Thursday, January 26, 2017

Shades of Gray Snapper, by Don Orth

Gray Snapper Lutjanus griseus is a very common snapper in the Atlantic and Caribbean.  It goes by two common names, Gray Snapper and Mangrove Snapper, but neither appears to be totally accurate. The Gray Snapper is more than its lackluster name may imply.   It is a member of the Lutjanidae family that includes over 100 species distributed throughout the Atlantic, Indian, and Pacific oceans and associated with reef environments.  Snapper are characterized by a continuous dorsal fin and canine teeth.  Yes, they look like dog teeth! There is even a species called the Dog Snapper Lutjanus jocu   The Gray Snapper has an emarginate caudal fin, rounded anal fin, and the dorsal and caudal fins have dark or reddish borders. 

The Gray Snapper is not always gray colored. "Lutjanus" is Latin for “snapper.” And the species name, "griseus," means "gray."  Gray Snapper was named in 1758 by Carl Linnaeus and the specimen used by Linnaeus to describe the species as “griseus” was old and gray. Like many fishes, color pattern alone may not be the most reliable way to a positive identification. Rather the color of the Gray Snapper is variable, sometimes grayish-red, sometimes grayish green or dusky olive on the back and sides. On occasion they may appear bright brick red or copper red.  The young are most variable.  Often young specimens have a dark strip from snout through the eye to the upper opercle and a less distinctive thin blue wavy line on the cheek below the eye. Sometimes the flanks are gray but interspersed with brick red spots on each scale, especially among the offshore and larger.  Sometimes, noticeable vertical bars are displayed on their sides.  See photos for varieties.
Juvenile Gray Snapper  Source
Small Gray Snapper Source
Gray Snapper  Source 
Gray Snappers near sea rod soft corals
Gray Snapper  Source 
Gray Snapper  Source 
Gray Snapper have large jaws on a pointed snout.  The outer pair of canine teeth in the upper jaw is much larger than those in lower jaw.  Gray Snapper are most similar to the Cubera Snapper Lutjanus cyanopterus, except the tooth patch on the roof of the mouth (called vomerine tooth patch) is V-shaped with an extension, resembling an arrow, whereas the tooth patch of the Cubera Snapper is simply V-shaped.  Be careful, you have to navigate past those canine teeth to get a look. 
Close up of the jaw teeth of Gray Snapper.  Photo by Chris G. Miller  source  
Small fish around 2 to 3 inches (5-7 cm) are very common in low salinity waters and range much farther into low-salinity estuaries than any other snapper species.  In fact, they have been captured in some lakes in Florida.  Small Gray Snapper are typical visitors to the lower Chesapeake Bay during summer and fall.   Young Gray Snapper are distributed in shallower water and are common on grass flats, among mangroves, and in other estuaries. They retain the wavy blue lines on their faces until they are 10 to 11 inches long (25-27 cm) —the entire time that they live inshore in bays. At that size they are willing feeders, and will quickly take a baited hook.  Larger fish are found in deeper water, both nearshore and offshore. 

Gray Snapper display an opportunistic feeding strategy, referred to as euryphagic carnivores.  They feed on crustaceans, such as shrimp and crabs,  and to a lesser degree on worms and mollusks,  but will also eat smaller fish. Juveniles feed diurnally and feed primarily on penaeid shrimp and crabs.  Larger fish also eat  cephalopods and become increasingly piscivorous, feeding more on fishes such as grunts (Haemulidae), if available. 
Distribution of the Gray Snapper.  Source:  IUCN.org
In Virginia waters the maximum size of adults is 18-24 inches. However, in more subtropical and tropical latitudes and offshore waters they may attain a larger size.  Typical size of the catch in shallow, inshore waters is between 8 and 14 inches. Gray Snapper is the most sought after recreational fish in southwest Florida.   They are easy to catch on shrimp or cut bait and are often caught near structures like wrecks, bridges, and docks. The minimum size is 10 inches in state waters and in federal waters (from 9-200 nautical miles) the minimum size limit is 12 inches.  The oldest Gray Snapper observed in Florida waters was 25 years.   The IGFA records of 17 pounds has stood since 1992. 
Twelve pound Gray Snapper.  Source 
Although the Gray Snapper is distributed from the mid-Atlantic south to Brazil, they may be one of the most common food fish in parts of the Caribbean where they occur in large aggregations. They migrate offshore to spawn in summer months. During the full moon, numerous Gray Snapper exhibit the spawning rush, where they swim up in the water column releasing large clouds of gametes. There is no courtship or mate selection nonsense, rather it is group sex worthy of the "Shades of Gray Snapper" blog title.  Watch the video.   The fertilized eggs develop and hatch within a day and the larvae remain planktonic for 20 to 33 days as they develop (Allman and Grimes 2002).  Gray Snapper juveniles settle into shallow seagrass beds where they grow for 8 to 10 months and expand their home range and reach a size of about 10 to 12 cm.  Here they are likely to colonize mangrove shoreline habitats (Faunce and Serafy 2007).  Some postulate that the shallow nearshore environments serve as “waiting room” habitats to allow the reef fishes to grow and avoid intense predation pressure before colonizing adjacent reef habitats (Grol et al. 2011).  Consequently, the mangroves may be important secondary or sequential habitat for supporting large populations of the Gray Snapper.     
 
