Use of reflex indicators for measuring vitality and mortality of the snow crab (Chionoecetes opilio) in captivity

The snow crab (Chionoecetes opilio) is one of the most important commercial crabs in the world; it is heavily exploited in Atlantic Canada, Alaska, the Sea of Japan and the Barents Sea. Catches in the Barents Sea north of Norway have increased dramatically in the last decade. Most of the world's catch is processed, frozen and exported overseas. However, recently there has been considerable interest in exporting live snow crab, particularly in Norway. The stress of capture and live transport can result in significant mortalities. In order to establish a live export industry for snow crab, the welfare of the animal must be monitored throughout all the steps of the live transport process. In this study the reactions of snow crabs exposed to increasing periods of air exposure were measured in terms of reflex indicators, incidence of mortality, blood lactate levels and blood protein and haemocyanin. Although this is not a specific live holding or live transport process the aim was to test the suitability of reflex indicators to reflect vitality (stress) and not just to predict mortality. This would be compared with traditional blood biochemistry techniques for measuring crustacean stress. The study demonstrated that the reflex index score (RIS) is suitable to assess the vitality of snow crab. Longer air exposure periods render higher mortality rates and less vital individuals. The authors believe using vitality reflex indicators would be a suitable way of measuring crab welfare during the live holding and transport process.     

Efficiency of the bottom trawl used for the Mediterranean international trawl survey (MEDITS)

The aim of the work presented in this paper was to assess the relative efficiency of the GOC 73 sampling trawl used for the Mediterranean international trawl survey programme (MEDITS) compared with that of a typical Italian commercial trawl. The latter was chosen because it is commonly used by fishermen in the central Adriatic, where the experiment was conducted, and therefore appeared as the best possible sampler of the commercial species present in those areas. Moreover, this trawl is similar to the various trawls used for the Italian national survey programme (GRUND). Four fishing trips were conducted between 1996 and 1997 in different areas and seasons to sample different species. Each trip was conducted in the same fishing area. A codend cover mounted on the commercial trawl ensured that the codends of the two nets had the same mesh opening. The two trawls were alternated daily. Net geometry (horizontal and vertical net opening) was measured during all tows. Catch data were converted into abundance per swept area before comparing the trawls. Efficiency comparisons were performed on ten fish species, one crustacean and four molluscs belonging to the MEDITS list of main reference species. The MEDITS trawl was significantly less efficient in terms of both weight and numbers of individuals fished for hake (Merluccius merluccius), common sole (Solea vulgaris) and Norway lobster (Nephrops norvegicus). A highly significant difference in favour of the commercial trawl was found in the weight, but not the numbers, of common pandora (Pagellus erythrinus). Efficiency differences were negligible for red mullet (Mullus barbatus), while the MEDITS trawl was significantly more efficient for the numbers of Atlantic horse mackerel (Trachurus trachurus). For all the other main reference species differences were not significant. The commercial trawl was more efficient for large individuals of some species. The relative efficiency of the MEDITS trawl was especially low for small-size classes of N. norvegicus. The results confirm the lower efficiency of the MEDITS compared with the commercial Italian trawl for benthic species, and its greater efficiency for some others released from the bottom as well as for the pelagic ones. These data allow the results of the MEDITS surveys to be compared with those of the GRUND programme and with commercial-fleet catches in areas where the commercial trawls used are similar to the one studied here.     

Escapement from the main body of the bottom trawl used for the Mediterranean international trawl survey (MEDITS)

