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1.
This paper reports on the composition, abundance and distribution of the larval fish assemblage in the nearshore coastal waters off the St Lucia Estuary mouth, South Africa. Ichthyoplankton samples were collected over a 12 month period from five stations located along a transect up to 2·5 km offshore, and from two stations north and south of the estuary mouth, respectively. In all, 6126 fish larvae, representing 89 families and 186 species, were collected. Larvae in the families Myctophidae and Tripterygiidae comprised 21% and 16% of the total catch, respectively. The most abundant species were an unidentified triplefin, Tripterygiid 1 and the lanternfish Benthosema fibulatum, together which contributed nearly 18% of the total catch. Larvae of marine spawners independent of estuaries dominated the catch both in terms of density (90%) and in terms of number of taxa (89%). Some larvae of estuarine-associated species were present, in addition to a few specimens of estuarine resident species. Overall the dominant environmental variable affecting larval densities was temperature, particularly for Trypterygiid 1 where temperature contributed to 9% of the variance model. Densities of fish larvae peaked in November and December 1990 (late spring and early summer) and were lowest from January to June 1991 (summer, autumn an early winter). Different taxa dominated the catch each month with reef- and shelf-associated species accounting for the peak in August and September 1990, oceanic species in November 1990 and a mixture of the two groups in December. Overall larval densities were significantly higher in bottom samples with a trend of increasing densities offshore for reef and shelf taxa. The larvae of reef and shore taxa were predominantly preflexion larvae, whilst the few estuarine spawner species that were collected were mainly postflexion. Ontogenetic patterns related to depth and distance offshore were evident for the dominant species in each estuarine-association category.The present study has shown that temporal and spatial variations in the larval fish assemblage off St Lucia are related to environmental conditions and ontogenetic behavioural patterns of certain species. The origin of many of the larvae in the assemblages off the coast of St Lucia is probably from both local spawning populations in the shelf waters off KwaZulu-Natal and spawning populations farther north in shelf waters off Mozambique. Additional studies with more detailed oceanographic measurements will further our understanding of the physical processes that supply larvae to the St Lucia region.  相似文献   

2.
There have been no previous studies of the composition of nearshore larval fish assemblages along the coast of Portugal. We aimed to describe the composition and horizontal distribution patterns of larval fish assemblages and their temporal dynamics near a rocky reef at depths shallower than 13 m (inshore) and at two miles (3.70 km) from shore (offshore), as well as along transects perpendicular to the shoreline, from the reef to 10 miles offshore (18.52 km). Samples were taken using 5 min sub-surface trawls at the rocky shore of the Arrábida Marine Park (W Portugal). A total of 1021 larvae were collected, belonging to 61 taxa inshore and to 29 taxa offshore. Along transects, 626 larvae of 52 taxa were collected. Most larvae belonged to coastal species associated with rocky reefs. Total larval abundance and diversity were higher from May to July, which is consistent with the spawning activity of adults. Diversity and total larval abundance decreased significantly with increasing distance from shore, both in the inshore/offshore comparison and in the transects, where this decrease was evident at a very small spatial scale (within the first mile from the reef). Species assemblages differed in the pattern of distribution, with most species clearly associated to the extreme nearshore. The distribution patterns obtained were independent of the spawning mode of species. Results are discussed in the light of the possible physical mechanisms that can potentially act at the Arrábida Marine Park to facilitate larvae retention and the role of larval behaviour.  相似文献   

