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1.
The flatfishes of the Newfoundland-Labrador region are a very significant component of Canadian fishery resources and comprise four major species. They are: witch flounder (Glyptocephalus cynoglossus), American plaice (Hippoglossoides platessoides), Greenland halibut (Reinhardtius hippoglossoides), and yellowtail flounder (Limanda ferruginea). The fisheries for these species are made up of 11 separate management units, all under quota control with a total allowable catch in 1989 equalling 184 500 t for all stocks combined.Witch flounder is a relatively deep-water species, predominant at depths of 184 to 366 m and prefers temperatures in the range of 2.0°C to 6.0°C. It reaches its northern limits at Hamilton Bank, near southern Labrador, but is otherwise found throughout the southern range of the study area. American plaice is a more shallow-water species, preferring colder water. It is most abundant in depths of 90 to 250 m and bottom temperatures of −0.5°C to 2.5°C. While it is found throughout the whole study area, it is found in higher concentration on the tops of hard banks—particularly Hamilton Bank, the Grand Bank and St. Pierre Bank. The Greenland halibut is the deepest of the flatfishes, preferring depths of 500 to 1000 m and greater at temperatures of 0.0°C to 4.0°C. It is most abundant in areas north of the Grand Bank along the continental slope and deep channels running between the fishing banks. Yellowtail flounder, on the other hand, is the shallowest of the four species, preferring depths of 37 to 82 m where temperatures are in the range of 3.0°C to 5.0°C. The main area of significant abundance is on the southeastern Grand Bank known as the Southeast Shoal, although it is caught in a very small area of St. Pierre Bank.All species exhibit reductions in the age range of the respective populations since the beginning of commercial exploitation. As well, there have been increases in the growth rates and reductions in the age at maturity, with a few exceptions. These changes have generally been coincident with reduced population sizes although it was not possible to correlate analytically.  相似文献   

2.
Immigration and settlement pattern of 0-group summer flounder (Paralichthys dentatus) and southern flounder (P. lethostigma) in an estuarine nursery are described. Flounders entering the estuary were transforming larvae. Despite their sympatric occurrence during larval immigration, the two species were found concentrated in different habitats. Sampling along transects within the estuary indicated that newly settled southern flounder were concentrated on tidal flats towards the head of the estuary while greatest numbers of summer flounder were captured on tidal flats in the middle reach of the system. Logistic regression analysis of presence/absence data indicated that salinity affected the distribution of southern flounder while substrate type was an important factor affecting the distribution of summer flounder. Numbers of both species on tidal flats declined in the spring, southern flounder appeared to move upstream to oligohaline riverine habitat and summer flounder appeared to move to high salinity salt marsh habitat. The segregated distribution apparent in juveniles is largely established during the immigration period. Differences in settling behaviour and subsequent movement and/or differential mortality occurring during settlement, appear important in determining the observed distribution of juvenile summer and southern flounder.  相似文献   

3.
This paper reviews the ecology of flatfish species associated with estuaries in southern Africa. Information from estuarine and coastal studies carried out in this region over the past 25 years indicates that only 4 of the 56 flatfish species occurring in the region utilize estuaries during part of their life histories. The suitability of estuaries and their role as nursery grounds for juvenile flatfish is assessed in terms of the proportion of the life cycle that each species spends within estuarine systems. Biological data on Pseudorhombus arsius, Bothus pantherinus, Heteromycteris capensis and Solea bleekeri extracted from broad based estuarine studies in the warm temperate and subtropical regions of southern Africa are presented in support of the thesis that in the absence of calm, shallow, turbid, marine shelf areas, juveniles of these species utilize estuaries as nursery grounds.  相似文献   

4.
A comprehensive sampling exercise was carried out at Cordemais Power Station during 1988 in order to evaluate the number of 0-group flounder, Platichthys flesus, removed from the Loire Estuary by the water intakes. Larvae drawn through the cooling system and juveniles impinged on the drumscreens were both taken into account. Statistical confidence limits of the estimates (which are useful for comparisons with the effect of other human activities) were estimated using non-linear regression and Monte-Carlo techniques. The method was developed for one of the two similar units working during the April–June period of high flounder abundance in the cooling water. For this unit 16.5 million fish were drawn through the cooling system and 1.13 million were trapped on the drumscreen. The effect of the Power Station is discussed in connection with small-meshed fisheries and assessments of the estuarine juvenile stock.  相似文献   

