Habitat partitioning and vulnerability of sharks in the Great Barrier Reef Marine Park

Sharks present a critical conservation challenge, but little is known about their spatial distribution and vulnerability, particularly in complex seascapes such as Australia's Great Barrier Reef Marine Park (GBRMP). We review (1) the distribution of shark species among the primary habitats of the GBRMP (coral reefs, inshore/shelf, pelagic and deep-water habitats) (2) the relative exploitation of each species by fisheries, and (3) how current catch rates interact with their vulnerability and trophic index. Excluding rays and chimaeras, we identify a total of 82 shark species in the GBRMP. We find that shark research in the GBRMP has yielded little quantitative information on most species. Reef sharks are largely site-fidelic, but can move large distances and some regularly use non-reef habitats. Inshore and shelf sharks use coastal habitats either exclusively or during specific times in their life cycle (e.g. as nurseries). Virtually nothing is known about the distribution and habitat use of the GBRMP's pelagic and deep-water sharks. At least 46 species (53.5 %) are caught in one or more fisheries, but stock assessments are lacking for most. At least 17 of the sharks caught are considered highly vulnerable to exploitation. We argue that users of shark resources should be responsible for demonstrating that a fishery is sustainable before exploitation is allowed to commence or continue. This fundamental change in management principle will safeguard against stock collapses that have characterised many shark fisheries

Patterns of genetic variation and covariation in ejaculate traits reveal potential evolutionary constraints in guppies

Ejaculates comprise multiple and potentially interacting traits that determine male fertility and sperm competitiveness. Consequently, selection on these traits is likely to be intense, but the efficacy of selection will depend critically on patterns of genetic variation and covariation underlying their expression. In this study, I provide a prospective quantitative genetic analysis of ejaculate traits in the guppy Poecilia reticulata, a highly promiscuous livebearing fish. I used a standard paternal half-sibling breeding design to characterize patterns of genetic (co)variation in components of sperm length and in vitro sperm performance. All traits exhibited high levels of phenotypic and additive genetic variation, and in several cases, patterns of genetic variation was consistent with Y-linkage. There were also highly significant negative genetic correlations between the various measures of sperm length and sperm performance. In particular, the length of the sperm's midpiece was strongly, negatively and genetically correlated with sperm's swimming velocity—an important determinant of sperm competitiveness in this and other species. Other components of sperm length, including the flagellum and head, were independently and negatively genetically correlated with the proportion of live sperm in the ejaculate (sperm viability). Whether these relationships represent evolutionary trade-offs depends on the precise relationships between these traits and competitive fertilization rates, which have yet to be fully resolved in this (and indeed most) species. Nevertheless, these prospective analyses point to potential constraints on ejaculate evolution and may explain the high level of phenotypic variability in ejaculate traits in this species