3.
The structure of the summer larval fish assemblage off the eastern coast of Tunisia and its relation to environmental conditions was studied, from ichthyoplankton samples taken during a survey conducted between 23rd June and 9th July 2008. A total of 68 larval fish taxa were identified, 52 to species level. The taxonomic composition and abundance of the larval fish assemblage showed high spatial heterogeneity. Mesoscale hydrographic features, such as eddies, seem to play an important role in the spatial distribution of fish larvae in the area, enhancing concentration and retention. The larval fish assemblage was dominated by the small pelagic species Sardinella aurita (26.6% of the total larval fish abundance), followed by Engraulis encrasicolus (22.6%), Spicara spp. (8.6%) and Mullus barbatus (6.8%). Shannon–Weaver index (H′) ranged between 0 and 2.62. The highest values were found offshore, at 95 miles east of Sousse, over depths around 250 m. The diversity was higher in this region as a result of transport by currents and retention by eddies. It has also been shown that the eastern coast of Tunisia is a spawning ground for the tuna species Auxis rochei, Thunnus thynnus and Thunnus alalunga. Larvae of mesopelagic fishes represented 5.46% of the total abundance, with Cyclothone braueri, Ceratoscopelus maderensis and Lampanyctus crocodilus being the most important species. Canonical correspondence analysis (CCA) indicated that depth was the most important environmental factor in explaining species distribution.  相似文献   

4.
A two-dimensional hydrodynamic and particle tracking model was used to estimate the dispersion and retention of barnacle larvae from their possible spawning sites in a tropical monsoon-influenced estuarine system (central west coast of India). Validation of the hydrodynamic simulations yielded a good match with field measurements. The pattern of larval dispersal in the region varied with the winds and currents. The seasonal changes in abundance could be attributed to physical forcing and weather conditions. The extent of barnacle larval dispersal from spawning sites varied from 10 to 78 km for different sites and seasons. During a 24-h cycle, the larval abundance showed one to two peaks in the estuarine area. The increased larval abundance is favored by the flood currents, pushing the larvae into the estuary. Physical forcing in the region helps in transport of the larvae from their spawning sites hugging to the coast and contributing to the population within the estuary. Field observations and numerical experiments suggest the occurrence of higher larval abundance in the estuary during post-monsoon. The dispersal pattern indicated that the barnacle population present in the estuary is well mixed, and with a seasonally changing pattern.  相似文献   

5.
The larval fish assemblage was investigated in the shallow, nearshore region of a proposed marine protected area in eastern Algoa Bay, temperate South Africa, prior to proclamation. Sampling was conducted at six sites along two different depth contours at ∼5 m and ∼15 m to assess shore association. Larvae were collected by means of stepped oblique bongo net tows deployed off a ski-boat, twice per season for 2 years between 2005 and 2007. In total, 6045 larval fishes were collected representing 32 families and 78 species. The Gobiidae, Cynoglossidae, Clupeidae, Engraulidae and Sparidae were the dominant fish families. Catches varied significantly among seasons peaking in spring with a mean of ∼200 larvae/100 m3. Mean overall larval density was higher along the deeper contour, at ∼15 m (40 larvae/100 m3). The preflexion stage of development dominated catches at the ∼5 m (80%) and ∼15 m (73%) depth contours. Body lengths of Argyrosomus thorpei, Caffrogobius gilchristi, Diplodus capensis, Heteromycteris capensis and Solea turbynei, all estuary associated species, were larger at the shallow sites nearer to shore. Larvae of coastal species that produce benthic eggs dominated catches (75%) in the shallow sites (∼5 m) but were less abundant (32%) farther from shore at the deeper (∼15 m) sites. All developmental stages of D. capensis, Engraulis capensis, H. capensis, Sardinops sagax and two Pomadasys species were found in the study area. It appears that some species use the shallow nearshore as a nursery area.  相似文献   

