Increment Counts Research Articles

Ontogenetic shifts in the distribution and reproductive patterns of Australian anchovy (Engraulis australis) determined by otolith microstructure analysis

Upwelling systems can provide ideal conditions for survival and growth of larval fishes. However, these unstable environments are highly dispersive and mortalities can be high. Anchovies (Engraulis spp.) utilise a range of behavioural strategies to increase egg and larval survival. Ontogenetic shifts in distribution have been proposed for Australian anchovy (Engraulis australis), but no supporting otolith-based age studies have been published to date. The present study used otolith increment counts to age larval, juvenile and adult Australian anchovy, which spawn throughout South Australian gulf and shelf waters. Only fish up to 1 year of age occurred in the northern Spencer Gulf, where eggs and larvae in high densities are retained in a nursery area favourable to anchovies. The southern gulf area was inhabited by 1, 2 and 3 year olds. Older anchovy were found in offshore shelf waters, where upwelling occurs and larval survivorship may be high. We hypothesise that Australian anchovy move offshore with age to utilise the wide range of environments that provide suitable spawning and nursery areas for this species.

Environmental influences on age and size at maturity ofLoligo vulgaris

Age and size-at-maturity of Loligo vulgaris from Portuguese waters were evaluated in order to explain its complex population structure, which is strongly influenced by continuous spawning. Age was obtained by increment counting in statoliths. Maturity ogives by age group indicated that males mature one month earlier (at 277 days) than females (at 298 days). Females mature at a ML50% of 17.6 cm, while males mature at smaller sizes. The later, however, showed a high degree of complexity in the size at maturity with evidence of two size at maturity groups. In both sexes, maturity was ultimately found to be primarily dependent on size rather than age. The effect of hatching season on age-at-maturity, size-at-maturity and reproductive investment was analysed by comparing two groups of squid hatched under distinct environmental conditions, namely the temperature during the first 3 months of life, the cold cohort (CC), hatching between December and March and the warm cohort (WC), hatching between May and September. Significant differences were found between cohorts on age-at-maturity, size-at-maturity and reproductive investment, giving indi- cation of the environmental influences on sexual maturity. CC squid mature ca. 2 months later in life than WC squid and at a significantly larger size. The reproductive investment as measured by GSI was higher in the WC squid. Much of the variability in age and size-at-maturity of females in the population was due to differences between cohorts but this was not the case for males.

Tracking and characterisation of transfused platelets by two colour, whole blood flow cytometry

We describe a flow cytometric technique to study transfused platelets in patients. By selecting donor/recipient pairs discrepant for HLA-A2, transfused platelets were identified using anti-HLA-A2 with a detection limit of <5%, and accuracy within 4.3% of predicted (r2 > 0.96, P < 0.0001). In two of three episodes, transfused platelets were present in greater numbers than predicted from increment counts. Platelets with bound fibrinogen fell from 20.9 +/- 23.6% of donor platelets pretransfusion to 1.7 +/- 0.3% 1 h post-transfusion, whereas P-selectin-positive platelets fell gradually, from 24.1 +/- 6.7 to 7.3 +/- 3.3% at 6 h. This method avoids radio or chemical labelling, and could be used to assess novel platelet preparations post-transfusion.

Preliminary examination of hatching season and growth of Engraulicypris sardella (Pisces: Cyprinidae) larvae and juveniles in Lake Malawi

The hatching period and the growth of Malawian cyprinid Engraulicypris sardella larvae and juveniles collected from two sites along the southwestern shoreline of Lake Malawi were investigated using otolith increment information. The lapillus was used to determine the age in days following previous studies. The hatching months of fish estimated on the basis of lapillus increment counts were from November to July (nine months of a year), demonstrating that this species had an extended spawning season. Based on the age analysis, the fish were separated into two hatching groups: fish that hatched in the rainy season and those that hatched in the dry season. The growth rate of the former (0.70 mm TL per day) was significantly higher than the latter (0.52 mm TL per day). This growth difference was considered to be due to water temperature in the lake.

