Is feeding behaviour related to glass eel propensity to migrate?

Several studies have shown that eel diadromy is facultative and that migratory divergences may appear during glass eel estuarine migration. The origin of the differences in migratory behaviour among glass eels remains unclear but initial evidence supports the role of individual energetic and thyroidal status. Even if starvation is usually associated with glass eel migration, feeding does seem to occur in some glass eels. The aim of the present study was to investigate feeding behaviour and glass eel growth in relation to the propensity to migrate. Feeding rate and weight gain were higher in fish having a high propensity to migrate (M⁺ fish) than in fish having a low propensity to migrate (M⁻ fish) in fed glass eels, whereas no clear difference in the variation in body weight was observed among unfed fish (controls). M⁻ fish initially had lower percent dry weight than M⁺ fish, which suggests a link between appetite, propensity to migrate, and energy content. We discuss the role played by endocrine signals on these processes. In fish, thyroid hormones contribute to the control of growth and development. In addition, they play a role in flatfish and leptocephalus metamorphosis and appear to be involved in smolt and glass eel migratory behaviour. As such, they represent a good candidate which would promote the propensity to migrate as well as digestive system development. Their role in the hormonal control of food intake however remains vague.     

Farming of spiny lobsters in sea cages in India

Pueruli and post‐pueruli, early juveniles and sub‐adults of the spiny lobster, Panulirus homarus and juveniles of P. ornatus were grown in different floating sea cages along the southeast coast of India from May 2003 to May 2007. The first type of cage had a galvanised iron pipe frame (2.0 m × 2.0 m × 1.2 m) with steel woven mesh and four inner detachable compartments (0.75 m × 0.75 m × 1.10 m). Fibre‐reinforced plastic was used subsequently to fabricate cages (1 m × 1 m × 1 m). Pueruli and post‐pueruli of P. homarus (1.58 ± 0.62 g SD), stocked at 60 individuals/m², grew to an average weight of 123.10 ± 26.22 g in 266 days with a survival rate of 70%. Sub‐adults of P. homarus with an average weight (± SD) of 123.61 ± 29.26 g reached 341.25 ± 46.22 g in 225 days at a stocking density of 21 individuals/m² with a survival of 73 ± 6%. The post‐pueruli grew by 0.46 ± 0.10 g per day with a specific growth rate (SGR) of 1.64, whereas sub‐adults had a growth rate of 0.97 ± 0.20 g per day with a SGR of 0.43. At a higher stocking density of 80 individuals/m², juveniles (51.83 ± 10.32 g and 58.20 ± 28.22 g) of P. homarus recorded growth rates of 0.86 ± 0.25 (SGR 0.82) and 0.97 ± 0.34 g (SGR 0.96) per day. This study indicates that post‐pueruli of P. homarus can be grown to over 200 g in 12 months and up to 350 g in 16 to 17 months in sea cages. Juveniles (average weight 76.35 ± 34.50 g) of P. ornatus, reared with P. homarus at a stocking density of 80 individuals/m², recorded a weight gain of 139 g in 155 days at arate of 0.89 ± 0.32 g per day with an SGR of 0.67. Marine live clam, Donax spp., was the main feed supplemented with the gastropod, Xancus pyrum, the green mussel, Perna viridis, marine crab (Charibdis sp.), squid (Loligo sp.), and fish such as clupeids and Leognathus sp. Pueruli and post‐pueruli settled in large numbers (up to 35 individuals/month in one cage) both inside and outside the cages.     

The influence of environmental cues on the activity of silver eels (Anguilla dieffenbachii) in Lake Manapouri,New Zealand

Lake Manapouri in the South Island of New Zealand has a significant hydroelectric generation facility, which potentially has a negative impact on the successful emigration of longfin eels (Anguilla dieffenbachii) from the upper Waiau catchment. Consequently, a trap-and-transfer programme has been implemented to allow silver (migratory) eels access to the sea. The present study analysed data on the timing of captures and numbers of silver eels over four seasons, including the influence of possible migration cues. Silver eels were captured over an extended season of seven months (November–May), with peak numbers during December and January. Flow at the lake outflow was found to have a weak relationship with the number of eels caught, as did lake level, but moon phase and rainfall had no significant effect. These results highlight the variability in silver longfin eel behaviour both in terms of timing and response to potential environmental cues.     

