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The conservation status of small cetaceans has significantly worsened since the 1980s, when the baiji was the only species of small cetacean listed as Endangered by IUCN. Now the baiji is almost certainly extinct and 13 other species, subspecies, or populations (hereafter units-to-conserve or units) of small cetaceans are listed as Critically Endangered (CR) on the IUCN Red List. Bycatch is the main threat to 11 of the CR units. Entanglement in gillnets contributed to the extinction of the baiji and is responsible for the imminent extinction of the vaquita. Unfortunately, there is no simple technical solution to the problem of bycatch of small cetaceans. If the 8 CR units with 100 or fewer remaining individuals are to be saved, conservation zones must be established where gillnets are eliminated and bans on their use are strictly enforced. Recent experience with the vaquita in Mexico demonstrates that enforcement of such conservation zones can be very difficult. Ineffective enforcement is also a problem for at least 4 of the other CR units. Time is very short and, unless major efforts are made now to address the bycatch problem, the prospects for CR small cetaceans and other at-risk aquatic megafauna are grim. The ultimate long-term solution to the bycatch problem is the development of efficient, inexpensive, alternative fishing gear that can replace gillnets without jeopardizing the livelihoods of fishermen. Good fishery governance and the direct involvement of fishing communities are also essential to the successful conservation of most threatened populations of small cetaceans.

Marine mammals can play important ecological roles in aquatic ecosystems, and their presence can be key to community structure and function. Consequently, marine mammals are often considered indicators of ecosystem health and flagship species. Yet, historical population declines caused by exploitation, and additional current threats, such as climate change, fisheries bycatch, pollution and maritime development, continue to impact many marine mammal species, and at least 25% are classified as threatened (Critically Endangered, Endangered or Vulnerable) on the IUCN Red List. Conversely, some species have experienced population increases/recoveries in recent decades, reflecting management interventions, and are heralded as conservation successes. To continue these successes and reverse the downward trajectories of at-risk species, it is necessary to evaluate the threats faced by marine mammals and the conservation mechanisms available to address them. Additionally, there is a need to identify evidence-based priorities of both research and conservation needs across a range of settings and taxa. To that effect we: (1) outline the key threats to marine mammals and their impacts, identify the associated knowledge gaps and recommend actions needed; (2) discuss the merits and downfalls of established and emerging conservation mechanisms; (3) outline the application of research and monitoring techniques; and (4) highlight particular taxa/populations that are in urgent need of focus.

Habitat fragmentation is a major concern of conservation biologists, since reduced gene flow between isolated subpopulations may further decrease the effective population size of a species. Rock wallaby (genus Petrogale) colonies provide a naturally occurring system to study the genetic consequences of habitat fragmentation. Colonies of less than 10 to more than 50 adult rock wallabies are restricted to isolated rock outcrops, and are thus expected to exhibit the genetic and demographic consequences of small population size. In this paper, we describe the characterization of a series of microsatellite loci from the allied rock-wallaby, Petrogale assirnilis, and their use to estimate genetic variation. Despite the small population sizes, a high degree of heterozygosity was observed at all the loci investiga ted.Single-locus microsatellite typing exploits the natural variability of simple repetitive sequences, and has been extensively employed in the medical sciences and in animal husbandry. Despite the potential applications of this technology in conservation genetics, few marsupial microsatellite loci have been characterized to date. In a wide range of eutherian mammals, microsatellites with the general form (TG), are by far the most common class in the genome (see, for example, Moore et nl. 1991). Our preliminary studies (Odorico et aI. 1992) imply that this is also true for marsupials. We therefore characterized a series of (TG), microsatellite loci from I? ussimilis, with the aim of developing microsatellite PCR systems for kinship and population studies.A partial genomic library was constructed for P. ussimilis and screened by standard techniques (Weber L May 1989;Tautz 1989; reviewed in Queller et nl. 1993). In the initial round of screening, seven clones containing (TG), microsatellites with n > 20 were identified; several additional clones contained imperfect or lower numbers of (TG), repeats. A further single clone contained ( n X o and another a complex locus containing two tetranucleotide repeats (Table 1). Oligonucleotide primers were designed to enable PCR amplification at several of these loci (Table 1); in one case the repeat region was too close to the end of the clone to permit this, and in a second case the microsatellite was monomorphic. For two other (TG), loci we do not yet have allelic data.PCR reactions were performed in 1 0 -m~ Tris containing 5 0 -m~ KC1, 1.5-m~ MgCl, 1 unit of Taq polymerase (Promega) and 50-100 ng of template DNA in a total volume of 25 ycL. For each locus, the dNTP (0.2-0.8 mM) and primer (1-8 IIM) concentrations were optimized, and in each case one of the primers was end-labelled using [y-XPI-ATP. Varying the primer and dNTP concentrations were found to have major effects on the amount of 'bandstuttering' (Tautz 1989; Luty et al. 1990) observed, and hence the interpretability of results. After an initial denaturation period of 5 min at 95 "C, 30 cycles of PCR were performed, each cycle consisting of 1 min denaturation at 93 "C, 30 s at the annealing temperature (Tab...