Embryonic development of Ganga river prawn Macrobrachium gangeticum (Bate)

Macrobrachium gangeticum (Bate) are commercially valuable prawns that are broadly distributed in the Ganga river that flows from northern to eastern India. We studied embryonic development from cleavage (blastomeres), segmentation, formation of optic vesicle, eye pigment development to larva formation, as these data are largely unknown in this species. We conducted this study using mature M. gangeticum broodstock placed in freshwater tanks. Just after spawning, females were kept in separate aerated tanks, where fecundity was estimated from the total number of eggs. Thereafter, egg samples from berried females were used to study their embryonic stages. The correlation coefficient between size and prawn weight, egg weight, egg number, body weight and egg mass of different sizes of prawns was analysed. Our results show that an increase in prawn size led to an increase in egg weight and egg number while decreases in body weight:egg mass ratio was noticed. Further results indicate that an increase in prawn weight had a positive impact on egg weight and egg number. The embryo development stages were used in this study as a tool to evaluate the development process of the prawn in a hatchery environment.     

Comparative fishing trials for <Emphasis Type="Italic">Charybdis japonica</Emphasis> using collapsible box-shaped and dome-shaped pots

ABSTRACT:   Comparative fishing trials were undertaken with two commercial collapsible pots for the crab Charybdis japonica . One pot was box-shaped with two slit entrances at the ends, while the other was dome-shaped with two open funnel entrances. Pots were placed at the bottom of a pond that is connected to Kagoshima Bay. Fishing trials were carried out using a 1-day soaking time; the bait used was mackerel. The box-shaped pot had higher catches of crabs and non-target organisms, but the number of large crabs (carapace width >8 cm) was almost half as many as that caught with the dome-shaped pot. The catch of non-target species was also greatly reduced in the dome-shaped pot, and fish caught were mostly enmeshed in the netting. The reduction in catches of small crabs and non-target organisms was due to the nature of the dome-shaped pot's larger mesh size and open entrances, which allowed for escape. The dome-shaped pot seemed more efficient for harvesting commercial size crabs, while the box-shaped pot seemed better for removing all crab sizes.     

A model for estimating prawn populations in ponds

The dynamic modeling approach considers the prawn population in a pond as a system where the number of prawn at any given time can be estimated when the relationship between survival and growth can be determined. Compared with existing statistical inference models, this approach allows for “forward estimation” in which future populations can be estimated. This feature is useful in production management.     

Genetic diversity and population structure of a giant freshwater prawn (Macrobrachium rosenbergii) breeding nucleus in China

The giant freshwater prawn breeding programme in China has been carried out as a closed nucleus from 2006. The programme aimed to improve the harvest body weight and pond survival and has achieved remarkable progress. In this study, the genetic diversity and population structure of the giant freshwater prawn breeding nucleus was analysed. Pedigree completeness, the status of genetic diversity, inbreeding accumulation and effective population size of the breeding nucleus were analysed according to the pedigree record. From 2006 to 2014, a total of 107,941 individuals with 555 males and 967 females in nine generations were included in the analyses. Pedigree completeness index in six generations was at least 0.92. After performing eight selections, the genetic diversity decreased by 3%, 67% of which was caused by random genetic drift. After performing 2 years’ selection, the inbreeding level began to show a marked upward trend. The regression of the average rate of inbreeding and the average rate of co‐ancestry was 0.0041 and 0.0051 from 2006 to 2014. The effective population size calculated from the above two parameters was 122 and 98 respectively. The effective population size is still within the recommended level for a population to continue the genetic improvement programme, but below the level required (500) for retaining the evolutionary potential. To restrain the increasing level of inbreeding and maintain effective population size, measures are required to develop a breeding programme which integrates management of genetic variability and selection.     

