The shortfin mako, Isurus oxyrinchus, is a large pelagic shark with a widespread global distribution. However, very little is known about most aspects of this species for the south-eastern Pacific. In the present paper, the age and growth parameters of the shortfin mako, caught by Chilean swordfish longline fisheries from 2004 to 2005, are reported. Ages were estimated by counting band-pairs from sections of vertebral centra from 547 individuals, ranging from 76 to 330 cm in total length (TL). Trends in the proportion of opaque edges for all ages combined and grouped into ages 0–6 and 7–26 years indicated that they are formed during summer and showed that annually, one band-pair is formed in the vertebrae of shortfin makos. Modal-progression analysis was used to verify the first three age classes (ages 0–2 years). For both sexes, the oldest estimated age was 25+ years. Von Bertalanffy growth parameters were estimated at L∞ = 325.29 cm TL, K = 0.076 year–1 and t0 = –3.18 years for females and L∞ = 296.60 cm TL, K = 0.087 year–1 and t0 = –3.58 years for males. The results indicated that this species is highly vulnerable to exploitation and, thus, urgent conservation measures are required.
Wild adult specimens of the Peruvian anchovy Engraulis ringens were captured and reared to validate the daily periodicity of otolith microincrement formation. The postcapture stress generated spontaneous spawning, making it possible to conduct a rearing trial on larvae first in an artificial nutrient-enriched system (ANES) for 52 days followed by an artificial feeding regime in a culture tank until day 115 post-hatch. Microincrements of the sagittal otoliths of sacrificed juveniles [mean ± S.D. total length (LT ) = 5·13 ± 0·37 cm, range 5-6 cm; c.v. = 7·5%] showed very distinct light and dark zones. The slope of the relationship between the total number of increments after the hatch check and days elapsed after hatching was not significantly different from 1. The transfer from ANES to the artificial feeding regime induced a mark in the sagittal otoliths. The number of microincrements after this induced mark coincided with the number of days elapsed after the transfer date. In parallel experiments, adult E. ringens (mean ± S.D. LT = 14·92 ± 0·55 cm, range 13-16 cm) were exposed to one of two fluorescent marking immersion treatments with either alizarin red S (ARS; 25 mg l(-1) per 6 h) or oxytetracycline hydrochloride (OTC; 200 mg l(-1) per 10 h). The microincrements between fluorescent bands were distinct, ranging from 0·89 to 2·75 µm (mean ± S.D. =1·43 ± 0·28 µm; c.v. = 32%) and from 0·71 to 2·89 µm (1·53 ± 0·27 µm; c.v. = 35%) for ARS and OTC, respectively. The relationship between the number of microincrements between marks and the number of elapsed days for ARS and OCT treatments indicated that there was a significant correspondence between the number of increases observed and the number of days. Hence, daily microincrements of otoliths of E. ringens are likely to be formed in juveniles and adults under natural conditions.
Life‐history traits of kite skates Dipturus chilensis were examined from two regions (c. 2286 km apart) in the sheltered fjords and channels of southern Chile. A total of 482 and 403 specimens were collected from the southern fjords (c. 42–46° S) and the fjords of Chilean Patagonia (c. 51–54° S), from September 2003 to 2004, respectively. Vertebra marginal increment analysis indicated an annual deposition of growth rings which was completed during the winter months. For each region, von Bertalanffy growth parameters showed that females attained a larger asymptotic size, L∞, had a lower growth coefficient, K, and lived longer than males. Growth analysis indicated that D. chilensis from the Patagonian fjords had a longer life span (females: 22 v. 21 years; males 19 v. 17 years), attained a larger L∞ (females: 150 v. 136 cm; males: 122 v. 118 cm total length, LT) and had a lower K value (females: 0·087 v. 0·104; males: 0·110 v. 0·116) than their counterparts in the southern fjords. Comparisons with previous studies indicated that D. chilensis from both southern and Patagonian sheltered fjords had larger L∞, and grew more slowly than their counterparts from central‐southern Chile (L∞= 119–123 cm, K= 0·123–0·127), suggesting latitudinal variations in growth. Females attained sexual maturity later than males in both regions. For both sexes, lengths at 50% maturity (L50%) between regions were similar (females: c. 103 cm; males: c. 87 cm LT); however, D. chilensis from Patagonia appeared to mature 1 year earlier (females: 13 v. 14 years; males: 10 v. 11 years). Specimens from Patagonia had a lower ovarian fecundity than those from the southern fjords. An increase in the proportion of mature females and males during summer, suggests that the reproductive peak occurs in this season, and no regional differences were found. The size of the egg cases increased with maternal LT and these were longer in Patagonia. The information provided here represents the first evidence of regional variations in life‐history traits for elasmobranchs in the south‐eastern Pacific.
Abstract. The Peruvian anchovy (Engraulis ringens) is a resource of considerable economic importance, whose stock unit is distributed between 16800 0 S and 24800 0 S and is shared between Chile and Peru. In the present study, daily growth patterns of juvenile and adult Peruvian anchovies in northern Chile were determined using micro-increments of sagittal otoliths for the recruitment and fishery seasons of 2009 and 2010. A characteristic feature was the existence of very distinctive daily micro-increments, through which a complete sequence of micro-increments was obtained from the primordium to otolith edge for juveniles (7.5-12-cm total length (TL)) and adults (12.5-18.0 cm TL), whose ages were in the range 56-166 and 137-409 days respectively. Hatch dates extended from July 2009 to July 2010, where juveniles recruited to a fishery in a given month were the survivors of a spawning that had occurred approximately 3-4 months before. A Laird-Gompertz model fitted to length-at-age data for juveniles estimated maximum instantaneous growth rates that ranged from 0.98 to 1.57 mm day À1, whereas overall mean individual growth rates back-calculated for the age range of juveniles ranged from 0.65 to 1.02 mm day À1. The von Bertalanffy seasonal parameters estimated through the entire life history showed high growth, with a growth coefficient K ¼ 1.1 and mean length at the first year of 16.3 cm TL. Consequently, E. ringens in northern Chile seems to maximize growth in the first year of life.
Licandeo, R., Cerna, F., and Céspedes, R. 2007. Age, growth, and reproduction of the roughskin skate, Dipturus trachyderma, from the southeastern Pacific. ICES Journal of Marine Science, 64: 141–148. Age, growth, and reproductive parameters of the roughskin skate, Dipturus trachyderma, in the southeastern Pacific are reported. Age was estimated by counting the growth rings of thin sections of vertebral centra from 201 fish (61–253 cm total length, LT). No systematic ageing bias was observed, and the precision of growth ring counts indicated a high level of reproducibility. Marginal increment analysis supported the hypothesis of annual deposition of growth rings, which form during winter. The oldest female and male were 26 and 25 y, respectively. Von Bertalanffy parameters for combined sexes based on length-at-age data were L∞=257.7 cm LT, K=0.081 y−1 and t0=–1.363 y. Skates from the southernmost areas attained a larger mean size than those from more northern areas, and females reached a larger adult size than males. Males began the maturation process at ∼186 cm LT, indicated by the abrupt enlargement of the claspers. Developed oviducal glands, uteri, and ovaries indicated that females began to mature at 200 cm LT. The length and age at which 50% of the population matured were 215 cm LT and 17 y for females and 195 cm LT and 15 y for males. The youngest mature female and male D. trachyderma were 15 and 13 y, respectively. The ovarian fecundity ranged from 28 to 68 follicles. Females carrying egg cases were found in March and July. Dipturus trachyderma is slow-growing, long-lived, attains large size, matures late, and has low fecundity, life history characteristics that make it highly susceptible to exploitation.
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