5.
Migration of larval plaice into a nursery area in the western Wadden Sea was monitored during three immigration seasons. Daily otolith increments were used to estimate age and hatch dates of the larvae, and the hatch dates were compared to egg-production curves. Different cohorts of larvae invaded the area, originating from different spawning grounds. During a cold year, most larvae probably came from the Western Channel, but during the two warm years most larvae originated from more northern spawning grounds. Settlement on a tidal flat showed a delayed response to immigration in the first part of the season, but a direct response later in the season. Length-frequency distributions of settled juveniles were compared to expected frequencies based on a simple growth model. It is argued that early in the season growth-related mortality may have been too high to ensure successful settlement, and that timing could be of significant importance for larval immigration to be successful.  相似文献   

6.
The population dynamics of juveniles of some flatfish species were studied in the Duplin River, a tidal creek in a subtropical salt-marsh area in Georgia, U.S.A. from April until September 1990. Seven species were found. Paralichthys dentatus, Paralichthys lethostigma, Paralichthys oblongus and Trinectus maculatus were relatively rare. Etropus crossotus, Citharichthys spilopterus and Symphurus plagiusa were abundant and settled during the period studied. E. crossotus was the most abundant species with a mean abundance of 18 ind·10−2 m−2 (max. 287). Demersal settlement of E. crossotus took place in shallow areas and over sandy bottoms from mid-May to August. Prolonged settlement hampered the calculation of growth rate and instantaneous mortality rate. However, laboratory growth experiments indicated a mean growth of about 0.50 mm·d−1 at 24–28°C. Juveniles of C. spilopterus were already present in the Duplin River in March. Settling continued until the end of April with a mean abundance of 3.5 ind·10−2 m−2 (max. 183). With increasing size the juveniles of this species tended to migrate to deeper waters and to the mouth of the river, possibly as a reaction to increasing water temperatures. Maximum growth rate was 1.4 mm·d−1 at about 26°C. The mean instantaneous mortality rate (z) was estimated at 0.03·d−1. Settling of S. plagiusa occurred from mid-May onwards. The mean abundance was 10.3 ind·10−2 m−2 (max. 98.3). Newly settled juveniles were most abundant on muddy sediments in the shallow river areas. The maximum growth rate was 1.3 mm·d−1 at about 28°C. The mean instantaneous mortality rate (Z) decreased from 0.04·d−1 in April to 0.01·d−1 in August. At all sites the abundance of juveniles of this species decreased with increasing water depth. Predation experiments indicated that blue crabs (Callinectes similis and C. sapidus) and sea robins (Prionotus sp.) are potential predators on juvenile flatfish. The high abundances of juvenile flatfish indicate that the tidal creeks are an important nursery area. The correspondence between growth rates estimated from field data and those observed in the laboratory suggests that growth in the nursery is mainly related to water temperature and not food limited.  相似文献   

7.
From January to July 1989 eight egg surveys were carried out in the southeastern North Sea. The first three surveys were designed to estimate the egg production of plaice (Pleuronectes platessa) and cod (Gadus morhua). The other five surveys were aimed at the eggs of sole (Solea solea) and horse mackerel (Trachurus trachurus) Of a selection of the samples collected in 1989 all fish eggs were identified to species. This paper presents data on the distribution, timing and intensity of spawning of the flatfish species plaice, flounder (Platichthys flesus), dab (Limanda limanda), long rough dab (Hippoglossoides platessoides), sole, solenette (Buglossidium luteum), turbot (Scophthalmus maximus) and scaldfish (Arnoglossus laterna).Egg mortality was studied in plaice and sole and compared to previous estimates. Plaice egg mortality in 1988 and 1989 was higher than in 1987, coinciding with higher ambient temperatures. Egg production in sole was recorded earlier in the year in 1988 to 1990 than in 1984, and at lower ambient temperatures. Sole egg mortality rates were shown to be lower in 1988 to 1990 than in 1984.  相似文献   