6.
Tautog, Tautoga onitis, is an abundant species of fish in estuaries of the northeastern United States. Planktonic tautog larvae are abundant in summer in these estuaries, but there is little information on rates of growth of tautog larvae feeding on natural assemblages of food in the plankton. We examined abundance and growth of larval tautog and environmental factors during weekly sampling at three sites along a nearshore‐to‐offshore transect in Buzzards Bay, Massachusetts, USA during summer 1994. This is the first study of a robust sample size (336 larvae) to estimate growth rates of field‐caught planktonic tautog larvae feeding on natural diets, using the otolith daily‐growth‐increment method. The study was over the entire summer period when tautog larvae were in the plankton. The sampling sites contrasted in several environmental variables including temperature, dissolved oxygen (DO), and chlorophyll a concentration. There was a temporal progression in the abundance of tautog larvae over the summer, in relation to location and temperature. Tautog larvae were first present nearshore, with a pronounced peak in abundance occurring at the nearshore sites during the last 2 weeks in June. Larvae were absent at this time further offshore. From late June through August, larval abundance progressively decreased nearshore, but increased offshore although never approaching the abundance levels observed at the nearshore sites. The distribution and abundance of tautog larvae appeared to be related to a nearshore‐to‐offshore seasonal warming trend and a nearshore decrease in DO. Otoliths from 336 larvae ranging from 2.3 to 7.7 mm standard length had otolith increment counts ranging from 0 to 19 increments. Growth of larval tautog was estimated at 0.23 mm·day?1, and length of larvae prior to first increment formation was estimated at 2.8 mm indicating that first increment formation occurs 3–4 days after hatching at 2.2 mm. Despite spatial and temporal differences in environmental factors, there were no significant differences in growth rates at any of three given sites over time, or between sites. Because larval presence only occurred at a narrow range of temperature (17–23.5 °C) and DO (6.5–9.3 mg·l?1), in situ differences in growth did not appear to be because of differences in larval distribution and abundance patterns relative to these parameters.  相似文献   

7.
张跃平  洪一川 《台湾海峡》2009,28(3):379-385
本文根据2007年3月至2008年2月期间在泉州地区3个海湾的调查资料，对其浮性鱼卵和仔稚鱼的种类组成与数量分布特点进行初步研究和探讨．结果表明，本调查海域共出现鱼卵和仔稚鱼51种（含未定种），隶属于21科，主要是近岸底层鱼类、近海中上层鱼类和港湾河口型鱼类三个生态类型．各站鱼卵总平均丰度是81．2彬网，仔稚鱼总平均丰度31．0个／网．数量平面分布呈现优势种明显，占总量比例大，不同季节不同海湾差别较大，规律性不强等特点．整体数量上与往年比有下降趋势．  相似文献   

8.
Surveys were conducted in four seasons in the eastern Beibu Gulf from July 2006 to November 2007,to determine the ichthyoplankton composition,abundance,as well as environmental factors impacted on their spatiotemporal distributions.The fish eggs and larvae were sorted from 303 zooplankton quantitative samples,in which at least 1 order,60 families,31 genera and 61 species of fish eggs and larvae were identified.The species number was highest in summer whereas lowest in winter.With the most abundant fish egg (the average density was 2.41 ind./m 3),spring was the main spawning season,while the greatest mean density of fish larva was 1.35 ind./m 3 in summer.In the whole year around,fish eggs had the trends to aggregate in the nearshore of Guangxi coast,fish larvae were more abundant in the northern water.Relationships between fish eggs and larvae abundance and environmental factors were analyzed by using the Yield-Density model.The spatiotemporal distribution of ichthyoplankton in eastern Beibu Gulf was closely related to the Chl a concentration,and the optimal temperature,salinity and Chl a were 19.4-21.7 C,31.8-33.1 and 1.5-4.8 mg/m 3,respectively.Additionally,the distribution of fish larvae could be effected by ocean currents in summer and autumn.  相似文献   

9.
As part of an investigation into the role of East African mangrove creeks as fish spawning and nursery areas, nocturnal ichthyoplankton sampling was carried out at five stations in Tudor Creek, Mombasa, Kenya, from September to November 1985. Throughout the creek, the salinity was close to that of seawater at about 35‰, but from the mouth to the upper creek there were gradients of increasing temperature and turbidity, and decreasing depth and dissolved oxygen concentration. Pelagic eggs and larvae of fish considered to be creek residents and creek non-residents were distinguished. Gradients of decreasing egg and larval abundance (particularly of non-residents), and of decreasing diversity of recognized types, were apparent from the mouth towards the upper creek. Such a distribution suggests that the mangrove system is not an important spawning or development area for the earliest life-history stages of non-resident species. The existence of the gradients also has implications both for sampling at fixed stations in tidal waters, and for investigating the existence of circatidal and semilunar spawning cycles in fish.  相似文献   

