Daily Increment Counts Research Articles

Life-history traits of the Magellan plunderfish Harpagifer bispinis (Forster, 1801) in the Beagle Channel (Tierra del Fuego, South America)

The Magellan plunderfish Harpagifer bispinis is a small and benthic sub-Antarctic notothenioid commonly found in shallow waters of the Beagle Channel, whose biology is poorly known. Based on a seasonal sampling conducted throughout a year, we provide original data on some biological parameters, such as reproductive traits and age structure. The sampled population of Magellan plunderfish was sex balanced, showing no dimorphism in fish size and isometric body growth. Macroscopic and histological analyses of gonads enabled us to infer that this species is a total spawner, with a single annual spawning season during the austral winter. Total fecundity was considerably low (mean of 574 eggs per female), even compared with other harpagiferids. Based on daily increment counts made in juveniles, larval hatching took place between late September and early October, likely enhancing their survival during the warmer months. The Von Bertalanffy growth parameters, estimated from the length-at-age data pairs for the whole population, were L∞ = 80.7 (± 0.82), K = 0.25 (± 0.01), and t0 = − 2.31. The estimated growth performance (3.21) and life span (7 years) of H. bispinis were both comparable to those reported for their most closely related species, H. antarcticus. The life-history traits of Magellan plunderfish are discussed from an ecological and evolutionary perspective, through a comparative approach with their Antarctic counterparts.

Age verification of north Atlantic sprat

Sprat is a pelagic species of increasing commercial interest in European waters, yet little is known about its biology or the drivers of its population fluctuations. As a result, the species is currently without an analytical assessment or forecast across much of the North East Atlantic. The objectives of this study were to: verify otolith-based age estimation of sprat; assess the precision, bias and reproducibility of these age estimates; and, determine the age structure of sprat within one North East Atlantic management unit (Celtic Seas ecoregion). Samples were collected over three years (2011, 2013 & 2014) from both commercial catches and scientific surveys. Counts of daily increments in otoliths were used to establish when the first annulus was formed. The seasonal development of annuli was validated using marginal increment analysis. Age estimates were found to be both accurate and reproducible with no intra-reader bias and limited inter-reader bias (average coefficient of variation 2.7%). The age estimates indicate that the stock is comprised primarily of age 0, 1 and 2 year olds. This study has provided previously unavailable information on the biology and age structure of this species which is required to improve assessment and sustainable management of the species.

Growth and mortality of larval Myctophum affine (Myctophidae, Teleostei).

The growth and mortality rates of Myctophum affine larvae were analysed based on samples collected during the austral summer and winter of 2002 from south-eastern Brazilian waters. The larvae ranged in size from 2·75 to 14·00 mm standard length (L(S)). Daily increment counts from 82 sagittal otoliths showed that the age of M. affine ranged from 2 to 28 days. Three models were applied to estimate the growth rate: linear regression, exponential model and Laird-Gompertz model. The exponential model best fitted the data, and L(0) values from exponential and Laird-Gompertz models were close to the smallest larva reported in the literature (c. 2·5 mm L(S)). The average growth rate (0·33 mm day(-1)) was intermediate among lanternfishes. The mortality rate (12%) during the larval period was below average compared with other marine fish species but similar to some epipelagic fishes that occur in the area.

Comparison of daily- and annual- increment counts in otoliths of bigeye (Thunnus obesus), yellowfin (T. albacares), southern bluefin (T. maccoyii) and albacore (T. alalunga) tuna