投喂策略对多纹钱蝶鱼幼鱼生长的影响

为研究投喂策略对多纹钱蝶鱼(Selenotoca multifasciata)幼鱼生长的影响,实验选取初始湿体质量为1.19±0.35 g的多纹钱蝶鱼幼鱼进行养殖,实验为期60 d.1)投喂频率实验:实验设计4组,分别为F1(8:00投喂1次),F2(8:00、20:00投喂2次),F3(8:00、14:00、20:0...     

Production of fish in two small streams in the north island of New Zealand

Data are presented on biomass, mortality, growth, and production of fish populations inhabiting two small streams in the Wairarapa district of the North Island of New Zealand. The main water of both streams contained a mixed population of bullies (Philypnodon breviceps Stokell), brown trout (Salmo trutta Linn.), and eels (Anguilla dieffenbachii Gray, and A. australis schmidtii Phillipps). The headwater tributaries of one of the streams contained a large population of Galaxias divergens Stokell and a few eels, but other fish species were absent. All species of fish appeared to be using the same food supply of small benthic invertebrates, mainly ephemeropteran and dipteran larvae. Biomass of benthos per unit area was appreciably higher in the headwater tributary examined than in the main waters downstream. Mean annual stock of benthos in the tributary (Hinau north branch) was 19.75 g/m², in the Hinau main water 10.71 g/m² and in the Hinaki main water 13.47 g/m² Nevertheless, production per unit area from the nearly monospecific fish population in the Hinau north branch (14.28 g/m²) was less than that of the mixed populations in the main waters (24.17 g/m² in the Hinau, 73.54 g/m² in the Hinaki). Possibly fish production in the headwaters might be greater if the species composition of fish was more diverse.     

Sodium fluoroacetate (1080) residues in longfin eels,Anguilla dieffenbachii,following exposure to contaminated water and food

Captive longfin eels (Anguilla dieffenbachii) were exposed to the vertebrate pesticide sodium fluoroacetate (1080) in the water column and through the ingestion of cereal pellet baits or possum muscle and gut tissue that contained 1080 residue. No mortality or unusual behaviour (in comparison with the controls) occurred in eels that were exposed to 1080. However, significantly greater weight loss occurred in eels exposed to 1080 compared with those eels that were not. No residue was detected in tissues of eels exposed to 1080 cereal baits through ingestion and direct (dermal and respiratory) absorption, or through direct absorption only. Low concentrations of 1080 were detected in muscle tissue of eels that consumed contaminated possum muscle (x = 0.0174 μg/g) or gut (x = 0.0306 μg/g) tissue. The primary factors affecting the concentration of 1080 detected in eel tissue included the dose of 1080 (mg/kg) that each eel" receiveddate="and number of days since the eel last fed on contaminated tissue. Based on the 1080 concentrations measured in eels in this study, the risk of acute poisoning to humans from eating contaminated eel flesh is considered extremely low. Even so, national and international perceptions and food safety standards have the potential to limit eel exports and/or close an eel fishery if 1080 residue was discovered in tissue.     

Variation in organotin accumulation in relation to the life history in the Japanese eel Anguilla japonica

In order to examine the ecological risks caused by organotin compounds (OTs) in diadromous fish migrating between sea and freshwaters, tributyltin (TBT) and triphenyltin (TPT) compounds and their breakdown products were determined in the catadromous eel Anguilla japonica, which has sea, estuarine and river life histories, collected in Japanese sea, brackish and freshwaters within the same region. Ontogenic changes in otolith strontium (Sr) and calcium (Ca) concentrations were examined along the life history transect to discriminate the migration type. There were generally three different patterns, which were categorized as ‘sea eels’, ‘estuarine eels’ and ‘river eels’ according to the otolith Sr:Ca ratio. The concentrations of TBT in silver eels (mature eels) were significantly higher than that in yellow eels (immature eels), and the percentages of TBT were also higher in silver eels than in yellow eels. A positive correlation was found between TBT concentration and the gonad-somatic index (GSI). It is thus considered that silver eels have a higher risk of contamination by TBT than yellow eels. TBT and TPT concentrations in sea eels were significantly higher than those in river eels, while no significant differences were observed in TBT and TPT concentrations in estuarine eels compared to sea and river eels. These results suggest that sea eels have a higher ecological risk of OT contamination than river eels during their life history, and the risk of OTs in estuarine eels is considered to be intermediate between that of sea and river eels. Positive linear relationships were found between Sr:Ca ratios and the concentrations of TBT and TPT. Therefore, these results suggest that the ecological risk of OTs increase as the sea residence period in the eel becomes longer. TBT and TPT concentrations in sea eels were significantly higher than those in river eels even at the same growth stage. Thus, it is clear that migratory type is the most important factor for OT accumulation during the life history.     