10.
于2007年和2008年6月、8月,用大型浮游生物网对莱州湾鱼卵、仔稚鱼种类组成与数量分布进行了4个航次调查。结果表明,采集到11271粒鱼卵,隶属于4目、15科、22种(不包括2个未定名物种);仔稚鱼2942尾,隶属于4目、9科、12种(不包括2个未定名物种)。6月份是莱州湾大部分鱼类主要产卵期,鱼卵、仔稚鱼种类达25种,鱼卵优势种以斑(Clupanodon punctatus)和凤鲚(Coilia mystus)为主;仔稚鱼优势种以凤鲚、梭鱼(Mugil soiuy)和斑为主。8月份产卵的鱼类较少,仅采集到15种鱼卵、仔稚鱼,优势种均以凤鲚和鲈鱼(Lateolabrax japonicus)为主。鱼卵、仔稚鱼平面分布极不均匀,黄河、广利河和老弥河口附近海域数量较多,莱州湾中部海域数量较少。通过SPSS软件分析发现,鱼卵数量与仔稚鱼、表层铵盐含量呈显著正相关(r=0.438,0.604,P0.01),与盐度、透明度呈负相关(r=-0.343,-0.329,P0.05);仔稚鱼数量仅与鱼卵数量和表层铵盐含量呈显著正相关(r=0.438,0.536,P0.01),与其它环境因子没有明显相关关系(P0.05)。  相似文献   

11.
Monthly sampling for ichthyoplankton was conducted at three stations very near to the coast (near to shore shallow stations before the surf zone in direction to the shoreline) of Atlantic northwestern Portugal within contrasting localities: rocky shore, in front of a sandy beach receiving an estuary and a fishing port with heavy anthropogenic impact. Sampling was conducted from August 2002 to October 2003, always at full moon, at low tide and high tide in daylight hours, at the water column using a 48 cm diameter plankton net with 335 μm mesh. Analysis of the physico-chemical parameters pointed out the spatial (horizontal) homogeneity of the sampling area. Fish larvae from 41 taxa belonging to 17 families were identified; Blenniidae, Labridae, Ammodytidae, Clupeidae, Gobiidae, Soleidae and Gobiesocidae were the most representative during the study period. Parablennius gattorugine, Ammodytes tobianus, Symphodus melops, Sardina pilchardus, Lipophrys pholis and Coryphoblennius galerita were the most representative species (percentage contribution to total abundance). Peak abundance of fish eggs occurred during May, June and August 2003 and fish larvae occurred during May and July 2003 and August 2002 and 2003; there was a pronounced winter/early spring (March 2003) peak in larval abundance dominated by the small sandeel A. tobianus. This study identifies the occurrence of a conspicuous assemblage of larval fishes at very nearshore shallow environments of a variety of species with different adult habitats: the fish larvae assemblage was dominated by intertidal species. The present study has shown that temporal and spatial variations in the larval fish assemblage are related to environmental conditions and biological dynamics: the results suggest that abiotic conditions mediate biotic parameters, and that both abiotic and biotic characteristics regulated the larval fishes at very nearshore shallow environments.  相似文献   

12.
利用 1 997年～ 1 999年“大洋一号”调查船在中国多金属结核开辟区用邦哥网所采集的样品 ,对仔稚鱼的种类组成、密度的平面分布和年间变化及其与环境因子的关系进行了研究。结果表明 :中国开辟区共有 2 2科 6 1种仔稚鱼 ,其中大洋性发光鱼类灯笼鱼科的种类最多 ,达1 7种 ,约占总种类数的 2 8% ,其次是钻光鱼科 (6种 )、金枪鱼科 (6种 )和拟白鲑科 (5种 ) ,分别约占总种类数的 1 0 %、 1 0 %和 8%。东、西两区的种类组成有较大的差异 ,共有种仅为 1 7种 ,东区种类数 (48种 )明显多于西区种类数 (3 0种 )。仔稚鱼的密度有明显的空间和时间变化 ,东区仔稚鱼的密度高于西区 ,东区 1 999年仔稚鱼的密度约为 1 997年的 5倍 ,西区 1 999年仔稚鱼的密度约为 1 998年的 3倍。仔稚鱼密度的年间变化可能与 El Nino事件有关  相似文献   