8.
From May 1988 to June 1989 selected areas of the German Wadden Sea, the Ems, Weser, Elbe and Eider estuaries as well as in Elbe tributaries were sampled for 0- and 1-group flounder (Platichthys flesus L.). Estuarine and Wadden Sea sampling was conducted on board commercial shrimp vessels equipped with beam trawls. The Elbe river system was sampled on board a research boat equipped with a similar 3-m beam trawl. Density indices were calculated for the various areas. To estimate the importance of rivers as nursery areas for flounder, river surface area was compared to the area of tidal flats in the Wadden Sea.In all surveys, there was no relationship between fish densities and tow directions with respect to tide. In the Elbe river system flounder densities were not correlated to substrate types but increased significantly with decreasing salinity. Abundances were always lowestt in polyhaline habitats and increased up to 10-fold in mesohaline estuarine areas. In the limnetic tidal sections of the Elbe river and its tributaries densities increased again by factors of 3 to 10. The succession of 1-group modal lengths from limnetic to polyhaline habitats demonstrated that smaller fish preferred less saline waters. 0-group specimens lagging behind in growth did not leave the limnetic river section in winter. The onset of the spawning migration in November was determined by monitoring the length-frequency distributions throughout the year.The possible sources of bias are discussed and gear efficiency is estimated from literature sources. The contribution of rivers to the 0- and 1-group flounder population on the tidal flats of the Wadden Sea is estimated at about 35.1%.  相似文献   

9.
Stock production modelling was used to estimate population parameters such as the carrying capacity (B∞), as well as management parameters such as maximum sustainable yield (MSY), the instantaneous rate of fishing mortality at MSY (FMSY) and the sustainable biomass at MSY (BMSY). The input data were not catch and effort data, which usually require adjustments for changes in catchability, but biomass and catch (or fishing mortality), which are frequently available from cohort analysis or direct surveys. The model does not require the assumption of stock equilibrium for estimating parameters.The model was applied to data from the Alaska plaice, Pleuronectes quadrituberculatus, and yellowfin sole, Limanda aspera stocks in the eastern Bering Sea, and the Pacific halibut, Hippoglossus stenolepis, stock in the Gulf of Alaska and Bering Sea. All three stocks are characterized by separation of nursery area and exploitable population. There are at least five age groups present in nursery areas and ten or more in the exploitable stock so that recruitment levels and exploitable stock sizes are well-buffered.Predictions from the surplus production model provided reasonable fits to the biomass time series for all three stocks examined, given the sources of uncertainty in the biomass estimates available. It appears that the stock dynamics for the three species can be described by a relatively simple density-dependent model assuming instantaneous responses in stock biomass via recruitment and growth.  相似文献   

10.
A ten year study of the population dynamics of the flatfish dab Limanda limanda, sole Solea solea and flounder Platichthys flesus was undertaken within Bridgwater bay in the Bristol Channel, England. Fish abundance was estimated from the rate of capture on power station intake filter screens at Hinkley Point Nuclear Power Station. The Bay was used as an 0-group nursery by all three species while flounder were alone in regularly using the area as adults. Using the coefficient of variation (CV) in annual catch as a measure of population stability these three flatfish were found to have some of the most stable populations within a fish community of 21 common species. When these species were classified according to their use of space as benthic, proximo-benthic or pelagic it was found that the benthic fish had the lowest CV values. It is argued that this stability is linked to their use of space. A notable feature was the differing seasonal occupancy of the Bay by the benthic fish which would act to reduce potential inter-specific competition. This suggests that spatial competition could only be intra-specific or against invertebrates. A search was made for biotic or physical factors correlated with year class abundance in the flatfish. The only significant correlation found was for sole, the abundance of which increased with increasing water temperature.  相似文献   

11.
The changes in growth of plaice and sole between 1957 and 1988, as estimated from samples of the commercial fishery and pre-recruit surveys, were analysed in order to study possible density dependent effects. Indices of potentially competitive biomasses of plaice and sole, based on Lloyd's index of mean crowding, were estimated from the average spatial distribution of various age groups during the summer growing period and from the population age structure as estimated by virtual population analysis.Growth of all age groups of sole increased in the 1960s and was stable in the 1970s and 1980s. In plaice only age groups 1 to 3 showed a similar increase in the 1960s, whereas the growth of 1-year-old plaice tended to decrease in the 1980s. Growth did not show a negative correlation with mean crowding, except in age group 1 of plaice and in age group 3+ of sole. It is concluded that these negative correlations do not provide unequivocal evidence for density dependent growth in plaice and sole, since they could equally well be caused by parallel but unrelated trends in time of one or more other factors. The simultaneous increase in growth in the 1960s of age groups of sole and plaice in the southern North Sea, and the absence of such an increase in age groups in the central North Sea, suggests that food availability must have increased in the Southern North Sea. This inference is supported by several macrobenthos studies. Whether the reduced growth of 1-group plaice in the 1980s, when recruitment was well above the average level, is caused by density dependent growth or to a reduced food availability remains an open question.  相似文献   