Abstract Williams, A. J., Leroy, B. M., Nicol, S. J., Farley, J. H., Clear, N. P., Krusic-Golub, K., and Davies, C. R. Comparison of daily- and annual-increment counts in otoliths of bigeye (Thunnus obesus), yellowfin (T. albacares), southern bluefin (T. maccoyii) and albacore (T. alalunga) tuna. – ICES Journal of Marine Science, 70: . Information on the age of individuals is often required for models assessing the status of stocks. Techniques used to estimate age of tuna have varied across species and agencies, precluding meta-analyses of age and growth. We compared age estimates obtained from commonly used ageing techniques for four important tuna species: bigeye tuna, yellowfin tuna, southern bluefin tuna, and albacore tuna. Estimates of age from counts of annual increments in transverse-sectioned otoliths were generally higher than those from counts of daily increments in transverse and longitudinal sections for all species, particularly for fish older than two years. However, annual counts produced younger estimates, on average, relative to daily counts for bigeye and yellowfin tuna younger than one year. Estimates derived from daily increments in longitudinal and transverse sections were generally similar, although longitudinal sections produced relatively older age estimates for individuals older than two years. A linear or non-linear increase in the magnitude of differences between ageing methods was the best-approximating model in all cases except when comparing daily-increment counts between transverse and longitudinal otolith sections for southern bluefin tuna. These observations are consistent with a narrowing of daily increments with increasing age, resulting in underestimates of age relative to those derived from annual increments. We conclude that (i) daily increments are unsuitable for ageing individuals over two years, especially for southern bluefin and albacore, (ii) longitudinal sections are more precise and produce older age estimates than transverse sections for daily-age estimates, (iii) there are considerable differences in these trends between species, likely dependent on longevity, and (iv) parameter estimates and/or conclusions based on meta-analyses using age data derived from different ageing methods are likely confounded with methodological biases. This result demonstrates that greater effort is required to provide consistent, validated methods for routine age determination to support the assessment and management of these valuable populations.

Age estimation and validation for South Pacific albacore Thunnus alalunga

Validated estimates of age are presented for albacore Thunnus alalunga, sampled from a large part of the south-western Pacific Ocean, based on counts of annual opaque growth zones from transverse sections of otoliths. Counts of daily increments were used to estimate the location of the first opaque growth zone, which was completed before the first assumed birthday. The periodicity of opaque zones was estimated by marginal increment analysis and an oxytetracycline mark-recapture experiment. Both validation methods indicated that opaque zones formed over the austral summer and were completed by autumn to winter (April to August). The direct comparison of age estimates obtained from otoliths and dorsal-fin spines of the same fish indicated bias, which was assumed to be due to poor increment clarity and resorption of early growth zones in spines, resulting in imprecise age estimates. As such, age estimates from otoliths are considered to be more accurate than those from spines for T. alalunga. This is consistent with results for a growing number of tropical and temperate tuna Thunnini species. It is recommend that validated counts of annual growth zones from sectioned otoliths is used as the preferred method for estimating age-based parameters for assessment and management advice for these important stocks.

Within-channel flows promote spawning and recruitment of golden perch, Macquaria ambigua ambigua – implications for environmental flow management in the River Murray, Australia

Restoring fish populations in regulated rivers requires an understanding of relationships between hydrology and population dynamics. In the present study, spawning and recruitment of golden perch, Macquaria ambigua ambigua, were investigated in relation to flow in the regulated lower River Murray. All life stages were sampled in three successive years, with peak flows of 8500 (2004–05), 15 000 (2005–06) and 7000 ML day–1 (2006–07). Larvae occurred only in November/December 2005, and young-of-year fish only in early 2006. Counts of daily increments in otolith microstructure indicated spawning in late October/early November 2005. Back-calculated birth years for adults, derived from otoliths and compared with the hydrograph for the preceding 25 years, revealed the dominance of three year classes spawned in association with increased discharge in 2000, 1998 and 1996. In 2007, an additional year class of 1-year-old fish appeared, following spawning in 2005. In each case, strong recruitment followed spring–summer spawning, when peak flows were >14 000 ML day–1 and water temperatures would have exceeded 20°C. Restoration of within-channel flows of 15–25 000 ML day–1 from late spring through summer would promote spawning and recruitment and improve the resilience of golden perch populations in the lower Murray.

Otolith microstructure of Japanese sea bass larvae and juveniles: interpretation and utility for ageing

Summary This paper interprets and discusses the usefulness of otolith microstructure for ageing Japanese sea bass (Lateolabrax japonicus) larvae and juveniles. Samples were collected from the Tango Sea along the Japan Sea coast, January–March 2007. Known-age (0-day and 10-day-old) larvae were obtained from the Ibaragi Prefectural Hatchery, Japan. Sagittal and lapillar otolith were processed and read using an otolith reading system. Clearly discernible hatch- and first-feeding marks were evident on sagitta, and development of accessory premordia (AP) appeared to be associated with larva-juvenile transition; however, no other marks indicating metamorphosis or settlement were evident. In lapillus, no discernible check mark was found. Known-age larvae showed that deposition of the first daily increment (DI) corresponded to first-feeding, which occurred at day-4 post-hatch. However, mean increment counts were significantly lower in lapillus than in sagitta, caused by poorly expressed increments around the centrum as well as relatively unclear centrum of the lapillus. The authors suggest that the use of lapillus can cause significant underestimation of age. Therefore, the sagitta is recommended for age and growth estimations of larvae and juveniles, although the presence of numerous subdaily increments warrants careful preparation and interpretation of the microstructure. A test for asymmetry showed the right and left otoliths to be quite symmetrical and their DI counts not significantly different, suggesting that either otolith can be used for studying age and growth of Japanese sea bass larvae and juveniles.

