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1.
The biology of the redspotted tonguesole Cynoglossus zanzibarensis, a common African cynoglossid inhabiting the Agulhas Bank, South Africa, is described. Growth studies based on sectioned sagittal otoliths revealed that C. zanzibarensis is relatively fast-growing and long-lived, attaining ages >8 years. Growth in length was rapid in immature fish, fish attaining 56% of their maximum size within their first year. By sexual maturity, fish had attained 28% of their maximum age and 68% of their maximum length. Total length-at-age was best described by the Von Bertalanffy growth model with combined-sex growth described as Lt = 354.78(1?e?0.43 (t+1.17)) mm TL. Sexually dimorphic growth patterns were evident, females attaining larger lengths, but at a slower growth rate than males. Despite the similar mean size of adult fish, the trawl-sampled adult population was dominated by females, with a sex ratio of 1 male:2.4 females. Female C. zanzibarensis mature in their second year of life (275 mm TL), after which they spawn small, pelagic eggs throughout the year. Approximations of the rates of total, natural and fishing mortality were estimated to be 0.62, 0.48 and 0.14 year?1 respectively.  相似文献   

2.
Ages of redeye round herring Etrumeus whiteheadi were estimated with associated errors and used to infer life-history information, such as age composition, age-at-maturity and instantaneous mortality rate. Samples were collected in November 2005 during a research survey aimed at estimating the biomass of spawning pelagic fish off South Africa’s west and south coasts. Replicate age estimates obtained from sagittal otoliths were collected with slight bias and relatively high precision. A von Bertalanffy model describing growth of the combined sexes, including juveniles, was Lt = 20.41(1 ? e?0.41(t ? 1.92)). Kimura’s likelihood ratio test revealed no statistically significant differences between growth parameters of males and females. Results suggested that otolith length is a better predictor of age than otolith weight. Maturity estimates for E. whiteheadi were similar to those previously documented.  相似文献   

3.
This paper describes the age structure, growth, diet and aspects of gonadal development in the cobbler, Cnidoglanis macrocephalus (Valenciennes), in the large Swan estuary in south-western Australia between August 1982 and June 1984. Analysis of otolith annuli showed that while the 0+ to 3+ age classes were regularly represented in monthly samples, the 4+ and more particularly the 5+ and 6+ were much less abundant. The weighted means for the back calculated lengths at the end of the first to fourth years of life were 181 mm (≡ 26 g), 314 mm (≡ 156 g), 418 mm (≡ 410 g) and 518 mm (≡ 833 g) respectively. The mean length at the end of the second year of life was similar to the minimum legal size for capture by commercial fishermen (320 mm). The von Bertlanffy growth curve calculated from the back calculated lengths was Lt = 917 [1 − e−0·20(t + 0·11)]. The relative weight of mulluscs, crustaceans and polychaetes in the intestine varied markedly between small and large fish, apparently reflecting differences in the size of these prey. The large mean diameter of mature eggs ( ) was correlated with a low mean absolute fecundity (2078). Trends shown by egg size, gonadosomatic index and time of appearance of spent females indicate that spawning takes place between October and December. The attainment of sexual maturity is both age- and size-dependent. Although sexually maturing and occasionally spent fish were found in the lower estuary, meristic values, commercial catch statistics and other data indicate that the cobbler found in the Swan estuary are part of a population which typically spawns at sea.  相似文献   

4.
Abstract

Growth rates of five species of surf clam were estimated on the Kapiti Coast, southern North Island, New Zealand. Length‐frequencies of sequential population samples were analysed by the computer program, MULTIFAN. Incremental growth of marked individuals was analysed by the computer program, GROTAG. The von Bertalanffy growth parameters k and L 8 estimated by MULTIFAN for Spisula aequilatera (Deshayes in Reeve, 1854) were 0.80 yr?1 and 52.1 mm; for Mactra murchisoni Deshayes in Reeve, 1854 were 0.60 yr?1 and 72.3 mm; and for M. discors Gray, 1837 were 0.35 yr?1 and 60.1 mm. MULTIFAN could not model growth of Paphies donacina (Spengler, 1793) and Dosinia anus (Philippi, 1848) from the population samples. The growth parameters estimated by GROTAG for D. anus were 0.53 yr?1 and 53.0 mm and for M. murchisoni 1.84 yr?1 and 72.4 mm. The growth rates of P. donacina, S. aequilatera, and M. discors were estimated for the size range of their incremental growth data and the estimates are usable for this limited size range only. Growth rates of each species varied with depth in the surf zone in the same way in the North and the South Island. The growth rate of two species was faster in the South Island and asymptotic size of all species was greater in the South Island.  相似文献   

