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1.
In the Shiretoko Peninsula, a World Natural Heritage site, the sustainable management of kelp forests has drawn public attention because of the economic and ecological importance of kelp. We spatially estimated the distributions of kelp forests in the Shiretoko Peninsula before and after harvest. Field surveys were conducted in coastal waters (23.74 km2) at the ends of July and August 2008, immediately before and after harvest. Data on the presence or absence and thickness of the kelp forests were collected via acoustic observation. The data were interpolated using geostatistical methods. Before harvest, the kelp forests were continuously distributed over 5.64 km2 (thickness 33–132 cm), especially near the north part of the study area. After harvest, they were sparsely distributed over 2.73 km2 (thickness 35–105 cm). In the southern part of the study area, the influence of harvests was observed as declines in forest area. In addition, relatively thickly forested areas formed the majority of the part most likely to be harvested. Selective harvesting for area and size was confirmed though quantitative mapping of kelp forests. The quantitative mapping of both the distribution and harvest of kelp forests was successful.  相似文献   

2.
Red snappers were examined for reproductive biology and age-0 habitat preferences. Spawning in red snappers occurred throughout the year in northern Australia and eastern Indonesia; at least 10–30% of females and 40–80% of males were in ripe or spawning condition in most months. Northern Australian populations showed a spawning peak from July to December (L. erythropterus) and September to March (L. malabaricus). Eastern Indonesian L. malabaricus had a less defined pattern with two peaks: January–March and October. Size at first maturity was 240 mm for males and 250–300 mm for females. L 50 estimates were similar between species in northern Australia: 270–280 mm (males) and 350–370 mm (females). Maximum batch fecundity was 676,100 oocytes for L. erythropterus and 997,000 oocytes for L. malabaricus. Higher mean abundances of age-0 L. erythropterus were found in silty and coarse sand/rubble estuarine habitats of northern Australia (456 ± 119 fish/km2) compared with sandy coastal habitats (5 ± 3 fish/km2). Most age-0 snapper caught at Sape (eastern Indonesia) were L. malabaricus (91%) with mean abundances of 312 ± 14 fish/km2. The similarities in the reproductive characteristics of red snappers suggest that successful management approaches adopted in northern Australia should be considered in eastern Indonesia.  相似文献   

3.
海南陵水湾口海域不同季节鱼类资源声学探查   总被引：3，自引：0，他引：3  
在2014年11月至2016年1月间的不同季节,利用便携式分裂波束科学探鱼仪对海南陵水湾口海域的鱼类资源进行了4次声学调查。通过回波积分方法并结合拖网采样对调查海域内渔业资源结构组成、数量密度、资源量密度及其空间分布进行了探查与评估。结果发现,2014年11月共捕获游泳生物和底栖无脊椎动物86种,其中55种声学评估种类平均资源数量密度和平均资源量密度分别为9.34×105尾/km2和5.08 t/km2。2015年8月共捕获游泳生物和底栖无脊椎动物114种,其中63种声学评估种类平均资源数量密度和平均资源量密度分别为1.12×105尾/km2和0.93 t/km2。2016年1月共捕获游泳生物和底栖无脊椎动物105种,55种声学评估种类平均资源数量密度和平均资源量密度分别为0.16×105尾/km2和0.32 t/km2。2015年5月共捕获游泳生物和底栖无脊椎动物56种,其中声学评估种类34种。2014年11月和2015年8月鱼类回波均匀分布于30 m以浅水层,2015年5月主要集中于10~20 m水层,2016年1月则主要分布于20 m以浅水层,20~30 m水层次之且略大于0~10、10~20 m水层的一半。调查海域内单体目标强度以小于–58 d B的小规格鱼类目标为主,目标强度有随水深增加而增大的趋势,且大于–50 d B的单体目标均分布于10 m以深水层。  相似文献   