Comparison of otolith growth and morphology with somatic growth and age in young‐of‐the‐year bluefin tuna

Otolith morphological characteristics were studied using image analysis techniques and the relationships between otolith growth and somatic growth and age, as estimated from counting daily otolith increments, were examined in young‐of‐the‐year (YOY) bluefin tuna Thunnus thynnus ranging in fork length (LF) from 8·5 to 55·5 cm. Whole otolith length, width, area and perimeter, and three shape indexes, circularity, E value and rectangularity, were extracted for each pair of sagittae. Since no statistical significant differences between left and right otolith morphometrics were found, only one otolith from each fish was used for correlations. Statistically significant relationships were observed between otoliths measurements and fish somatic growth when a linear regression was applied after logarithmic transformation of all variables tested. Among the variables, otolith length was the one that showed the highest correlation with LF, followed by otolith area and perimeter, whereas otolith rectangularity exhibited the lowest correlation. Statistically significant relationships were also observed between the otolith variables tested and the age of the fish, which ranged from 20 to 129 days. The ages estimated using otolith mass were very close to those assessed using daily increment counts (bias ranged from 1 to 24 days). Therefore, otolith mass could represent a valuable criterion for age estimation in YOY bluefin tuna that is objective, economic and easy to perform compared to daily increment counting method.

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 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.

Age validation in horse mackerel (Trachurus trachurus) otoliths

Two methods were used to validate age determination of horse mackerel otoliths. In the first, whole otoliths were examined with a light microscope. Age was determined by identifying and counting annuli. Marginal increment widths were also measured and served to estimate ages, which ranged from 0.6–4.3 years. In the second method, otoliths were examined with a scanning electron microscope and fish ages were determined by daily increment counts. Sixty-four otolith specimens from the Southeast Atlantic and 24 from the Northeast Atlantic were aged by counting the daily growth increments. The number of daily increments was highly variable within each growth zone. Ages exceeding 365 days in the first annual growth zone indicated that the first annulus was not always deposited in some fish. The variable daily increment counts in the first year's growth zones may be related to the very protracted spawning season of horse mackerel. Examination of subsequent growth zones indicated that false rings and annuli are often of a similar visual appearance and that true annuli can only be identified if concurrent measurements of growth zone widths are available. Estimated ages agreed with ages derived by counting daily increments, thus validating the ages of horse mackerel up to four years.

Age validation of nagroor, Pomadasys kaakan (Cuvier, 1830) (Family: Haemulidae) in Kuwaiti waters

Daily increments in the sagittal otoliths of young nagroor, Pomadasys kaakan (Family: Haemulidae) were investigated using alizarin complexone (ALZ). Counts between annual marks and marginal increment analysis of adult wild fish were used to validate the annuli and time of their formation. Young nagroor deposited daily otolith increments under laboratory conditions at 17–20°C. Compared to cultured fish, the daily increments of wild fish were relatively easy to discern and count. The annulus was composed of striated aggregations all round the otolith’s thin transverse sections. The average daily increment counts between the annuli were 266, 326 and 276 for the first 3 years, respectively; however, this method is unsuitable for validation of the second and later annuli due to a lower increment number than expected of 365 increments. The recent annuli formed on the otolith edge were observed in most of the March–May otolith samples. All data of marginal increment of otoliths were pooled for the years 1992–1995, which indicated that the peak formation of annuli was during March–June. The data also indicate that juvenile and immature fish (14–22 cm total length) form the first annulus before the onset of ovarian maturation.