5.
Culture of pearl oysters is rapidly increasing worldwide, including the western Indian Ocean. The oyster Pinctada margaritifera L., which produces the most highly valued black pearls, occurs in East Africa, a nd as been exploited there for the shell for many decades. The growth patterns of P. margaritifera from a natural population in the sheltered back-reef, and fro oysters translocated to a tidal current-swept site, both sites within Gazi Bay, Kenya, are described. The growth rate in the natural population ranged from 31.3mm year?1 (60–65mm size-class) to 7.6mm year?1 (105–110mm size-class). The von Bertalanffy growth coefficient (K), calculated with a fixed L∞ of 127.2mm, was 0.30 for the natural population and 0.38 for the translocated oysters. The mean growth rate during the north-east monsoon season was approximately double that for during the south-east monsoon season. The dailyrate of nacre deposition ranged from 1.3μm to 5.9μm (mean 3.45μm); it declined with the size of oysters and was marginally higher at the high-energy current site. At that rate, it would take approximately two years to produce a marketable cultured half pearl with a 2.5mm layer of nacre. The results of the study are relevant to the understanding of the influence of the environment on growth, and are applicable to the optimisation of growth rate of pearl oysters in the inshore region along the east coast of Africa.  相似文献   

6.
Chronological variation in otolith chemistry can be used to reconstruct migration histories of fish. The use of otolith chemistry to study migration, however, requires knowledge of relationships between the chemical properties of the water and elemental incorporation into otoliths, and how water chemistry varies in space and time. We explored the potential for otolith chemistry of snapper, Pagrus auratus, to provide information on movement history between a large semi-enclosed bay, Port Phillip, and coastal waters in south-eastern Australia. Comparisons of water chemistry across two years demonstrated that ambient barium (Ba) levels in Port Phillip Bay were approximately double those in coastal waters (11 μg L−1 versus 6 μg L−1). Ba levels in otolith margins of wild juvenile snapper were highly positively correlated with ambient levels across 17 sampling locations, and levels in otolith margins of adult snapper collected from Port Phillip Bay were approximately double those of snapper collected in coastal waters. Mean partition coefficients for Ba (DBa) were similar for juvenile (0.43) and adult (0.46) otoliths, suggesting that otolith Ba incorporation relative to ambient levels was similar across life-stages. Low Ba variation across otoliths from adult snapper maintained in tanks for three years indicated that annual temperature and/or growth cycles did not strongly influence otolith Ba variation. We concluded that chronological Ba variation in snapper otoliths would be a reliable proxy for life-history exposure to variable ambient Ba. We used water chemistry data and Ba levels across otoliths of ocean resident snapper to estimate otolith Ba levels indicative of residence in Port Phillip Bay (>10 μg g−1) or coastal waters (<6 μg g−1). Peaks in Ba exceeding 10 μg g−1 were common across otoliths of snapper collected in Port Phillip Bay and a nearby coastal region. The location of strong Ba peaks within otoliths was consistent with residence in Port Phillip Bay during the spring/summer when snapper move into the Bay from coastal waters to spawn. Our results for snapper support the use of otolith Ba as a proxy for ambient levels throughout the life-history, however, confident interpretation of migration history from otolith Ba chronologies will most likely require matching time series of ambient Ba in the water bodies of interest.  相似文献   

7.
The life history of Plesionika edwardsi (Brandt, 1851) around the Canary Islands in the Eastern Central Atlantic was investigated, based on a total of 11 434 shrimps ranging in length between 8 and 40 mm carapace length (CL). The species carries out seasonal migrations; they concentrate in deep water during winter, move shallower in summer and return to deep water again in autumn. Ovigerous females occur throughout the year, but a spawning peak was determined between April and September. The size at maturity for females was approximately 26 mm CL. Shrimp size generally increased with increasing water depth. The growth parameters for males were L ∞ = 25.75 mm CL and K = 0.55 year?1, and L ∞ = 28.28 mm CL and K = 0.66·year?1 for females. The species displays the typical reproductive pattern of tropical pandalids and is dioecious.  相似文献   