Escapement through the body or under the footrope of the sampling trawl used for the Mediterranean international trawl survey programme (MEDITS) was assessed i) by means of visual observations performed with a towed operating vehicle equipped with a high-sensitivity video camera, and ii) by attaching small bags to the outside of the trawl body and under the footrope. Due to the small size of most of the individuals present in the study area and to the towing speed, fish behaviour in front of the trawl could not be frequently observed. In contrast, their behaviour was easily observed inside the net, especially upstream and inside the codend. Some species, such as horse mackerel (Trachurus sp.), showed greater swimming endurance compared with others such as annular seabream (Diplodus annularis). In three fishing trips conducted in different seasons in 1996 and 1997 to obtain data on several species in different areas of the Adriatic, six small net bags were mounted outside the body of the MEDITS trawl to quantify escapement through the trawl belly and under the footrope. Significant escapement of many species occurred in the near-bottom part of the side panels. Norway lobster (Nephrops norvegicus) had the highest rate (64 %), mainly represented by small-size individuals. The escapement of greater forkbeard (Phycis blennoides) was also high (53 %). For hake (Merluccius merluccius), common pandora (Pagellus erythrinus) and poor cod (Trisopterus minutus capelanus), rates ranged from 10 to 16 %. The escapement of red mullet (Mullus barbatus) was very low despite their great abundance. Blue whiting (Micromesistius poutassou) escaped mainly through the mid-height part of the side panel. This great variability of escapement values could affect the proportion rates of the species sampled during a standard survey. Different escape behaviours among size classes were observed for M. poutassou, T. minutus capelanus and P. erythrinus, with smaller individuals tending to escape towards the bottom and larger ones towards the higher parts of the trawl body. In the species where the escape rate was size-dependent, therefore, the size-frequency distributions obtained from the codend catch may not reflect actual size-frequency distributions.     

Regime shifts and recruitment dynamics of snow crab,Chionoecetes opilio,in the eastern Bering Sea

Shifts in climate regime are prominent features of the physical environment of the eastern Bering Sea and in recent years have been documented in approximately 1977 and 1989. Average snow crab (Chionoecetes opilio) recruitment decreased sharply after the 1989 fertilization year. Models in which control of snow crab recruitment shifts between drivers dependent on climate ‘regime’ are presented. These models are evaluated using cross‐validation and retrospective analysis, both of which indicate that the relationships are relatively robust to varying levels of information. Larval survival as influenced by food availability in the pelagic phase and advection to suitable nursery grounds are the hypothesized mechanisms driving recruitment dynamics.     

Influence of temperature on embryo developmental cycles and mortality of female Chionoecetes opilio (snow crab) on the Scotian Shelf,Canada

Chionoecetes opilio (snow crab) in Atlantic Canada is a valuable fishery. A key factor in the conservation and sustainability of C. opilio is the length of its reproductive cycle, which in different regions has been observed to be ca. 1 or 2 years and temperature dependent. Ten years of embryo colour (a proxy for embryo development) data from the Scotia Shelf (SS) is analyzed using a binomial Generalized Linear Model. The influences of temperature and time variations upon the transition of early developmental stages are described. Over 80% of the females were estimated to follow a ～1 year reproductive cycle, corresponding to the relative proportion of springtime SS bottom temperatures greater than 1 °C. As an upper bound, total annual larval production is expected to have ranged from 280 billion and 32 trillion since 1997 with an associated female mortality from larval stage to maturity of 63–81% per annum (Z = 1–1.65). Climate variability can therefore have a large influence upon the total potential reproductive output. Global Circulation Models predict that there will be more positive North Atlantic Oscillation years for the North Atlantic, assuming this to be the case we speculate that the associated warmer bottom temperatures along the central and west SS would lead to even greater percentages of the C. opilio females entering a 1 year reproductive cycle, whereas cooling along the eastern shelf (where the majority of the population resides) would shrink the warm water habitat available and potentially force more females into a two year cycle. If the magnitude of warming extends beyond C. opilio's preferred range, the entire population may shift north-east.     

Bridle efficiency of a survey trawl for flatfish: measuring the length of the bridles in contact with the bottom

A bottom trawl catch of flatfish is composed of fish that were initially in the path of the net and fish that were initially in the path of the bridles and were subsequently herded into the net path. Bridle efficiency (i.e. the proportion of fish in the bridle path herded into the net path) can be estimated by fitting a model to catch and trawl measurement data collected in a field experiment in which the bridle path is varied in width by varying bridle length. Since flatfish are herded by the direct contact or close approach of the bridles with the bottom, part of the necessary field work is estimating the length of the bridles in contact with the bottom. Previously, bottom contact of the bridles has been determined using video cameras, but this is not possible when the bridles are entirely obscured by the mud clouds generated by the trawl doors. As an alternative approach, a bridle-mounted bottom contact sensor (BCS) was developed to allow measurement of the off-bottom distance of a bridle and the percentage of time it is in contact with the bottom. For the survey trawl studied, approximately 43% of the lower bridle was sufficiently close to the bottom to presumably elicit a herding response; however, the middle of the three bridles sagged to such an extent that it touched the bottom ahead of the lower bridle and extended the length to 51%.     