13.
Knowledge of stock structure is key for the effective management of any fish species. Amphidromous fish, which live and spawn in freshwater but spend a pelagic larval period at sea, have typically been assumed to disperse widely during their larval phase, resulting in populations being sourced from a single unstructured larval pool. We used otolith microchemical analysis to examine the stock structure of bluegill bully (Gobiomorphus hubbsi), a declining amphidromous eleotrid endemic to New Zealand, along the west coast of South Island, New Zealand. Some drainages – even those in close proximity (c. 20?km) – were readily distinguishable based on otolith trace element concentrations, while little structure was evident between other geographically disparate locations. These results indicate that, at least in some cases, locally retained larvae, rather than a single unstructured larval pool, dominates recruitment. Management of bluegill bully and other amphidromous species must therefore consider the possibility of regionally distinct populations.  相似文献   

14.
为探明舟山近海海域仔稚鱼丰度的分布、出现概率及与环境因素的综合关系,进一步研究该海域渔业资源的补充机制,根据2019年3、4、7、11月在舟山近海海域开展的4个航次仔稚鱼生态调查资料,研究了舟山近海仔稚鱼的出现概率、群落结构(种类组成及优势种数量)的动态变化,探讨仔稚鱼群落的季节变化和对环境变化的响应,以及环境变化对仔稚鱼补充量的影响。结果显示:空间上,调查海区水深范围5～50 m,仔稚鱼集中分布于水深10～20m的近岸河口岛礁区;时间上的季节变化比较大,春夏季丰度高,冬季少。GLM模型结果显示:近岸河口型仔稚鱼在近岸出现的概率为0.65～0.95,在近海出现的概率为0.26～0.60;近海型仔稚鱼在近岸出现的概率为0.12～0.34,在近海出现的概率为0.32～0.54。仔稚鱼优势种春夏季各出现1种,秋冬季各出现2种,全年仔稚鱼优势种有4种。数量分布为:仔稚鱼种类数春季(19种)、夏季(16种)、秋季(10种)、冬季(5种),具有明显的季节性变化。按种类适温属性划分,调查海区仅出现暖温性和暖水性两种,其中暖温性15种(占已知适温类型种类的60%),暖水性10种(占40%);按生态类型...  相似文献   

15.
Habitat use by larval fishes in a temperate South African surf zone   总被引：1，自引：0，他引：1  
Larval fishes were sampled in the Kwaaihoek surf zone on the south east coast of South Africa. On six occasions between February and May 2002, larval fishes were collected in two habitat types identified in the inner surf zone using a modified beach-seine net. The surf zone habitats were classified as either sheltered trough areas or adjacent exposed surf areas. Temperature, depth and current measurements were taken at all sites. Trough habitats consisted of a depression in surf topography characterised by reduced current velocities and greater average depth than adjacent surf areas. In total, 325 larval fishes were collected. Of these, 229 were collected in trough and 96 in surf habitats. At least 22 families and 37 species were represented in the catch. Dominant families were the Mugilidae, Sparidae, Atherinidae, and Engraulidae. Dominant species included Liza tricuspidens and Liza richardsonii (Mugilidae), Rhabdosargus holubi and Sarpa salpa (Sparidae), Atherina breviceps (Atherinidae) and Engraulis japonicus (Engraulide). Mean CPUE of postflexion larvae of estuary-dependent species was significantly greater in trough areas. The proportion of postflexion larval fishes in trough habitat was significantly greater than that of preflexion stages, a result that was not apparent in surf habitat sampled. CPUE of postflexion larvae of estuary-dependent fishes was negatively correlated with current magnitude and positively correlated with habitat depth. Mean body length of larval fishes was significantly greater in trough than in surf habitats. These results provide evidence that the CPUE of postflexion larvae of estuary-dependent fishes is higher in trough habitat in the surf zone and this may be indicative of active habitat selection for areas of reduced current velocity/wave action. The implications of this behaviour for estuarine recruitment processes are discussed.  相似文献   