4.
Japanese eels (Anguilla japonica) perform large‐scale oceanic migrations between their spawning ground and growth habitats in continental waters during life history. However, between these migrations, they spend most of time in growth habitats such as rivers. To investigate the diel and seasonal activities, homing behaviour and home range of yellow‐phase Japanese eels in the lower reach of the Tone River, we tracked them throughout a year using a fine‐scale positioning system (VPS) based on acoustic telemetry. The tracked eels were generally nocturnal, but not exclusively. They were mainly mobile from spring to autumn, with little or no activity observed during winter. A transport‐release experiment showed that most eels returned to their original capture area within 13 days after release. The eels had very small home ranges (mean ± SD = 0.085 ± 0.068 km2), core areas (0.014 ± 0.014 km2) and linear home ranges (744 ± 268 m). They also tended to be distributed on one particular side of the river (right or left bank) and in one particular shore type (revetment or vegetation), rarely moving from one to the other. This study provides evidence for nocturnal, dormancy, homing behaviours, limited habitat use and small home range size in Japanese eels. The eels clearly showed strong fidelity to a “familiar” site, which contrasts with the long distances travelled during upstream and downstream migration phases in the river, and during spawning migrations in the ocean.  相似文献   

5.
The effects of dietary mannan oligosaccharides (MOS) on the survival and growth of Astacus leptodactylus juveniles were evaluated. Experimental diets were prepared by using supplementation of 0 (Control), 1.5, 3.0, and 4.5 g MOS kg−1 commercial trout larvae diet containing 43 g kg−1 protein and 15.74 g kg−1 lipid. A. leptodactylus juvenile with an average total length of 3.6 ± 0.46 cm (TL) and average weight of 1.25 ± 0.43 g was stocked in 0.2-m2 aquariums at a rate of 50 crayfish/m2 and reared for 60 days at 22.8°C. The experiment consisted of four treatments with three replicates each. Each aquarium contained ten crayfish. Crayfish juvenile fed with 0, 1.5, 3.0, and 4.5 MOS attained 6.15 ± 0.49, 5.94 ± 0.29, 7.34 ± 0.39, and 5.94 ± 0.27 cm final total length and 50, 56.67, 46.67, and 50% survival rates, respectively. Moreover, molting frequencies in 0, 1.5, 3.0, and 4.5 g kg−1 MOS groups were detected as 44.44, 61.11, 83.33, and 38.88%, respectively. At the end of the experiment, a general enhanced growth performance (P < 0.05) and feed conversion ratio were observed in crayfish fed on the diet containing 3.0 g kg−1. Crayfish juveniles fed with 3.0 g kg−1 MOS had the highest final length (7.34 ± 0.39 cm), although their survival was the lowest (46.67%) compared to other treatments but not significant. Specific growth rates were significantly different (P < 0.05) among the treatment groups at the end of the 60-day experiment. There were no significant differences (P > 0.05) in percentage moisture, protein, and ash (wet-weight basis) in the tail meat of A. leptodactylus juvenile among treatments (diet) that averaged 82.3, 16.1, and 1.2%, respectively. However, lipid value was significantly different among the diets P < 0.05), with values between 0.13 and 0.32. From the current results, it could be advised to use MOS at the rate of 3.0 g kg−1 in A. leptodactylus juvenile diets.  相似文献   

6.
The effects of culture density and bottom areas on cuttlefish (Sepia officinalis) culture were studied. Cuttle fish were cultured under three experimental combinations of culture density and bottom area: (1) high density and small bottom surface area; (2) low density and large bottom area; (3) high density and large bottom area. Each experimental protocol was repeated in triplicate. Average weights at the end of the experiment were of 65.8 ± 5.8, 87.1 ± 5.6 and 78.7 ± 5.9 g for cuttlefish cultured under the conditions of protocol 1, 2, and 3, respectively; these differences were significant between each of the three groups. Total biomass increased faster (up to 7.5 kg per tank) under the high density/large bottom area conditions (protocol 3) due to the larger number of animals and low mortality in those tanks. Growth rates (%bw day−1) were different between protocols, with growth rates of 2.1 ± 0.1, 3.0 ± 0.2, and 2.5 ± 0.1%bw day−1 obtained for cuttlefish cultured according to protocol 1, 2, or 3, respectively. Average feeding rates were similar for the three groups—10.7 ± 0.8, 9.7 ± 2.0, and 9.6 ± 1.1%bw day−1 for cuttlefish cultured according to protocols 1, 2, and 3, respectively, while food conversions (%) were different—21.5 ± 3.2, 32.4 ± 2.5, and 27.0 ± 1.1%bw day−1, respectively. Total mortality was high in the high density/small bottom area tanks, 30%, while it was very low for the groups cultured under conditions of low and high density/large bottom area, 4%. Based on these results, we conclude that culture conditions that provide large bottom areas also provide good survival conditions and promote growth in comparison those with small bottom areas, even under conditions of lower culture densities.  相似文献   