Age and growth of madeira scorpionfish, Scorpaena maderensis Valenciennes, 1833, in the central Mediterranean

Abstract Age and growth of Scorpaena maderensis were investigated by annual growth increment counts (annuli). Overall, age and growth were estimated from 353 specimens of S. maderensis ranging from 48 to 131 mm as TL. A significative dimorphism in size has been observed in this species, being males larger than females. Both annual deposition of annuli and location of the first annulus have been validated by marginal increment analysis and daily growth increment counts, respectively. The estimated age range was between 0–5 years for females and 0–4 years for males. The estimated values of Von Bertalanffy asymptotic length L ∞ (cm) and k (year-1) were 9.6 and 0.44 for females and 14.8 and 0.23 for males. Thus, females of S. maderensis appeared to live longer and attain their maximum size faster than males. The growth performance index of this species ranged between 1.6 and 1.7, which is at the lower end of the range observed in other Mediterranean scorpaenids.

Impact of environmental factors on survival of larval and juvenile Cape anchovy Engraulis encrasicolus (G.) in the southern Benguela upwelling region, determined from hatchdate distributions: implications for recruitment

March larval and May juvenile Cape anchovy of the unusually strong 1999/2000 year-class were collected off South Africa. Age estimates were obtained from daily increment counts on otoliths using light microscopy for March larvae (14–70 mm standard length, SL, n = 193, 92% success rate), and scanning electron microscopy for May juveniles (52–110 mm SL, n = 80, 22% success rate). Differences between March and May hatchdate distributions were related to the prevailing temperatures. March larval hatchdate distributions showed slight modes in October/November 1999 and January/February 2000, each a month later than May juvenile hatchdate distributions (September/October and November/December). Thus, mortality rates of larvae hatched after mid-December seem to have been higher. Large areas of warm water (19–26°C sea surface temperature) on the Agulhas Bank, mid-November 1999 to March 2000, indicated conditions conducive to spawning and reduced offshore advection of spawning products. A period of strong upwelling, March to May 2000, is likely to have increased availability of planktonic food for older larvae; also causing offshore dispersal of younger larvae and food patches required by these, possibly leading to starvation mortality of younger larvae during strong upwelling. The critical period thus seemed to be later than at first-feeding.

Age, Growth, and Reproductive Biology of Blueline Tilefish along the Southeastern Coast of the United States, 1982–1999

Abstract The blueline tilefish Caulolatilus microps is a long-lived, slow-growing deepwater demersal species patchily distributed along the outer continental shelf of North America from Cape Lookout, North Carolina, to Campeche Bank, Mexico. Commercial landings of blueline tilefish for the southeastern United States peaked in 1983 at 530 metric tons (mt), fell to 31 mt by 1985, and exceeded 100 mt only once between 1986 and 1999. We collected blueline tilefish off North Carolina and South Carolina (approximately 32°N to 33°N) during 1982–1987 and 1996– 1999 with fishery-independent gear, and whole tilefish were sampled from commercial catches during 1996–1998. Specimens were assigned an age from counts of increments on a transverse section of the left sagitta. Sex and reproductive state of all individuals were determined from histological sections of the gonad. The mean size of males was significantly larger than that of females (583 versus 537 mm total length), and the mean lengths of males and females d...

Validating Otolith Annuli for Annual Age Determination of Common Carp

Abstract Common carp Cyprinus carpio are an important pest species in Australia, yet little is known regarding their age and growth there. We examined otolith sections of common carp to validate their utility for age determination. For the 1999 year-class in Hut Lake near Barmah, we confirmed the absolute age at first annulus formation as age 1 by repeated sampling of a discrete young-of-year cohort. We confirmed the annual periodicity of annulus formation for common carp in a mark–recapture experiment when 19 recaptured adult common carp (from an original stocking of 141 fish marked by injection with oxytetracycline (OTC)) showed visible fluorescent marks on their otoliths. Time at liberty for these fish ranged from 6 to 25 months, and their ages on recapture ranged from 3 to 14 years. Increment counts outside the OTC mark agreed completely with time at liberty. We calculated precision estimates on age determinations as the average percent error (APE) and estimated the coefficient of variation (CV = −0.1...

