2008 SOUTHEASTERN NATURALIST 7(4):651–664 Comparison of Red Grouper Populations from Campeche Bank, Mexico and West Florida Shelf, United States Linda A. Lombardi-Carlson1,*, Mark A. Grace2, and David E. De Anda Fuentes3 Abstract - Epinephelus morio (Red Grouper) is an important component of commercial fisheries for the United States and Mexico. Fishery-independent long-line surveys that utilized standardized sampling designs were conducted along the west Florida shelf, Florida and Campeche Bank, Mexico (2001–2002). Detecting true differences in abundance and sizes are difficult, but by using standard collection and aging methodologies, the level of bias was kept at a minimum. Relative abundance was higher in the Campeche Bank compared to the west Florida shelf (1.74 and 0.63 Red Grouper/100 hook hr, respectively). Fish from the Campeche Bank were also significantly smaller at length and weight. Differences in length, weight, and relative abundance of Red Grouper may be because of historical fishing pressure and management regulations, or the available carrying capacity of each area for Red Grouper. These differences have a substantial impact on how an overfished population can recover and be sustained. Introduction Epinephelus morio (Valenciennes) (Red Grouper) is a shallow-water teleost in the family Serranidae and is distributed along hard bottom throughout waters off the southeast United States, the Gulf of Mexico, and Caribbean Sea. Several studies have examined the life history of the Red Grouper, including age and growth (Johnson and Collins 1994, Stiles and Burton 1994), reproduction (Brulé et al. 1999, Fitzhugh et al. 2006), and diet (Brulé and Rodriguez-Canche 1993). Red Grouper is a protogynous hermaphrodite with spawning occurring from January through May in the Gulf of Mexico. Unlike most groupers, Red Grouper do not appear to spawn in aggregations (Coleman et al. 1996). Existing tag-recapture data indicate Red Grouper do not undergo long-distance migrations (<40 nautical miles [nm]) and likely exist in sub-populations (i.e., fishing stocks) throughout the Gulf of Mexico (Moe 1966, 1972). Red Grouper are a very important commercial fish. Cuban fishers have harvested Red Grouper since the mid-1800s throughout the entire Gulf of Mexico (SEDAR 2006a, Tashiro and Coleman 1977), and Red Grouper is still an important component of commercial fisheries for both the United 1NOAA Fisheries, Southeast Fisheries Science Center, 3500 Delwood Beach Road, Panama City, FL 32408. 2NOAA Fisheries, Southeast Fisheries Science Center, PO Drawer 1207, Pascagoula, MS 39568-1207. 3Instituto Nacional de la Pesca, CRIP Yucalpeten, A.P. 73 Progresso, Yucatan, Mexico C.P. 97320. *Corresponding author - Linda.Lombardi@noaa.gov. 652 Southeastern Naturalist Vol. 7, No. 4 States and Mexico today. This species comprises approximately 80% of the grouper fishery (Brulé and Déniel 1996, Schirripa et al. 1999). Red Grouper landings also differ extensively between these two Gulf of Mexico areas with annual (1986–2000) fish landings in the Campeche Bank 3.5 times higher than landings in the west Florida shelf (Giménez-Hurtado et al. 2005, NMFS 2002). On an average, 11,000 metric tons (mt) of Red Grouper are harvested from the Campeche Bank compared to only 3000 mt from the west Florida shelf (Giménez-Hurtado et al. 2005, NMFS 2002). Furthermore, the United States and Mexico have differed in fishery regulatory measures (i.e., catch and size limits) and historical trends of harvest and management. The first federal Red Grouper regulations within the United States Exclusive Economic Zone were sanctioned in 1990. The United States federal regulations established a size limit of 508 mm, recreational bag limits (5 per person), a commercial quota of 4173 mt, and established gear-specific (long-line vs vertical line) fishing zones (Gulf of Mexico Reef Fish Management Plan, Amendment 1; SEDAR 2006b). In 2000, all shallow-water grouper harvesting was