Biological Intercept Method Research Articles

Otolith micro structure analysis of rainbow trout alevins (Oncorhynchus mykiss) under rearing conditions

Otolith microstructure (MO) analysis was used to back-calculate growth patterns from hatching to the yolk-sac absorption in Rainbow trout alevins ( Oncorhynchus mykiss ), under experimental conditions, from winter to spring in Central-Chile. MO showed the following main features: (i) occurrences of multiple primordia in the central region of otolith (MP); (ii) several increments (22 ± 3 rings) before a prominent hatch check surrounding MP and (iii) existence of a very distinctive check associated to yolk-sac absorption. Further findings were the validation of daily periodicity of micro-increments and a significant linear relationship ( P < 0.001; r² = 0.91) between the maximum otolith length (MOL) and total length (TL) of alevins. The linear MOL-TL relationship validated the use of the biological intercept method to back-calculate daily growth rates. Growth rates profiles followed a decreasing trend from hatching to the end of yolk-sac period (16 ± 1 days), ranging from 0.34 mm d -1 to 0.22 mm d -1 (0.30 ± 0.037). MO analysis demonstrated to be a powerful tool in back-calculating growth patterns of alevins once they had absorbed their yolk-sac.

Effects of river flow on larval growth and survival of Japanese seaperch Lateolabrax japonicus (Pisces) in the Chikugo River estuary, upper Ariake Bay

The abundance and growth history of larval and juvenile Japanese seaperch Lateolabrax japonicus were investigated in the Chikugo River estuary, upper Ariake Bay, from 1990 to 2000. Growth during the larval period (up to 15 mm standard length, LS, the size at recruitment into the estuary) was backcalculated using sagittal otolith microstructures by the biological intercept method. Growth rates in length declined at body sizes &gt;14 mm LS. High freshwater discharge through the Chikugo River was associated with high temperatures of the upper Ariake Bay where the larvae spend their planktonic life. Mean larval stage duration (days) from hatch to 15 mm (D15) varied between 48·8 and 76·2 days and was inversely correlated with the estimated mean temperature history [mean daily temperature (° C) experienced by the larvae during the period from hatch to 15 mm, T15]. Mean abundance (number m−2) of larvae and juveniles was highest in years when T15, D15 and freshwater discharge were at intermediate levels. Although the abundance was not correlated with either of these variables, an exponential relationship between abundance and D15 was found when data collected during the highest river discharge years (1990, 1991 and 1998) were excluded. The increase in freshwater discharge through the Chikugo River probably had the potential to enhance or diminish Japanese seaperch recruitment in two ways: 1) it could increase recruitment probability by increasing temperature and larval growth and 2) high river flow also had the potential to decrease the probability of immigration into the river by increasing larval seaward dispersion, predation due to decreased turbidity and starvation due to decreased zooplankton prey abundance in the estuary.

Growth-dependent recruitment of Pacific bluefin tuna Thunnus orientalis in the northwestern Pacific Ocean

To estimate the survival process of Pacific bluefin tuna Thunnus orientalis during the larval period, estimated growth histories were compared between larvae collected in late spring and juveniles collected in the boreal summer of 2004, which were considered to be survivors of the larval cohorts. Larval tuna (3.3 to 9.6 mm standard length, SL) were collected from mid-May to early June around the Ryukyu Islands, northwestern Pacific Ocean, and juvenile tuna were collected offshore of Kochi and Nagasaki prefectures in July-August. Preflexion, flexion and postflexion larvae were col- lected, and their ages ranged from 4 to 18 d. Back-calculated SLs by the biological intercept method showed that larval tuna in the postflexion phase were larger-at-age than preflexion and flexion larvae, suggesting that only larger and faster growing larvae were able to survive to the postflexion phase. The logarithms of otolith radii (ln OR: proportional to SL) of larvae with slower growth and development were smaller than the minimum ln OR of surviving juvenile tuna, which indicated the smallest possible size required for larvae to successfully recruit to the fishery. These results indicate that the survival of larvae of Pacific bluefin tuna depends largely on size and growth rates during early life history.