8.
Grow-out studies of the scallop Pecten sulcicostatus, endemic to the South African coast, contribute to an investigation of the suitability of this species for commercial culture. Hatchery-reared juvenile scallops were placed in a suspended culture system at 5 m depth in Saldanha Bay on the west coast of South Africa. Scallops of 78 days old and ranging in size from 4.5 mm to 11.0 mm shell height (mean 6.9 mm), as measured on 2 February 2010, were deployed in Saldanha Bay on 9 February 2010. Subsequent growth was assessed monthly through increments in shell height in relation to changing environmental conditions as determined through continuous measures of temperature and chlorophyll a. Upon termination of the experiment on 15 February 2011, scallops ranged in size from 42.1 mm to 48.7 mm (mean 45.1 mm), representing an increment in shell height of 38.2 mm over one year. The mean growth rate of 0.10 mm day?1 (mean specific growth rate of 0.0046 day?1) compares favourably with other commercially cultured species and exceeds previous estimates of growth of naturally occurring populations of P. sulcicostatus. Scallop growth was poorly correlated with either temperature or chlorophyll a concentration, but scallop mortality was closely aligned to the temperature regime of Saldanha Bay, exhibiting high mortalities during mid-summer.  相似文献   

9.
The West Coast dusky kob Argyrosomus coronus is an understudied yet important fishery species in Angola. During a five-year study (2005–2009), the species was recorded in all fishery sectors, but was most important in the inshore recreational fishery in southern Angola (Cunene Estuary to Namibe). Early juveniles (<300 mm total length, TL) were captured in the offshore artisanal fishery at Praia Pinda, whereas juveniles (300–600 mm TL), subadults (600–870 mm TL) and adults (>870 mm TL) were captured in all fisheries as far north as Namibe, and shoals of large adult fish (>1 000 mm TL) were occasionally captured in the offshore purse-seine commercial fishery between the Cunene Estuary and Lucira. Because some Argyrosomus species are morphologically cryptic, a DNA barcoding method was used to confirm the taxonomic status of the biological samples used in this study. The male:female sex ratio of examined samples was 1:1.4 (n = 225). The length-at-50% maturity was 823 mm and 904 mm TL for males and females respectively. Age-at-50% maturity was 4.4 and 4.3 years for males and females respectively. The periodicity of otolith ring formation was confirmed to be one year using a marginal zone and a chemical marking analysis. Growth (in mm TL) was best described by: Lt = 1 826(1—e?0.12(t + 1.60)). Argyrosomus coronus fed predominantly on fish, mainly Sardinella aurita (62% frequency of occurrence). Early juveniles appeared to frequent the offshore zone (50–100 m depth), moving into the inshore region at approximately 300 mm TL. Juveniles and subadults were resident (57% recaptured at the same site) and were particularly abundant around the mouth of the Cunene Estuary as well as in central and northern Namibia. Adults undertake migrations that correspond with the movement of the Angola–Benguela frontal zone, moving north as far as Gabon in winter and returning to southern Angola in spring, when spawning appeared to take place offshore. There are currently no catch restrictions on A. coronus in Angolan waters. However, declining catches and increasing fishing effort suggest that some management intervention is required, commencing with a proposed closure of the Cunene Estuary mouth region to fishing.  相似文献   

10.
The deep-water trawl fishery along the KwaZulu-Natal coast of South Africa targets several crustacean species, with the knife (or pink) prawn Haliporoides triarthrus contributing most of the catch. Logbook data of fishing effort and catch between 1988 and 2010 were used to assess the distribution and abundance of H. triarthrus on fishing grounds. Generalised linear models were used to quantify the effects of year, month and depth on catch rates. Standardised trends indicated a general decline in abundance between 1990 and 1998, followed by an increase between 2001 and 2008. Catch rates peaked in March, and they were highest between 200 and 499 m depth. Biological samples collected during commercial fishing were used to assess size and sex composition, growth rates and reproductive activity of H. triarthrus. Females became larger than males and mean carapace length (CL) varied by month. The youngest female cohort appeared in November (modal CL of 25 mm), and dissipated after two years (39 mm). Sex ratios were equal for all data combined, but fluctuated by month and CL. Few reproductively active females were recorded. Length-based methods and the standard von Bertalanffy growth function were used to estimate growth parameters (L∞ and K) of females (40.6 mm CL and 1.06 y–1) and males (35.2 mm and 1.27 y–1) respectively. Our findings were compared with information on H. triarthrus from Mozambican waters.  相似文献   