restricted from February 15th– March 15th to protect spawning fish. Further, efforts to reduce overfishing and restore the stock facilitated the commencement of a 10-yr rebuilding plan that reduced shallow-water grouper complex quotas to 3991 mt and established a separate Red Grouper quota of 2404 mt (NMFS 2004a). Since the establishment of a separate Red Grouper quota, all commercial landings of any species classified in the shallow-water grouper complex was restricted in 2004 and 2005 (NMFS 2004b, 2005). During the most recent US stock assessment, Red Grouper was classified as not overfished and not undergoing overfishing (SEDAR 2006b), a slight improvement from earlier assessments (NMFS 2002). The Red Grouper fishery of the Campeche Bank was historically harvested by three fishing fleets: Mexican minor (artisanal), Mexican major (mid-sized), and Cuban (see Arreguín-Sánchez et al. 1996, Giménez- Hurtado et al. 2005). There is no official federal management plan for Red Grouper in Mexico despite it being the target species of these fleets. Mexican fleets have free access to the fishery, but the Cuban fleet catch quota was reduced from 10,000 mt in 1976 to 850 mt in 2002. A minimum size limit of 300 mm was established in 1999 (Giménez-Hurtado et al. 2005), and a seasonal closure (February 15th–March 15th; Burgos-Rosas et al. 2003) was recently established to protect spawners. In 1999, the Cuba-Mexico experts committee considered the Red Grouper fishery overexploited due to decreasing catch-per-unit-effort (CPUE) as documented from research cruises (Giménez-Hurtado et al. 2005) and commercial logbook data (Hernandez and Seijo 2003). Because of interests in Red Grouper stocks by commercial and recreational fisheries management initiatives, two fishery-independent long-line 2008 L.A. Lombardi-Carlson, M.A. Grace, and D.E. De Anda Fuentes 653 surveys were conducted along the west Florida shelf, FL and the Campeche Bank, Mexico during summer 2001 and 2002. These standardized surveys allowed for the direct comparison of the abundance and age structure of Red Grouper from two areas in the Gulf of Mexico subjected to varying environmental and fishery conditions. Our objectives were to compare catch rates and life-history parameters (age and growth) from Red Grouper using equivalent sampling and aging methodologies between these two Gulf of Mexico areas. Methods Fishery-independent long-line surveys were conducted by the NOAA R/V OREGON II in the northeastern Gulf of Mexico (west Florida shelf) and by the Mexican R/V ONJUKU in the southeastern Gulf of Mexico (Campeche Bank) using standardized sampling designs and gear (Grace et al. 2004) in the summer (June, September) of 2001 and 2002. The gear consisted of a monofilament mainline (426 kg, 1 nm length), two radar refl ector buoys (attached at the start and end of the mainline), 5-kg weights clipped on the mainline at the beginning, mid-line, and end to enable the mainline to rest on the ocean fl oor, and 100 gangions (3.66 m length) with #15/0 circle hooks clipped to the mainline at a spacing of one per tenth of a nautical mile. Gangions were baited with Scomber scombrus L. (Atlantic Mackerel; approximately 0.12 kg per hook) in the west Florida shelf and with Sarda sarda (Bloch) (Atlantic Bonito; approximately 0.12 kg per hook) in the Campeche Bank. These are the baits of choice of the commercial fishers in the respective areas. As gear was deployed, vessel speed ranged from 5 to 7 knots; the gear was allowed to soak for one hour. Vessel speed was approximately 4 knots during gear retrieval. Sampling sites were randomly selected among three depth strata (9–55 m, 56–183 m, and 184–366 m; Grace et al. 2004). The number of sites randomly selected within 60 nm of contiguous sampling zones was proportional to the area of continental shelf within each depth stratum. Based on estimates of shelf area within the strata, 50% of sites were allocated in the first depth stratum, 40% in