Patterns of growth in the early life history of the round herring Etrumeus teres

Early life history traits of young‐of‐the‐year (YOY) round herring Etrumeus teres, caught in Tosa Bay (south‐western Japan), were studied using otolith microstructure analysis for the 2000–2003 year classes. Hatch dates ranged from October to March, and were restricted to either autumn or winter within each year class. YOY ranged from 50 to 123 mm total length (LT) and from 57 to 192 days in age. The relationship of LT to otolith radius was linear. Individual growth rates (GI) were backcalculated between the 70th and 150th days (the size range of most YOY caught) using the biological intercept method. GI ranged from 0·3 to 1·4 mm day−1 and decreased in most cases as season progressed irrespective of year class, although GI in winter cohorts were significantly higher than in autumn cohorts. Otolith growth rates (GO) ranged from 2·13 to 12·25 μm day−1 for autumn spawned YOY and from 3·12 to 12·41 μm day−1 for YOY spawned in winter. The GO trajectories followed three consistent patterns: (1) an increase in increment widths after first feeding through the second week of larval life, then (2) a plateau in increment spacing before increment widths increased again until reaching the maximum growth rate, followed by (3) a gradual decrease in increment widths until the end of the fifth month. The three stages occurred irrespective of spawning season, although YOY spawned in October and December had higher GO during stages (1) and (2) than YOY spawned in February and March, whereas higher GO was observed for late‐winter cohorts in stage (3). Otolith growth from YOY spawned in December and January showed an intermediate pattern between YOY hatched in the early autumn (October to December) and late winter (February to March). The GO trajectories were cross‐matched to the calendar date to estimate time series of otolith growth rates (GOTS) for each year. A parabolic trend was found with maximum GOTS in autumn and spring and minimum values in winter. This trend was significantly correlated to daily sea surface temperature variations. The differences in otolith growth trajectories suggest that the otolith microstructure of E. teres may be used as a natural tag for identifying autumn and winter spawned cohorts.

Growth of larval and early juvenile Japanese anchovy, Engraulis japonicus, in the Kuroshio‐Oyashio transition region

Larvae, juveniles, and adults of Japanese anchovy, Engraulis japonicus, were distributed throughout the Kuroshio‐Oyashio transition region off northern Japan as far offshore as 170°E in 1996 and 1997. The growth trajectories of individual larvae and early juveniles were backcalculated using the biological intercept method based on the allometric relationship between otolith radius and somatic length. Mean larval growth rates ranged from 0.49 to 0.71 mm day–1 in the transition region, and were comparable to those reported from the Pacific coastal waters of central Japan, which is the principal distribution range of E. japonicus. In terms of growth, the Kuroshio‐Oyashio transition region seemed to be a favourable nursery area for larval E. japonicus. Larval growth tended to decline from the inshore to the offshore waters in the transition region. Thermal conditions did not show an inshore–offshore trend in the survey area and did not explain the longitudinal trend in growth rates.

Comparison of somatic growth and otolith increment growth in laboratory-reared larvae of Pacific saury, Cololabis saira , under different temperature conditions

The relationship between somatic growth and incremental growth of otoliths of Pacific saury, Cololabis saira (Brevoort), larvae under different temperature conditions was studied in the laboratory for three age groups (0 to 9, 10 to 20 and 20 to 30 d posthatch). Larvae were incubated from hatching to 9 d at 24, 20, and 16 °C. Further, larvae initially reared at an ambient temperature of 21.7 °C were transferred to experimental temperatures of 22, 18, and 14 °C on Day 10 and reared to Day 20 and similarly from Day 20 and reared to Day 30 posthatch. Growth trajectories of larvae sampled at the end of the three experiments were back-calculated using the biological intercept method and compared to the measured values 0 and 5 d after the start of each experiment. Back-calculated knob length at the different temperatures indicated no significant difference to the measured knob lengths except for the cases at 20 °C from hatching to 9-d-old larvae and at 14 °C from 20- to 30-d-old larvae. The close correlation between somatic and otolith growth shown in this study indicated the feasibility of estimating the growth history of Pacific saury larvae using otolith readings.

Size-specific changes in amount of lipid and daily growth rate of early larval sardine, Sardinops melanostictus , in the main Kuroshio Current and its offshore waters off eastern Japan

The size-specific nutritional conditions of larval sardines, Sardinops melanostictus, from the main Kuroshio Current and its offshore waters off eastern Japan were assessed by lipid analysis. A rapid lipid analysis technique (diagnostic kits for human serum lipids) was used to measure the different lipid components of individual sardine larvae as indicators of their nutritional condition. Size-specific growth trajectories of individual larvae were estimated by the biological intercept method, and the recent daily growth rate of standard length (SL) was calculated from the 3 d outer increment width on the otolith. Relationships between the amount of larval phospholipid (PL; tissue weight indicator) and SL, and the recent daily growth rate of larva (Gr) and SL, could be expressed by the equations PL = 0.459 SL1.77 and Gr = 0.0809 SL − 0.341, respectively. There was no notable difference in these values between the two survey areas. The relationship between the amount of triglyceride (TG) and SL could be expressed allometrically (TG = 0.013 SL2.63). The relationship between the index of starvation tolerance (TG/PL) and SL could be expressed by the allometric equation TG/PL = 0.0288 SL0.865, suggesting that larger sardine have a higher starvation tolerance than smaller sardine. The TG of the 8 to 9 mm SL size-class larvae in the offshore area was higher than in the main Kuroshio Current. To test whether the TG for each larval sardine in the 8 to 9 mm SL size-class could be correlated with variables (temperature, chlorophyll a and distribution density of the sardine larvae) measured at the sampling stations, correlation analyses were performed. A highly significant negative correlation between TG and distribution density of the sardine larvae was found. A density-dependence effect seemed to influence the fluctuation of the larval storage energy component for short-term needs.

