Rough and smooth skates (Dipturus nasutus (Banks 1841) and/), innominatus (Garrick & Paul 1974)) were aged by counting growth bands on X-rays of thick sections of vertebral centra. Band counts were imprecise, but there was no betweenreader bias. Age estimates were not validated. The oldest rough skate was 9 years old, but few were more than 6 years old. Females may live longer than males. The combined sexes von Bertalanffy growth curve was L r = 91.3 (1 -e -0.16 [ t + 1.20 ]). Half the males matured by c. 52 cm pelvic length (PL) and 4 years, and females by 59 cm PL and 6 years. The oldest smooth skate in the sample was 24 years, but longevity probably exceeds that. Females appear to live longer than males. The combined sexes von Bertalanffy growth curve was: L t = 150.5 (1 -e -0.095[t + 1.06] ). Half the males matured by c. 93 cm PL and 8 years, and females by 112 cm PL and 13 years. Smooth skate are late maturing and long-lived relative to other skates, whereas rough skate are early maturing with a moderate life span.
Rig (Mustelus lenticulatus) specimens were aged by
counting growth bands in whole vertebrae that were illuminated laterally with
fibre-optic lights. Bands were counted by two readers who used information on
the diameter of the vertebrae of new-born young and 1-year-old juveniles to
identify the inner bands. The greatest estimated age was 12.1 years for a
female of 137 cm total length, but few rig were more than 8 years old. For
west coast South Island (WCSI) rig, there was no significant difference in
growth rates of males and females. After pooling both sexes, there was no
significant difference in growth rates between WCSI and east coast South
Island (ECSI) rig. The combined WCSI and ECSI von Bertalanffy growth curve was
Lt = 147.2 (1 – e
−0.119[t + 2.35]). This curve
agreed well with growth curves derived from length–frequency data, but
validation of the ageing technique is still required. WCSI males mature at
~85 cm and 5–6 years, and females at ~100 cm and 7–8
years. ECSI rig probably mature at similar lengths and ages. Tagged rig have
been recaptured after nearly 14 years at liberty. Longevity probably exceeds
15 years, and may exceed 20 years.
Fisheries harvest has pervasive impacts on wild fish populations, including the truncation of size and age structures, altered population dynamics and density, and modified habitat and assemblage composition. Understanding the degree to which harvest‐induced impacts increase the sensitivity of individuals, populations and ultimately species to environmental change is essential to ensuring sustainable fisheries management in a rapidly changing world. Here we generated multiple long‐term (44–62 years), annually resolved, somatic growth chronologies of four commercially important fishes from New Zealand's coastal and shelf waters. We used these novel data to investigate how regional‐ and basin‐scale environmental variability, in concert with fishing activity, affected individual somatic growth rates and the magnitude of spatial synchrony among stocks. Changes in somatic growth can affect individual fitness and a range of population and fishery metrics such as recruitment success, maturation schedules and stock biomass. Across all species, individual growth benefited from a fishing‐induced release of density controls. For nearshore snapper and tarakihi, regional‐scale wind and temperature also additively affected growth, indicating that future climate change‐induced warming and potentially strengthened winds will initially promote the productivity of more poleward populations. Fishing increased the sensitivity of deep‐water hoki and ling growth to the Interdecadal Pacific Oscillation (IPO). A forecast shift to a positive IPO phase, in concert with current harvest strategies, will likely promote individual hoki and ling growth. At the species level, historical fishing practices and IPO synergized to strengthen spatial synchrony in average growth between stocks separated by 400–600 nm of ocean. Increased spatial synchrony can, however, increase the vulnerability of stocks to deleterious stochastic events. Together, our individual‐ and species‐level results show how fishing and environmental factors can conflate to initially promote individual growth but then possibly heighten the sensitivity of stocks to environmental change.
Fin spines from elephantfish Callorhinchus milii were sectioned and viewed with transmitted white light under a compound microscope. The sections displayed growth bands but their interpretation and significance were unclear. Three different methods were used for counting growth bands. The results were compared with reference growth curves based on length-at-age estimates for six juvenile year classes derived from length-frequency distributions, and tagging data that showed longevity is at least 20 years. None of the three ageing methods showed good correspondence with the reference curves and all methods departed markedly from the reference curves at ages above 2 years old. Therefore, growth bands present in C. milii spines are not useful for ageing, at least with the three methods tested here. Spine bands may not represent age marks, but instead may be layers of material deposited irregularly to strengthen the spine. K E Y W O R D S ageing, Callorhinchus milii, fin spine, growth, New Zealand
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