Size structure of mutton snapper, 

 Lutjanus analis, associated with 

 unexploited artificial patch reefs 

 in the central Bahamas 



Karl W. Mueller 



Caribbean Marine Research Center 

 805 East 46th Place. Vera Beach, Florida 32963 

 Present address: West Coast Blue Mussel Company 

 305 South Main Street. Coupeville. Washington 98239 



The mutton snapper, Lutjanus 

 analis (Cuvier, 1828) (Pisces: Lut- 

 janidae), is an important component 

 of shallow water reef fisheries in 

 the tropical western Atlantic (Bor- 

 tone and Williams, 1986). However, 

 overfishing of shelf-edge spawning 

 aggregations has contributed to a 

 major decline in landings and, in 

 some locations off Florida and 

 Cuba, to a total collapse of the fish- 

 ery (Brownell and Rainey, 1971; 

 Gulf of Mexico Fishery Manage- 

 ment Council, 1992). Much of what 

 we know about L. analis (i.e. age 

 and growth, reproductive, and 

 trophic biology) is based on samples 

 from commercial and recreational 

 catches (Rojas, 1960; Erhardt and 

 Meinel, 1977; Erhardt, 1978; Pozo, 

 1979; Claro, 1981, 1983; Mason and 

 Manooch, 1985; Palazon and Gon- 

 zalez, 1986). Quantitative behav- 

 ioral studies are few (Mueller, 1994; 

 Mueller et al., 1994), and field in- 

 vestigations concerning the popu- 

 lation structure of L. analis under 

 natural conditions are lacking. 



Visual censuses are useful for 

 comparison of temporal changes in 

 the size structure of fish popula- 

 tions on exploited reefs with those 

 of fish populations on unexploited 

 reefs (Craik, 1981; Russ, 1985). 

 However, such methods have sev- 

 eral inherent biases. At best, visual 

 censuses provide reasonably pre- 

 cise records of the fish fauna that 



are not greatly influenced by con- 

 ditions of water clarity (Sale and 

 Douglas, 1981). Because counting 

 all the fish in a given area is nearly 

 impossible, size frequencies derived 

 from visual censuses should be 

 used for relative comparisons be- 

 tween populations (Craik, 1981). 

 Using visual census techniques, I 

 describe a preliminary study of sea- 

 sonal variation in the size structure 

 of L. analis on unfished reefs for the 

 purpose of making comparisons 

 with fish of this species that are 

 subjected to fishing pressure. 



Materials and methods 



Size frequencies of L. analis asso- 

 ciated with two artificial patch 

 reefs off Lee Stocking Island, 

 Exuma Cays, Bahamas (23°46.21'N, 

 76°06.59'W), were monitored dur- 

 ing snorkeling excursions between 

 22 May 1991 to 14 December 1992. 

 The primary reef (reef 1, area=491 

 m 2 ) was located in a shallow (2.7 

 m), moderately dense Thalassia 

 testudinum Koenig meadow (biom- 

 ass=40-80 g dry wt-m -2 , Stoner and 

 Sandt, 1991), whereas a smaller 

 reef (reef 2, area=78 m 2 ) was lo- 

 cated in deeper water (4 m), 107 m 

 west of reef 1. A distinct, gently 

 sloping contour in the seagrass bed 

 was evident between the two reefs. 

 Both reefs were composed of man- 



made materials and had a sparse 

 cover of the living corals Millepora 

 alcicornis Linnaeus and Porites 

 pontes (Pallas). The position of and 

 distance between the reefs were 

 determined by using a Magellan™ 

 global positioning system unit. Reef 

 areas were determined by using a 

 waterproof measuring tape during 

 SCUBA dives. Although natural 

 patch reefs occurred in the area, 

 this site was selected because it was 

 unexploited and had a large num- 

 ber of L. analis associated with 

 the reefs. 



Data were collected every 4-11 

 weeks, only during the flood tide 

 (greatest water clarity) between 

 0600-1900 h (daylight hours) to 

 maximize visibility. By comparing 

 my position with the known dis- 

 tance between reef structures at 

 reef 1, 1 inferred that the maximum 

 limit of my visibility during flood 

 tide was approximately 20 m. Cur- 

 rent directions of the flood and ebb 

 tides at the study site were west 

 (180°) and east (0°), respectively. 

 During flood tide, I was able to drift 

 (>30 cm per second) from reef 2 to 

 reef 1 in five minutes or less. Us- 

 ing the natural water flow and bot- 

 tom topography as references, I fol- 

 lowed the same path between the 

 two reefs during each census. All 

 fish observed within 20 m (the ap- 

 proximate limit of my visibility) to 

 either side or end of this quasi- 

 transect (total search area includ- 

 ing reefs =5,600 m 2 ) were counted 

 and measured. Fork lengths (FL) 

 were estimated visually within 5 m 

 of fish by comparing subjects to a 

 known scale, the 30-cm length of a 

 hand-held underwater slate. Fish 

 were placed into one of three size 

 classes relative to my slate: 20, 30, 

 and >40 cm FL (shorter than, equal 

 to, and longer than the slate, re- 

 spectively). Lutjanus analis swam 

 into the current (positive rheo- 

 taxis); therefore once I had passed 



Manuscript accepted 1 February 1995. 

 Fishery Bulletin 93:573-576 ( 1995). 



573 