7.
No data have previously been reported on Eurasian perch Perca fluviatilis L. in Lake Varese. In this study, the growth, diet, and reproductive biology of the Eurasian perch population were investigated with the aim of providing information that may serve as a basis for efficient resource management. A total of 240 specimens were caught during the monthly sampling campaign from November 2006 through October 2008. The length-to-weight relationships were W t = 8.4 × 10−3 L t3.10 (males) and W t = 4.1 × 10−3 L t3.36 (females). The parameters for the von Bertalanffy growth function for pooled sexes were L ∞  = 33.17 cm, k = 0.20 year−1, and t 0 = −1.34 year. Perch in Lake Varese spawn from April through May. Sexual maturity is reached when males are 2 years old, in females mostly when they are 3 years old. Relative fecundity (F rel) and absolute fecundity (F abs) were assessed for females. Fecundity values were similar to data reported for other European populations: females of age 2+ F rel = 102,457 ± 12,275, age 3+ F rel = 131,767 ± 5,891, and age 4+ F rel = 131,252 ± 15,555. Perch diet spectrum was wide and somewhat characterized by season. Perch in Lake Varese feed on macroinvertebrates, mainly Chironomidae and Chaoborus, zooplankton, and juvenile rudd Scardinius erythrophthalmus.  相似文献   

8.
Stable carbon (δ13C) and nitrogen (δ15N) isotope ratios were measured to investigate the migration of John’s snapper Lutjanus johnii and its dependence on the food resources provided within the large Matang Mangrove Forest Reserve (40,151 ha), Malaysia. John’s snapper, and its main prey food such as penaeids, Acetes shrimps and mysids, showed generally depleted δ13C values in the inner mangrove area but more enriched values in the river mouth and coastal area. Some juveniles migrated into the inner mangrove areas, although they were also distributed near the river mouth areas. Isotopic signatures of snapper fish and prey reveal the ontogenetic migration of the youngest juvenile fish (<5 cm in total length) from the coastal area into the mangrove area, shifting their dependence from the coastal food web to the inner mangrove food web with their growth. The study shows the importance of the complex interconnected mangrove waterways and associated prey animals present in the large mangrove system to juvenile John’s snapper.  相似文献   

9.
Although emperors (Lethrinidae) are commercially important fisheries resources in tropical and subtropical waters, their home range size and its spatial arrangement have not been sufficiently clarified. In the present study, the size and spatial arrangement of the daytime home range of the thumbprint emperor Lethrinus harak were investigated by using a portable GPS receiver. In a 150 m × 200 m quadrat, 21 individuals of the species were identified by their color pattern, and individuals were divided into four arbitrary size classes (class 1 < 20 cm TL ≤ class 2 < 25 cm TL ≤ class 3 < 30 cm TL ≤ class 4). Fish tracking by snorkeling was conducted with the portable GPS receiver. Daytime site fidelity of this species was high and there was a significant positive correlation between the home range size and fish total length. Home ranges of same-sized individuals abutted each other (20.3% area overlap), whereas those of different-sized individuals overlapped (48.3% area overlap). Agonistic behavior (attacking) occurred significantly more frequently between same-sized individuals than between different-sized individuals. These results suggest that daytime home ranges of Lethrinus harak can be regarded as territories against same-sized individuals, but not different-sized individuals.  相似文献   