12.
MS-222对大鳞鲃幼鱼麻醉效果的初步研究   总被引：1，自引：0，他引：1  
旨在研究MS-222对大鳞鲃幼鱼的麻醉效果。在26±0.5℃的水温条件下,观测了大鳞鲃幼鱼在不同浓度MS-222处理下的麻醉效果,包括麻醉和复苏过程中的行为变化、麻醉过程中呼吸频率的变化以及不同空气暴露时间对麻醉幼鱼复苏时间、复苏率的影响。试验结果表明,大鳞鲃幼鱼的麻醉过程可分为6期,复苏过程分为4期。MS-222对大鳞鲃幼鱼的有效麻醉浓度范围为120~160mg/L。随着麻醉时间及浓度的加大,大鳞鲃幼鱼呼吸频率总体呈下降的趋势。进入5期麻醉的幼鱼,当空气暴露时间在4min以内时,复苏时间随空气暴露时间的增加而减少,当暴露时间在6min以上时,复苏时间随暴露时间的增加而增加,暴露10min以内均能复苏。实验证明,MS-222对大鳞鲃幼鱼有较好的麻醉效果,本实验可为大鳞鲃幼鱼的活体运输以及实验操作等提供理论支持。  相似文献   

13.
使用石蜡切片技术对1-35日龄星斑川鲽的仔稚鱼消化系统进行组织学观察和研究。结果表明,星斑川鲽消化系统的发育主要分成三个阶段：从初孵到3日龄是卵黄阶段,其消化道为一细长的管道;从3日龄到5日龄是后卵黄阶段(混合营养阶段),卵黄被逐渐吸收,是卵黄阶段转向外源性营养阶段的过渡,消化道明显分化成口咽腔、食道、胃、前中肠、后肠和肛门,仔鱼消化系统具备了摄食和消化外源性食物的能力。此后,随着鱼体的生长,粘膜层的褶皱增加,消化道上皮细胞进一步分化,消化系统从功能和结构上逐步完善。16日龄,胃腺出现,标志着稚鱼期的开始,表明星斑川鲽是一种发育较快的鱼类。  相似文献   

14.
Several aspects of the biology of Solea bleekeri in Lake St Lucia were investigated, these included occurrence, distribution, reproduction and recruitment, food and feeding, size frequency distribution and the role of estuaries in the species' life cycle. Solea bleekeri was found to occur throughout the system in muddy turbid areas and was largely absent from the eastern shores of the lake where clear water sandy substrata occur. The preferred diet of the species was bivalve siphon tips of the species Solon cylindraceus, when these were in abundant supply. However, when numbers of large (length > 20 mm) specimens were not available then S. bleekeri fed on whatever prey was available in or near the substratum. Analysis of stomach contents under the latter conditions showed that food consumption reflected the composition of the benthos. Large numbers of S. bleekeri spend their entire post-larval and juvenile phases as well as the greater part of their adult life within estuaries. Evidence is presented to support the idea that S. bleekeri breeds in certain areas of the lake and that spawning takes place between September and November. The current data suggest that there may be two populations in St Lucia: one migrates from the system to spawn at sea during winter along with the other marine fish species which utilize estuaries as nursery areas, while the other population breeds within the system. Alternatively there may simply be a single population which normally breeds at sea, but which may breed within the system when conditions are suitable. Recruitment of S. bleekeri into the St Lucia estuarine system takes place from the muddy offshore marine banks and possibly from within the system as well. Solea bleekeri appears not to be totally dependent on estuaries for the completion of its life cycle. The advantages of utilizing these systems for their development relate to the shallow, calm, turbid food-rich areas which estuaries offer. The fact that breeding takes place within St Lucia means that adults and juveniles are present in varying numbers throughout the year.  相似文献   

15.
During April/May 1985–1987 some of Ursin's (Ursin, 1960) stations on the Dogger Bank from April/May 1951–1952 were revisited. This paper concentrates on results from the ‘Tail End’, the northeastern part of the Dogger Bank. The polychaete species Ophelia borealis and Goniada maculata, which were dominant species in 1951–1952, showed similar distributions in 1985–1987 on the whole of the Dogger Bank. Changes in the macrofauna distribution are obvious in the increase of opportunistic small polychaete species like Spiophanes bombyx, Scoloplos armiger and Magelona spp. In 1985–1987 these species occurred in high individual numbers per m2 all over the Dogger Bank in contrast to 1951–1952, when they were found only in few individuals. Extensive patches of the bivalve species Spisula subtruncata discovered at the northeastern border of the Dogger Bank in the fifties were not found. Only small, fast-growing species like Abra prismatica, Tellina fabula and Montacuta bidentata occurred in high individual numbers per m2. In 1987 the total biomass shows a reduction of about 30% in the area compared with 1950–1954Some hypotheses are given to explain the changes in macrofauna distribution on the Dogger Bank between 1950–1954 and 1985–1987, taking into account the increasing eutrophication and pollution.  相似文献   

