the northern Adriatic Sea in relation to the main fishing gears employed

The cuttlefish (Sepia officinalis Linnaeus 1758) represents one of the most important coastal fishery resources of the Mediterranean Sea. For Italy, 45% of cuttlefish landings (2,328 t) originates from coastal regions of the northern Adriatic Sea: Veneto, Marche, Emilia Romagna and Friuli Venezia Giulia. In terms of economic value this species represents about 8% (~€ 16.5 million) of the production from this basin. From May 2004 to October 2005, cuttlefish were purchased from commercial landings of the Grado fishery fleet. At least 30 specimens were randomly taken each month from each fishing method employed for this species: bottom trawl (cod end mesh size 40 mm), rapido trawl, trammel net (mesh size of inner panel 30 mm) and cuttlefish specific trap. The main biological aspects, such as size, sex ratio, reproductive stage and diet in relation to both the season and type of fishing gear were analyzed. 1,495 specimens, ranging from 3.5 to 18.0 cm mantle length, were analyzed. In relation to the observed size and reproductive stage of individuals caught, trammel nets and cuttlefish traps both appeared to target sexually mature individuals, whilst trawling gear were not selective for either recruits or spawners. In total 34 prey taxa were found in the stomachs of S. officinalis: crabs and bony fish species were the most important prey, although the latter appeared mostly in the largest specimens. Finally the fullness index revealed that cuttlefish caught by trawling were more suitable for diet analysis than those caught by static gear. In this way the contribution of the present paper was to give new insights on the biological parameters of this species in relation to the main fishing gears employed in the northern Adriatic Sea.

The Ichthyofauna of Gediz River (Turkey): Taxonomic and Zoogeographic Features

Aims: This study was carried out to determine the fish fauna in the Gediz River and by comparing the fish fauna with that of neighboring basins from a zoogeographical point of view. Place and Duration of Study: In order to establish the taxonomic and zoogeographic features of the fish fauna of the Gediz River Basin (Turkey), fish samples were collected using elektrofishing equipment gill nets trammel nets, seine nets and cast nets from June 2010 to July 2012. Methodology: The fish were collected using electrofishing equipment, gill nets (mesh size of 9x9 mm and 12x12 mm), trammel nets (various mesh seize), seine nets (2 mm) and cast nets. The samples were fixed and preserved in a 4% formalin solution. Meristic characters such as number of gill rakers, pharyngeal teeth, dorsal and anal fin rays, total lateral line scales were counted under a stereomicroscope. The last two branched dorsal and anal fin rays are counted “1/2”. The number of vertebrae in the Cyprinidae and Nemacheilidae was determined by radiography. Results: Among the samples, 19 (Anguillidae (1), Cyprinidae (10), Siluridae (1), Nemacheilidae (1), Cobitidae (2), Poeciliidae (1), Gobiidae (1), Percidae (1) and Salmonidae (1)) species belonging to 9 families were identified. Determination of the species; Alburnus battalgilae, Barbus pergamonensis, Luciobarbus lydianus, Capoeta bergamae, Squalius fellowesii, Chondrostoma Original Research Article Guclu and Kucuk; ARRB, 6(3): 202-214, 2015; Article no.ARRB.2015.079 203 holmwoodii, Ladigesocypris mermere, Cobitis kurui, Cobitis fahireae, Oxynoemacheilus simavicus and Knipowtischia mermere are endemic; Gambusia holbrooki and Oncorhynchus mykiss are nonnative species. Conclusion: As a result, in the Gediz River where there were 19 fish taxa, 44% of taxa were endemic. The endemic species on the basis of the IUCN criteria must be especially protected.

Stock Assessment of a Non-Commercial Fish Sciaena coitor (Hamilton, 1822) from Middle Stretch of River Ganga

Based on the length frequency data growth, mortality, and population parameters of Sciaena coitor from the scoop net (mesh size 0.5–2 cm) catches from middle stretch of Ganga at Allahabad were estimated. The length-weight relationship for pooled data was log W = 76.39315 L2.48487. The asymptotic length (L∞) and growth coefficient (K) were estimated to be 198 mm, and 0.868 year−1, respectively. The total, fishing and natural mortality coefficients were estimated as 3.31, 1.55 and 1.76 respectively while the ‘E’ 0.468 year−1. The recruitment was continuous with one peak per year. The Lc50 was obtained at 115 mm. Yield isopleth diagram generated, give optimum yield at E of 0.4 and Lc/L∞ = 0.58.