the second depth stratum, and 10% in the third depth stratum. However, no Red Grouper were caught in waters >40 m, thus comparisons were limited to the first depth stratum (9–55 m). Depths were then binned in 10-m increments (e.g., 1–10 m, 11–20 m, 21–30 m, 31–40 m). Capture location (latitude, longitude) and depth were recorded as the first refl ector buoy was deployed and retrieved. Catch-per-unit-effort (CPUE; number of Red Grouper per 100 hook hr) was calculated by area (west Florida shelf, Campeche Bank) and compared by depth bin. Log transformed CPUE data were statistically compared between areas and between areas with depth interactions using a generalized linear model (R function GLM; R Developing Core Team 2007). 654 Southeastern Naturalist Vol. 7, No. 4 Red Grouper were weighed (kg) and measured (mm fork length [FL], and total length [TL]), and both sagittal otoliths were extracted. Standardized aging methodologies were utilized for all age determinations following Johnson and Collins (1994) and Lombardi-Carlson et al. (2008). Two readers participated in aging otoliths. The date of capture, reader count, and edge type were used to assign annual ages (Lombardi-Carlson et al. 2008). Several methods were used to determine the precision among initial age estimates: (1) average percent error (APE), (2) coefficient of variation (CV), and (3) percent of readings in agreement (PRA) within ±1 or ± 2 bands (Campana 2001). The primary reader’s ages were used in further analysis. Differences in age, total length, and whole weight were examined using single-factor, random-effects analysis of variance by area (ANOVA; Zar 1999). Size-at-age data were also compared between areas using ANOVA; comparisons were restricted to age classes with at least five samples per area. Results The R/V OREGON II made 157 long-line sets on the west Florida shelf (30o–25oN, 86o–82oW; Fig. 1) during September of 2001 and 2002. The R/V ONJUKU made 68 long-line sets on the Campeche Bank (22o–19oN, 91o– 90oW; Fig. 1) during June and July of 2001 and 2002. Figure 1. Map of the Gulf of Mexico showing sampling locations from the west Florida shelf and the Campeche Bank. 2008 L.A. Lombardi-Carlson, M.A. Grace, and D.E. De Anda Fuentes 655 Relative abundance (CPUE) of Red Grouper differed by area and depth. Surveys on the west Florida shelf captured 99 Red Grouper in 157 sets (CPUE = 0.63 grouper per 100 hook hr) while surveys on the Campeche Bank collected 118 Red Grouper in 68 sets (CPUE = 1.74 grouper per 100 hook hr). Regardless of area, the highest CPUE occurred in the 11–20 m depth bin (1.32 and 3.41 west Florida shelf and Campeche Bank, respectively; Fig. 2). Red Grouper abundance was significantly different between areas (GLM: df = 224, t value = -4.43, P < 0.001) and between areas with depth interactions (GLM: 1–10 m: df = 28, t value = 0.79, P = 0.43; 11–20 m: d.f. = 68, t value = -3.40, P < 0.001; 21–30 m: df = 47, t value = -1.72, P = 0.24; 31–40 m: d.f. = 18, t value = -7.83, P < 0.001). The size ranges of Red Grouper caught were similar between areas (285 mm–880 mm TL), but significant differences were found in average size (Fig. 3). Red Grouper from the Campeche Bank were significantly shorter (df = 211, F = 10.94, P < 0.001; mean ± s.d.: 480 ± 110 mm TL at Campeche Bank versus 532 ± 123 mm TL at west Florida shelf) and smaller in weight (1.6 ± 1.4 kg at Campeche Bank versus 2.5 ± 2.0 kg at west Florida shelf) than fish collected on the west Florida shelf (ANOVA df = 210, F = 12.71, P < 0.001). Red Grouper were aged (n = 151) using otoliths. The average percent error (APE) between readers for all samples was 5.3%, the coefficient of variation (CV) was 7.5, and the percentage of readings in agreement (PRA) Figure 2. CPUE (number of Red Grouper/100 hook hour) for Red Grouper from the west Florida shelf and the Campeche Bank by depth. Asterisk indicates significant differences between areas (P < 0.001), as determined from ANOVA. 