Some IUCN Specialist Groups are long established and particularly active with the result that certain groups of organisms have been assessed much more thoroughly than others. For instance, all mammals and birds have now been assessed. Coverage of fishes has been limited to species covered by the Caribbean Inland Freshwater Fish, Coral Reef Fish, Freshwater Fish, Shark, Sturgeon and, most recently, the Grouper and Wrasse Specialist Groups. However, a new initiative, the Global Marine Species Assessment, organized by IUCN and Conservation International, seeks to conduct Red List assessments for many marine species over the next few years.

Assessing the conservation status of marine fishes presents some unique problems under an assessment procedure that applies to all flora and fauna. Moreover, there is very little known about the biology or fishery of a great many marine fishes. This is partly due to the scarcity of scientific studies on marine fishes, partly to the large number of species involved (around 14,000), and partly to the many difficulties inherent in estimating abundance of highly mobile and widely distributed marine species. Even in the groupers and wrasses, which include almost 1,000 species, many of which are important commercially and relatively well-studied, there is not enough published information to complete many full assessments.

Fortunately, IUCN guidelines encourage the use of estimates using unpublished data, where the published biological information is not available, to enable categorization of species to levels other than simply "data deficient." Much of our time is spent in developing species assessment involves not only literature reviews but filling in data gaps by making reasonable estimates of various parameters. To do this we rely heavily on experts in many countries to obtain up-to-date accounts of the species in their region or country of expertise, and use proxy approaches to making abundance estimates, such as UVC (Underwater Visual Census) estimates of density which can be factored up using habitat areas, catch per unit effort, etc.

In brief, the assessment procedure requires that each species be judged under 5 sets of criteria (A-E) that have been chosen to cover all scenarios that might increase a species' vulnerability to extinction. Each criterion will produce an assessment of the species that is (in order of most to least threatened) Critically Endangered, Endangered, Vulnerable, Lower Risk or Data Deficient. The most threatened rating that is obtained from any one of the 5 criteria is the one used to categorize the species. The 5 criteria in brief are "Declining Population" (A), "Small Distribution and Decline or Fluctuation" (B), "Small Population Size and Decline" (C), "Very Small or Restricted" population (D) and "Quantitative Analysis" (E) which uses techniques such as Population Viability Analysis (PVA). Most groupers and wrasses that have been assessed so far have received their most threatened rating from "Declining Population" (A).