Influence of temperature on the microstructure of statoliths of the thumbstall squid Lolliguncula brevis

A laboratory study investigating the influence of temperature on the microstructure of statoliths of Lolliguncula brevis is described. Groups of squid were subjected to various temperature regimes for periods in excess of 30 d. Statoliths extracted from 20 squid were examined using a confocal microscope in laser scanning mode. The parts of the statoliths deposited during the course of the experiments were identified using either putative daily increment counts or from checks produced in response to capture and handling. These checks appear to consist of a series of prominent increments rather than reflecting a period of interrupted statolith growth. Increments deposited during the experiment generally displayed reduced contrast and clarity in comparison to the “wild” parts of the statolith, presumably in response to the constant conditions imposed in the laboratory. Average statolith growth rates observed over the course of the experiment showed a strong positive relationship to ambient temperature. A significant sex effect was apparent, with statoliths of female squid generally growing faster than those of males. Observed statolith growth rates at 15 °C were generally below 1 μm d−1, suggesting that the widths of daily increments produced under these conditions may approach the resolution limits of a light microscope. The implications for studies using increment numbers to estimate age are discussed.

Use of Daily Growth Increments on Otoliths to Assess Stockings of Hatchery-Reared Kokanees

Abstract Hatchery-reared kokanees Oncorhynchus nerka may form discernible “stress” checks on their otoliths when they are stocked into lakes and rivers. We established the reliability of this mark for distinguishing age-0 hatchery fish from wild fish in Lake Pend Oreille, Idaho. Hatchery fish marked with dietary oxytetracycline (OTC) were recaptured 1–3 months after they had been stocked in the lake. All specimens with OTC marks on their bony structures also had a stress check. We also validated daily otolith increments for age-0 kokanees by comparing increment counts external to the stress check with known days between release and recapture of hatchery fish. Then, counts of daily increments allowed us to correctly identify fish from several co-occurring release groups that had been stocked at different times in the same season. Such discrimination will enhance evaluations of alternative stocking strategies. Because some otolith growth increment counts varied slightly from days at large, and because fish ...

Otolith microstructure of three larval gadids in the Gulf of Maine, with inferences on early life history

A detailed analysis of the assumptions underlying the application of otolith microstructure was undertaken for three gadid species from the Gulf of Maine. Daily increment counts provided a precise and accurate index of age in cod (Gadus morhua) and appeared to do so in haddock (Melanogrammus aeglefinus). However, the widths of increments formed shortly after hatch in cod and haddock otoliths approached the resolution limit of light microscopy, resulting in an underestimation of age by 2–3 d for all fish. Daily increments were also formed in the otoliths of pollock (Pollachius virens) but, perhaps because of more severe resolution problems, the microstructure associated with the early larval stage was unclear. Factors that could confound growth back-calculation efforts included differing otolith length – larval length relationships among samples and an inverse correlation between hatch check diameter and temperature. Estimates of hatch date and growth rate developed in this study were not affected by slight deviations from the underlying assumptions, but might be affected by such deviations under different environmental conditions. Larval pollock growth was comparable to that of cod and haddock, despite a later hatch date. Pollock hatched primarily in November, while peak dates for cod and haddock hatching occurred in March–April and May, respectively. Cod on Georges Bank hatched significantly earlier than those on Browns Bank, although the latter included a less abundant component that hatched in the fall.

Methods of Estimating Larval Fish Mortality from Daily Increments in Otoliths

Two methods are presented for estimating instantaneous daily mortality rates of larval fishes with otolith-increment data. The first involves construction of a histogram of the numbers of daily increments per larva from a sample of larvae, and estimation of mortality from the decline in the loge-transformed increment-frequency curve. The second approach is to convert larva lengths to number of increments with a growth curve derived from otolith data, and then to estimate mortality from the descending limb of a loge-transformed increment-frequency histogram. Counts of daily increments in otoliths of larval anadromous alewives Alosa pseudoharengus collected from a coastal Massachusetts pond were used to compare results from these two methods with results from a third method that uses the decline in catch per unit effort of larvae through time. The estimate of instantaneous daily mortality for larval alewives from otolith methods was 0.122, which was an average rate for larvae 6.0 to 13.9 mm total length over a 1-month sampling period. The three methods generally produced similar mortality estimates over large sampling periods; however, otolith-derived mortality estimates from single sampling dates were highly variable. Major advantages of otolith increment methods over traditional catch-curve methods for estimating larva mortality are elimination of the need for fitting a growth curve to estimate mortality and the ability to obtain better estimates of mortality for individual cohorts of larvae.