Love is the Air for Groupers – February Fish of the Month: Groupers of the Genus Mycteroperca

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Love is the Air for Groupers

 

February Fish of the Month: Groupers of the Genus Mycteroperca

Dr. Geoffrey Smith

NWFSC Biology Instructor

 

Groupers are one of a number of important fisheries species in the Gulf of Mexico and South Atlantic waters, and they are important to both our regional and state economies. Collectively, the groupers consist of several genera (closely related/sister species) belonging to the seabass family (Serranidae). This post will focus on one of these genera: Mycteroperca. This genus consists of numerous species worldwide, with several common species found in waters offshore of northwest Florida including Gag (Mycteroperca microlepis), Scamp (Mycteroperca phenax), Black Grouper (Mycteroperca bonaci), and Yellowmouth Grouper (Mycteroperca interstitialis) (Figure 1). All of these species are found in offshore waters around reefs, wrecks, natural underwater springs, and other structures and are prized for their fighting ability when hooked and their quality as table fare. All of our local Mycteroperca species have spawning seasons starting in late winter (December to January) and lasting through mid to late spring (March-April), which corresponds with closed harvest seasons for each of these species. For up to date information on the size limits, bag limits, and state and federal closed seasons for each of our local grouper species refer to FWC or download the Fish Rules app on a smart phone.

The more interesting aspect of this post is not the spawning season itself, but the way in which many seabasses, including the Mycteroperca mature and reproduce. The seabasses are one of several families of fish that display various degrees of hermaphroditism, in which a single individual functions as both a male and female at some point in its life. The Mycteroperca and several other groups of seabasses are what are known as a protogynous (translates roughly to female first) hermaphrodite, meaning that all individuals start their lives as females in terms of reproduction, but at some specific size/age range they change to a male in terms of reproduction. The genetics for both sexes are present when they are born and different chemical signals initiate the changes over time. This type of reproduction has led to an unusual situation in terms of overfishing and conservation. In most species, populations are limited by females and the number of eggs that are produced. However with Mycteroperca and other protogynous hermaphrodites, all individuals start as females and there is not generally a shortage of eggs. But the largest individuals, which are often some of the first to be harvested, are males. And as smaller individuals are harvested, there are fewer and fewer that grow large/old enough to become males. This results in a situation where there are not enough males to fertilize all the available eggs and creates scenarios where management that allows maximum harvest while also maintaining sustainable populations is quite complex to model and difficult to implement. This is one of the main reasons quotas and regulations for these species change more frequently than many other species, as different management strategies are modeled, implemented, and adjusted when new information becomes available.

Figure 1: Clockwise from top left, Gag, Scamp, Black Grouper, Yellowmouth Grouper. Images from myfwc.com (© 1992 Diane Rome Peebles)

Figure 2: Predicted age at 50% male (age where half of the mature fish have switched from female to male) for Gag based on mature individuals collected from the Madison Swanson marine protected area (Image from Lowerre-Barbieri et al. 2020).

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