Top PDF Sex-dependent habitat use by the Japanese eel Anguilla japonica in Taiwan

Sex-dependent habitat use by the Japanese eel Anguilla japonica in Taiwan

Sex-dependent habitat use by the Japanese eel Anguilla japonica in Taiwan

Yu San Han, Wann Nian Tzeng* Institute of Fisheries Science, College of Life Science, National Taiwan University, Taipei, Taiwan 106, ROC ABSTRACT: The Japanese eel Anguilla japonica is a catadromous fish, but it has recently been dis- covered that the use of freshwater habitat at the yellow eel stage is facultative. To determine if habi- tat use by Japanese eels differs between the sexes we examined the strontium:calcium (Sr:Ca) ratios in otoliths of 221 eels by electron probe micro-analyzer to reconstruct their environmental history.
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Use of the Sex Ratio as a Means of Resource Assessment for the Japanese Eel Anguilla japonica: A Case Study in the Kaoping River, Taiwan

Use of the Sex Ratio as a Means of Resource Assessment for the Japanese Eel Anguilla japonica: A Case Study in the Kaoping River, Taiwan

A negative relationship between the proportion of females and the population density was found when compil- ing historical data of both wild and cultured Japanese, European, and American eels. Based on the relation- ship, the population status of the Japanese eel Anguilla japonica was assessed. Japanese eel samples were collected from the lower reaches of the Kaoping River in southwestern Taiwan from 1998 to 2002, and the pop- ulation density was estimated by mark-recapture experiments in 2001 and 2002. The sex ratio of the eel was skewed towards females, accounting for 81.3%-88.3% in the total samples of yellow and silver eels and for 63.6%-81% in the silver stage eels. The significant female-skewness of the sex ratio validated that the popula- tion of Japanese eels in the Kaoping River has declined to a very low level in recent years. The population density of the Japanese eel in the lower reaches of the Kaoping River was approximately 0.01 eels/m 2 in 2001 and 2002. The decline in the Japanese eel population in the Kaoping River has probably resulted from both overfishing of glass eels in the estuary for aquaculture needs which severely influences recruitment, and degra- dation of the growth habitat of the yellow eel along the river. The sex ratio therefore is a fast and reliable indi- cator for eel resource assessment. http://zoolstud.sinica.edu.tw/Journals/45.2/255.pdf
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Historical decline in the Japanese eel Anguilla japonica in northern Taiwan inferred from temporal genetic variations.

Historical decline in the Japanese eel Anguilla japonica in northern Taiwan inferred from temporal genetic variations.

1 Department of Zoology, National Taiwan University, Taipei, Taiwan 10764, R.O.C. 2 Institute of Zoology, Academia Sinica, Taipei, Taiwan 11529, R.O.C. (Accepted June 27, 2003) Mei-Chen Tseng, Wann-Nian Tzeng and Sin-Che Lee (2003) Historical decline in the Japanese eel Anguilla japonica in northern Taiwan inferred from temporal genetic variations. Zoological Studies 42(4): 556-563. The existence of temporal genetic variations was tested for in 6 polymorphic microsatellite DNA loci of 89 Japanese eel Anguilla japonica collected from a single location in the Tanshui River Estuary, northern Taiwan during 1997- 1999. The high Nei’s genetic identity coefficients (0.868-0.941) and exact test of temporal genetic structure revealed no significant differentiation (p > 0.05) among cohorts. Parameters of genetic diversity were examined including mean observed heterozygosity (H o ) (0.695-0.732) and change in the total number of alleles per year (na) (73-81). Significant deviations from Hardy-Weinberg equilibrium appeared in 5 of 6 loci, due to an insuffi- cient number of heterozygous individuals in all cohorts. Totals of 22 private and 14 solitary missing alleles were found in all 6 loci. The decrease in numbers of total alleles and private alleles and the increased number of solitary alleles in consecutive years suggested that genetic polymorphism was gradually decreasing. By Bayesian parameters assay, we found that the effective population size was declining. The demographic decline estimated to be 3500-8000 years ago, is significant due to large-scale events such as oceangeographic changes since the most recent glacial stage. http://www.sinica.edu.tw/zool/zoolstud/42.4/556.pdf
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Surface seawater temperature as a potential cause of delayed arrival of the Japanese eel Anguilla japonica elvers on the coast of Taiwan.