Quantifying the effects of bycatch reduction devices in Queensland''s (Australia) shallow water eastern king prawn (Penaeus plebejus) trawl fishery

This study presents results from an experimental 10-day research charter that was designed to quantify the effects of (a) a turtle excluder device (TED), (b) a radial escape section bycatch reduction device (BRD) and (c) both devices together, on bycatch and prawn catch rates in the Queensland shallow water eastern king prawn (Penaeus plebejus) trawl fishery. The bycatch was comprised of 250 taxa, mainly gurnards, whiting, lizard fish, flathead, dragonets, portunid crabs, turretfish and flounders. The observed mean catch rates of bycatch and marketable eastern king prawns from the standard trawl net (i.e., net with no TED or BRD) used during the charter were 11.06 kg/hectare (ha⁻¹) (S.E. 0.90) swept by the trawl gear and 0.94 kg ha⁻¹, respectively. For the range of depths sampled (20.1–90.7 m), bycatch rates declined significantly at a rate of 0.14 kg ha⁻¹ for every 1 m increase in depth, while prawn catch rates were unaffected. When both the TED and radial escape section BRD were used together, the bycatch rate declined by 24% compared to a standard net, but at a 20% reduction in marketable prawn catch rate. The largest reductions were achieved for stout whiting Sillago robusta (57% reduction) and yellowtail scad Trachurus novaezelandiae (32% reduction). Multidimensional scaling and analysis of similarities revealed that bycatch assemblages differed significantly between depths and latitude, but not between the different combinations of bycatch reduction devices. Despite the lowered prawn catch rates, the reduced bycatch rates are promising, particularly for S. robusta, which is targeted in another fishery. Prawn trawl operators are not permitted to retain S. robusta and the devices examined herein offer the potential to significantly reduce the incidental fishing mortality that this species experiences.     

对虾虾头、虾壳副产品综合利用的研究概况

对虾在加工过程中会产生大量的虾头及虾壳等副产品,其副产品中含有丰富的营养物质.近年来,随着对虾产量的递增,其副产品的产量也越来越多,但产生的副产品大多被低值化利用或直接被废弃.既浪费资源又对环境造成了污染.为解决这一问题,本文就虾副产品在食品、化工、医学等方面的综合利用作简要概述,以期为对虾食品加工企业提高虾的综合利用...     

Genetic diversity of oriental river prawn(Macrobrachium nipponense De Haan)revealed by ISSR markers

