Gray Snapper, Lutjanus griseus (Linnaeus, 1758)

Transcription

1 Gray Snapper, Lutjanus griseus (Linnaeus, 1758) Gray snapper are tropical, marine reef fish that occur from the U.S. mid-atlantic south to Rio de Janeiro, Brazil. Using the analysis of allele and genotype distributions at 13 microsatellites and mitochondrial (mt) DNA haplotype distributions, Gold et al. (2009) found three distinct genetic groups of gray snapper collected from U.S. waters: northwestern and northcentral/northeastern Gulf groups, and an east coast Florida group. Juveniles are common to inshore waters throughout Florida, and adults are found in areas of moderate to high relief on the continental shelf. Spawning occurs during summer (June September) in offshore waters around reefs, wrecks, and other bottom structures (Stark 1971; Domeier et al. 1996). Maturity occurs at about 7.5" standard length (Koenig 1993), which is probably the size when some gray snapper reach age-1 or age-2 (Manooch and Matheson 1981). Gray snapper reach about total length (TL) at age 1, can grow to about 30", and can live at least 25 years (Table 1; Manooch and Matheson 1981; Johnson et al. 1994). noted that growth rates for gray snapper in northeast and southeast Florida differed: fish from northeast Florida attained a greater maximum size and age than those from southeast Florida. Catch curves showing estimates of total annual mortality ranged from 0.35 in northeast Florida to 0.94 in southeast Florida (Burton 2001). Table 1. Von Bertalanffy growth parameters and length-weight relations for gray snapper Inches TL = L (1-e -K(age-t 0 ) ) K L (inches TL) to (years) Source Combined sexes, Florida Atlantic coast Manooch and Matheson (1981) Males, Gulf of Mexico Johnson et al. (1994) Females, Gulf of Mexico Males, Florida Atlantic coast Females, Florida Atlantic coast Combined sexes, Northeast Florida Combined sexes, Southeast Florida Johnson et al. (1994) Weight in lbs = a (inches TL) b a b Source Sex combined, Florida Atlantic coast Manooch and Matheson (1981) Sex combined, Florida and Louisiana Johnson et al. (1994) Sex Combined, Southeast Florida Males, Florida Atlantic coast Females, Florida Atlantic coast Adult gray snapper are nocturnal predators that forage away from their reef habitats. Juveniles feed diurnally among seagrass beds (Bortone and Williams 1986) and feed primarily on penaeid shrimp and crabs (Rutherford et al.1989a). Adult gray snappers feed on fish (largely grunts), shrimp, and crabs. (Harrigan et al. 1989; Hettler 1989). Gray snapper landings totaled 2,493,779 pounds in The recreational fishery made Florida Fish and Wildlife Conservation Comm., FWRI (2014) GRAY SNAPPER - 187