10.
We compared the assemblage structure, spatial distributions, and habitat associations of mountain whitefish (Prosopium williamsoni) morphotypes and size classes. We hypothesised that morphotypes would have different spatial distributions and would be associated with different habitat features based on feeding behaviour and diet. Spatially continuous sampling was conducted over a broad extent (29 km) in the Calawah River, WA (USA). Whitefish were enumerated via snorkelling in three size classes: small (10–29 cm), medium (30–49 cm), and large (≥50 cm). We identified morphotypes based on head and snout morphology: a pinocchio form that had an elongated snout and a normal form with a blunted snout. Large size classes of both morphotypes were distributed downstream of small and medium size classes, and normal whitefish were distributed downstream of pinocchio whitefish. Ordination of whitefish assemblages with nonmetric multidimensional scaling revealed that normal whitefish size classes were associated with higher gradient and depth, whereas pinocchio whitefish size classes were positively associated with pool area, distance upstream, and depth. Reach‐scale generalised additive models indicated that normal whitefish relative density was associated with larger substrate size in downstream reaches (R2 = 0.64), and pinocchio whitefish were associated with greater stream depth in the reaches farther upstream (R2 = 0.87). These results suggest broad‐scale spatial segregation (1–10 km), particularly between larger and more phenotypically extreme individuals. These results provide the first perspective on spatial distributions and habitat relationships of polymorphic mountain whitefish.  相似文献   

11.
Generalized additive models (GAMs) were fitted to sardine (Sardina pilchardus) egg distribution data from three daily egg production method surveys. The results showed that the area of egg cover off Portugal decreased significantly from 11 800 km2 in 1988 to 7000 km2 in 1997 and 7400 km2 in 1999. This is because of a significant reduction in sardine egg presence off northern Portugal, GAM estimated areas being similar or higher in the late 1990s for southwestern and southern Portugal. The distributional area covered by larvae was not estimated for 1988 (larval distribution extended beyond the survey area), although it was probably higher than the 9600 km2 for 1997 and 5500 km2 for 1999. In 1997 and 1999, the Gulf of Cadiz was also sampled, indicating extensive areas with sardine eggs and larvae (more than 50% of the total area of distribution off Portugal). Standardized data from 15 ichthyoplankton surveys between 1985 and 2000 show a decline in the mean probability of egg presence within the Portuguese continental shelf from the mid‐1980s to the late‐1990s, because of a marked reduction in egg presence off northern Portugal. Sardine larval data from the same surveys suggest that the reduction in mean probability of presence in the north is less marked than for eggs (although this comparison ignores the presence of sardine larvae beyond the continental shelf in the 1980s). Similar changes off northern Portugal and western Galicia are observed in commercial sardine catches and the acoustically estimated area of fish distribution. It is possible that the observed decline in spawning area off northwestern Iberia during the 1990s is indirectly reflecting the prevalence of environmental conditions detrimental to sardine recruitment (northerly winds during winter that favour coastal upwelling and offshore transport), which have reduced the spawning contribution of young fish in that area.  相似文献   

12.
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13.
The shore crab Carcinus maenas is a commercially important species, utilised as sea angling bait as well as supporting a European-wide fishery. Hatchery production could provide an alternative source of bait crabs, alleviating potential competition between these sectors and environmental concerns regarding bait collection practices. A series of experiments were carried to investigate the potential for hatchery production, focusing on effects of dietary regimes and stocking densities through the zoeal stages and the influence of tank substrates and stocking density during the megalopa stage. Inclusion of the rotifer Brachionus plicatilis as live food for early larval stages conveyed no advantage in terms of survival or rate of development compared to a diet of Artemia nauplii. Increasing zoea stocking densities (from 94 to 557 l−1) had a significantly negative effect upon survival to the megalopa stage (from 75% down to 47%), although this was off-set by a significant increase in production, with 260 megalopae−1 produced from an initial density of 557 zoeae l−1. The inclusion of substrates for megalopa stages had no impact on production or development rate, compared to tanks with no substrate. The completely benthic behaviour of megalopae indicates that tank floor area will be a limiting factor for crab production. Increasing stocking density of megalopae was found to significantly and negatively influence survival, although above 10,000 megalopae m−2 the rate of decline in survival stabilised and maximum production (3,114 juveniles m−2) of juvenile crabs could be achieved at the highest stocking densities tested (40,000 m−2).  相似文献   