16.
The temporal and spatial distributions of zooplankton biomass and larval fish recorded during 27 months (December 1995-December 1998) off the Pacific coast of central México are analyzed. A total of 316 samples were obtained by surface (from 40-68 to 0 m) oblique hauls at 12 sampling sites using a Bongo net. Two well-defined periods were observed: a pre-ENSO period (December 1995-march 1997) and an ENSO event (July 1997-September 1998) characterized by impoverishment of the pelagic habitat. The highest biomass concentrations occurred at coastal stations during the pre-ENSO period. During the El Niño period no spatial patterns were found in coastal waters. The months with highest biomass were those in which the lowest sea surface temperature (SST) occurred (January-May), and this pattern was also observed during the ENSO period. A typical, although attenuated, seasonal environmental pattern with enhanced phytoplankton (diatoms and dinoflagellates) was prevalent during the El Niño event in nearshore waters. During the El Niño period the phytoplankton was mainly small diatoms (microphytoplankton), while dinoflagellates were practically absent. The most parsimonious generalized linear models explaining spatial and temporal distribution of larval fish species included the ENSO index (MEI), upwelling index (UI) and distance to the coast. The environmental variability defined on an interannual time-scale by the ENSO event and the seasonal hydroclimatic pattern defined by the UI (intra-annual-scale) controlled the ecosystem productivity patterns. The small-scale distribution patterns (defined by a cross-shore gradient) of plankton were related to the hydroclimatic seasonality and modulated by interannual anomalies.  相似文献   

17.
We have studied the relation between the hydrography, the composition and horizontal structure of the larval fish community, and the horizontal distribution patterns of larval fish abundances in an area characterised by strong mesoscale oceanographic activity, located between the Canary Islands and the African coast (the Canaries Coastal Transition Zone), during August 1999. Upwelling, upwelling filaments, cyclonic and anticyclonic eddies and island wakes are typical mesoscale features of the northwest African coast in summer. A single upwelling filament off Cabo Juby was joined in mid-August by a second that originated about 100 km to the north. The two filaments flowed together and merged 100 km offshore. The merged filament was partially entrained around a cyclonic eddy, trapped between the Canary Islands and the African coast, and interacted with cyclonic and anticyclonic eddies shed from Gran Canaria. Mesoscale oceanographic features strongly influenced the horizontal distributions of fish larvae. Eddies acted as a mechanism of concentration, while upwelling filaments were dispersive, transporting larvae from the African neritic zone into oceanic areas and towards the Canary archipelago. This transport was the major cause of the predominance of neritic larvae in the composition of the larval fish community of the area. The results also suggest: (1) that anchovy larvae are good indicators of the offshore displacement of upwelled water; (2) that the alternation between anchovy and sardine as species dominant in the larval fish community of the area during summer depends upon the water temperature in the African upwelling region, anchovy dominating at higher temperature; (3) that a coupling of anchovy and sardine spawning with the mesoscale oceanographic structure formed by the upwelling filaments and trapped eddy overcomes the negative effect that Ekman transport has on their populations.  相似文献   

