The growing otoliths of fish incorporate radiocarbon in concentrations that are equivalent to that found in ambient seawater dissolved inorganic carbon. Therefore, pulses of anthropogenic radiocarbon produced by the atmospheric detonation of nuclear weapons can ultimately be detected in otol~ths. This study estimates the age of large southern bluefin tuna Thlinnus maccoyii using an age estimation procedure based on the determination of levels of bomb-derived radiocarbon In their otoliths. Radiocarbon data from selected regions of southern bluefin tuna otoliths indicate that this species may reach ages in excess of 30 yr Furthermore, individuals that approach the asymptotic length are likely to be 20 yr of age or older. The data agree generally with accepted models of southern bluefin growth, but show that these fish live longer than was believed previously. Comparisons between otolith section and bomb radiocarbon age estimates indicate that reading otolith sections is an effective method to estimate the age of larger southern bluefin. The presence of a significant number of individuals greater than 20 yr of age in the southern bluefin population may alter estimates of natural mortality rates currently used in Virtual Population Analysis models for stock assessment of this species.

The geographical distribution and ages of larvae of the blue grenadier, Macruronus novaezelandiae, based on ichthyoplankton surveys in southern Australian waters in 1984 and 1985, indicate that the species spawns primarily off the west coast of Tasmania in winter, and may spawn on a lunar cycle. Winter spawning off Tasmania is also suggested by adult gonad morphology: gonado-somatic indices peaked in winter, and mature and spent individuals were collected off the west coast of Tasmania. Small numbers of larval blue grenadier were also collected off north-eastern Tasmania, suggesting the occurrence of small-scale and sporadic spawning in that area. The date of first spawning differed by a month between 1984 and 1985, and was apparently related to broad-scale interannual differences in the oceanography of southern Australian waters. Use of oceanographic features to retrocast spawning dates for blue grenadier suggests that shifts in the date of first spawning of approximately one month are common in this species.

Bacteria use two-component system (TCS) signaling pathways to sense and respond to peptides involved in host defense, quorum sensing, and inter-bacterial warfare. However, little is known about the peptide-sensing capabilities of these TCSs. Here, we develop a high-throughput E. coli display method to characterize the effects of human antimicrobial peptides (AMPs) on the pathogenesis-regulating TCS PhoPQ of Salmonella Typhimurium. We find that PhoPQ senses AMPs comprising diverse sequences, structures, and biological functions. Using thousands of AMP variants, we identify sub-domains and biophysical features responsible for PhoPQ activation. We show that most of the newfound activators induce PhoPQ in S. Typhimurium, suggesting a role in virulence regulation. Finally, we find that PhoPQ homologs from Klebsiella pneumoniae and extraintestinal pathogenic E. coli, which occupy different in vivo niches, exhibit distinct AMP response profiles. Our high-throughput method enables new insights into the specificities, mechanisms, and evolutionary dynamics of TCS-mediated peptide sensing in bacteria.