Surface seawater temperature as a potential cause of delayed arrival of the Japanese eel Anguilla japonica elvers on the coast of Taiwan.

(Received, March 08, 2006; Revised, April 23, 2006; Accepted, April 25, 2006) ABSTRACT The Japanese eel Anguilla japonica is one of the most important food fish in Taiwan. For cultivation, elvers of the eel are caught from the wild population in estuaries during their upstream migration. The relationship between recruitment timing of elvers and surface seawater temperature was analyzed based on the daily catch data of elvers in an estuary of northeastern Taiwan since 1980. It was found that most elvers recruited to the estuary during the period from December to January, with a rhythmic activity that follows the lunar cycle. However, the peak recruitment period in the years of 1986-87, 1990-91 and 1995-96 occurred in March, delayed approximately two months.
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The sex-ratio reversal of the Japanese eel Anguilla japonica in the Kaoping River of Taiwan: The effect of cultured eels and its implication

The sex-ratio reversal of the Japanese eel Anguilla japonica in the Kaoping River of Taiwan: The effect of cultured eels and its implication

The sex ratio of wild Japanese eels in the Kaoping River of southwestern Taiwan has been extremely skewed towards females in the recent years. However, the sex ratio skewed towards males after Typhoon Mindulle, July 2, 2004 then recovered to the previous female-dominated status in the following year. To determine why the sex ratio drastically changed, eels captured in the river were examined by both morphologic characteristics and otolith elemental signatures by solution-based inductively coupled plasma mass spectrometry (SB-ICPMS) and laser-ablation ICPMS (LA-ICPMS). Most of the eels collected in the river after the typhoon had a blue-gray colored back, with morphology and sex ratio similar to that of cultured eels, which differed from wild yellow eels which had a green colored back. The chemical signature in otoliths of eels with a blue-gray colored back was similar to that of cultured eels, with significantly lower Sr/Ca ratios but slightly higher Mn/Ca ratios than for wild eels. This confirmed that the reversal in eel sex ratio in the Kaoping River estuary resulted from cultured eels that had escaped from eel farms. Eel farmers estimated that about 30,000 eels escaped during the typhoon, sufficient to reverse the sex ratio of the eels in the river. Furthermore, silver eels caught in the estuary in the winter 2004 were also mostly males. The chemical signature in otoliths of these silver eels was similar to that of escaped cultured eels. Their morphology and mean GSIs, however, were comparable to wild silver eels. Thus, cultured eels that have escaped from eel farms can silver normally in the wild. Consequently, cultured eels may help to balance the sex ratio of the wild eel population and may contribute to the spawning stock of Japanese eel.
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Population Genetic Structure among Intra-Annual Arrival Waves of the Japanese Eel Anguilla japonica in Northern Taiwan

Population Genetic Structure among Intra-Annual Arrival Waves of the Japanese Eel Anguilla japonica in Northern Taiwan

DISCUSSION Values of H O for genetic variability of the Japanese eel among spatial (Tseng et al. 2006), inter-annual (Tseng et al. 2003), and intra-annual (this study) samples were 0.758, 0.708, and 0.677, respectively. This indicates that genetic differenti- ation was highest among samples from different locations, intermediate among annual cohorts of the same habitats, and lowest among intra-annual cohorts of the same habitats. Several lines of evi- dence support the Japanese eel, although exhibit- ing spatial genetic differentiation, still being geneti- cally stable temporally at the same location. First, the overall temporal genetic variation among arrival waves of elvers in consecutive months of the same habitat was not significant. Pair-wise F ST values showed that only the pair of samples between Nov. and Dec. 2000 exhibited subtle but significant genetic variation. This might have been due to the phenomenon of genetic patchiness, in which random variations in parental contributions
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Modelling the growth of Japanese eel Anguilla japonica in the lower reach of the Kao-Ping River, southern Taiwan: an information theory approach

Modelling the growth of Japanese eel Anguilla japonica in the lower reach of the Kao-Ping River, southern Taiwan: an information theory approach