牛磺酸对鲫鱼(Carassius auratus)生长、肠道细胞增殖及蛋白消化吸收相关基因表达的影响

本文探讨牛磺酸在鲫鱼生长、肠道细胞增殖分化以及蛋白质消化吸收相关基因的表达等方 面的作用。试验以480 尾[初始体质量(29.07±0.19)g]鲫鱼(Carassius auratus)为研究对象, 随机分成6 组, 每组设定4 个重复, 每个重复有鱼20 尾。鲫鱼基础饲料中添加的牛磺酸的剂量分别是0.0、1.0、 2.5、4.0、6.0 以及9.0 g/kg, 以0.0 g/kg 添加组为对照组, 试验持续8 周。结果表明: (1) 牛磺酸对鲫 鱼有促生长作用, 6.0 g/kg 添加组的鱼的增重率, 特定生长率, 蛋白质效率, 饲料系数等都显著高于 对照组(P<0.05).(2) 牛磺酸能促进肠绒毛的生长, 降低隐窝深度。(3) 牛磺酸提高了鲫鱼血清中T3、 T4 的含量, 添加6.0 g/kg 时显著高于对照组, 且此时血清尿素氮浓度显著低于对照组和其它处理组 (P<0.05).(4) 氨肽酶N(APN)、小肽转运蛋白(PepT1)、基因系尾型同源盒基因(CDX2)、L-氨基酸转 运载体蛋白(LAT2)等基因的相对表达量随牛磺酸剂量增加而上调, 6.0 g/kg 时显著高于对照组和其它 实验组(P<0.05).由此可见, 适量添加牛磺酸能影响鲫鱼生长、肠道细胞增殖及蛋白消化吸收相关基 因的表达。     

不同饵料对两种帘蛤科贝类生长性能的影响研究

为探讨不同饵料对青蛤(Cyclina sinensis)与文蛤(Meretrix meretrix)生长和存活的影响,本实验选用紫菜(Pyropia)、浒苔(Enteromorpha prolifera)、海带(Laminaria japonica)、小球藻(Chlorella vulgaris)和人工配合饲料5种饵料,采用单一饵料投喂方式进行饲养.结果表明:小球藻组中特定生长率、存活率及饲料转换率与各饵料组均有显著性差异(P<0.05),青蛤的增质量率显著低于紫菜组、海带组及人工配合饲料组(P>0.05).在人工配合饲料组中青蛤与文蛤的特定生长率与各饵料组均有显著性差异(P<0.05),青蛤的增质量率与各饵料组无显著性差异(P>0.05),文蛤的增质量率显著高于紫菜组、浒苔组及人工配合饲料组(P<0.05).在3组大型藻中,海带组中青蛤的特定生长率为0.07％,增质量率为4.59％,饵料转换率为7.09％,存活率为74％;文蛤的特定生长率0.13％,增质量率为8.36％,饵料转换率为1.41％,存活率为55.6％.综上,小球藻和人工配合饲料有利于青蛤和文蛤的生长,在3组大型藻中,投喂海带有利于文蛤和青蛤的生长和存活.     

Reexamination of the spawning migration of Anguilla dieffenbachii in relation to water temperature and the lunar cycle

ABSTRACT

The oceanic spawning migration of female Anguilla dieffenbachii eels was previously studied using pop-up satellite transmitting tags (PSAT). The swimming depths and experienced-temperature data of 3 eels released in May 2006 were re-examined in relation to water temperature data, and also lunar cycle and regional hydrography as these latter aspects were not considered in the original study. Eel 2 and Eel 3 initially experienced lower water temperature above 600?m, suggesting they remained south of the subtropical-convergence front longer than Eel 1. Their experienced nighttime minimum depths showed linear relationships with the lunar cycle, because they swam shallower during new moon than during full moon. The eels experienced narrow deep-day temperature ranges at a wide range of depths compared to experiencing narrow shallow-night depth ranges where temperatures varied more widely, indicating that several different factors determine their day and night depth ranges.     