16.
Interspecific and intraspecific trophic resource partitioning between coexisting plaice, Pleuronectes platessa L. and dab, Limanda limanda (L.) populations were investigated at three subtidal locations in the Irish Sea: Two inshore locations off the coast of Anglesey, North Wales and one off-shore location. In shallow inshore waters, the two species had similar diets dominated by the polychaete Pectinaria koreni. Offshore dab appeared to concentrate on Ensis ensis whilst the plaice took a wider variety of prey including bivalves, polychaetes, crustaceans and sand eels. Trawls made over a 24-hour period indicated some crepuscular and nocturnal feeding by individuals of both species. The observed patterns of resource partitioning were due to the abundance of prey species which vary spatially and seasonally and are discussed in relation to current work on resource partitioning between fishes.  相似文献   

17.
Flatfish selection by scavenging herring gulls and lesser black-backed gulls was studied onboard a commercial beamtrawler in the southern North Sea, June2 -August 1993. Dab (median total length 18 cm), plaice (23 cm), sole (22 cm) and solenette (10 cm) dominated the flatfish discard fraction of the catch. The overall consumption amounted to 30.5% of the discarded flatfish. Flatfish were selected on the basis of fish width rather than length or species, with very low consumption rates (percentage consumed of number offered) of flatfish >8 cm width. All discarded solenette, 98% of all sole and 92% of all dab were of suitable size for these gulls, whereas only 12% of all discarded plaice were small enough to be consumed. Consumption rates of discarded flatfish of ‘suitable size’ for herring gulls and lesser black-backed gulls (<8 cm width) ranged from 25.9% (plaice) to 40.5% (dab). Success indices and selected size classes of flatfish in scavenging herring gulls and lesser black-backed gulls feeding on flatfish were similar, but the first were more efficient than the latter and lost fewer flatfish as a consequence of kleptoparasitism. In contrast to earlier suggestions (based on dietary studies in colonies), there was no evidence that herring gulls were outcompeted by lesser black-backed gulls when feeding on discarded fish.  相似文献   

18.
不同育苗方式对烟株生长发育和烤后烟叶产质量的影响   总被引：2，自引：1，他引：1  
为了提高烟苗自身素质,促进烟苗早生快发,将改良式漂浮育苗与沙培育苗、常规漂浮育苗进行了对比,研究其对烟株生长和烤后烟叶产质量的影响。试验结果表明：改良式漂浮育苗较沙培育苗和常规漂浮育苗,苗期生长发育得到促进,各阶段生育期提前,烟苗素质较优,移栽后还苗期缩短;改良式漂浮育苗处理,烟株打顶后茎围较粗,株高、节距不及对照处理,烤后烟叶中上部烟叶烟碱含量明显提高,产值较对照提高。改良式漂浮育苗可明显提高烟苗素质,促进福建烟区低温条件下烟苗早生快发,提高烤后烟叶产值。  相似文献   

19.
早稻旱育秧形态、组织结构和生理特性   总被引：20，自引：0，他引：20  
卢向阳  彭丽莎 《作物学报》1997,23(3):360-369
本文分析了杂交早稻威优４８－２旰育秧和湿润育秧若干形态，组织结构和生理特性差异，讨论了旱育对秧苗根系和根系活力的影响以及南方早稻旱育高产栽培技术的增机制。结果表明：与湿润育秧比较，旱育秧地上部矮壮，分蘖和叶片表皮毛增多，气孔开度增大，叶脉变薄，气腔变小；根系发达，总根数、白根数、根干重、根毛和根系吸收面积增大；根尖和叶肉细胞体积变小，排列更紧密，原生质浓度增高；要系ＰＯＤ和ＰＡＬ活性显著增强；但根  相似文献   

20.
Sand elimination during the first days after fishing was studied quantitatively in commercially fished Mytilus edulis. Three phases can be distinguished in the elimination process: a first stage with a large and rapid discharge (15 minutes), a second stage of an exponentially decreasing rate (4 hours) and a last stage procedding slowly (4 to 48 hours). The results of the experiments are compared with published reports on the effect of activities of ciliary systems on feeding and internal transport in mussels.  相似文献   

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