日本沼虾(Macrobrachium nipponense)是中国分布范围广、经济价值较大的一种重要淡水虾类.随着养殖规模的不断扩大,如何保持养殖群体的遗传品质已引起了人们的重视.但迄今为止,养殖的日本沼虾均来自未经系统遗传选育的野生群体,而养殖病害的日趋严重和养成规格、品质的下降已严重影响到日本沼虾养殖产业的健康发展.研究野生群体的遗传结构和遗传分化,揭示其遗传多样性是制定合理有效的保护和管理策略的前提和基础.ISSR(Inter-simple sequence repeats,简单重复序列中间区域)标记技术具有实验重复性好、信息量大、多态性高等优点,是一种理想的检测群体遗传变异的分子标记.因此,本研究应用ISSR标记技术对日本沼虾5个地理群体进行了初步的遗传分析,以期为合理开发和利用日本沼虾天然资源,以及建立和保护日本沼虾种质资源库及基因库提供理论依据.本研究对采自江苏苏州、江西南昌、云南西双版纳、湖北宜都和新疆博湖的5个地理群体进行了初步研究.从50个ISSR引物中筛选出9个条带清晰、稳定性和重复性好,且产生相对较多条带的引物用于全部DNA样品的PCR扩增.对日本沼虾5个地理群体的群体遗传分析表明,在所有榆测到的清晰且可重复的142个有效位点中,多态位点有138个.物种水平上,多态位点百分率(PPL)、等位基因数(No)、有效等位基因数(Ne)、Nei's基因多样性指数(H)和Shannon信息指数(Ⅰ)分别为97.18%、1.972、0.312、0.120和0.323.而在群体水平上,5个地理群体的多态位点百分率为29.58%～61.97%;等位基因数(No)为1.296～1.620;有效等位基因数(Ne)为1.165～1.281;Nei's基因多样性指数(H)为0.098～0.172;Shannon信息指数(Ⅰ)为0.147～0.267.从各个地理群体看,江西南昌群体的遗传多样性最高(PPB:61.97%,No:1.620,Ne:1.281,H:0.172,I:0.267),而湖北宜都群体最低(PPB:29.58%,No:1.296,Ne:1.165,H:0.098,I:0.147).群体内遗传多样度(HS)和总基因多样度(HT)分别为0.135和0.201,根据遗传多样性水平在群体内(HS)和群体间(HT-HS)的分化,各个群体之间的Nei's基因分化系数[GST=(HT-HS)/HT]是0.327.AMOVA分析表明,群体间的遗传变异占总遗传变异的38.59%,而61.41%的遗传变异源于群体内,群体之间表现出较高水平的遗传分化.与其他群体相比,新疆博湖群体和江苏苏州群体差异最小(FST:0.1923,遗传距离D:0.0542),而新疆博湖群体与云南西双版纳群体差异最大(FST:0.5950,D:0.1559).采用UPGMA法构建的分子系统树显示,5个地理群体明显地聚为2个族群,来自新疆博湖和江苏苏州的日本沼虾群体聚为一支,而江西南昌、湖北宜都和云南西双版纳的群体聚在一起.本研究使用9条引物对5个地理群体进行了扩增,共检测到138个多态位点,各群体的多态位点百分率(PPL)为29.58%～61.97%.与其他相关研究结果进行比较,发现对日本沼虾而言,ISSR技术是一个理想的检测群体遗传变异的分子标记.与其他群体相比,新疆博湖群体和江苏苏州群体各遗传参数均相近,且UPGMA系统树亦显示新疆博湖群体和江苏苏州群体的亲缘关系较近,推测它们可能来自同一个祖先群体.与其他野生群体相比,江西南昌群体的遗传多样性最高,该群体采自江西省鄱阳湖,鄱阳湖是中国最大的淡水湖泊,它接纳赣江、抚河、信江、饶河、修河5大河及博阳河、漳田河、潼津河的来水经调蓄后由湖口注入长江,是一个过水性、吞吐型、季节型的湖泊.上游河流汇入鄱阳湖引起群体迁移使不同生态型的基因交流,增加了迁入地的遗传多样性.从遗传角度来讲,一个物种保持足够的遗传变异性是适应不同生境、生存和进化的首要保证.因此,较高水平的遗传多样性对于保护和利用野生群体具有重要意义.本研究表明,在日本沼虾的多样性研究方面,ISSR标记技术是一个非常有效的检测群体遗传变异的遗传标记.研究结果可以为合理开发和利用日本沼虾自然野生资源,以及建立和保护日本沼虾种质资源库及基因库提供基础资料.     

马氏沼虾的成虾形态及特征鉴别

马氏沼虾是我国从斯里兰卡新引进的淡水虾类，外观略呈纺锤形，虾体共分为20节，除尾节外，虾体的每一节各具l对附肢，雌虾和雄虾在第五步足基部分别具有“A”和“M”状突起。头胸甲的胃区、心区、触角区表面较粗糙，两侧还有数条与虾体平行的浅棕色斑纹。虾苗时期多数个体呈淡褐色，性成熟后体色呈浅褐、淡青偏褐色或淡灰色。额角尖端微微上翘向前伸展，但不超出第二触角的触角片末端，上翘高度不超过额角上缘鸡冠状隆起的顶端，齿式为7～13／4～6。其生物学特性与罗氏沼虾和日本沼虾相比有许多相似之处，但在体色、额角、头胸甲和腹甲侧片等形态特征上差异十分明显。本文描述了马氏沼虾的外部形态及结构，比较了上述几种虾的主要特征，并就“雄虾特化”现象以第二步足与体长之比作为依据提出了质疑。     