饲料添加多维对花鲈生长、非特异性免疫指标及消化酶活性的影响

本试验旨在研究饲料中不同水平的多维含量对花鲈（Lateolabrax japonicus）生长性能、非特异性免疫指标及消化酶活性的影响。以初始体质量为（38.54±0.05） g的花鲈为试验对象,随机分为6组（每组3个重复,每个重复30尾鱼）,基础饲料中分别添加不同水平（0.5%、1%、2%、3%、4%、5%）的多维,在室内循环养殖系统中饲喂28 d。结果表明:多维添加量对花鲈的体成分、存活率、肝指数、饲料系数和肥满度均没有显著影响（P>0.05）;当多维添加量为2%时,花鲈的增重率（WGR）和特定生长率（SGR）均最大,与多维添加量为2%相比较,随着多维添加量继续增多,花鲈的WGR和SGR显著降低（P<0.05）;当多维添加量为5%时,花鲈的肠蛋白酶活性较0.5%和1%添加量组显著提高（P<0.05）,而多维添加量为0.5%时,花鲈的肠淀粉酶活性显著高于其余任意一组（P<0.05）,各组之间肠脂肪酶活性无显著差异（P>0.05）;与多维添加量为0.5%相比,多维添加量为5%时,能够显著提高花鲈血清中超氧化物歧化酶、碱性磷酸酶活性以及血清中总蛋白含量（P<0.05）,而血清溶菌酶活性没有显著变化（P>0.05）。结果表明:饲料中添加多维含量为5%时,能够明显提高花鲈的非特异性免疫指标及肠道蛋白酶活性,而在含量为2%时,能够明显提高花鲈的生长性能。     

欧鳗(Anguilla anguilla)饲料

本文初步概述饲养欧洲鳗鲡（Anguillaanguilla）的食性特征，对蛋白质的表现消化率和日粮蛋白质的需求量、驯饵、饲料形态、给饲率以及实用的欧鳗配合饲料。建议采用膨化颗粒饲料，制订欧级饲料实验方法和条件的规范。     

大西洋鲑幼鱼适宜投喂频率和胃排空研究

为探究大西洋鲑(Salmo salar)幼鱼的适宜投喂频率和胃排空规律,进行了养殖实验和胃排空实验.养殖实验设置了1次/天(F1组)、2次/天(F2组)、3次/天(F3组)、4次/天(F4组)和连续投喂(C F组)共5种投喂频率.胃排空实验采用连续测定胃含物的方法,用数学模型对胃含物数据进行拟合.研究表明:F1组日摄食...     

中国近海洄游日本鳗鲡(Anguilla japonica)玻璃鳗肠道微生物菌群分析

为研究长江口日本鳗鲡玻璃鳗肠道菌群的结构与多样性特征,初步探究野生鳗鲡仔鱼的营养需求,分别采集浙江台州市、舟山市以及江苏盐城市邻近海域的玻璃鳗样品,利用16S rDNA扩增子测序技术,分析三个采样点玻璃鳗肠道优势菌群及营养代谢相关的功能差异。结果显示,三个采样点的玻璃鳗肠道菌群均以变形菌门(Proteobacteria, 68.7%～82.0%)和放线菌门(Actinobacteria,4.2%～19.0%)为主要优势菌门。在属分类水平上,不动杆菌属(Acinetobacter, 12.4%～17.3%)和假单胞菌属(Pseudomonas, 8.07%～13.03%)丰度较高,属固定优势菌属。此外,每个采样点样本中都含有丰富的独特细菌群,包括台州市的气单胞菌属(Aeromonas)、舟山市的内生单胞属(Endozoicomonas)和丙酸杆菌属(Cutibacterium)以及盐城市的嗜冷杆菌属(Psychrobacter)和稳杆菌属(Empedobacter),推测是受采样点不同水环境因素影响。不动杆菌、假单胞菌、内生单胞菌等菌属在多种鱼类肠道中有着消化蛋白质的功能,气单胞菌虽属于...     