Information theory was applied to select the best model fitting total length (L T )-at-age data and calculate the averaged model for Japanese eel Anguilla japonica compiled from published literature and the differences in growth between sexes were examined. Five candidate growth models were the von Bertalanffy, generalized von Bertalanffy, Gompertz, logistic and power models. The von Bertalanffy growth model with sex-specific coefficients was best supported by the data and nearly overlapped the averaged growth model based on Akaike weights, indicating a similar fit to the data. The Gompertz, generalized von Bertalanffy and power growth models were also substantially supported by the data. The L T at age of A. japonica were larger in females than in males according to the averaged growth mode, suggesting a sexual dimorphism in growth. Model inferences based on information theory, which deal with uncertainty in model selection and robust parameter estimates, are recommended for modelling the growth of A. japonica. © 2009 The Authors Journal compilation © 2009 The Fisheries Society of the British Isles
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Vital population statistics based on length frequency analysis of the exploited Japanese eel (Anguilla japonica) stock in the Kao-Ping River, southern Taiwan

Vital population statistics based on length frequency analysis of the exploited Japanese eel (Anguilla japonica) stock in the Kao-Ping River, southern Taiwan

Given that this study is the first to describe the maturation of A. japonica, no comparative published data are available for this species. For A. Anguilla, c max appeared to be more variable for females compared to males, being 0.12 ± 0.03 for females in the Valli di Comacchio Lagoon in Italy (De Leo and Gatto, 1995) and 0.60–1 in southern France (Bevacqua et al., 2006). For males in the two regions, c max generally approached 1. For A. japonica in Kao Ping River in southern Taiwan, c max was 1 for both sexes in this study, suggesting that for A. anguilla and A. japonica, nearly all males tend to silver upon reaching some critical size, while for females the tendencies to become silver eels vary among regions and species. In other words, the conditions for females to become silver eels seem to be more plastic than for males.
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Comparison of Recapture Rates and Estimates of Fishing and Natural Mortality Rates of Japanese Eel Anguilla japonica between Different Origins and Marking Methods in a Mark-Recapture Experiment in the Kaoping River, Southern Taiwan

Comparison of Recapture Rates and Estimates of Fishing and Natural Mortality Rates of Japanese Eel Anguilla japonica between Different Origins and Marking Methods in a Mark-Recapture Experiment in the Kaoping River, Southern Taiwan

Recapture rates of marked wild eels did not significantly differ between individuals marked by microchips and pectoral fin clipping (p = 0.51), but did differ between cultured eels marked by microchips and caudal fin clipping (p = 0.01). For wild and cultured eels marked by microchips, cultured eels had a significantly higher recapture rate than wild eels (p < 0.001), and eel length at release did not affect the recapture rates (p = 0.38). According to the Akaike information criterion corrected for the sample size, estimates of fishing and natural mortality rates differed between pectoral fin clipping and microchips in wild eels. However, neither rate differed between pectoral fin clipping and microchip in cultured eels. Both eel origin and marking method might influence the recapture rate and mortality rate estimates. Different behaviors of cultured eels in the wild and reaction to the marking process are possible reasons. Higher mortality rates of wild eels marked by pectoral fin clipping were unexpected, probably due to a size-related mortality rate, behavioral changes, or mortality associated with pectoral fin clipping. http://zoolstud.sinica.edu.tw/Journals/49.5/616.pdf
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Temporal analysis of population genetic composition in the overexploited Japanese eel Anguilla japonica

Temporal analysis of population genetic composition in the overexploited Japanese eel Anguilla japonica

2932 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 56, NO. 9, SEPTEMBER 2008 Fig. 7. Simulated and measured gain patterns G versus  in decibels in the xy-plane at 2.45 GHz. III. S IMULATION AND M EASUREMENT R ESULTS To prove the concept, a 2.4–2.5 GHz switched-beam antenna for WLAN applications is designed using an FR4 substrate with thickness 0.8 mm. Infineon BAR64-02 V PIN diodes are used in this work, with forward resistance 2.1 Ohms, reverse parallel resistance 3000 , diode capacitance 0.17 pF, and lead induc- tance 0.6 nH. The reflection coefficients were measured by Agi- lent 8364B network analyzer at National Taiwan University and the gain patterns by SATIMO SG64 3-D anechoic chamber at ASUSTeK.
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Use of otolith Sr:Ca ratios to study the riverine migratory behaviors of Japanese eel Anguilla japonica