Interpretation of statolith microstructure in reared hatchling paralarvae of the squid Illex argentinus

To identify sub-daily or aperiodic increments of statolith growth in the ommastrephid squid Illex argentinus, we examined statolith microstructure, especially with regard to the natal ring, where counting of daily growth increments should begin, and the widths of subsequent daily increments. Paralarvae obtained by artificial fertilisation were incubated on board at different temperatures ranging from 11.4 to 25.4°C, and were starved throughout the experiments. We observed statolith growth from newly hatched to 10-day-old paralarvae and used alizarine complexone staining to attempt validation of the growth. The maximum statolith radius (MSR) of newly hatched paralarvae was constant at 21.1 μm across the full range of temperatures, with the exception of 25.4°C. Daily growth of MSR was analysed separately in two phases, the pre-yolk-absorption phase (i.e. yolk sac still present) and the post-yolk-absorption phase. During the pre-yolk-absorption phase, the daily growth rate (DGR, y) of the MSR varied from 3 to 7 μm day–1 depending on rearing temperature (x) and was expressed as y = 0.37x – 1.77. We concluded that the natal ring forms at 21 μm MSR. The initial increment width obtained from the DGR of MSR seems applicable for distinguishing daily rings from sub-daily rings, although this application should be limited to hatchling paralarvae in the pre-yolk-absorption phase.

Population biology of northern shortfin squid (Illex illecebrosus) in the Northwest Atlantic Ocean and initial documentation of a spawning area

Abstract Growth, maturity, and age structure of the northern shortfin squid (Illex illecebrosus) population were characterized from samples collected during a stratified, random bottom-trawl survey conducted in May 2000. The survey was conducted on the continental shelf of the east coast of the US and utilized a commercial squid fishing vessel and standardized sampling protocols and gear. Statolith increment counts of 391 individuals, representing the full maturity spectrum from juveniles to mated females (34–250 mm), ranged in age from 69 to 215 d. Substantial variability in the precision of individual age estimates was encountered. The population consisted of a predominant winter cohort of maturing and mature squid (hatched during October–February, with a peak in January) and a spring cohort of juveniles (hatched during February and March, with a peak in March). Recruitment patterns to northern and southern fishing grounds are discussed. The first evidence of a spawning area, located on the continental shelf in the Mid-Atlantic Bight, is presented. Growth in length and weight was best described by a Gompertz model and a power model, respectively. The age range of mated females (115–215 d) indicated a shorter lifespan than expected based on maturity and age information for Newfoundland squid. A latitudinal cline in female size-at-maturity was evident, whereby maturity stages of squid in the southern part of the survey area were more advanced than those in the northern part. Also, females from US waters reach maturity and spawn at smaller sizes and younger ages than females from Newfoundland waters. The results suggest that females from the Mid-Atlantic Bight may exhibit faster rates of growth and maturation, and possibly a shorter lifespan, than their Newfoundland counterparts.

Age and growth of Argyrozona argyrozona (Pisces: Sparidae) in a marine protected area: an evaluation of methods based on whole otoliths, sectioned otoliths and mark-recapture