656 Southeastern Naturalist Vol. 7, No. 4 Figure 3. Red Grouper from the west Florida shelf and the Campeche Bank (a) total length, (b) whole weight, and (c) age-frequency histograms. 2008 L.A. Lombardi-Carlson, M.A. Grace, and D.E. De Anda Fuentes 657 within ±1 band was 83%, increasing to 95% within ±2 bands. The indexes of aging error from each area differed greatly (west Florida shelf: APE = 2.0%, CV = 2.9, PRA ± 1 band = 94%, PRA ± 2 bands = 98%; Campeche Bank: APE = 10.7%, CV = 15.2, PRA ± 1 band = 67%, PRA ± 2 bands = 89%). Annuli (opaque zones) from the Campeche Bank otoliths were faint with a feathery appearance compared to the clear annuli from the west Florida shelf otoliths (Fig. 4), which influenced otolith interpretations and the indexes of precision. Overall, there was no significant difference in mean age between areas (ANOVA: df = 150, F = 3.12, P = 0.08; Fig. 3c). Red Grouper from the west Florida shelf were slightly older than fish from the Campeche Bank (6.4 ± 2 yr versus 5.6 ± 3 yr). Of the age classes (age 5, 6, and 7) with sufficient samples (n ≥ 5), no significant differences were found in length and weight of fish at age 6 (length, ANOVA: df = 27, F = 1.51, P = 0.23; weight, ANOVA: df = 27, F = 0.58, P = 0.46) and at age 7 (length, ANOVA: df = 17, F = 0.06, P = 0.80; weight, ANOVA: df = 17, F = 1.02, P = 0.33). Age-5 Red Grouper from the Campeche Bank were significantly smaller in length (ANOVA: df = 35, F = 7.54, P < 0.01; mean ± s.d.: 488 ± 61 mm TL at Campeche Bank versus 549 ± 70 mm TL at west Florida shelf) and weight (ANOVA: df = 35, F = 10.45, P < 0.01; mean ± s.d.: 1.52 ± 0.55 kg at Campeche Bank versus Figure 4. Red Grouper annuli patterns from whole (13 x, left) and sectioned (25 x, right) otoliths from (a) the west Florida shelf and (b) the Campeche Bank. Both fish were age 5 yr. 658 Southeastern Naturalist Vol. 7, No. 4 2.38 ± 0.91 kg at west Florida shelf) compared to age-5 Red Grouper from the west Florida shelf (Fig. 5). Figure 5. Size-at-age plots (mean ± s.d.) for (a) length and (b) weight from the west Florida shelf and the Campeche Bank. Samples sizes greater than five for each area and age class. 2008 L.A. Lombardi-Carlson, M.A. Grace, and D.E. De Anda Fuentes 659 Discussion Our results indicate differences in size and relative abundance of Red Grouper between the west Florida shelf and Campeche Bank. Fish from the Campeche Bank were significantly smaller in length and weight. Size-at-age comparisons were limited because of sample sizes and the quality of increment clarity; nonetheless, age-5 Red Grouper from the Campeche Bank were significantly smaller in length and weight. Relative abundance was also higher in the Campeche Bank compared to the west Florida shelf (1.74 and 0.63 grouper per 100 hook hr, respectively). Detecting real differences in abundances and size estimates is difficult due to methodological differences (Cailliet et al. 1990); however, variations due to sampling bias and aging methodologies were sufficiently controlled, as the same sampling gear and methods were used in both areas of the Gulf of Mexico. Unfortunately, our second objective—comparing size-at-age data between the areas—was not executed. Our efforts to correctly assign annual ages to fish collected from the Campeche Bank were inhibited by the clarity of the increments in both whole and sectioned otoliths. Similar problems in otolith interpretation have been documented for species of pomacentrids in the tropical western Atlantic (Caldow and Wellington 2003). Otolith increment clarity has been reported to be affected by the average water temperature and the annual range in water temperatures characteristic of subtropical and tropical regions (Caldow and Wellington 2003, Fowler 1995, Morales-Nin and Panfili 2005). The Campeche Bank (mean ± s.d. = 28 ± 2 oC) average water temperature is 4 oC higher than that of the west Florida shelf (24 ± 4 oC), and the Campeche Bank has a smaller range in annual temperatures (Campeche Bank = 23–33 oC, west Florida shelf = 18–33 oC; NOAA National Data Buoy Center, www.ndbc.noaa.gov). Thus, the higher average water temperature and lower range in annual water temperature in the Campeche Bank affected the interpretation of otoliths and the appropriate assignment to annual age classes, which was refl ected in the indexes of precision and percent agreement between readers. The value of comparing catch rates between the two areas contributes to the understanding of the difference in magnitude of the landings data (Fig. 6). Because the catch-per-unit-effort data were based on randomized surveys using standardized methodologies throughout the spatial range of Red Grouper (Hernandez and Seijo 2003; SEDAR 2006b), the catch rates can be considered to be in proportion to Red Grouper abundances (Hilborn and Walters 1992). Therefore, Red Grouper in the Campeche Bank occur at higher densities but at smaller sizes than Red Grouper along the west Florida shelf. Understanding the factors responsible for the differences in size and abundance between these two areas is not straightforward. Nonetheless, these two areas provide the opportunity to evaluate the effects of fishing 660 Southeastern Naturalist Vol. 7, No. 4 on red grouper. As observed from landings data, fishing pressure on the Campeche Bank is much higher. A classic compensatory response from intense fishing pressure, as described through density-dependence, is that as larger adults are removed more readily by fishing gear, population size will initially decrease, and the available food supply for the smaller fish will promote an increase in growth rate and therefore a smaller size-at-maturity (Trippel 1995). Fishers catch the larger, faster growing individuals (Law 2000) and over time, a decrease in fish size and size-at-maturity can occur, as seen in salmon in the Pacific (Ricker 1981) and Pagrus pagrus (L.) (Red Porgy) from the US southeastern coast (Harris and McGovern 1997). The effects of fishing on the Campeche Bank could be responsible for the decrease in Red Grouper size-at-maturity (509 mm TL [Brulé et al. 1999], 380 mm TL [Giménez-Hurtado et al. 2003]). Detecting density-dependence is difficult and requires replicating sampling in time and space or manipulative experiments that may provide some evidence of density-dependence (Jenkins et al. 1999, Webster 2003). Our study was replicated in time and space, but detecting differences between areas requires a much longer time series since Red Grouper have life spans up to 30 years (Lombardi-Carlson et al. 2008). Future studies should investigate density-dependent mechanisms that may explain why differences in Red Grouper size and abundance exist between these two areas. Figure 6. Red Grouper landings (combined commercial and recreational) from the west Florida shelf and the Campeche Bank. Campeche Bank landings data interpreted from Giménez-Hurtado et al. (2005, Fig. 2). West Florida shelf landings data from NMFS (2002, Table A1). 2008 L.A. Lombardi-Carlson, M.A. Grace, and D.E. De Anda Fuentes 661 Acknowledgments This research was possible through the assistance of the crews of the NOAA R/V OREGON II and the Mexican R/V ONJUKU and to all the scientific staff, especially Dean Landi, Lisa Jones, Karen Mitchell, Melissa Cook, and to our Mexican colleague José Leonardo Castillo-Géniz (Instituto Nacional de la Pesca, CRIP, Ensenada). We offer our appreciation to John Carlson for his assistance in collecting samples and for comments on earlier drafts of this manuscript. Finally, our gratitude extends to Marta Ribera for her knowledge of GIS. Financial support was provided by the US Department of Commerce. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily refl ect the views of the Department of Commerce or NOAA or any of its sub-agencies. Literature Cited Arreguín-Sánchez, F., M. Contreras, V. Moreno, R. Burgos, and R. Valdés. 1996. 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