蟹笼渔具逃逸口位置对三疣梭子蟹逃逸行为的影响

为了检验蟹笼渔具逃逸口对三疣梭子蟹逃逸行为的影响,实验使用红外水下摄像装备观察了三疣梭子蟹对3种不同配置逃逸口(位于侧网底部、开口高度3.2 cm和4.0 cm以及位于侧网顶部、开口高度4.0 cm)的反应行为。水下观察结果显示,三疣梭子蟹在笼底的探索行为使其能轻易发现和接近底部逃逸口,而垂直搜索行为能使其发现和接近顶部逃逸口,虽然发现并接近顶部逃逸口所需的时间显著大于底部逃逸口,但平均次数无显著性差异;87%接近逃逸口的个体企图穿越逃逸口,且逃逸口位置对此无显著影响;所有个体均采用侧身姿态穿越逃逸口,甲高是决定个体成功逃逸的关键因素;穿越顶部逃逸口的三疣梭子蟹需要花费更多的时间和精力调整姿态和位置以更好地匹配逃逸口,但广义线性混合模型(GLMM模型)拟合结果显示,逃逸口位置对个体逃逸成功率没有显著影响,表明三疣梭子蟹具有较高的个体姿态操纵能力,而笼内个体数量对逃逸成功率具有显著的影响。结合水下观察,研究认为个体在探索行为的活跃程度和浸泡时间会影响逃逸口的性能;考虑到东海近海蟹笼的结构和渔业现状,研究认为在蟹笼侧网靠近底部安装一个逃逸口是目前可行的技术措施。     

Fate and consumption of discarded by-catch in the Spencer Gulf prawn fishery, South Australia

Discarded by-catch in prawn fisheries is likely to affect trophic balance including the population structure and function of both the exploited species and scavengers on discards. The Spencer Gulf prawn fishery consists of 39 trawlers operating about 60 days a year with a management system allowing large differences in spatial effort. Such a system provides opportunities to study spatial effects of fishing in relation to habitat and fishing effort. In this study, the occurrence and consumption of scavengers on the Spencer Gulf prawn fishing grounds were studied at five sites subjected to different historical fishing effort and further estimated through field and laboratory experiments. Baited video experiments showed that the most common scavengers on discarded by-catch were Degens leatherjacket (Thamnaconus degeni), blue crabs (Portunus pelagicus) and sealice (a group of several species of isopods and amphipods), notably Natatolana woodjonesi, with variable abundances between sites and day/night. Scavenger abundance and consumption was higher at night than during the day. Total abundance and consumption during the day showed a negative correlation to historical trawl hours, while during the night showed a positive correlation. In the laboratory, in contrast to groups, individual leatherjackets showed little interest in bait. Consumption rates for both leatherjackets and blue crabs showed a logarithmic trend depending on bait species. The results showed that during the day blue crabs and leatherjackets were the dominating scavengers while during the night it was Port Jackson sharks and in particular sealice. The effects of site, historical trawl hours and relative importance of the scavenging species are discussed.     

Genetic variation of wild and cultured populations of the Kuruma prawn Marsupenaeus japonicus (Bate 1888) using microsatellites

The microsatellite DNA technique was used to detect the genetic variations between wild and cultured populations of Kuruma prawn Marsupenaeus japonicus Bate 1888. All the six microsatellite loci screened in this study showed high polymorphism for their PIC (0.6701–0.8989), which was much more than the standard value of 0.5. A total of 73 alleles were observed over six loci from 93 shrimps. The mean number of allele locus ranged from 9.83 (cultured) to 11.83 (wild). The number of effective alleles varied from 6.86 (cultured) to 8.58 (wild). The average of observed heterozygosity (H_o) of populations varied from 0.6935 (cultured) to 0.7370 (wild), and that of expected heterozygosity (He) was 0.8169 (wild) and 0.8209 (cultured). Tests of Hardy–Weinberg showed that these loci deviated significantly or highly significantly in one or both populations. Compared with the wild population, the cultured population showed little reduction in genetic variation. The total number of alleles (71, 59) was not significantly (P=0.296) different between wild and cultured populations. The paired‐samples t test of observed heterozygosity and expected heterozygosity implied that there was no significant difference (P=0.572 and 0.891 respectively) between wild and cultured populations. However, some rare allele loss might have occurred in the cultured population. A total of 14 unique alleles were found in the wild population, but only two unique alleles were observed in the cultured population. Therefore, there is a need to monitor genetic variability of cultured population, and to improve the hatchery program for the conservation of wild Kuruma prawn resources.     