18.
Spatial patterns of interannual sea level variations in the South China Sea (SCS) are investigated by analyzing an EOF-based 2-dimensional past sea level reconstruction from 1950 to 2009 and satellite altimetry data from 1993 to 2009. Long-term tide gauge records from 14 selected stations in this region are also used to assess the quality of reconstructed sea levels and determine the rate of sea level along the coastal area. We found that the rising rate of sea levels derived from merged satellite altimetry data during 1993–2009 and past sea level reconstruction over 1950–2009 is about 3.9 ± 0.6 mm/yr and 1.7 ± 0.1 mm/yr, respectively. For the longer period, this rate is not significantly different from the global mean rate (of 1.8 ± 0.3 mm/yr). The interannual mean sea level of the SCS region appears highly correlated with Niño 4 indices (a proxy of El Niño-Southern Oscillation/ENSO), suggesting that the interannual sea level variations over the SCS region is driven by ENSO events. Interpolation of the reconstructed sea level data for 1950–2009 at sites where tide gauge records are of poor quality (either short or gapped) show that sea level along the Chinese coastal area is rising faster than the global mean rate of 1.8 mm/yr. At some sites, the rate is up to 2.5 mm/yr.  相似文献   

19.
Larval fish community structure was studied in the northeastern Aegean Sea (NEA) over an area influenced by the advection of Black Sea water (BSW). Sampling was carried out in early summer during a period of 4 years (2003–2006). Taxonomic composition and abundance presented high variability in space that remained relatively constant among years. Tow depth and indicators of trophic conditions in the upper water column (i.e., zooplankton displacement volume, fluorescence) explained significantly the structure of larval assemblages during all surveys. The northern continental shelf (Thracian and Strymonikos shelf), where a large amount of enriched, low salinity BSW is retained, was dominated by larvae of epipelagic species, mainly anchovy (Engraulis encrasicolus). Interannual changes in horizontal extension of the BSW seemed to match closely observed changes in the distribution of anchovy larvae. Mesopelagic fish larvae were particularly abundant beyond the continental shelf (over the North Aegean Trough) where a strong frontal structure is created between the low salinity waters of BSW origin and the high salinity waters of the Aegean Sea. Larvae of certain mesopelagic species (e.g., Ceratoscopelus maderensis) may occasionally be transported inshore when the prevailing current meanders towards the coast or feeds anticyclonic gyres over the continental shelf.  相似文献   

20.
《Journal of Sea Research》2011,65(4):494-504
Turbot (Psetta maxima Linnaeus) is a high value commercially exploited marine flatfish which occurs in European waters, from the Northeast Atlantic to the Arctic Circle, the Baltic and Mediterranean Sea. In Ireland, turbot are the most valuable commercial non-quota species. Very little is known about their population dynamics in the wild, in particular during the sandy beach nursery phase of the life history. In 2000, a survey was established to assess flatfish species on nursery grounds on the west coast of Ireland. Eleven sandy beaches were assessed for 0+ turbot by beach seining, over an eight year period (2000–2007) during the months of August and September. The objective of the study was to estimate juvenile turbot abundance and size structure to determine if any spatial and annual trends existed. Large scale variability in the recruitment of fish to nursery grounds may be indicative of fluctuations in the adult stock. Turbot were found to recruit to five beaches consistently over the eight year period. Temporal and spatial variability in the relative abundance and length of turbot was discerned, with no apparent overall trend. However, certain nursery grounds were shown in most of the years examined to support higher abundances of turbot in comparison to other areas over the eight year period. Turbot abundances on nursery grounds were significantly correlated with mean spring sea temperatures during the pelagic stage. The condition of turbot did not significantly differ on an annual or spatial scale. Mean densities of 0+ turbot along the Irish coast were found to be similar and at times higher than other areas in Europe, ranging from 0.1 (± 0.3) individuals 1000 m− 2 to 18.5 (± 6.9) individuals 1000 m− 2. Mean turbot total length on beaches ranged from 3.8 cm (± 0.6) to 6.6 cm (± 4.3). The observed spatial and temporal variability in abundance and length highlights the need for long-term studies when assessing juvenile flatfish populations. Results from the present study have provided much needed baseline data on wild juvenile turbot populations which is severely lacking for this species both on an Irish and on a European scale.  相似文献   

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