Argyrozona argyrozona is an important component of the South African commercial linefishery. The purpose of this study was to develop a reliable protocol for estimating age and calculating growth. Methods based on both otoliths and mark-recapture data were investigated. Transverse sagittal sections from the Tsitsikamma National Park (TNP) showed clear opaque and translucent growth increments. Marginal growth zone analysis and mark-recapture of chemically tagged fish (Oxytetracycline) revealed that these were deposited on an annual basis: opaque in summer and translucent in winter. The first translucent check was shown by daily increment counts to mark the completion of the first annulus (i.e. not a juvenile/false check). Within reader (between counts) and between readers average percentage error (APE) was 5.3 and 1.8, respectively, showing that readability of carpenter otoliths is high. Comparison between whole and sectioned otoliths showed that the former significantly underestimated the age of fish older than 10 years ( P<0.01). The maximum age obtained from whole otoliths was 16 years while that obtained from otolith sections was 27 years. Based on realistic L ∞ estimate and the distribution of residuals, the three parameter von Bertalanffy growth function adequately fitted the observed length-at-age data derived from otolith sections. Growth rates did not differ significantly between sexes ( f=2.217, P=0.09). Growth of carpenter in the TNP is described by the following equation: L t=623(1− e −0.08(t−1.96)) A large proportion (68%) of the individual growth rates derived from mark-recapture data were below those predicted by the otolith based von Bertalanffy growth model ( P<0.01). This was attributed to the negative influence of external tags as hydroids, frequently occurring on the tags of recaptured fish, were observed to cause severe lesions and in some cases, extensive fin damage. This brings into question the use of mark-recapture studies to calculate growth of some species.

Growth Rates of Juvenile Winter Flounder under Varying Environmental Conditions

Abstract Fluctuations in juvenile winter flounder growth have been attributed to large-scale fluctuations in temperature, mesoscale fluctuations in salinity, and smaller-scale factors such as prey abundances. This study examines individual growth rates determined through otolith increment counts of free-living juvenile winter flounder during the 2000 settlement period (April 11–July 7) in Navesink River–Sandy Hook Bay estuary in New Jersey. The fish grew at highly variable rates (mean = 1.02, range = 0.25–1.91 mm/d) and did not demonstrate localized differences in growth. In addition, growth rates determined by changes in length of fish from two local areas (river and bay) were compared in the laboratory. Growth in these fish was highly variable, did not differ with location, but did decline significantly during the settlement period in the river (mean = 0.17 mm/d, range = 0.00–0.54 mm/d) and bay (mean = 0.27 mm/d, range = 0.02–0.61 mm/d). The laboratory observations supported field results of no signific...

The effects of an extraordinary El Niño / La Niña event on the size and growth of the squid Loligo opalescens off Southern California

The population structure of the California market squid Loligo opalescens was studied for the Channel Islands region off Southern California between June 1998 and March 2000. During this time Californian waters were exposed to an extraordinary El Nino event that was possibly the most dramatic change in oceanographic conditions that occurred last century. There was then a rapid transition to record cool La Nina conditions. Statolith increments were used to determine age parameters and increment periodicity was validated for the first 54 days of life. Based on statolith increment counts, the oldest males and females were 257 and 225 days respectively and individuals matured as young as 129 and 137 days respectively. No distinct hatching period was detected. There was a general trend of increasing body size throughout the study period. Squid that hatched and grew through the El Nino were strikingly smaller and had slower growth rates compared to squid that grew through the La Nina. This was related to oceanography and associated productivity. There was a positive correlation between squid mantle length and upwelling index and a negative correlation between mantle length and sea temperature. The 'live-fast die-young' life history strategy of squid makes them ideal candidates for following the effects of the dramatic changes in oceanographic conditions off California. We propose that squid can serve as ecosystem recorders and productivity integrators over time and space and are useful organisms to tie oceanography to biology.