Temporal changes in benthic macroinvertebrates and their interactions with fish predators after restoration in theCheonggyecheon, a downtown stream inSeoul,Korea

AbstractTheCheonggyecheon (Cheonggye stream), a downtown stream inSeoul,Korea, was restored by the historicCheonggyecheon Restoration Project (2003–2005), and its discharge and other environmental conditions are artificially regulated throughout the year. The aim of this study was to assess temporal changes in benthic macroinvertebrates and their interactions with fish predators in theCheonggyecheon. Sampling was conducted twice a year (spring and autumn) at three sections of the stream from 2006 to 2010 using a Surber sampler (50 × 50 cm) for benthic macroinvertebrates and a cast net (mesh size, 10 × 10 mm) and a kick net (mesh size, 5 × 5 mm) for fishes. Analyses of annual precipitation and most water quality parameters showed no significant differences across the study period (P&gt; 0.05). The species richness and density of benthic macroinvertebrates and fishes varied across the sampling period. Analyses of functional feeding groups and trophic guilds showed distinct trends, such as an increase in the number of insectivorous fish in the absence of invertebrate predators. Correlation and regression analyses for five major groups of benthic macroinvertebrates and fishes demonstrated that the density of certain groups of benthic macroinvertebrates (e.g.Tubificidae,Erpobdellidae,Baetidae, andChironomidae) and insectivorous fishes (e.g.Gobioninae,Leuciscinae,Danioninae, andGobiidae) were negatively correlated. In conclusion, in an artificially regulated stream like the restoredCheonggyecheon, where physical environments are nearly unchanged, fish predation can be a major factor controlling benthic macroinvertebrate communities.

The relationship among spawning period, length at first maturity and depth distribution of Mullus barbatus and Upeneus moluccensis inhabiting the Northeastern Mediterranean coast of Turkey

This study examined the spawning characteristics and distribution of Mullus barbatus and Upeneus moluccensis in Babadillimani Bight, in the northeastern Mediterranean (near Mersin, Turkey) between of May 1999 and April 2000. Sampling was carried out monthly at depths of 0-50 m, 50-100 m and >100 m using commercial trawl net mesh size 22 mm knot to knot. The results showed no difference between the length at first maturity of males and females (t-test, P>0.001) in either M. barbatus or U. moluccensis . This length for the combined sexes was calculated to be 11.7 cm and 10.9 cm in M. barbatus and U. moluccensis , respectively. When monthly changes in the Gonadosomatic Index (GSI) values were evaluated, the spawning period was determined as July-November for M. barbatus and May-August for U. moluccensis . The mean total lengths from the individuals belonging to M. barbatus from depth layers of 0-50 m, 50-100 m and >100 m were calculated as 8.65 cm, 8.70 cm and 12.70 cm, respectively. Total lengths for U. moluccensis were calculated as 8.40 cm, 11.66 cm and 13.32 cm, respectively. The mean total length of M. barbatus and U. moluccensis increased from coastal areas to deeper waters. Therefore bottom trawl fishing must be conducted in waters deeper than 100 m for both M. barbatus and U. moluccensis .

Heterorhizy can lead to underestimation of fine-root production when using mesh-based techniques

This study investigates the relationship between fine-root morphology and net mesh size in fine-root production (FRP) measurements (ingrowth core and net method). The data collected show that when a fine root has an apical diameter equal or bigger than the mesh size, the degree of difficulty in passing through the net determines a response that arrests growth or deviation from the initial direction of growth. Both reactions prevent the root from crossing the net and induce the fine root to produce new laterals with thinner diameters. The investment in biomass necessary to form the new laterals is smaller than that needed to support the parental fine root and this leads to determines an underestimation of FRP. In particular, a considerable reduction of fine-root biomass in the area outside the netting was detected with a mesh size below 1.5 mm. The choice of net mesh size to be used for FRP measurement cannot be arbitrary, but should be evaluated through a preliminary analysis of fine-root morphology of experimental species prior to net installation.