Effect of Protein Level and Varying Protein – Lipid Concentrations on Growth Characteristics of Juvenile Spotted Grunter Pomadasys Commersonnii (Haemulidae)

A 60-day feeding trial was conducted to evaluate the effects of dietary crude protein level on growth, feed conversion and protein efficiency ratio of juvenile (3–6 g) spotted grunter Pomadasys commersonnii. In the experiment, six semi-purified diets containing casein and fishmeal as protein sources, and with crude protein levels ranging from 35 to 60%, were fed to three replicate groups of fish per treatment in a recirculating system at the optimum temperature for growth. The relationships between dietary crude protein level and growth parameters were analysed by broken-line regression models. Results suggest that 48 – 50% dietary protein is needed for optimum growth and feed conversion for P. commersonnii. In a second experiment, three protein levels (35, 45 and 55%) at three different lipid concentrations (6, 8 and 12%) were used to formulate nine semi-purified diets that were fed for 60 days to triplicate groups of fish per treatment. Results suggest that a diet of at least 45% protein with a 12% lipid inclusion level is required for the best specific growth rate (5.96% per day) and feed conversion ratio (1.72) at this specific stage in the growth phase of P. commersonnii.     

Growth,feed conversion and faecal discharge of yellowtail kingfish (Seriola lalandi) fed three commercial diets

Abstract

A study was undertaken to provide data on growth, feed conversion ratio (FCR) and faecal discharge of yellowtail kingfish (Seriola lalandi) fed three commercial diets used previously to culture this species in New Zealand. Fish were raised in tanks from 0.4 to 1.2 kg over the spring (water temperature 14–17°C) and summer (17–22°C) periods. There were considerable differences in volumetric and mass‐specific feed intake, and energy intake amongst diets. Daily crude protein intake was similar amongst diets, although it increased from the cold (4.05–4.50 g protein kg^?1 day^?1) to warm period (6.48–7.67 g protein kg^?1 day^?1). The biological and economical FCR varied with diet (BFCR 1.22–2.17, EFCR 1.30–2.62), as did the cost of feed per unit biomass produced (NZ$38–3.78 kg^?1). Growth rates were broadly similar amongst diets, and the warmer summer temperature period greatly improved both growth (increase from 0.51–0.64% to 1.18–1.23% mass gain day^?1) and BFCR (decrease from 1.37–2.17 to 1.22–1.46). The Salmofood ESF diet resulted in only half of the faecal setüeable solids and settleable total nitrogen (T N) and total phosphorus (T P) output compared with Skretting NME, which was in turn only half or less of that of Reliance SF     

鳗鲡目鱼类线粒体蛋白质编码基因易位及系统演化关系分析

鳗鲡目鱼类线粒体基因组的基因组成较为保守,在58个线粒体基因组中,仅有3个物种存在基因数量的差异。在19个鳗鲡目鱼类线粒体基因组中存在主编码基因的重排。主编码基因的变异位点分析结果支持nad5、nad4和nad2基因作为cox1和lrRNA基因辅助的分子标记。鳗鲡科Anguillidae的20个种(亚种)聚在一起,强烈支持鳗鲡科为单系群(BPP=100)。鳗鲡科下属的3个类群(大洋洲类群、大西洋类群和印度洋-太平洋类群)也同时得到有力的验证(BPP均为100)。线鳗科Nemichthyidae和锯齿鳗科Serrivomeridae亲缘关系最近,二者聚类后,与鳗鲡科Anguillidae构成姊妹群(BPP=100)。在囊喉鱼亚目Saccopharyngoidei中,宽咽鱼科Eurypharyngidae与囊鳃鳗科Saccopharyngidae聚类(BPP=100),同时,单颌鳗科Monognathidae与月尾鳗科Cyematidae聚类(BPP=100),4个科聚在一支,支持囊喉鱼亚目为单系群(BPP=100)。在囊喉鱼亚目线粒体基因组中,3个物种(吞鳗Eurypharynx pelecanoides、拉文囊鳃鳗Saccopharynx lavenbergi和杰氏单颌鳗Monognathus jesperseni)存在主编码基因的重排。16种鳗鲡(细美体鳗Ariosoma shiroanago、短吻颈鳗Derichthys serpentinus、凯氏短尾康吉鳗Coloconger cadenati、鸭颈鳗Nessorhamphus ingolfianus、龟草鳗Thalassenchelys sp.、粗犁齿海鳗Cynoponticus ferox、百吉海鳗Muraenesox bagio、巨斑花蛇鳗Myrichthys maculosus、大吻沙蛇鳗Ophisurus macrorhynchos、几内亚副康吉鳗Paraconger notialis、哈氏异康吉鳗Heteroconger hassi、小头鸭嘴鳗Nettastoma parviceps、弱头鳗Leptocephalus sp.、斑点长犁齿鳗Hoplunnis punctata、尖吻小鸭嘴鳗Facciolella oxyrhyncha和星康吉鳗Conger myriaster),与鳗鲡目线粒体主编码基因的原始排列相比,共享nad6基因的易位。同时,基于线粒体基因组13个蛋白质编码基因构建的系统演化树,强烈支持这16个物种聚为一支(BPP=100)。然而,由此而带来的海鳗科Muraenesocidae、拟鯙科Chlopsidae和糯鳗科Congridae是否为单系群的问题,值得今后深入探究。     

