Life history implications of a tagging study of the largetooth sawfish, Pristis perotteti, in the Lake Nicaragua-Río San Juan system

Abstract

SynopsisOf a total of 377 Pristis perotteti tagged in the Lake Nicaragua-Rio San Juan System, 214 (56.8% were recovered. Eighty were recovered at the original tagging site; four m'oved downstream the full length of the river; and 127 tagged at the source of the river were recovered in all parts of the lake. Only one was recovered in a different river system, 58 km down the coast from the main mouth of the Rio San Juan.A life span of 30 years is suggested, with rapid growth (3040 cm per year) in the first three years, slowing to about 4 or 5 cm per year in the later years of life. Maximum sizes collected were 384 cm for males, 429 cm for females, smaller than maximum lengths reported elsewhere.The lake sawfish are not physically landlocked, but individuals rem,sin in fresh water for very long periods; parturition takes place in fresh water; all sizes are found in the lake; and it appears that this stock finds all of its ecological needs met in the lake. Individuals may spend all of their lives in fresh water, although, as a species, P. perotteti has not completely abandoned the sea, since some are known to occur in salt water. The Lake Nicaragua-Rio San Juan sawfish are a discrete stock, with only limited gene flow with neighboring stocks.P. perotteti is farther along in its adaptation to fresh water, in being able both to osmoregulate and reproduce there, than other known euryhaline elasmobranchs, except for the African stingray, Dasyatis garouaensis, of the Niger-Benue System, and the completely adapted South American freshwater rays (family Potamotrygonidae).

Kemp's Ridley Sea Turtle Saga and Setback: Novel Analyses of Cumulative Hatchlings Released and Time-Lagged Annual Nests in Tamaulipas, Mexico

“…However, very little information exists on size classes other than juveniles, which make up the majority of sawfish encounters; therefore, much uncertainty remains in estimating life history parameters for smalltooth sawfish, especially as it relates to age at maturity and post-juvenile growth rates. Based on age and growth studies of the largetooth sawfish (Thorson 1982) and research by Simpfendorfer (2000), the smalltooth sawfish is likely a slow-growing (with the exception of early juveniles), late-maturing (10-20 years) species with a long lifespan (30-60 years). Juvenile growth rates presented by Simpfendorfer et al (2008) suggest smalltooth sawfish are growing faster than previously thought and therefore may reach sexual maturity at an earlier age.…”

Sharks, rays and chimaeras: the status of the chondrichthyan fishes

“…After a five month gestation, young are born from early October to perhaps early December (Oetinger 1978). Size and age at sexual maturity for both males and females is 2.4-3.0m at about 10 years old (Thorson 1982b). Mean generation time for this species is thought to be about 20 years.…”

“…Life history data for sawfishes are largely lacking. Thorson's (1976Thorson's ( , 1982aThorson's ( , 1982b) studies of P. perotteti in Lake Nicaragua are the major data sources on the species, with limited peripheral or anecdotal information available elsewhere (e.g. Bigelow and Schroeder 1953;Thorson et al 1966).…”

“…The late 1960s population was estimated by Thorson (1982b) as 'numbered in the hundreds of thousands, including all sizes'. In the early 1980s, following an intense directed commercial fishery in the 1970s and early 1980s, they had all but disappeared from the lake (Thorson 1982b).…”

“…It is noted for running far upstream in fresh water and has been recorded at least 1,340km from the ocean in the Amazon (Manacapuru, Brazil); in Lake Nicaragua and the San Juan and other various east coast rivers of Nicaragua; Lake Yzabal and Rio Dulce, Guatemala; Rio San Juan and Magdalena River, Colombia; Mali or Senegal in the Falm River; Saloum River of Senegal; Gambia; and the Geba River of Guinea-Bissau (Boulenger 1909;Fowler 1936Fowler , 1941Beebe and Tee-Van 1941b;Bigelow and Schroeder 1953b;Gunter 1957;Thorson et al 1966;Dahl 1971;Thorson 1974Thorson , 1976Thorson , 1980Thorson , 1982aThorson , 1982bThorson , 1987Vasquez-Montoya andThorson 1982a, 1982b;Daget 1984;Compagno and Cook 1995a).…”