11.
Magellania venosa, the largest recent brachiopod, occurs in clusters and banks in population densities of up to 416 ind m?2 in Comau Fjord, Northern Chilean fjord region. Below 15 m, it co‐occurs with the mytilid Aulacomya atra and it dominates the benthic community below 20 m. To determine the question of why M. venosa is a successful competitor, the in situ growth rate of the brachiopod was studied and its overall growth performance compared with that of other brachiopods and mussels. The growth in length was measured between February 2011 and March 2012 after mechanical tagging and calcein staining. Settlement and juvenile growth were determined from recruitment tiles installed in 2009 and from subsequent photocensus. Growth of M. venosa is best described by the general von Bertalanffy growth function, with a maximum shell length (L∞) of 71.53 mm and a Brody growth constant (K) of 0.336 year?1. The overall growth performance (OGP index = 5.1) is the highest recorded for a rynchonelliform brachiopod and in the range of that for Mytilus chilensis (4.8–5.27), but lower than that of A. atra (5.74). The maximal individual production (PInd) is 0.29 g AFDM ind?1 year?1 at 42 mm shell length and annual production ranges from 1.28 to 89.25 g AFDM year?1 m?2 (1–57% of that of A. atra in the respective fjords). The high shell growth rate of M. venosa, together with its high overall growth performance may explain the locally high population density of this brachiopod in Comau Fjord. However, the production per biomass of the population (‐ratio) is low (0.535) and M. venosa may play only a minor role in the food chain. Settling dynamics indicates that M. venosa is a pioneer species with low juvenile mortality. The coexistence of the brachiopod and bivalve suggests that brachiopod survival is affected by neither the presence of potential brachiopod predators nor that of space competitors (i.e. mytilids).  相似文献   

12.
Japanese seaperch Lateolabrax japonicus migrate from Ariake Bay to the estuarine turbidity maximum (ETM) zone of the Chikugo River and inhabit there through the post-migration period (15–20 mm in standard length). The feeding, growth and mortality during the post-migration period of Japanese seaperch were analyzed in relation to seasonal changes in temperature and prey concentration. Larvae and juveniles were collected from ten sampling stations at 4–7 day intervals from 24 February to 24 April 2005 in the Chikugo estuary. Based on the otolith microstructure analysis the sampled fish were divided into nine cohorts, each cohort covering a 5 day hatch date period (22 December 2004 to 4 February 2005). The growth coefficient (G, day−1) was higher and the mortality coefficient (M, day−1) was lower in the later cohorts. The ratio of G to M as an index of stage-specific survival during the post-migration period significantly increased as the season progressed and exceeded 1.0 in the last cohort examined. Variability in abundance of the major prey organism, Sinocalanus sinensis, had a significant effect on the Japanese seaperch ingestion rate. Increase in temperature and spring bloom of S. sinensis is concluded to provide the later cohorts with a higher survival probability through increasing ingestion and growth rates during their post-migration period in spring 2005.  相似文献   

13.
Caging and a mark–recapture design were used to estimate the growth rate of the brittle, infaunal bivalve Soletellina alba in the Hopkins River estuary. The growth of both caged and uncaged individuals was monitored at three sites near the mouth of the estuary over 180 days. Growth rates did not differ for caged and uncaged bivalves, or for bivalves subject to different amounts of handling, or between sites. Growth did differ between consecutive time intervals, which was attributable to negligible growth occurring during the colder months of autumn/winter. Comparisons of the condition (as indicated by total mass for length3) of S. alba were inconsistent between sites for caged and uncaged bivalves and for those subject to different amounts of handling. Soletellina alba is a rapidly growing bivalve with mean growth rates for the three time intervals being 0.04±0.002 mm day−1 in summer, 0.02±0.001 mm day−1 in autumn and 0.03±0.001 mm day−1 from summer to winter. Using existing literature, it was shown that a significant relationship exists between maximum shell length and onset of sexual maturity in bivalve molluscs. This relationship predicts that S. alba should reach the onset of sexual maturity at 15.8 mm length. Therefore, it appears that it may be possible for juvenile S. alba (<1 mm) to grow, reach sexual maturity and reproduce in between annual mass-mortality events caused by winter flooding.  相似文献   