Behavioural responses of red king crab to crab pots

High bycatch of female and sublegal sized male king crabs in the fishery is of concern to fishermen and management agencies; the efficiency of gear currently used in the fishery needs to be improved. This study examined behavioural responses of red king crabs to pots under laboratory conditions with time-lapse video. Crabs approached the pot from downstream, 82% of searches were confined to within 135 ° of the downstream direction, and 78.3% of crabs searched less than 90 ° before leaving or entering. The probability of entry success increased with the number of approaches. Crabs which failed to enter made an average of 2.6 approaches compared with 3.9 approaches for crabs which entered pots. The entry success rate was 8.1%. No significant differences in approach, search, and entry were found between ovigerous females, juvenile females, legal-sized males, and sublegal-sized males. Legal males (≥ 178 mm carapace width) had a significantly lower escape attempt rate and escape rate than sublegal males and females. Crabs depend on chemical cues during foraging, approaching, and searching. The current king crab pot is inefficient because crabs have difficulties in accessing the entrances and non-legal crabs have difficulties in escaping.     

微波消解-FAAS测定虾肉中钙的质量分数

采用微波消解-火焰原子吸收光谱法（flame atomic absorption spectrometry,FAAS）测定虾肉中钙（ca）元素的质量分数,对微波消解前处理的条件进行了研究。试验结果显示,最佳的微波消解体系为取样量0．500g,以硝酸（HNO,）作为消解溶剂,用量5．0mL,最适微波消解程序为多步消解程序D,包含3个步骤：1）功率400W,比例100％,升温5min,消解温度120℃,保持5min;2）功率800W,比例100％,升温5min,消解温度150℃,保持10min;3）功率800W,比例100％,升温10min,消解温度180℃,保持10min。样品消解液在常温或冷藏条件下保存48h之内的稳定性良好。经微波消解前处理后虾肉样品中”（ca）的相对标准偏差（relative standard deviation,RSD）为5．284％,加标回收率为91％-98％。微波消解-FAAS测定虾肉中的w（Ca）具有样品处理时间短、试剂用量少、结果准确和安全性高等优点。     

3种淡水对虾在冻藏过程中蛋白质特性的变化

以目前市场上主要的3种养殖对虾为对象,以肌原纤维蛋白盐溶解度、Ca2+-ATPase活性与蛋白质表面的巯基含量为指标,探讨了不同温度冻藏过程(-10、-20、-30、-40℃)对虾虾肉蛋白质生物化学特性的变化,评价了不同冻藏温度对对虾品质的影响。结果表明,第一,3种蛋白质的冷冻变性指标应用于对虾时出现一定差异。Ca2+-ATPase活性比较灵敏,能较好反映-10～-40℃不同冻藏温度引起的蛋白质变性的程度。肌原纤维蛋白盐溶解度能够反映-20℃以上冻藏过程中蛋白质变性程度的差异,而-20～-40℃的差异难以区分。-10℃冻藏时,肌原纤维蛋白的盐溶解度下降明显,而-20℃冻藏时下降程度较小,-20、-30、-40℃冻藏时肌原纤维蛋白的盐溶解度没有明显区别。-10～-40℃冻藏对于巯基含量变化都不大。第二,冻藏过程中3种对虾蛋白质冷冻变性较轻度,比一般鱼类在冻藏过程中稳定,虾比大部分鱼类更耐冻。第三,冻藏温度越低Ca2+-ATPase活性下降程度越小,-10～-40℃冻藏时其差异性有比较明显区分,表明Ca2+-ATPase活性更适合于虾的质量评价。第四,-20℃冻藏对于虾类是比较经济合理的,实用冻藏温度可取-20℃...     

