Age, growth, maturity, longevity and natural mortality of the shortfin mako shark (Isurus oxyrinchus) in New Zealand waters

Abstract

EXECUTIVE SUMMARY BishopShortfin mako sharks were aged by counting growth bands in sectioned vertebrae collected from recreational fishing competitions and the tuna longline fishery. Replicate counts were made from images taken under reflected light. No systematic ageing bias was present within or between readers and count precision was high. Growth is rapid in early years and quickly declines. Vertebral data showed that males and females grow at similar rates until age 7-9 years, after which the relative growth of males declines. Von Bertalanffy growth parameters were: male L ∞ = 302.16 cm fork length (FL), K = 0.0524 and t 0 = -9.04 years: female L ∞ = 732.41 cm FL, K = 0.0154 and t 0 = -10.79 years. MULTIFAN analysis of length-frequency data from the tuna longline fishery estimated substantially faster growth than that derived from vertebral ages. MULTIFAN growth rates were considered reliable up to age 2-3 years, and thereafter vertebral ages were more reliable. Longevity estimates based on the maximum ages from vertebral band counts were 29 and 28 years for males and females respectively. Natural mortality estimates calculated from Hoenig's (1983) equation were 0.14 for males and 0.15 for females. Ages at 50% maturity determined by probit analysis of paired age and maturity data were 6.9 years for males and 19.1 years for females. Indirect age at maturity estimates from conversion of length at maturity data were 8-9 years for males and 20-21 years for females. Median maturity in males corresponded with the age at which male growth rate declined.The shortfin mako is a large, slow-growing, and late-maturing species with high longevity and low natural mortality. Comparison of growth curves reported here with overseas studies suggest that there are no regional differences in growth rates. Stock size and structure are unknown for this species internationally, and management should be of a precautionary nature.

Age, growth and mortality of <em>Sciaena umbra</em> (Sciaenidae) in the Gulf of Tunis

“…(F>F opt =0.12 for males and F>F opt =0.09 for females). Estimates for females are considered more relevant for population modelling, because aspects of female population dynamics, including age-specific and total life-time fecundity and mortality, determine the potential increase in population numbers (Bishop et al 2006). In the Gulf of Tunis, during the study period, the stock of S. umbra was slightly overexploited (E>0.4 and F>F opt ).…”

Biology, Taxonomy and Distribution of south-east Pacific Cartilaginous Fishes

“…Zealand (Bishop et al, 2006). Size-at-maturity (L 50 ) in both species appears consistent with previous results despite the relatively absence of mature females in the current study.…”

“…Zealand (Bishop et al, 2006), Mediterranean Sea (Boero & Carli, 1979), northeast Pacific (Pawson & Vince, 1999), northwest Atlantic coast of USA (Baum et al, 2003) and Canada (Campana et al, 2005). A major difference between our study area and these other regions is in the measures taken to regulate the catch and landing of sharks.…”

Size, Age, and Spatial–Temporal Distribution of Shortfin Mako in the Mexican Pacific Ocean

“…One of the biological variables that has the most influence on population analysis of any species is age, since this is the basis for calculating mortality and productivity rates (Campana 2001). Most studies have reported deposition of one age ring per year for Shortfin Makos (Cailliet and Bedford 1983;Ribot-Carballal et al 2005;Bishop et al 2006;Natanson et al 2006;Semba et al 2009). We chose the growth parameters reported by Ribot-Carballal et al (2005) to estimate the age structure of the Shortfin Mako individuals, because those authors conducted their work in the same study area.…”