Age and growth of sharks: do vertebral band pairs record age?

Inaccurate age estimates can have severe consequences in the management of elasmobranchs. Numerous studies in shark age validation have demonstrated a disconnect between band pair counts and age, resulting in age underestimation, particularly in older individuals. To investigate the relationship between band pairs, vertebral shape and growth, we quantified intracolumn differences in centrum morphology (size and structure) and band pair counts in seven shark species: Squatina dumeril, Carcharodon carcharias, Lamna nasus, Isurus oxyrinchus, Alopias vulpinus, Prionace glauca and Carcharhinus obscurus. In all species examined, band pair deposition was closely related to body girth and the structural properties of the cartilaginous skeleton, relative to maximum size, and body type. These results have strong implications for accurately assessing age for fisheries management of these species.

Age validation of the blue shark (Prionace glauca) in the eastern Pacific Ocean

The blue shark (Prionace glauca) is subjected to high levels of fishery catch and by-catch worldwide; thus, knowledge of their productivity and population status is vital, yet basic assumptions of band-pair deposition rates in vertebrae used for age and growth models are being made without direct validation studies in the Pacific Ocean. As such, the purpose of the present study was to validate vertebral band-deposition rates of blue sharks tagged and recaptured in the eastern Pacific Ocean. Vertebrae of 26 blue sharks marked with oxytetracycline (OTC) were obtained from tag–recapture activities to determine timing of centrum growth-band deposition. Results from band counts distal to the OTC mark on each vertebra indicated that a single band pair (1 translucent and 1 opaque) is formed per year for blue sharks ranging from 1 to 8 years of age. Length–frequency modal analysis was also used to obtain growth estimates from a dataset spanning 26 years of research and commercial catch data. Results provide support for annual band-pair deposition in blue shark vertebrae and will aid in future blue shark age and growth studies in the Pacific Ocean.

Modulation Instability and Extreme Events Beyond Initial Three Wave Systems

One possible mechanism that models the dynamics of extreme events in the ocean is the modulation instability (MI). The latter has been discovered in the 60s and significant progress in understanding the physics of modulationally unstable deep-water waves has been achieved since then. The MI instability starts its dynamics from a minor periodic perturbation of a regular Stokes wave, which enhances in amplitude, generating therefore periodic large waves, within the specific range of modulation period. In the spectral domain the same process starts from in amplitude very small symmetric side-band pair, lying in the unstable range from the main carrier frequency peak, which then starts to grow while generating by their own a side-band cascade. We report a new type of periodically modulated and unstable Stokes waves which initial dynamics starts from more that one unique unstable side-band pair. Laboratory experiments have been conducted in a large water wave basin, while numerical simulations have been performed using the modified nonlinear Schrödinger equation and the boundary element method. Both, experiments and numerical simulations are in reasonable agreement. Furthermore, the validity, limitations and applicability of such models will be discussed in detail.

Asteroidal Dust and the Zodiacal Emission

The contribution to the brightness of the infrared background by asteroidal dust, distinguished both by lower color temperature and ‘band-pair’ morphology, is determined using IRAS observations. Dust band pairs are associated with at least 7 asteroid families and groups, but very little is detected from the remainder of the asteroid belt, indicating that asteroid families and groups are the source of asteroidal dust.