2 89% of the statewide landings. Landings were greater on the gulf coast, where about 72% of the statewide landings were made in Commercial landings, made throughout the state, were highest in Monroe County on the gulf coast (Fig. 1a). High recreational landings occurred in all regions (Fig. 1b) of Florida. The 2013 total landings were 67% higher than the average landings in the previous five years ( ) and were 25% higher than the historical average landings (Fig. 2). Total annual landings of gray snapper have been relatively low since 1982 on the Atlantic coast. On the gulf coast, landings have shown a cyclic pattern since 1992 with peaks in 1994, 2004, 2008, and 2013 and lows in 1999, 2006, and 2011(Fig. 2). Commercial landings rates on the Atlantic coast remained relatively stable from , fell to slightly lower values in , and have shown a recent upward trend in (Fig. 3a). Gulf coast commercial landings rates have trended upwards steadily from (Fig. 3b). Recreational total catch rates on the Atlantic coast have trended upwards slightly during , and remained relatively stable from (Fig. 3c), while gulf coast total catch rates have been relatively stable from (Fig. 3d). Relative abundance indices from fishery-independent-monitoring demonstrate that young-of-the-year (YOY) gray snapper are only occasionally caught on the Atlantic coast. There is evidence for occasional large year classes; seen as higher than usual abundance indices in 2005 on the Atlantic coast (Fig. 4a). On the gulf coast YOY gray snapper are captured much more frequently; the index showed a general increasing trend to a peak in 2004 and have since shown a decreasing trend through 2011 (Fig. 4b). Post-YOY abundances show a general increase from on the Atlantic coast, flattened out, and have dropped recently in (Fig. 4c). On the gulf coast post-yoy abundances have varied without trend but were noticeably higher in and 2008 (Fig. 4d). The proportion of gray snapper >75 mm with gross external abnormalities was highest in on the Atlantic Coast and highest in 2010 on the Gulf coast (Fig. 5a,b). Manooch and Matheson (1981) found that yield-per-recruit would increase in South Florida in the early 1980s if the age-at-recruitment was increased. At that time gray snapper recruited to the fishery at about 12 TL. Similarly, Rutherford et al. (1989b) found that gray snapper were too small, in terms of yield per recruit, when harvested (< 10 FL) in Everglades National Park during the early 1980s. noted that in northeast Florida gray snapper were fully recruited into the headboat fishery between ages 5 and 6 (13 22 TL), to the commercial fishery between ages 7 and 8 (14 24 TL), and into the private recreational fishery between ages 4 and 7 (12 24 TL). In southeast Florida, gray snapper were fully recruited into all fisheries between ages 4 and 5 (9 20 TL). Regional estimates of fishing mortality for gray snapper were 0.16 per year for northeast Florida and 0.66 per year for southeast Florida (Burton 2001). A 10" size limit, which included prohibition of the sale of any gray snapper less than 12" total length, was implemented in A bag-limit of 5 gray snapper was also implemented in 1990 as part of the 10-fish-aggregate snapper bag limit. Florida Fish and Wildl. Conserv. Comm., FWRI (2014) GRAY SNAPPER - 188

3 a. Commercial landings (pounds) b. Recreational landings (numbers) Figure 1 (a)-(b). Geographic distribution of gray snapper landed during (a) Commercial landings (pounds) by county; (b) Recreational landings (numbers of fish) by region. Figure 2. Total annual landings (pounds) of gray snapper on the Atlantic and gulf coasts of Florida, Florida Fish and Wildl. Conserv. Comm., FWRI (2014) GRAY SNAPPER - 189

4 a. Atlantic Coast, commercial landings rates (pounds/trip) b. Gulf Coast, commercial landings rates (pounds/trip) c. Atlantic Coast, recreational total catch rates (numbers/trip) d. Gulf Coast, recreational total catch rates (numbers/trip) Figure 3 (a)-(d). Annual standardized catch rates for gray snapper in Florida. Commercial landings rates (pounds/trip), : (a) Atlantic Coast; (b) Gulf Coast. Recreational total catch rates (numbers/trip), : (c) Atlantic Coast; (d) Gulf Coast. Florida Fish and Wildl. Conserv. Comm., FWRI (2014) GRAY SNAPPER - 190

5 a. Atlantic coast YOY b. Gulf coast YOY c. Atlantic coast post-yoy d. Gulf coast post-yoy Figure 4(a)-(d). Proportion of fishery-independent-monitoring sets that captured gray snapper from Young-of-the-year (YOY): (a) Atlantic coast; (b) Gulf coast. Post-YOY: (c) Atlantic Coast; (d) Gulf coast. Florida Fish and Wildl. Conserv. Comm., FWRI (2014) GRAY SNAPPER - 191

6 a. Atlantic coast proportion to total collected b. Gulf coast proportion to total collected Figure 5(a)-(d). Gross external abnormalities of gray snapper 75mm collected in fishery-independent-monitoring sets, Breakdown of gross external abnormalities by coast: (a) Atlantic coast; (b) Gulf coast. Florida Fish and Wildlife Conservation Comm., FWRI (2014) GRAY SNAPPER - 192