Patterns of annual increment formation in otoliths of pomacentrids in the tropical western Atlantic: implications for population age-structure examination

Only recently have managers and scientists begun to collect age and growth informa- tion necessary for effective management of tropical marine ichthyofaunal communities. The majority of studies that have taken place in the tropics have focused on the Pacific Ocean, primarily on Aus- tralia's Great Barrier Reef. In this study, otoliths were collected from 2 pomacentrids at 5 locations in the tropical western Atlantic, and examined for their ability to provide information on age. The col- lection sites for these 2 species, Stegastes planifrons and S. partitus, represent different ranges of annual temperature variation. Otoliths were examined for the presence of clear and interpretable increments as well as timing of increment formation. Annual increment quality varied between species and between regions, with the trend being decreasing clarity with decreasing temperature range. However, interpretable increments were discovered in areas with as little as a 3°C annual water temperature fluctuation. Marginal increment analysis of S. planifrons otoliths revealed that increments formed on the otoliths were deposited once a year during the spring or early summer, suggesting that pomacentrids in the tropical western Atlantic may be aged using the same tech- niques as in other tropical regions and temperate environments. Counts of annual increments revealed that S. planifrons was significantly longer-lived than predicted by other methods. Informa- tion on age and growth collected for reef fishes in studies such as this should provide managers with the life-history information needed to assess population stability and production. This information will be more difficult to obtain in low-latitude regions of the tropical western Atlantic.

Interpretation of otolith microstructure in the early life history stages of two temperate reef wrasses (Labridae)

Notolabrus fucicola and N. tetricus larvae were reared in the laboratory at a constant temperature of 11°C; both species hatched after 4 days. Mortality was high throughout the post-hatching stage, with no N. tetricus surviving beyond 24 hours post-hatching. Notolabrus fucicola late yolk sac larvae showed no clear incremental structure in their sagittal otoliths up to 9 days post-hatch. The radius of the sagittae of these late yolk sac larvae corresponded with the radius of a non-incremental region around the primordium of sagittae taken from post-settlement juveniles of both species captured in the wild. Therefore, it is likely that the first increment is formed at or near yolk sac absorption in these species. Post-settlement juveniles of both species were exposed to oxytetracycline (OTC) and held in aquaria for up to 33 days. Post-OTC increment counts showed that increments were formed daily in the sagittae of both species.

Validation of the ageing of 0+ carp (Cyprinus carpio L.)

Forty carp larvae were reared from eggs spawned in the Torrens River, Adelaide, South Australia, and their otoliths were examined at the time of hatching or at 6, 10, 15 or 20 days after hatching (post-hatch). Using light- and scanning electron microscopy (SEM), otolith increments were counted and compared with known post-hatch ages. Typically, the counts were one day (range 0–2 days) more than the known post-hatch age, but increment formation was daily to at least age 20 days. Thus, age estimates derived from otolith increment counts of wild-caught 0+ carp should be reduced by one day. Comparison with SEM data showed that light microscopy alone offers sufficient resolution for ageing 0+ carp.

Otolith micro-increment formation in herring Clupea harengus larvae in relation to growth rate

Estimating the age of individual fish larvae using otolith micro-increments has become a widely used tool in early life-history ecology. A basic assumption of the method is that the micro- increments are formed on a regular (usually daily) basis. Validation experiments are recommended to test this assumption, since otolith microstructure varies between species and interpretation of the structures can be problematic. Whilst many such experiments have demonstrated daily deposition rates, those examining slow-growing larvae have often not supported this assumption. In response, it has been suggested that increments are in fact being formed on a daily basis, but that they are too narrow to be resolved by optical microscopy. In this study, we raised herring larvae over a range of growth rates by manipulating prey levels. At 16 and 37 d old, the otoliths were marked by immersion of the larvae in a solution of alizarin complexone. The rearing experiment was terminated at 51 d post-hatch, and after suitable preparation, otoliths were examined using both light and scanning electron microscopy. Micro-increment counts based on light microscopy were lower than expected (assuming daily deposition) when larval growth rates were less than 0.42 mm d -1 . These results are in accord with previous reports in the literature. Examination of the otolith region between the alizarin marks by scanning electron microscopy (SEM) produced slightly higher increment counts compared with light microscopy (average + 2), but this was not sufficient to support the assumption of daily deposition of micro-increments between Days 16 and 37 in slow-growing larvae. Rather than leading to the regular deposition of narrow increments, slow growth in laboratory-reared herring larvae often appears to affect otolith structure. This results in fewer than the expected number of increments being deposited, and affects counts made both by light and scanning electron microscopy. Growth rates attained in this laboratory study are typical of those that may be experi- enced by cohorts of herring larvae in the wild, particularly from autumn spawning stocks. The use of otolith microstructure to estimate absolute ages of slow-growing herring larvae may therefore lead to significant underestimates of true age, even if SEM is used.