Adjusting technical efficiency to reflect discarding: The case of the U.S. Georges Bank multi-species otter trawl fishery

Discarding undesirable catch is recognized as a major problem confronting fishery managers. It is widely perceived by managers, however, that reductions in discards can only be accomplished via reductions in good or desirable outputs and technical efficiency. Yet there appear to be few studies which actually examine the relationship between discard reduction and technical efficiency. In this paper, we present an alternative concept of technical efficiency, which explicitly recognizes that measures of technical efficiency should be adjusted for discard levels. This is because traditional measures of efficiency do not consider the resources used in order to discard. We also offer a framework based on data envelopment analysis for assessing efficiency in the presence of undesirable outputs. We examine the relationship between vessel efficiency and regulatory discards in the U.S. Georges Bank multi-species otter trawl fishery on a tow-level basis. We then examine differences between efficient and inefficient tows, and extend our results to the trip level. Further examination of trip-level results then yield insights into the potential impact of trip-limit regulations. Results show that in order to reduce discards, vessels are limited in the amount they can increase their total output, and that trip-limit regulations may have unintended consequences.     

Strategies for improving fuel efficiency in the Portuguese trawl fishery

The recent rise in oil prices has brought renewed attention to energy savings in the fishing industry, and particularly in trawling. Coastal trawlers spend most of their time on fishing grounds near the coast. In such cases, the most successful energy-saving modifications ought to result from changes in the fishing gear and towing conditions. The purpose of this study was to identify the energy-economy potential for Portuguese fish trawlers after altering a vessel's operating conditions and improving its trawl gear performance. Two trawlers, named Tricana de Aveiro and João Macedo were selected as subjects in this project. Both vessels work with gear of similar design and size. Experimental sea trials were carried out to elucidate the actual vessel and gear performance. A model trawl was then built and tested in a flume tank, which provided the basis for improving the gear design. Full-scale trials were then carried out with both vessels using the modified trawls in order to assess changes in gear performance. The new trawls maintained their previous ability to catch species of different ecological groups and consumed less fuel at the same commercial trawling speed. An economic study showed potential increases in the net cash flow (NCF) of up to 27% over the range of operational navigation and trawling speeds. Having demonstrated the performance of the new trawls, the skippers of both vessels subsequently adopted the new design for commercial fishing.     

Examining the importance of consistency in multi-vessel trawl survey design based on the U.S. west coast groundfish bottom trawl survey

Generalized linear mixed-effects models can be used to combine bottom trawl data from multiple vessels, each with a different fishing power, into a single time series of relative abundance. However, how important might it be to have a consistent set of vessels and vessel characteristics from year to year given we can model differences in fishing power among vessels? We demonstrate how changes in the suite of fishing vessels performing the survey can affect the results of the data analysis using sablefish catches in the U.S. west coast groundfish bottom trawl survey from 1998 to 2000. The results do not indicate that one must have a consistent set of vessels over time to provide useful data, but rather that there is benefit to consistency even when the survey data are analyzed using advanced statistical models. Further research should be undertaken to quantify these benefits specifically to aid in contracting and bidding of survey vessels.     

拖网的网袖结构对其性能的影响

文章以国内较典型的单船底拖网 (72 ◇×18 m) 为研究对象,基于L₉(3⁴) 正交试验表,设计了网具总长度与网口周长之比 (L/C)、浮沉子纲长度之比 (S₁/S₂)、网身长度与网具总长度之比 (L_b/L)“三因素三水平”的正交试验,并利用平均值和极差分析方法检测3种主要结构参数对网具阻力、网口垂直扩张和能耗系数的影响趋势,旨在对大网目底拖网结构进行优化设计。结果表明,不同水平扩张下,3种因素对网具阻力的影响由主到次均为L/C> S₁/S₂>L_b/L,对网口垂直扩张的影响由主到次均为S₁/S₂>L/C>L_b/L,对能耗系数的影响由主到次均为L/C>S₁/S₂>L_b/L。拖网L/C相对于小网目拖网应偏小,且比值越小阻力越小,但L/C=0.2是网口垂直扩张和能耗系数作为指标时的最佳水平;S₁/S₂相对于小网目应更大,且比值越大网口垂直扩张越好;S₁/S₂在试验范围 (0.83~0.99) 内对阻力影响不显著,而S₁/S₂=0.99是能耗系数作为指标时的最佳水平;L_b/L随着网目尺寸增大而减小,但减小幅度随之逐渐降低,L_b/L=0.65应更适应于中低速拖网,L_b/L=0.75更适应于高速快拖。     

