Yellowmouth grouper  (Mycteroperca interstitialis)

Classified as Vulnerable (VU) on the IUCN Red List (1).

The yellowmouth grouper is a fairly large and robust fish which gains its common name from the yellow colouration around the contours of the mouth. The rest of the body is generally a light brownish-grey, paler below, with small, densely packed brown spots on the upper side. The front part of the dorsal fin has a yellow margin, while the rounded pectoral fins are clear, with a white edge and dark coloured fin rays (2) (3) (4) (5). Some individuals are more uniformly brown, while others have faint vertical bars (2) (3). The tail of the yellowmouth grouper has a notched margin. Another distinctive feature is the angular operculum (the bony flap covering the gills), which has a distinct notch and a spiny lobe (2) (3) (4) (5). Although potentially growing to over 70 centimetres, most yellowmouth groupers measure closer to 40 centimetres (4) (5).

In contrast to the adult, the juvenile yellowmouth grouper is quite strikingly bicoloured, being dark brown above, sometimes with broad dark bars or saddle-like blotches, and white below, with a white stripe down the midline of the back from the tip of the lower jaw to the base of the dorsal fin (2) (3) (4). The yellowmouth grouper is very similar in appearance to its close relative Mycteroperca phenax, with both commonly identified as ‘scamp’ (2) (6). The two are only really separated on the basis of slight differences in body and fin proportions, and by the yellowmouth grouper’s lack of dark spots on the dorsal and anal fin (2).

The yellowmouth grouper occurs in the western Atlantic Ocean, where it has been recorded from Florida and Bermuda, through the Gulf of Mexico and the Caribbean, and as far south as southern Brazil (1) (2) (3) (4).

This species occurs on coral reefs, and is mainly found over rocky or coral bottoms, to depths of up to 150 metres (1) (2) (3) (5). Smaller individuals often occur in mangrove-lined lagoons, and the species is reported to be more common in island waters than along the coast (1).

The yellowmouth grouper feeds on fish (1) (2) (3) (4) (6), and juveniles show an intriguing behaviour in order to approach otherwise wary prey. Known as ‘aggressive mimics’, the colouration of the juveniles mimics that of the clown wrasse, Halichoeres maculipinna, a species that is harmless to the yellowmouth grouper’s prey. The deception is further enhanced by folding down the fins, adding to the wrasse imitation (1) (7).

Like many groupers, the yellowmouth grouper has an unusual life history, known as protogynous hermaphroditism. All yellowmouth groupers start life as females, reaching maturity at around 40 to 45 centimetres in length, at an age of 2 to 4 years. However, between the ages of around 5 to 14 years old (at a length of 50 to 64 centimetres), individuals change sex and become male (6). Yellowmouth groupers may spawn at any time of year, although peaks have been recorded between April and May in the Gulf of Mexico (6). Juveniles grow rapidly during the first two years of life, after which growth slows significantly. The lifespan of this species may be long, reportedly up to 41 years (6) (8).

The yellowmouth grouper is believed to be naturally uncommon throughout its range, and as such is not a major target species in fisheries (1), although it is targeted commercially in some areas (1) (2) (4). The species is often taken along with the similar but more abundant M. phenax, and the two are marketed together as “scamp” (1) (6). Population declines have been noted for this species, which, like many groupers, is particularly vulnerable to overexploitation due to its slow growth, long life span and unusual life history (1) (9). Many of the larger grouper species come together in large numbers at specific locations to spawn, and these spawning aggregations are often targeted by fisheries, posing a further threat to these species (9) (10). However, this may be slightly less of a threat to the yellowmouth grouper, since it spawns throughout the year and so is less likely to form such large aggregations (6).

There are not known to be any specific conservation measures currently in place for the yellowmouth grouper, although it may receive some protection from its occurrence in several Marine Protected Areas (1). In unprotected areas, management of harvests is needed (1), and there are also calls for the better protection and management of the spawning aggregations of grouper species (9) (10).

View information on this species at the UNEP World Conservation Monitoring Centre.

To find out more about the conservation of groupers see:

• IUCN/SSC Groupers and Wrasses Specialist Group:
  http://www.hku.hk/ecology/GroupersWrasses/iucnsg/
• Society for the Conservation of Reef Fish Aggregations (SCRFA):
  http://www.scrfa.org/