Efficacy of insect nets for cabbage production and pest management depending on the net removal frequency and microclimate

In Africa, synthetic pesticide applications are overly frequent and above labelled rates. We assessed the efficacy of an insect net physical control system on field cabbage (Brassica oleracea var. capitata) production in France and Benin. Various mesh sizes and netting removal frequencies were compared under contrasting climatic conditions. Studies under Mediterranean climatic conditions (spring season) compared two mesh sizes (0.73 mm and 1.6 mm). Studies under subequatorial climatic conditions (cool and hot seasons) tested nets of mesh size 0.4 mm and 0.9 mm used either as permanent cover, removed daily, or 3 days per week. The results showed that a fine mesh did not improve the netting efficacy against pests but had a major impact on the microclimate. In Mediterranean climatic conditions, the netting efficacy and beneficial microclimate improved crop yields. In subequatorial conditions, crop yields were lowest with permanent net protection due to high temperatures under the nets and poor aphid and Spodoptera littoralis control. Removing the nets 3 days per week was a good technical/economic trade-off, ensuring acceptable efficacy with minimal effects on the microclimate.

The influence of gear selectivity and spawning behavior on a data-poor assessment of a spawning aggregation fishery

We applied several data-poor techniques to perform an assessment of the Gulf corvina (Cynoscion othonopterus) fishery in the Gulf of California from 1997 to 2012 and to investigate the effects of gear selectivity and age-dependent variation in spawning frequency on estimates of sustainability in spawning aggregation fisheries. The length composition of the catch varied significantly among years but showed no clear directional pattern. However, the average length was above the long term average after the implementation of a regulation that standardized mesh size of nets, and the average length of fish captured after the implementation was significantly higher than during previous periods. Results using three simple metrics based on catch length compositions indicated that fishing activities were sustainable due to the exclusion of juveniles from the fishery and the targeted harvest of adults at the optimal length. However, the low proportion of older, fecund fish in the fishery is a serious cause for concern. Modeled estimates of spawning potential ratios (SPR) were consistently higher when spawning frequency was assumed to be age invariant and were significantly higher after the implementation of gear regulations. However, SPR values only reached levels above 35%, a common reference point for sciaenid fishes, during the current fishing period (2010–2012) under conditions of age invariant spawning frequency. Results of this study support previous claims that suggest estimates of reproductive potential are highly sensitive to age-dependent variation in spawning frequency and imply that such details related to spawning behavior require more attention, particularly for fisheries that target spawning aggregations. Our results also suggest that spawning aggregations can be harvested sustainably through conventional regulations if juveniles are excluded, fish are harvested at optimal length, and older, fecund individuals are protected from harvest. Given the uncertainty of the status of the corvina fishery based on the discordant results of this study and the inherent vulnerability of the species to overfishing, We recommend the precautionary approach be applied to management decisions until more robust information is acquired on stock abundance, the relationship between spawning frequency and age or length, and reproductive output.

Age-growth models for tilapia Oreochromis aureus (Perciformes, Cichlidae) of the Infiernillo reservoir, Mexico and reproductive behaviour

In presence of a decrease in the catch from Infiernillo reservoir, Michoacán-Guerrero, Mexico, age and growth of tilapia Oreochromis aureus (Steindachner 1864) were estimated, as indispensable attributes for fishery management. Evaluations included scales and opercular bones readings and length frequency analysis. The population structure was determined too. Due to the great variation of tilapia individual growth and with the objective to have reliable growth estimations, linearized, non-parametric and non-linear methods were used and their applicability discussed. Comparison of ages determined from these methods revealed that opercular bones readings had advantages over scales. Reproduction and competition for space and food were considered as responsible factors for ring-formation on tilapia hard structures. The non-linear method was considered the best for modelling populations highly variable, which is characteristic of tilapia and tropical fish with multiple spawns. The growth parameters estimated were Linfinity = 479 mm, K = 0.46/yr, t0 = -0.055 yr. The tilapia population in Infiernillo reservoir is dominated by juveniles less than 1.5 years old. The fishery activity is affecting the tilapia population growth because are caught when they have not yet spawned. Therefore, this fishery is in urgent need of regulation. Increasing the mesh size of the gill nets might contribute to protect the reproductive potential of the stock.