Use of otolith Sr:Ca ratios to study the riverine migratory behaviors of Japanese eel Anguilla japonica

W. N. Tzeng 1, *, J. C. Shiao 1 , Y. Iizuka 2 1 Department of Zoology, College of Science, National Taiwan University, Taipei 10617, Taiwan, ROC 2 Institute of Earth Science, Academic Sinica, Nankang, Taipei 11529, Taiwan, ROC ABSTRACT: To understand the migratory behavior and habitat use of the Japanese eel Anguilla japonica in the Kaoping River, SW Taiwan, the temporal changes of strontium (Sr) and calcium (Ca) contents in otoliths of the eels in combination with age data were examined by wavelength disper- sive X-ray spectrometry with an electron probe microanalyzer. Ages of the eel were determined by the annulus mark in their otolith. The pattern of the Sr:Ca ratios in the otoliths, before the elver stage, was similar among all specimens. Post-elver stage Sr:Ca ratios indicated that the eels experienced different salinity histories in their growth phase yellow stage. The mean (± SD) Sr:Ca ratios in otoliths beyond elver check of the 6 yellow eels from the freshwater middle reach were 1.8 ± 0.2 × 10 – 3 with a maximum value of 3.73 × 10 – 3 . Sr:Ca ratios of less than 4 × 10 – 3 were used to discriminate the fresh- water from seawater resident eels. Eels from the lower reach of the river were classified into 3 types:
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The silvering of the Japanese eel Anguilla japonica: season, age, size and fat

The silvering of the Japanese eel Anguilla japonica: season, age, size and fat

2 Taiwan Fisheries Research Institute, 199 Hou-Ih Road, Keelung, Taiwan Abstract This study aims to understand the changes in age, total length, body weight, and muscle fat content in the Japanese eel Anguilla japonica during silvering, from yellow to silver eels, and their physiological significances. Eels were collected from the downstream of the Kaoping River of southern Taiwan from November 1998 through November 1999. The female eels were classified into three developmental stages based on external skin coloration and oocyte diameter, namely yellow, pre-silver and silver eel stages. The male eels were classified into yellow and silver eel stages only.
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Population Genetic Structure of the Japanese Eel Anguilla japonica: Evidence for Panmixia in Spatial and Temporal Scales.

Population Genetic Structure of the Japanese Eel Anguilla japonica: Evidence for Panmixia in Spatial and Temporal Scales.

Yu-San Han 1, 2, *, Chia-Ling Hung 2 , Yi-Fen Liao 2 , Wann-Nian Tzeng 1, 2 1 Department of Life Science and 2 Institute of Fisheries Science, College of Life Science, National Taiwan University, Taipei 106, Taiwan ABSTRACT: Since the 1970s, the population of the Japanese eel Anguilla japonica has dramatically declined in East Asia. Consequently, conservation and resource management of this species are urgently required. However, the population genetic structure of this species, in temporal and spatial scales, is still poorly understood. We used 8 polymorphic microsatellite DNA loci to investigate its genetic composition. For cohort analysis, juvenile (glass) eels were collected yearly between 1986 and 2007 from the Danshui River, Taiwan; for arrival wave analysis, glass eels were collected monthly from Fulong Estuary, Taiwan; and for spatial analysis, glass eels were collected from Taiwan, China, Korea and Japan. Genetic differentiation among annual cohorts, arrival waves and spatial samples was very low; a significant difference was observed among annual cohorts and spatial samples, but not among arrival waves. However, specific temporal or spatial scale patterns were not seen in either pairwise genetic comparisons or the phylogenetic tree of all samples. Occasional genetic variations among samples occurred randomly, but a stable lasting genetic structure could not be formed. The isolation by distance (IBD) test showed no evidence of genetic structuring at the spatial scale, and the results of the isolation by time (IBT) test were insignificant among arrival waves. Genetic heterogeneity over a 21 yr time scale showed marginal significance, potentially reflecting a genetic drift in the Japanese eel. Our results suggest the existence of a single panmictic population of Japanese eel in East Asia.
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Serum estradiol-17 beta and testosterone levels during silvering in wild Japanese eel Anguilla japonica.