14.
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   

15.
Habitat use by the European eel Anguilla anguilla in Irish waters   总被引：2，自引：0，他引：2  
The apparent use of marine and freshwater habitats by European eel Anguilla anguilla was examined by analyzing the strontium (Sr) and calcium (Ca) concentrations in otoliths of the eels collected from Irish coastal and fresh waters. The age and growth of eels were also examined using their otolith annuli. The sizes and ages of the female eels were greater than those of the males. The somatic growth rates ranged from 15 to 62 mm/year, which is typical for Ireland and other European countries. Analyses of Sr:Ca ratios along a life history transect in each otolith showed peaks (maximum more than 25 × 10−3) between the core and elver mark corresponding to the period of their leptocephalus and early glass eel stages in the ocean. Outside the elver mark, the Sr:Ca ratios indicated that eels had remained in different habitats that included freshwater (average Sr:Ca ratios, 0.98–1.78 × 10−3) and areas with relatively high salinities (average Sr:Ca ratios, 6.73–8.89 × 10−3). Some individuals showed clear evidence of shifts from sea to fresh waters. These findings suggest that Irish eels have the same behavioral plasticity regarding whether or not to enter freshwater or remain in marine environments as has been recently documented in this species and several other temperate anguillid species. However, patterns of habitat use in Irish waters were somewhat different than those previously reported for other habitats.  相似文献   

16.
Status assessment of exploited fish populations is a general requirement to ensure sustainability of fisheries in both global and local contexts. The blue jack mackerel Trachurus picturatus (Bowdich, 1825) remains unassessed in a data-limited fishery in the eastern central Atlantic, within the waters of the Canary Islands (Spain) off the coast of northwest Africa. This is the most southwestern targeted fishery in the species’ distributional range. To obtain basic life-history information, a total of 2 472 specimens were analysed, ranging from 10.2 to 31.9 cm total length, from samples collected monthly between March 2005 and March 2006. Length–weight relationships (a = 0.0023; b = 3.418; R 2 = 0.97) showed no significant difference between sexes. Deposition periodicity and coherence of the ageing criteria were verified by analysis of the monthly evolution of the otolith edge. Ages were estimated by counting annual growth rings on whole otoliths, with these fish ranging from age 0 to 6 years. The von Bertalanffy growth model, which was used to estimate growth parameters from both direct readings and back-calculated length-at-age data, gave good statistical fits. The parameters from the direct readings were: L∞ = 34.9 cm; k = 0.214 y–1; t 0 = ?2.545 y (R 2 = 0.84), and the natural mortality rates estimated from empirical methods varied between 0.20 and 0.55 y–1.  相似文献   

17.
Growth rates of dusky kob Argyrosomus japonicus calculated from mark-recapture and otolith-reading methods were compared. Mark-recapture data showed that A. japonicus are resident in an area between the Breede River Estuary and Cape Agulhas on the south-east coast of South Africa. Maximum recapture length was 1 150mm. A von Bertalanffy growth curve, fitted to length-at-age data derived from otolith sections of 168 specimens (1–42 years) from the Breede Estuary and adjacent marine environment, was differentiated to provide instantaneous length-based growth rates. Comparison of mark-recapture and otolith-based growth rates revealed that external dart tags suppress growth of A. japonicus <750mm, but do not affect the growth of larger fish.  相似文献   