Feeding and growth of early juvenile Japanese sardines in the Pacific waters off central Japan

Larval and early juvenile growth was backcalculated for individual Japanese sardines Sardinops melanostictus using the biological intercept method based on the allometric relationship between otolith radii and fish lengths. Sardines grew at 0·81 mm day−1 during the larval stage. In the early juvenile stage, they grew from 32·3 to 45·4 mm fork length (L) over a 20-day period (0·64mm day−1). Using the observed relationship between L and wet body weight (W), W = 0·00942 L2.99, W of the sardine juveniles was calculated to increase from 306 to 832 mg during the 20-day period. The carbon (C) requirement to achieve this growth in weight was estimated to increase from 5·7 to 9·6 mg day−1. Stomach contents of the sardines were composed mostly of copepods (73%) and larvaceans (25%). Wet stomach content weight (Ws) was expressed by a power function of the W, Ws=0·731 W0·658. Carbon and nitrogen constituted 41·7 ± 1·5 and 10·0 ± 0·4% of the dry Ws, respectively. Stomach C content increased from 2·0 to 3·9 mg during the 20-day period. Three to four cycles of the daily turnover of stomach contents during the 16 h of daytime, corresponding to a gastric evacuation rate of 0·2–0·3 h−1 under continuous feeding, met the C requirement to achieve the backcalculated growth in early juvenile sardines. The Kuroshio frontal waters seem to provide Japanese sardine juveniles with favourable growth conditions.

Feeding and growth of early juvenile Japanese sardines in the Pacific waters off central Japan

Larval and early juvenile growth was backcalculated for individual Japanese sardines Sardinops melanostictus using the biological intercept method based on the allometric relationship between otolith radii and fish lengths. Sardines grew at 0·81 mm day−1 during the larval stage. In the early juvenile stage, they grew from 32·3 to 45·4 mm fork length (L) over a 20‐day period (0·64mm day−1). Using the observed relationship between L and wet body weight (W), W = 0·00942 L2.99, W of the sardine juveniles was calculated to increase from 306 to 832 mg during the 20‐day period. The carbon (C) requirement to achieve this growth in weight was estimated to increase from 5·7 to 9·6 mg day−1. Stomach contents of the sardines were composed mostly of copepods (73%) and larvaceans (25%). Wet stomach content weight (Ws) was expressed by a power function of the W, Ws=0·731 W0·658. Carbon and nitrogen constituted 41·7 ± 1·5 and 10·0 ± 0·4% of the dry Ws, respectively. Stomach C content increased from 2·0 to 3·9 mg during the 20‐day period. Three to four cycles of the daily turnover of stomach contents during the 16 h of daytime, corresponding to a gastric evacuation rate of 0·2–0·3 h−1 under continuous feeding, met the C requirement to achieve the backcalculated growth in early juvenile sardines. The Kuroshio frontal waters seem to provide Japanese sardine juveniles with favourable growth conditions.

Temporal variation in the early life-history characteristics of the King George whiting (Sillaginodes punctata) from analysis of otolith microstructure

This study describes the duration of the settlement season, the somatic and otolith growth rates, and presettlement durations for Sillaginodes punctata at Barker Inlet, South Australia. The settlement season was from June to November, with settlement occurring in two phases over this period. Somatic growth rates ranged from &lt;0.1 to 0.25 mm day-1 depending on age and time of year, making size (SL) a relatively poor indicator of age. Alternatively, otolith size (OL) was strongly related to age, but the linear relationships varied systematically among sampling occasions. Because of variation in somatic growth rates, the SL-OL relationships were relatively poor. The biological intercept method was used to back-calculate fish sizes from otolith increment widths for three samples of fish. These growth trajectories differed considerably, two being logistic in shape and the third being an exponential relationship. Presettlement durations increased from 80 to 130 days between June and September and were inversely related to growth rate. Settlement competence is related more to size than to age. The broad natural variation in early life-history characteristics is likely to relate to water temperature regimes along larval advection pathways through the long settlement season.

Comparison of Otolith-Based Back-Calculation Methods to Determine Individual Growth Histories of Larval Striped Bass, Morone saxatilis

In rearing studies on 6- to 22-d-old larval striped bass, Morone saxatilis, we applied several back-calculation methods to known-growth larvae. A growth effect occurred on otolith diameter – standard length relationships, where slower growing larvae had relatively larger otoliths. Otolith growth was less affected by feeding regime than was somatic growth. Due to the conservative nature of otolith growth, proportional based (Biological Intercept Method) and simple linear regression methods linearized somatic growth transitions and did not estimate periods of negative growth. A quadratic regression method which used age as an additional predictor resulted in the accurate back-calculation of size at age in all groups of laboratory-reared larvae. However, when model coefficients were applied to a test population of pond-reared larvae, the quadratic model performed poorly. While differences in relative otolith size between pond- and laboratory-reared larvae could be ascribed to a temperature effect, the inability to apply the model also indicates a problem specific to regression-based methods. Theoretical rationale and experimental proof provided evidence for the inclusion of age in back-calculation models, but parameterization will have to occur for each field application.