人工选育中国对虾两个群体WSSV感染相关免疫与生化因子的变化

通过分析中国对虾人工选育两个群体WSSV感染相关免疫与生化因子的变化，研究选育的两个中国对虾群体对WSSV的敏感性和抵抗力。结果表明，两个群体感染WSSV后，总细胞数（THC）在24h达到最大，随后呈下降趋势；两个群体血淋巴蛋白在感染初期和中期变化不同，但在后期均呈下降趋势；相比而言2＇对虾群体比6＇对虾群体血蛋白含量和THC下降幅度稍慢；2＇对虾群体和6＇对虾群体感染24h后酸性磷酸酶（ACP）稍有下降，随后保持较高的活性，而碱性磷酸酶（AKP）的变化除2＇对虾群体在感染48h有显著增大外，6＇对虾群体变化不明显；过氧化氢酶（CAT）、活性氧（ROS）、超氧化物歧化酶（SOD）与WSSV感染有密切的联系，两个群体抗氧化酶活性随WSSV增殖的变化略有不同；细胞内酚氧化酶（proPO）原变化趋势也表现出差异，斑点杂交结果显示6＇对虾群体比2＇对虾群体阳性反应较早，揭示不同群体间对WSSV感染的敏感性存在一些差异。     

中国对虾对维生素B2、B5、B6营养需要的研究

研究了三种水溶性维生素Ｂ２，Ｂ５和Ｂ６在以酪蛋白为蛋白源的饲料中的不同含量对中国对虾的存活率，体重增重率，体长增长率，蛋白质消化率及实验维生素在体内的累积量等方面的影响。结果表明，在每１００ｇ饲料中维生素Ｂ２、Ｂ５和Ｂ６的含量分别在１０（体重１．５３ｇ）－２０ｍｇ（体重６．００ｇ）、４０ｍｇ、１４ｍｇ时，上述指标均达最佳，维生素缺乏或过量都会阻碍对虾生长，在适宜添加量范围中，随着饲料中维生素Ｂ６的     

Reuse strategy of wastewater in prawn nursery by microbial remediation

A strategy of reusing the prawn nursery wastewater was developed by the previous remediation with Bacillus subtilis and nutrients addition. The suggested method was preliminarily verified in rearing prawn larval. Bacteria assimilation is proved as a main and powerful mechanism for removing dissolved organic matter (DOM) and total ammonia nitrogen (TAN) in the experiments. The process of microbial remediation could be featured as two sequential stages: DOM degradation and TAN reduction. In the first stage (from day 0 to day 2), DOM was degraded directly as the bacterial carbon and nitrogen sources. The 48-h COD removal efficiencies (R_COD) in the treatment were 57.7±5.5%, showing significantly different from 12.2±4.1% in control. In the second phase (from day 2 to day 5), the deficiencies of C and P source relative to N source might limit bacteria proliferation and TAN removal. The glucose and/or phosphate addition significantly influenced the TAN removal performance, while the addition of vitamin mixture and/or microelement solution was not. When the initial TAN level was nearly 5 mg N/l, the optimal TAN removal efficiencies from day 2 to day 5 were above 85% in the treatments with both glucose and phosphate additions, where the white microbial floccules were observed to suspend. The C/N or N/P weight ratio of 5.4:1or 5–7:1 was suggested for remediating the nursery effluents. The situation that the maximum bacterial levels did not exceed 10⁸ CFU/ml was estimated to correlate with the formation of microbial floccules. After 5 days of microbial remediation by these adequate methods, the wastewater had been became the “microbially matured” water suitable to reuse. In the practical operations, the nutrient supplements were directed by Glucose/TAN weight ratio of 13:1 and KH₂PO₄/TAN weight ratio of 0.6–0.9:1. The results of the application trial pointed out that the remediated water reclaimed to the larvae culture tanks did not produce observable deleterious effects on the water quality and on the mortality of the prawn larvae. The method of reusing the remediated wastewater by microbial agents and nutrients additions will be advantageous to reduce both production cost and environmental pollution in the inland hatchery and nursery for prawn.     

