Faunce et a\ Age, growth, and mortality of Cichlasoma uiophtha/nnis 



43 



Map of southeastern 

 HC'=Highway Creek i. 



Martinez-Palacios and Ross, 1986; 

 Flores-Nava et al., 1989; Ross and 

 Bt'veridge, 1995) and on the po- 

 tential for range expansion in the 

 United States I e.g. Stauffer and 

 Boltz, 1994). Few studies have ad- 

 dressed the life history of the Ma- 

 yan cichlid, and only scant infor- 

 mation e.xists on the age structure 

 and growth rate of this species. 

 From the seasonal length-frequen- 

 cy distributions for Celestun La- 

 goon, Mexico, Martinez-Palacios 

 and Ross (1992) concluded that 

 Mayan cichlids from 70 to 130 

 mm standard length had complet- 

 ed their first spring and were re- 

 productively active, whereas in- 

 dividuals from 131 to 200 mm 

 standard length had entered their 

 second reproductive year. Observ- 

 ing no fish >200 mm, Martinez-Pa- 

 lacios and Ross (1992) concluded 

 that the population of Mayan cich- 

 lids in the lagoon comprised fast- 

 growing fish with one, or two (rarely), reproductive seasons 

 in their lifetimes. Aging of Mayan cichlids using a validat- 

 ed method is needed to determine the accuracy of previ- 

 ously reported age and growth estimates and to compare 

 the age structure between populations from Mexico and 

 Florida. Here we provide a first account of the age, growth, 

 and mortality of the Mavan cichlid from Florida waters. 



Methods 



Mayan cichlids were collected from the dwarf mangrove 

 forests of southeastern Florida. This habitat is dominated 

 by small (0.5-2.0 m tall) red mangrove trees (Rhizophora 

 mangle) in an expansive, seasonally inundated wetland 

 of typically shallow water (average maximum depth=30 

 cm). These mangroves increase in canopy width and 

 height nearer to continuously inundated deeper creeks. 

 The system is inundated mostly by fresh water during 

 July-February but becomes more saline ( 10-35"^^? ) during 

 the dry season (March-June). 



Cichlids <65 mm standard length (SL) were collected by 

 using drop traps (Lorenz et al., 1997) to determine when 

 Mayan cichlids first recruit. Drop-trap samples were col- 

 lected every six weeks from August 1990 to September 



1996 at Highway Creek, Joe Bay, and Taylor River (Fig. 1 ). 

 Larger cichlids (>65 mm SL) were collected by using hook- 

 and-line gear comparable to that used in other studies 

 (Martinez-Palacios and Ross, 1992). Hook-and-line collec- 

 tions were conducted monthly from March 1996 to October 



1997 in Taylor River, a major freshwater distributary of the 

 Everglades emptying into northeastern Florida Bay. Each 

 fishing effort continued until approximately 40 fish were 

 obtained. Fish collected by both methods were measured 

 (SL and total length |TL|, mm), weighed to the nearest 



Figure T 



Florida showing sampling locations (TR=Taylor River, .JB=Joe Bay, 



0.1 gram, and their sex was determined macroscopically 

 when possible (Faunce and Lorenz, 2000). Fish captured 

 during 1994—97 were used for age-and-growth analyses. 

 All lengths reported hereafter are standard lengths. 



Sagittal otoliths were removed, blotted dry, and stored 

 in vials until they were sectioned. The left sagitta, unless 

 broken, was used for age determination. Otoliths were sec- 

 tioned by using a low-speed Beuhler Isomet saw with dia- 

 mond blade. Three or four 0.5-mm thick transverse sections, 

 one through the core, were cut and mounted on microscope 

 slides with Histomount '■'^' adhesive and allowed to dry. Sag- 

 ittae from fish <100 mm were embedded in Spurr, a high- 

 density plastic medium (Secor et al, 1992) and a 1-2 mm 

 thick transverse section containing the otolith core was 

 then cut. The sections were mounted on a microscope slide 

 with Crystal Bond^-^' 509 adhesive, and polished with wet 

 and dry sandpaper of grit sizes 220-2000 until growth 

 rings were visible. A polishing cloth with 0.05-gamma alu- 

 mina powder was used to remove scratches. 



A standardized protocol for interpreting otolith growth 

 zones was followed. When viewed with reflected light, the 

 transverse sections of Mayan cichlid otoliths had two dis- 

 tinct regions; 1) an "inner region" extending from the core 

 to the first visible opaque zone (ring), and 2) an "outer re- 

 gion" extending from the first visible opaque zone to the 

 edge of the otolith (Fig. 2). The inner region was typically 

 more opaque than the outer region and sometimes con- 

 tained a visible growth zone or numerous check marks, 

 or both. LTnfortunately, these marks were difficult to inter- 

 pret, inconsistent between sections from individual fish, 

 and in many cases absent altogether Consequently, we did 

 not count any marks from the inner region in our age es- 

 timations. However, the translucent appearance of the out- 

 er region of the otolith made it possible to count distinct, 

 separate, opaque rings when present. The number of rings 