Combined use of trawl fishery and research vessel survey data in a multivariate autoregressive state-space (MARSS) model to improve the accuracy of abundance index estimates

Fishery-dependent catch per unit effort (CPUE) data have been used as an abundance index (AI) in fish stock assessments. However, fishery-dependent CPUE data are influenced not only by changes in fish abundance but also by other factors, such as the choice or restrictions of fishing grounds to operate. Accordingly, bias may arise in AIs due to a lack of data from unfished or rarely fished areas. To improve the accuracy of AI estimates, spatially arranged CPUE datasets from both trawl fisheries and research vessel surveys in the East China Sea were concurrently analyzed in the present study using a multivariate autoregressive state-space (MARSS) model. Survey datasets complemented information on stock status in the fishing areas where fishery-dependent datasets were limited. As a result, the combined use of datasets from both sources effectively improved the accuracy of estimates of AIs and the spatial distribution of the population density of each fish species.     

优质蟹种生态高效培育技术

<正>江苏省金坛市地处太湖流域,境内湖荡众多,水草螺蚬等资源丰富。河蟹养殖业应运而生,经年累月发展至今,渔民已有丰富的养殖经验和较高的技术水平,普遍认识到外地购买的蟹种存在长途运输易损伤、环境差     

成蟹养殖池塘套养鳜鱼 Siniperca chuatsi(Basilewky)技术

中华绒螯蟹成蟹养殖池套养鳜鱼技术是当前生产上探索的新课题。本文作者详细介绍操作技术，具体包括：池塘条件、鳜鱼种培育、苗种认养、饲养管理等，本文对生产单位有一定的参考价值。     

Size at maturity for grooved Tanner crab (Chionoecetes tanneri) along the U.S. west coast (Washington to California)

We conducted a multiyear study to examine interannual variability in the mean size (carapace width, mm), maturity size (mm) and depth (m) for grooved Tanner crab (Chionoecetes tanneri (Rathbun, 1893)) along the U.S. west coast. An additional goal was to provide updated estimates of carapace width (mm) at 50% maturity (W₅₀) for male and female grooved Tanner crab and assess changes over time. Randomly selected samples came from trawl surveys undertaken annually by the Northwest Fisheries Science Center at depths of 55 to 1280 m. We used allometric relationships between carapace width (CW) and either abdominal width (AW) (females) or chela length (CL) (males) to determine functional maturity by sex. We evaluated maturity by fitting logistic regression models to proportion mature grooved Tanner crab. W₅₀ varied significantly between males (125.2 mm) and females (89.1 mm) but interannual differences were slight. The annual mean CW were greater for mature males (139.9–143.4 mm) relative to females (98.8–100.4 mm). The average sizes of immature grooved Tanner crab varied between sexes with males (75.7–84.6 mm) larger than females (66.7–71.9 mm). Size frequency distributions indicated little overlap in the size of mature male and female grooved Tanner crab but considerable overlap between immature grooved Tanner crab. The best model expressing complexity in growth incorporated width, sex and maturity stage. Depth ranged from 195–1254 m with the average depth of a mature grooved Tanner crab (females, 737 m; males, 767 m) significantly shallower than an immature (females, 949 m; males, 918 m) grooved Tanner crab.     

东海区底拖网渔业资源变动分析

以2000~2005年底拖网渔业资源的常规监测资料为依据,对东海区底拖网渔获物种类组成、主要经济鱼种单位捕捞努力量渔获量(CPUE)以及生物学特征进行了分析。结果表明,东海区底拖网渔业资源利用结构正在向低值和低营养层次鱼种转化,主要经济鱼种的CPUE不断下降,生物学特征未见明显好转,而渔获物中幼鱼比例不断上升,渔业资源总体状况仍然存在继续衰退趋势。建议降低目前的海洋捕捞努力量,延长伏季休渔时间,加强渔业资源养护和管理力度等。     

