Chia-Hui Wang

The timing of metamorphosis and growth rates of American and European eel leptocephali:: A mechanism of larval segregative migration

Abstract Elvers of the American eel Anguilla rostrata (Le Sueur) and of the European eel Anguilla anguilla Linnaeus were collected, mostly during the 1995 fishing season, from six estuaries along the Atlantic coast of North America and from five European estuaries. The time of metamorphosis from leptocephalus to glass eel was determined from otolith daily growth increments in which the increment width and strontium:calcium ratios changed drastically. The overall mean age of European elvers was 350 days at metamorphosis ( T m ) from leptocephalus to glass eel and 448 days at estuarine arrival ( T t ), with 98 days between metamorphosis and estuarine arrival ( T t–m ). These ages were all significantly greater than those of American elvers ( T m was 200 days; T t , 255 days and T t–m , 55 days) ( p p

Elemental composition of otoliths as a discriminator of life stage and growth habitat of the European eel, Anguilla anguilla

The hypothesis that elemental composition of otoliths of the eel (Anguilla spp.) changes with life stage and growth habitat was tested in the present study. The minor elements Cl, Na, K, Mg, Ca, Sr and P in otoliths of European eels (Anguilla anguilla) were examined by using an Electron Probe Microanalyser (EPMA) equipped with wavelength dispersive spectrometers (Cameca SX-50). Yellow-stage eels were collected from coastal waters and lakes of Sweden in 1987, 1988, 1991, and 1994, with ages ranging from 5 to 18 years old. Strontium maps and profiles of Sr : Ca ratio, as well as the elver check in otoliths, were used to classify life history stages of the eels as leptocephalus, and freshwater- and seawater-resident yellow eels. Canonical score plots of the otolith elemental compositions of the freshwater-resident yellow eel were completely separated from those of leptocephalus and seawater-resident yellow eel, but the latter two partially overlapped. Strontium is the primary component in determining the discrimination, but the nutrient-related (S and P), and the physiologically controlled elements (Na and Cl), may also play an important role in the discrimination. These results indicate that multiple-elemental information can provide additional insight into the migratory environmental history of diadromous fishes.

Origin of the mass mortality of the flathead grey mullet (Mugil cephalus) in the Tanshui River, northern Taiwan, as indicated by otolith elemental signatures

A massive fish kill of approximately 50 tons of flathead grey mullet (Mugil cephalus) occurred in August 2006 in the Tanshui River, northern Taiwan. To clarify the origin of these mullets, 42 individuals were randomly collected to determine their ages by reading otolith annuli and to measure the trace elements in the otolith. The total lengths of the fish averaged 32.7±4.4 cm, and most of the individuals were 2 years old, indicating that the mullets in the mass fish kill event were in the immature and growth stages. The Sr/Ca and Ba/Ca ratios of a subsample of 14 otoliths showed that half of the fish killed were estuarine residents, and the rest originated from marine and freshwater habitats. The multiple causes involved in this fish kill implied that additional unknown factors influenced the mullet populations on a large scale and induced them to move quickly and gather at this estuary.

Population connectivity of neon damsel, Pomacentrus coelestis, inferred from otolith microchemistry and mtDNA

Understanding dispersal patterns and population connectivity is crucial to the conservation and management of fish assemblages in reef ecosystems. To reveal the population connectivity of reef fishes in the northern West Pacific, we examined the otolith chemistry and the mtDNA control region of Pomacentrus coelestis collected from six localities between Hainan Island (China) and Okinawa (Japan). The results of otolith chemistry analyses on pre-settlement signatures showed that fishes in north-west Taiwan may have a similar origin, whereas those in southern Taiwan might have a separate origin from the South China Sea. Furthermore, the elemental ratios of post-settlement signatures showed clear separation among localities, reflecting their sedentary behaviour after settlement and the influence of local environment. Population genetic analyses revealed that significant genetic differentiation occurred between populations in north-west Taiwan and populations in the South China Sea and the Kuroshio ecosystems. This study demonstrated that otolith chemistry and mtDNA analyses revealed consistent and complementary results of the dispersal and connectivity of P. coelestis populations, and provided evidence supporting that fish populations around Taiwan should be considered as two stocks. Thus, two marine protected area networks should be established for the conservation and management of reef fishes in this area.

Otolith Sr:Ca and Ba:Ca may give inconsistent indications of estuarine habitat use for American eels (Anguilla rostrata)

Temporal patterns in otolith Sr:Ca and Ba:Ca ratio values of American eels Anguilla rostrata from two sites in western Newfoundland gave insight into the use of freshwater and saline habitats. Mean Sr:Ca and Ba:Ca values at the core zone did not differ between sites, indicative of a common oceanic origin. At the otolith edge, representing continental life, both Sr:Ca and Ba:Ca values varied between sites consistent with ambient element:Ca ratio values and salinity, with typically higher Sr:Ca and lower Ba:Ca values in saline than in fresh waters. Most eels (73%) from Muddy Hole, an estuarine site, were evaluated as estuarine residents while most (70%) eels from Castors River, a freshwater site, were evaluated as freshwater residents, with the remaining eels from each site evaluated as inter-habitat migrants. An otolith element:Ca critical value appropriate for distinguishing between fresh and saline water residence is fundamental for estimating the proportion of eel residence in freshwater and their subsequent classification into habitat residence groups. Such classification is moderately robust to the critical value selected. For inter-habitat migrants, moderate otolith Sr:Ca values between the elver check and otolith edge suggestive of estuarine residence may coincide with Ba:Ca values suggestive of freshwater residence. No general critical value for separating fresh and estuarine habitats was found for otolith Ba:Ca. Otolith Ba:Ca temporal patterns may assist the use of Sr:Ca in the evaluation of historical habitat residence and inter-habitat movement but the use of otolith Ba:Ca values should be applied cautiously for American eels and perhaps of other estuarine/freshwater migratory fishes.