Current status and prospects of farming the giant river prawn Macrobrachium rosenbergii (De Man) in Bangladesh

Giant river prawn (Macrobrachium rosenbergii) farming plays an important role in the economy of Bangladesh. Presently, it is cultured in around 50 000 ha area with total annual production of 23 240 t. Traditional extensive prawn farming has been expanding over the last three decades through the introduction and adoption of improved culture systems, such as culture of prawn‐carps, prawn‐shrimp‐fish and prawn‐fish‐rice as concurrent and rotational systems. Efforts for the development of improved techniques on broodstock management, seed production and rearing and grow‐out of prawn have been made over the last decade. The outcomes are low‐cost feed for broodstock, production of post‐larvae in net cages (hapa), all‐male prawn culture, periphyton based prawn‐tilapia culture, C/N based prawn culture, organic prawn farming, prawn‐mola culture and prawn‐carp‐mola polyculture. Despite the development of culture technologies, a number of challenges for sustainable development of prawn farming need to be overcome to realize the potentials of this promising sector. Good aquaculture practises at all levels and application of measures for quality control and food safety would ensure sustainable development of prawn farming in Bangladesh.     

Growth and spawning of hatchery-reared Chinese white prawn Penaeus (Fenneropenaeus) chinensis released in the Ariake Sea, Japan

SUMMARY: Growth and reproduction of hatchery-reared Chinese white prawn Penaeus chinensis released in the Ariake Sea, Japan, were examined. Chinese white prawn grew rapidly, reaching a body length of 154 mm in males and 198 mm in females by November (219–229 days after hatching). Maximum body length of sampled individuals was 164 mm in males and 223 mm in females. Growth curve of the Chinese white prawn was fitted to the Pitcher and MacDonald's formula, L_t = 155.0{1 − e ^{2.925sin[2π(t − 16.151)/365] − 0.0623( t − 10.712)}} for males and the logistic curve, L_t = 200.3/[1 + e ^{(1.985–0.034 t )}] for females (where L_t is the body length t days after release and t is the number of days after release). Females reached sexual maturity in late February and spawning occurred until April. Minimum size at ripe and spawned stages was 189 mm and 193 mm body length, respectively.     

A large scale BACI experiment to test the effects of prawn trawling on seabed biota in a closed area of the Great Barrier Reef Marine Park, Australia

A multiple Before-After-Control-Impact experiment was conducted to estimate the large scale effects of a single coverage by prawn trawlers on an offshore inter-reef area in the northern Great Barrier Reef that was closed to fishing. Prospective power and cost-benefit analyses facilitated the design and optimization of the experiment, the effect size of which was guided by prior publications at the time that had indicated impacts of 10–100×. The optimal design, given the number of factors to be tested and the constraint of available ship time (100 days) and resources needed to process samples, was for 12 control and 12 impact plots each measuring 2.8 km × 1.2 km. The final design specification was capable of detecting an average −80% effect size (5×). The experiment was divided over two seasons, wet and dry. During the experimental trawl impact phase, a total of 32 t of benthic biota was removed from six shallow plots (15–25 m depth) and 6 t from six deep plots (30–50 m depth). Sampling before and 6 months after impact was conducted by an epibenthic dredge, a prawn trawl and a fish trawl. Analysis of means before and after impact, relative to controls, showed very few significant differences. This indicated that the impact of a single prawn trawl was less than the design specification. The lower than expected impact, compared to previous studies, may have been partly because this study included all benthic groups, not just the most sensitive as earlier studies had focussed on. Comparison of catch rates from the prawn trawl and the dredge indicated the overall impact on total biomass was around −3% but ranged from close to 0% for some species to around −20% for sensitive sessile species. A review of effect sizes in 30 other recent trawl experiments indicated that this result was not exceptional; i.e. the reported effects of single trawls generally were not large, and prawn trawls appeared to have smaller effect sizes than fish trawls, beam trawls and scallop dredges—also, several studies reported recovery within ca. 6 months. Analysis of fishery effort data indicated that this result was appropriate for the majority of trawl fishing grounds, where effort is sparse and infrequent. Many published experiments had confounded designs and most had not used a priori power analyses or pre-specified effect sizes. Nevertheless, recurrent trawling can be expected to have cumulative impacts on benthos, as has been demonstrated by repeat-trawl depletion experiments. On the other hand, the spatial extent of fishing grounds trawled as intensively as these depletion experiments is quite limited.