Serum estradiol-17 beta and testosterone levels during silvering in wild Japanese eel Anguilla japonica.

d Received 19 June 2003; received in revised form 5 September 2003; accepted 6 September 2003 Abstract To understand the changes of serum levels of sex steroids in the wild Japanese eel Anguilla japonica during silvering process, eels collected from the Kaoping River of Taiwan from August 2000 through June 2001 were examined. The maturational stages of female eels before and during silvering were divided into four stages: juvenile, sub-adult, pre- silver and silver stages based on skin coloration and oocyte diameter. Male eels were investigated only in the silver stage. Radioimmunoassays were employed to measure serum levels of estradiol-17b (E ) and testosterone (T). The 2
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Synchronous changes of morphology and gonadal development of silvering Japanese eel Anguilla japonica.

Synchronous changes of morphology and gonadal development of silvering Japanese eel Anguilla japonica.

Abstract The gonadal development of Japanese eel Anguilla japonica during silvering was examined via gonadal histology and morphometric characteristics. Specimens were collected from the Kaoping River of Taiwan between November 1998 and November 2001. Female eels predominated, constituting 87.6% of the sex-determined eels. The degree of gonadal development was assessed by skin coloration, with female eels divided into yellow, pre-silver, and silver phases. Males were divided into yellow and silver phases because of small sample size. Silver phase eels predominated in the winter. Mean ( F S.E.) total length of silver-phase eels was significantly larger in females (642.2 F 10.4) than males (564.8 F 14.6) ( p < 0.001). The mean ( F S.E.) gonadosomatic index (GSI) of females increased significantly from 0.27 F 0.01 for yellow phase, to 0.55 F 0.03 for pre- silver and 1.32 F 0.07 for silver phase. Oocyte development progressed from the chromatin nucleolus stage in the yellow phase eel, through the peri-nucleolus stage in the pre-silver phase eel and to the oil-drop stage in the silver phase eel. Spermatogenesis was active for silver phase males which had a larger mean GSI (0.15 F 0.01) than yellow phase males (0.07 F 0.02), but the gonadal development of males was slower than that of females. GSI, ocular index (OI), and fin-index (FI) were positively correlated, and gut-index (GI) was negatively correlated with total length in both sexes. Residual analysis of the regression of the indices GSI, OI, FI, and GI on TL indicated that the variation of the indices with growth was greatly influenced by the developmental phase of the eel.
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Identification and growth rates comparison of divergent migratory contingents of Japanese eel (Anguilla japonica)

Identification and growth rates comparison of divergent migratory contingents of Japanese eel (Anguilla japonica)

Advantages include such aspects as increased food supply, avoidance of potentially harmful environmental conditions and/or a movement to more favorable ones, the occupation of habitats that have specific or specialized habitat requirement, and the availability of more living space. Costs of migration include mortalities resulting from migration itself, changed environmental conditions that may be intolerable (in diadromous fishes, specifically osmoregulatory stress) (McDowll, 1988). Gross (1987) proposed that diadromy occurs when the gain in fitness from using a second habitat minus the migration costs of moving between habitats exceeds the fitness from staying in only one habitat. When the elvers migrate from offshore seawater to upstream freshwater for living habitat and feeding, they have to overcome the osmotic pressure of salinity gradient environment. If they stayed in estuary their osmoregulatory cost would be lower than those in both freshwater and sea water. Meanwhile, the stability of water volume, living space and food abundance for the eel is generally superior in the estuary than the upper stream of the river in the island countries, such as Japan and Taiwan. The estuary functions as a nursery and feeding ground for the juveniles of many inshore fish and offers commercially important fish (Wallace et al., 1984;
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Salinity preference of silvering Japanese eel Anguilla japonica: evidence from pituitary prolactin mRNA levels and otolith Sr:Ca ratios

Salinity preference of silvering Japanese eel Anguilla japonica: evidence from pituitary prolactin mRNA levels and otolith Sr:Ca ratios

