Grouping the groupers: the importance of taxonomy for fisheries management

People often think they know a lot about a species in a particular area through common knowledge gleaned through ecological and fishing interests. Often, however, it is only when scientists establish specific taxonomic characteristics of that species through systematic observation and extensive on-site recording of its actual distribution, that an accurate picture can be established. This has strong implications for those involved in fishing and fisheries management.

Taxonomy is the science of classifying organisms and providing a solid foundation for the research needed to conserve life on earth. Taxonomy is becoming more and more important as scientists struggle to identify species in order to understand the subtle relationships and complex interactions of ecosystems threatened by human activities.

For example, groupers are large species of the Serranid family which are very important in marine ecosystems. They are often the main predators in these ecosystems and play a basic role in the food chain. The genus Mycteroperca is represented by 15 different species which, because they are large, are a popular fisheries target.

There is a great deal of fishing activity in the areas in which these fish are found and the main features of the life cycles of most of these species are usually well known. However, in the case of an island grouper, Mycteroperca fusca (M. fusca), found in the waters of the Canary Islands, Azores, Cape Verde Islands and Madeira off the northwest coast of Africa,  there was no information about the characteristics of its life cycle, even though ecological and fishing interests in the eastern Atlantic Islands are strong.

Dr Phillip Heemstra, internationally renowned taxonomist, author and Curator Emeritus at the South African Institute for Aquatic Biodiversity (SAIAB), a research facility of the National Research Foundation (NRF), established that for many years M. fusca was confused with Myceteroperca rubra (M. rubra) which is limited to the west coast of Africa and Mediterranean waters. As a result, the life cycle of this species was unknown and the effect of extensive fisheries activity on the species could not be gauged.

Heemstra discovered that M. fusca and M. rubra are two distinct species and that there is little overlap in their respective ranges. “The two species are separate. They look the same but they scatter and spread in different areas,” said Heemstra. It is important to understand that they are different species in order to be able to manage them. Without specific classification, information and naming systems to identify species, scientists would find it very difficult to describe the relationships among them accurately. Heemstra suggests that as these are two isolated species with different population, there should be fishery restrictions to avoid exploitation of the smaller populations of the island species.

It is also vital to bear in mind the geographical distribution of the two species: M rubra is found only along the continent of Africa and in the Mediterranean Sea. As a result, if this species is to be fished sustainably, it is important to consider its island population. During reproduction the species come together in large numbers in a small area. These gatherings are known as spawning aggregations. The process requires the females to release the eggs at the same time the males are present. The males in turn release sperm to fertilise the eggs which then float on the open ocean. If the island population is threatened it may affect the continental population. If the continental population is over-exploited the species may not get any recruits from the island population. As Heemstra explains, “If it starts becoming rare in some parts of its range, one may have to take measures to conserve this species - like having a closed season on the spawning, or not permitting fishing of spawning aggregations that contain a lot of groupers.”

SAIAB’s strengths in taxonomy and the ability of taxonomists like Heemstra to categorise and recognise species relationships, gain knowledge of species distribution and determine keystone species can make valuable contributions to fisheries management and to developing sustainable fishing practice.