14.
We analysed the genetic diversity of Melicertus kerathurus (Penaeidae), a commercially valuable penaeid shrimp that is distributed in the Mediterranean Sea and eastern Atlantic Ocean. We examined the polymorphism of a 494 bp DNA segment of the mitochondrial COI region in 173 individuals, sampled in nine Mediterranean and two Atlantic samples, covering the whole range of the species from the tropical waters of the Gulf of Guinea to the eastern part of the Mediterranean Sea. The mean nucleotide and haplotype diversities were π = 0.00275 and h = 0.718, respectively, for the global data set, with the highest values occurring in the African samples and the lowest in the Adriatic Sea. A clear sample differentiation was found (F st = 0.194), but this did not reflect a geographical pattern and there were only faint traces of an Atlantic–Mediterranean subdivision. Mismatch analysis and a high significant negative value of Tajima’s D suggested that M. kerathurus is not at mutation drift-equilibrium, but underwent a recent expansion after a period of low effective sample size. A postglacial recolonisation of the Mediterranean from an Atlantic refuge could be hypothesised based on these data.  相似文献   

15.
The effects of ration levels on growth, conversion efficiencies and body composition of fingerling Heteropneustes fossilis (6.8 ± 0.04 cm, 5.0 ± 0.02 g) were studied by feeding isonitrogenous (40% crude protein) and isocaloric (19.06 MJ kg−1 gross energy) diets representing 1, 3, 5, 7 and 9% of the body weight (BW) day−1 to triplicate groups of fish . Growth performance of the fish fed at the various ration levels was evaluated on the basis of live weight gain percentage (LWG%), feed conversion ratio (FCR), specific growth rate percentage (SGR%), protein retention efficiency (PRE%) and energy retention efficiency (ERE%) data. Maximum LWG% and SGR were obtained at a feeding rate of 7% BW day−1, whereas best FCR (1.6), PRE% and ERE% were recorded at a feeding rate of 5% BW day−1. Maximum body protein was also obtained for the group receiving the diet representing 5% of their body weight. However, a linear increase in fat content was noted with the increase in ration levels up to 7% BW day−1. The SGR, FCR, PRE and ERE data were also analyzed using second-degree polynomial regression analysis to obtain more precise information on ration level, with the results showing that the optimal ration for these parameters was 6.8, 6.1, 5.9 and 6.2% BW day−1, respectively. Based on the above second-degree polynomial regression analysis, the optimum ration level for better growth, conversion efficiencies and body composition of fingerling H. fossilis was found to be in the range of 5.9–6.8% of the BW day−1, corresponding to 2.36–2.72 g protein and 88.20–101.66 MJ digestible energy kg−1 diet day−1.  相似文献   

16.
Recent advances in intensive rearing of astacid juvenile crayfish have greatly improved the results. This challenges the current application possibilities of the studies performed previously, and new research on density is required. A 100-day experiment was carried out under controlled conditions to evaluate density effects on survival and growth rates of juvenile crayfish in optimal conditions of feeding. Juvenile stage 2 Pacifastacus leniusculus were stocked in fibreglass tanks (1 m2, 200 l water) at 20 ± 1°C and fed a dry diet for salmonids supplemented with restricted amounts of Artemia nauplii. Stocking densities were 100, 300, 600 and 1,000 crayfish m−2. Mean survival rate was reduced significantly with increased stocking density, ranging from 86.33% (100 m−2) to 39.13% (1,000 m−2). All checks showed that at the lowest initial density (100 m−2) animals grew significantly faster those at higher densities, recording a final carapace length of 15.28 mm and weight of 1.08 g. Among the treatments of 300, 600 and 1,000 m−2 no differences were found either in carapace length or in weight throughout the experimental period, with a final mean growth of 14 mm carapace length and 0.72 g weight. The final proportion of animals with chelae autotomy rose significantly with increasing stocking density, ranging from 14.44% (100 m−2) to 41.45% (1,000 m−2). This study shows that diet is a decisive factor for stocking successfully high densities under controlled conditions and provides useful information to set adequate densities in accordance with the production objectives.  相似文献   