18.
Fishery-dependent and fishery-independent distribution analyses together reveal four discrete areas of white stumpnose Rhabdosargus globiceps abundance between Port Nolloth and the Kei River off the Cape Province of South Africa: the Western Cape (Saldanha Bay), the South-Western Cape, the Southern Cape and the South-Eastern Cape. On the basis of migratory patterns determined from tagging and catch data, and on differences in growth rate and size-at-maturity, it is concluded that these areas of abundance represent four separate stocks. Each stock apparently disperses offshore in winter (to c. 130 m depth) and concentrates inshore (<60 m depth) in response to ocean ographic patterns during summer. Growth rate and size-at-50% maturity (L 50) increased clinally from the South-Eastern Cape through to the South-Western Cape, and in all three regions males matured at larger size than females. Sizes at maturity for male and female R. globiceps were respectively 18.6 and 15.3 cm (fork length, FL) in the South-Eastern Cape, 22.1 and 18.1 cm in the Southern Cape and 24.3 and 23.6 cm in the South-Western Cape. The fitted Von Bertalanffy growth equations for the three regions were: Lt = 349 (1?e?0.114(t+3.60)) mm for the South-Eastern Cape; Lt = 337 (1?e?0.207(t+1.05)) mm for the Southern Cape; and Lt = 379 (1?e?0.290(t+0.16)) mm for the South-Western Cape. Maximum ages recorded in each region were 21 years for the South-Western Cape, 20 years for the Southern Cape and 10 years for the South-Eastern Cape. Lack of older fish in the South-Eastern Cape sample, attributed to inadequate sample size, has probably resulted in overestimates of both L ∞ and K in this region. Spawning is from August to February, with a peak in spring (September–November). Early juvenile R. globiceps recruit into estuarine and surf-zone marine nursery areas at around 2–5cm (±3 months), but move progressively farther offshore with growth; those trawled deeper than 50 m east of Cape Agulhas were predominantly adults (20–35 cm FL). Because of cooler water temperatures west of Cape Agulhas, adults there are found from the surf zone to depths of only 20 m in summer.  相似文献   

19.
This study using tuna otoliths as working standards established a high lateral resolution and precision analysis to measure δ18Ootolith by secondary ion mass spectrometry. This analytical approach of the ion probe was applied to deep-sea fishes to reconstruct the likely depths inhabited by the fishes at different life history stages based on the measured δ18Ootolith values as a proxy of water temperature. Dramatic increases up to 5–6‰ in δ18Ootolith, representing a temperature decrease of approximately 20 °C, were detected in a blind cusk eel (Barathronus maculatus) otolith and in the otoliths of Synaphobranchus kaupii during leptocephalus metamorphosis to glass eel, inferred from the drop of otolith Sr/Ca ratios and increase of otolith growth increment width. δ18Ootolith profiles clearly divided the fish's life history into a planktonic stage in the mixed layer of the ocean and a benthic stage on the deep-sea ocean bottom. The habitat shift signal was recorded within a 150 µm width of otolith growth zone, which was too narrow to be clearly detected by mechanical drilling and conventional isotopic ratio mass spectrometry. However, variations down to −7‰ were found in δ18Ootolith profiles as the result of Cs2+ beam sputter in the core and larval portions of the otoliths. Carbon mapping by electron probe microanalyzer and staining by toluidine blue suggested abundant proteins existed in the areas with anomaly negative δ18Ootolith values, which cannot be interpreted as a habitat change but due to the isotopic fractionation by O emission from the proteins. These results implied that careful design and understanding of the chemical composition of the analytical areas or tracks on the heterogeneous otolith was essential for highly accurate and precise analysis.  相似文献   

20.
Black oreo (Allocyttus niger) and smooth oreo (Pseudocyttus maculatus) are commercially exploited deepwater fishes in New Zealand. They are considered to be long-lived with unvalidated maximum otolith growth zone counts of 153 years and 86 years, respectively. Bomb radiocarbon dating results supported the otolith age estimates for A. niger, but those for P. maculatus provided only partial support. Oxygen isotope (δ18O) results for A. niger otoliths suggested that juveniles were in near-surface waters and adults in depths of 700–1300 m. In contrast, P. maculatus otoliths suggested a variable depth history (500 to at least 1500 m) throughout life. Carbon isotope (δ13C) results showed a steady enrichment from core values to c. 20 years for both species, owing to changes in diet and metabolic rate from the juvenile to the adult fish, associated with a depth increase. Von Bertalanffy growth parameters are provided for both species.  相似文献   

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