Tracing populations of Atlantic herring (Clupea harengus L.) in the Irish and Celtic Seas using otolith microstructure

Otolith microstructure of juvenile herring was used to distinguish autumn- and winter-spawned fish collected in the Celtic and Irish Seas in 1999 and 2000. Juveniles showed two distinct patterns of larval otolith growth; widely spaced increments (fast growers) and tightly packed increments (slow growers). Fast- and slow-growing fish exhibited a clear bimodal distribution and the two groups were completely distinct at increments 60–70. Otolith increment counts confirmed that the fast-growing fish originated from the winter spawning season and that slow-growing fish were spawned in autumn. This characteristic pattern of otolith growth was used to determine the relative proportions of autumn- and winter-spawned fish at nursery grounds in the Irish and Celtic Seas. Although the proportions in each area varied between years, nursery grounds in the western Irish Sea were generally dominated by winter-spawned fish whereas autumn-spawned fish were mostly at eastern stations. Given the distribution of spawning adults in the region, the vast majority of winter-spawned fish are likely to originate from the Celtic Sea. Larval growth differences between nursery areas suggest that Celtic Sea herring drift into the Irish Sea during the larval phase. There was significant variation in fish size between nursery areas for both autumn- and winter-spawned fish. Juvenile length was greatest in the Celtic Sea, intermediate in the eastern Irish Sea, and lowest in the western Irish Sea. Therefore, larval dispersal of Celtic Sea herring into the Irish Sea produces components in the surviving juvenile population with characteristic growth patterns. This population segregation could potentially impact on subsequent growth, survival and recruitment. 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd.

Verification of annual increment formation in the white anglerfish, Lophius piscatorius using the illicia and sagitta otoliths

Marginal and edge state analysis was carried out on sagitta otoliths and illicia of white anglerfish taken from ICES Sub-area VI and Division IVa between April 1999 and September 2000. This demonstrated that an annulus comprised a multi-ring opaque zone and a wide translucent zone. Narrow translucent zones within the wide opaque zones were found to be significantly narrower than the translucent zones separating them, suggesting that these were false rings. Opaque material was predominantly deposited during the summer months (July–September) and translucent material during the winter (December–February). Precision of increment readings was tested from repeated increment counts of the calcified structures. This indicated that the most consistent age readings came from sagitta otoliths sectioned through the sagittal plane.

Otolith features and growth of juvenile Opsaridium microcephalum (Pisces: Cyprinidae) from the southwestern shoreline of Lake Malawi

Sanjika, Opsaridium microcephalum, were collected from two sites (Nkhotakota and Chia) along the southwestern shoreline of Lake Malawi. The sagitta of the otolith was arrowhead-shaped with an obvious nucleus. Increments in the sagittae were observable until the bases of the rostra but invisible in the rostra. The asteriscus was oval-shaped with an ambiguous nucleus, leading to difficulty in identifying the first increment. The lapillus was ‘a’-shaped with an obvious nucleus and increments were observable from the nucleus to the margin. The lapillus was therefore considered the most suitable structure for interpreting daily growth increments in this species. The estimated hatching months of fish based on lapilli increment counts were from November to July, suggesting that this species has a long breeding period of at least eight months per year. The growth rate of fish born in the rainy season (0.74 mm TL per day) was higher than those in the dry season (0.56 mm TL per day). This growth difference was considered to be due to the difference in water temperature in the lake.