ABSTRACT: The salinity preference of Japanese eel Anguilla japonica during silvering was vali- dated from the viewpoints of physiological ecology by examining the pituitary prolactin (PRL) mRNA expression and the otolith strontium:calcium (Sr:Ca) ratios of the eels of different sexual maturity stages collected in an estuary of Taiwan. The PRL possessed a putative signal peptide of 24 amino acids and a mature peptide of 185 amino acids. RT-PCR and real-time quantitative PCR analyses indi- cated that the transcript levels of PRL mRNA significantly decreased from yellow to silver stage. On the contrary, the Sr:Ca ratios at the otolith edge of silver eels, which recorded their latest experience of salinity history, significantly increased. The increase in otolith Sr:Ca ratios and the decrease in PRL mRNA expression are consistent with the timing of migration from freshwater to seawater during silvering of the eel.
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Salinity preference of silvering Japanese eel Anguilla japonica: evidence from pituitary prolactin mRNA levels and otolith Sr: Ca ratios.

Salinity preference of silvering Japanese eel Anguilla japonica: evidence from pituitary prolactin mRNA levels and otolith Sr: Ca ratios.

ABSTRACT: The salinity preference of Japanese eel Anguilla japonica during silvering was vali- dated from the viewpoints of physiological ecology by examining the pituitary prolactin (PRL) mRNA expression and the otolith strontium:calcium (Sr:Ca) ratios of the eels of different sexual maturity stages collected in an estuary of Taiwan. The PRL possessed a putative signal peptide of 24 amino acids and a mature peptide of 185 amino acids. RT-PCR and real-time quantitative PCR analyses indi- cated that the transcript levels of PRL mRNA significantly decreased from yellow to silver stage. On the contrary, the Sr:Ca ratios at the otolith edge of silver eels, which recorded their latest experience of salinity history, significantly increased. The increase in otolith Sr:Ca ratios and the decrease in PRL mRNA expression are consistent with the timing of migration from freshwater to seawater during silvering of the eel.
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Occurrence of Anguillicola crassus (Nematoda: Dracunculoidea) in Japanese eels Anguilla japonica from a river and an aquaculture unit in SW Taiwan

Occurrence of Anguillicola crassus (Nematoda: Dracunculoidea) in Japanese eels Anguilla japonica from a river and an aquaculture unit in SW Taiwan

3 Institute of Fisheries Sciences, College of Life Science, National Taiwan University, Taipei, Taiwan 106, ROC ABSTRACT: The infection by swimbladder nematodes of the genus Anguillicola (Dracunculoidea: Anguillicolidae) was examined in 2 populations of the Japanese eel Anguilla japonica in SW Taiwan. Wild eels from the Kao-Ping river were compared with cultured eels from an adjacent aquaculture unit. Only the cosmopolitan species Anguillicola crassus was present. Among wild eels, prevalence of infection varied between 21 and 62%, and mean intensity between 1.7 and 2.7 for adult worms.
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Phenotypic plasticity of habitat use by three temperate eel species, Anguilla anguilla, A. japonica and A. rostrata

Phenotypic plasticity of habitat use by three temperate eel species, Anguilla anguilla, A. japonica and A. rostrata

ABSTRACT: Habitat use patterns of 3 species of temperate eels, Anguilla anguilla, A. japonica and A. rostrata, were investigated using otolith strontium:calcium ratio life history transects. Published and unpublished data from 6 sites (Canada, United States, Sweden, France, Taiwan and Japan) sam- pled across the geographical range of each eel species were compiled. Sr:Ca patterns indicated that the 3 species displayed similar patterns of habitat use. In all sites, patterns of habitat use consisted of either residency in one habitat (fresh, brackish, or marine) or movements between habitats. One movement pattern consisted of either a single change or 2 changes of habitat from fresh to brackish waters, or from brackish water to freshwater. Seasonal movements between fresh and brackish waters were observed for all 3 species. When only a single habitat switch event was detected, it occurred between 3 and 5 yr of age. Occurrence of eels with no freshwater experience was demon- strated, but such eels accounted for a smaller proportion of the overall sample than eels with some (even brief) freshwater experience. Contrary to the common convention that these are obligate catadromous species, we must now consider them as facultative catadromous, with far more flexibil- ity in habitat use. The most variable parameter among study sites was the relative proportion, rather than the diversity, of lifetime spent in the various habitat use patterns. Eels found at higher latitudes exhibited a greater probability of remaining in the lower reaches of watersheds in brackish water.
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