东海区拖网网囊网目选择性研究

通过东海区拖网网囊网目对带鱼和小黄鱼的选择性试验,对拖网最适网囊网目尺寸进行了分析研究。结果表明：1．网囊网目45mm,小黄鱼和带鱼的逃逸率均较低,渔获中兼捕大量当年生经济幼鱼;2．网囊网目54mm,小黄鱼的50％选择体长尚小于其优势体长组范围,带鱼的50％,选择体长已部分进入其优势体长组范围;3．网囊网目65mm,选择体长范围与选择鱼种的优势体长组范围基本一致。综合分析认为：目前东海区最理想的拖网网囊网目不小于60mm。     

Age,growth and demographic characteristics of <Emphasis Type="Italic">Sillago flindersi</Emphasis> exploited in a multi-species trawl fishery

This study investigated variability in the growth, length, and age compositions and the rates of mortality of Flinders’ sillago Sillago flindersi exploited in a demersal trawl fishery in eastern Australia. Sampling was done over 2 years across three depth strata at two locations approximately 400 km apart. Ageing of sectioned sagittal otoliths indicated that the observed maximum age of females was 6 years and that of males 5 years, that growth was variable and that the von Bertalanffy growth parameters significantly differed according to gender and location. Females attained a greater L _∞ than males, but males displayed greater k values. The L _∞ values of both sexes and the mean length-at-age for fish aged 3–5 years were greater at the location of highest latitude. Length and age compositions differed according to depth, with smaller (<15 cm FL) and younger (<2 years) fish generally more predominant in the shallow (<30 m) strata than in the deeper (>31 m) strata. S. flindersi appear to use the shallow strata as a juvenile habitat, moving to deeper waters as they grow. This depth stratification between cohorts may reduce intraspecific competition and could potentially be used as a spatial management tool to reduce any fishing-associated impacts on juveniles. Fish between 1 and 3 years old dominated the age compositions of populations combined across all depths, with estimated total mortality ranging between 2.24 and 2.40. Fishing mortality ranged between 1.54 and 1.70 and was more than twice the derived natural mortality. Exploitation rates were approximately 0.70, indicating that the species was heavily fished.     

A bio-economic indicators suite for the appraisal of the demersal trawl fishery in the Southern Adriatic Sea (Central Mediterranean)

The state of demersal fishery in the Southern Adriatic Sea (GFCM-GSA 18, Central Mediterranean), years 1996–2003, from a biological, social and economic point of view was analysed using 47 indicators: 22 biological indicators obtained from fishery-independent data through yearly experimental bottom trawl surveys (“Medits” Programme), and 25 socio-economic indicators estimated from fishery-dependent data, available from the monitoring system of the Italian Institute for Economic Research on Fisheries and Aquaculture (IREPA). Biological indicators were applied for “single-species” (Eledone cirrhosa, E. moschata, Illex coindetti, Merluccius merluccius, Mullus barbatus, Nephrops norvegicus, Parapenaeus longirostris, Raja clavata, Zeus faber) and for “multi-species” analysis. Economic indicators describing economic performance, productivity, costs and prices, and the overall economic sustainability of fishery were estimated. Social indicators and a general indicator summarising social sustainability were also considered. Indicators’ values were displayed using the Traffic Light system. Both fishery-independent and fishery-dependent indicators highlighted a progressive decline of the trawl fishery system in the GSA 18. This decline was mainly related to the ongoing depletion of the traditional fishery target species (mostly long-living, late-maturing species) partially replaced by the increase of traditional accessory species (generally short-living species), as well as to the reduction of productivity and increasing costs. The whole procedure was proposed as a contribution to the identification and applicability of bio-economic indicators for fishery management purposes.     

中华绒螯蟹、日本绒螯蟹及其杂交F_1代群体的遗传多样性AFLP分析

通过4对引物组合对辽河水系中华绒螯蟹群体,俄罗斯的日本绒螯蟹群体及其杂交F1代(辽河蟹♀×俄罗斯蟹♂)的遗传多样性进行了AFLP分析。结果表明,4对引物共扩增出233条带(100bp~1000 bp),其中辽河群体多态条带184条,多态位点比例78.97%;俄罗斯群体177条多态带,多态位点比例75.97%;杂交群体182条多态带,多态位点比例78.11%。3个群体的群体内遗传相似度分别为0.7074±0.0469,0.7171±0.0475,0.7406±0.0449,香农多样性指数分别为0.185±0.128,0.194±0.119,0.176±0.138。变异来源有79.13%来自群体内,20.87%来自群体间。