Mean size of Gray Snapper increases with distance from inlet presumable due to exclusion of small fish. Hashed area is size of Gray Snapper in sea grass beds.  From Faunce and Serafy (2007)
Using acoustic tagging, Luo et al. (2009) revealed that Gray Snappers display a distinct diel migration pattern, whereby shallow seagrass beds are frequented at night and mangroves and other complex habitats were frequented during the day.  This pattern may maximize growth and minimize predation risk.  Survivors eventually obtain large size and move from shallows to bay to ocean reefs. 
Juvenile Gray Snapper associate with Sea Grass beds (Turtle Grass Thalassia testudinum). Photo from San Salvador Island, Bahamas.  Source  
The ontogenetic and diel movements of the Gray Snapper provide direct support for the strategy of conserving both inshore seagrass and mangrove habitats as well as offshore coral reefs.  Gray Snapper are also at risk from harvest in shrimp trawls. The juvenile Gray Snapper often overlaps in soft-bottom habitats that support abundant shrimp populations.   Consequently, shrimp trawlers account for a large portion of the fishing mortality of Gray Snapper.  Gray Snapper are also harvested as bycatch in commercial fisheries for Red Snapper. 

No-take sanctuaries are one strategy for protecting exploited populations, critical habitats, community structure, and corals.   Gray Snapper in one no-take zone in Florida were larger than other waters (Faunce et al. 2002). No-take zones enhance the abundance of another highly valuable snapper (Malcolm et al. 2015); perhaps it is time to expand the application of the strategy.

Gray Snapper is a common component of coral reef ecosystems, which are among the most diverse, albeit frequently altered, marine ecosystems.  Coral reefs are not limited by solar energy, but by nutrients stored and cycled by living organisms.  Consequently, the Gray Snapper must be a key processor and recycler of nutrients because their biomass is high and they annually recruit new individuals to the reef.  In a recent study, Allgeier et al. (2016) demonstrated that fishing reduced fish-mediated nutrient processes by nearly half. Coral reef fish, such as the Gray Snapper, slowly and steadily feed (via concentrated urine) the coral reef ecosystems that, in turn, provide food and shelter to the fish. Selective fishing removes the nutrient pool and the fertilization effect. In the Florida Keys and presumably elsewhere, Gray Snapper are often overfished (Ault et al. 1997).  The recovery and restoration of damaged coral reefs is a long term prospect that depends on protecting the coral reef fishes, such as the Gray Snapper, in addition to protecting the coral reefs. Time for fish biomass to return to equilibrium levels after fishing has ended can take 25 years (McClanahan et al. 2016).  Protect large fishes, such as grouper, snapper or barracuda, and you protect the storage and slow release of nutrients. Gray Snapper and their pee provide ecosystem services that sustain healthy coral reefs. 
Gray Snapper. Photo by Ned DeLoach  Source 
References
Allgeier, J.E., A. Valdivia, C. Cox, and C.A. Layman. 2016. Fishing down nutrients on coral reefs.  Nature Communications DOI: 10.1038/ncomms12461
Allman, R.J., and C.B. Grimes. 2002.  Temporal and spatial dynamics of spawning, settlement, and growth of gray snapper (Lutjanus griseus) from the West Florida shelf as determined from otolith microstructures. Fisheries Bulletin 100:391-401.
Ault, J.S., J.A. Bohnsack, and G.A. Meester.  1997. A retrospective (1979-1996) multispecies assessment of coral reef fish stocks in the Florida Keys.  Fishery Bulletin 96:395-414.
Faunce, C.H., J.J. Lorenz, J.A. Ley, J.E. Serafy. 2002.  Size structure of gray snapper (Lutjanus griseus) within a mangrove 'no-take' sanctuary. Bulletin of Marine Science 70:211-216.
Faunce, C.H., and J.E. Serafy.  2007.  Nearshore habitat use by Gray Snapper (Lutjanus griseus) and Bluestriped Grunt (Haemulon sciurus): environmental gradients and ontogenetic shifts.  Bulletin of Marine Science 80:473-495.
Florida Fish and Wildlife Conservation Commission.  2014.  Species Account Gray Snapper, Lutjanus griseus (Linnaeus, 1758).  Website.  http://myfwc.com/research/saltwater/status-trends/finfish/gray-snapper/ Accessed January 24, 2016.
Grol, M.G.G., I. Nagelkeken, A.L. Rypel,  C.A. Layman. 2011. Simple ecological trade-offs give rise to emergent cross-ecosystem distributions of a coral reef fish.  Oecologia 165:79-88.
Malcolm, H.A., A.L. Schultz, P. Sachs, N. Johnstone, and A. Jordan. 2015.  Decadal changes in the abundance and length of snapper (Chrysophrys auratus) in subtropical marine sanctuaries. PLOS One       http://dx.doi.org/10.1371/journal.pone.0127616.
McClanahan T.R., J.M.Maina, N.A.J. Graham, and K.R Jones.  2016. Modeling reef fish biomass, recovery potential, and management priorities in the western Indian Ocean. PLOS ONE 11(6): e0156920. doi: 10.1371/journal.pone.0156920


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