日本鳗鲡(Anguilla japonica)精养殖水体生物膜原位修复低碳养殖技术的研究

采用水体中设置弹性填料对比实验的方法,在12口聚乙烯水槽实施淡水精养殖日本鳗鲡,进行对鳗鲡精养殖水体生物膜原位修复节水增效效果、机理及应用前景的研究。结果表明,在207天的养殖期间,生物膜原位修复技术应用处理组的平均日换水率仅1.2%,比对照组显著节水减排74%(P0.01);处理组的主要水质因子pH、DO、TAN、NO2-N、NO3-N、COD等浓度均符合相关的渔业水质标准;处理组的起捕尾重、产量、生长速度分别比对照组高106%(P0.2)、108%(P0.2)和220%(P0.15),饲料系数低于对照组38.4%(P0.1)。此外,处理组弹性填料设置的适宜密度为填料占水体体积的10%。因此,精养殖水体生物膜原位修复技术,具有节水、减排与节能效果显著,投资与运行成本低,环保、低碳、安全,操作简便、易推广等优点。该革新性的生态工程低碳养殖技术对推动我国水产养殖发展方式从高耗费资源型向资源节约与环境友好型转变将产生重大影响。     

Prey selection and dietary overlap of shortfinned (Anguilla australis) and longfinned (A. dieffenbachii) eels during summer in the Horokiwi Stream,New Zealand

Benthic macroinvertebrates were collected and the diets of shortfinned eels (Anguilla australis) and longfinned eels (Anguilla dieffenbachii) inhabiting a small coastal New Zealand stream were examined to investigate intraspecific and interspecific trophic partitioning and prey selection. Our results showed intraspecific segregation of preferred prey among three size classes of juvenile shortfinned eels, but there was significant overlap between different size classes of longfinned eels. All size classes of both species of eel fed nocturnally on similar prey, and so there was no indication of temporal or trophic segregation. Therefore, habitat separation is assumed to be the main mechanism to reduce interspecific competition in these two co‐occurring species of eels.     

The feeding ecology of skates (Batoidea: Rajidae) off the Cape south coast,South Africa

Six species of skates were trawled commonly on the continental shelf off the Southern Cape during routine surveys of demersal fish between 1986 and 1990. Raja miraletus is a small skate found principally in shallow (<50 m) water that feeds mainly on small crustaceans, such as mysids and macrurans. The large Raja alba occurs over most of the continental shelf, is a piscivore throughout its life and preys heavily on flatfish, especially Cynoglossus zanzibarensis. R. cf. clavata is ubiquitous on the shelf but most abundant between 50 and 150 m deep. Feeding predominantly on crustaceans, this skate switches from carids, penaeids and mysids when small to brachyurans and small benthic fish when larger. R. pullopunctata is found over a similar depth range but attains a much larger size. It eats small mysids and macrurans when small, but brachyurans and fish become more important in the diet with increasing size of the predator. R. wallacei is most commonly taken at depths of 80–>200 m, feeds initially on small crustaceans, but switches to fish, including eels, as it grows. The small Cruriraja parcomaculata is found at the edge of the continental shelf and over the upper slope; it preys on small crustaceans, including mysids, isopods and macrurans. The distribution pattern of the skates and their prey suggest overlap in prey taken, the overlap being greatest in those species which feed on crustaceans. The large biomass of skates in the area suggests that they are an important component of the demersal faunal assemblage of the continental shelf there, and also that they may have a significant impact on the benthic fauna.