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18.
2019年10月24日至26日,使用便携式Simrad EY60科学探鱼仪对珠海桂山岛海上风电场水域的渔业资源进行了声学调查,研究了该水域的渔业资源组成、数量密度、资源量密度及其空间分布。本次调查共捕获游泳生物和底栖无脊椎动物72种,其中34种参与声学评估。扫海面积法估算的鱼类平均数量密度与资源量密度分别为1.09×104尾/km2,227.48 kg/km2;声学方法估算的鱼类数量密度与资源量密度分别为5.97×105尾/km2,15.13 t/km2。风电场水域鱼类聚集性分布明显,在风电场西北与东南外围水域密度较高,中间水域的密度较低。鱼类单体目标强度（TS）分布范围为-68~-41dB,其中-68~-58 dB的单体TS占主要部分（79.12%）,对应鱼类的体长范围为3~8 cm;随着水深的增加,单体平均TS先减小后增大。本研究是桂山风电场水域渔业资源的首次声学调查,结果较准确地反映了风电场水域多种鱼类的资源量及其分布信息,可为科学评价海上风电场建成运营后对渔业资源的长期影响提供基础数据。  相似文献   

19.
Detailed measurements of gill area and constituent variables (total filament number, total filament length and mean filament length), and immunolocalization of the α-subunit of Na+/K+-ATPase and Na+/K+-ATPase activity were performed on both hemibranchs of all five arches of freshwater potamotrygonid stingrays (Paratrygon aiereba and Potamotrygon sp.). Both species exhibit similar mass-specific gill area, 89.8 ± 6.6 and 91.5 ± 4.3 mm2 g−1 for P. aiereba and Potamotrygon sp., respectively. The density of Na+/K+-ATPase-rich MRCs and Na+/K+-ATPase activity was higher in the 4th gill arch in both species. The Na+/K+-ATPase activity was positively correlated to the Na+/K+-ATPase-rich (Na+/K+-ATPase rich) mitochondrion-rich cell (MRC) distribution among the gill arches of P. aiereba but not in Potamotrygon sp. The levels Na+/K+-ATPase activity were not correlated to the gill surface area among the arches for both rays’ species. Considering that the Na+/K+-ATPase-rich MRC is the main site for active ion transport in the gill epithelia and Na+/K+-ATPase activity plays a crucial role in osmoionoregulatory function, we suggesting that 4th gill arch is more relevant for osmoregulation and ion balance in these potamotrygonids.  相似文献   

20.
Prostaglandins are involved in the reproductive processes in a variety of animals, including crustaceans. It was found that polychaetes, the best maturation diet for shrimp broodstock, possessed the greatest variation of prostaglandin E2 (PGE2) when compared with other live feeds. The level of PGE2 varied according to sizes, feed intake, sources and type of polychaete. The matured and also larger sand polychaete Perinereis sp. contained higher PGE2 levels than younger and smaller sand polychaetes (18.16 ± 5.82 ng PGE2 mg−1 protein for polychaetes at an average length of 10 cm up to 160.8 ± 37.09 ng PGE2 mg−1 protein for polychaetes at an average length of 17 cm). The PGE2 levels in ovaries and haemolymph of female shrimp fluctuated with the developmental stage of the ovaries. The highest concentration of PGE2 in haemolymph was at stage 3 of ovarian development, whereas the highest concentration of PGE2 in shrimp ovaries was at stage 4. In vitro incubation of Penaeus monodon pre-vitellogenic oocytes with polychaete extract and synthetic PGE2 demonstrated that both PGE2s enhanced oocyte development, especially during late development and ovulation. The putative role of PGE2 from polychaetes or the presence of PGE2 in polychaetes may be a factor in their role as a dietary constituent required for shrimp oocyte development.  相似文献   

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