Thursday, February 9, 2017

Pike Killifish: A Small, Specialized Ambush Piscivore

The Pike Killifish (Belonesox belizanus) is fascinating small fish. Rudolf Kner, an Austrian ichthyologist and physician, described the Pike Killifish in 1860, and created a new genus, Belonesox, for this distinctive fish.  What do you see?   How do the morphological traits translate to behavior? This distinctive, small fish has a fusiform body shape and is slightly compressed in posterior region. It has a large eye and a dorsal fin far back from the center of gravity.  Its mouth is oblique and the lower jaw is longer than the upper jaw.   This form is adapted for a surface-feeding ambush predator.  But there is much more to learn about this fascinating little fish.   
Male and Female Pike Killifish.  Photos by Frank Tiegler 
Belonesox implies a cross between a needlefish and a pike. The Latin word, belonÄ“, meaning needle, was first applied to the needlefish by Pliny the Elder in The Natural History (77-79 AD).  Esox is the genus of pikes and pickerels. The teeth and jaw protrusion abilities make the Pike Killifish a little killing machine. The Pike Killifish lies in wait for prey and ambushes, stalks or pursues its fish prey with minimal stealthy movements.  When it locates a suitable prey, it makes one explosive lunge at the prey. Greven and Brenner (2008) discovered that the prey of Pike Killifish were struck within 36 milliseconds and captured at velocities of approximately 11 body lengths per second.  The jaws are greatly enlarged for this small fish and are extended in a long pointed beak filled with canine teeth. The outer series of teeth are conical and curved backwards and smaller than the inner series of teeth. Furthermore, the maximum gape, at 44% of the head length, may be a record for similar sized fish.  The large toothy gape can hold struggling prey while the orientation of the teeth makes it easy for prey to enter, but impossible to escape. Any small, surface-dwelling fish, such as mosquitofishes, swordtails, platies, and even other Pike Killifish, are easy prey.
Note the teeth are unicuspid and have multiple orientations.  Photo of head source Photo of teeth on premaxilla from Grevner and Brenner (2008).
Pike Killifish are in the Order Cyprinodontiformes, the toothed carps, and the Family Poeciliidae.  Poeciliidae is a species-rich family with over 300 species, many of which are known by common names, such as the guppy, molly, swordtail, topminnow, and mosquitofish. Pike Killifish may reach 22 cm and females are much larger than males. The Pike Killifish is the largest species in this family and the only one with the elongated jaws.    Marchio and Piller (2013) concluded based on genetic analyses that there is only one valid species throughout Central America.   
Phylogeny of Belonesox and closest relatives (Ferry-Graham et al. 2010)
Whereas most cyprinodont fishes are micro-carnivores, or pickers, with a small gape designed for nipping, the Pike Killifish is a specialized piscivore.  Pike Killifish achieve this enlarged gape (~20mm) by a mobile premaxilla that is capable of rotating dorsally and a ventrally rotating lower jaw (Ferry-Graham et al. 2010).  While most fishes have to grow into the specialized piscivore niche, the Pike Killifish is capable of the large gape essentially from birth.
Cranial and jaw anatomy. In top diagram the maxilla and adductor mandibulae (A) are removed to show muscle insertions.  Ferry-Graham et al. (2010)
Pike Killifish live in slow-moving streams and rivers, mangrove and weedy swamps, and inlets salty bays, where they associate with abundant submersed vegetation.  They are endemic to Central America from northern Costa Rica through parts of Mexico.  Pike Killifish emerged as a small, but top carnivore, among other small poeciliid fishes many millions of years ago.  Many of these habitats were formed via dissolution of karst topography creating unique aquatic lake types (aguadas, reumideros, and cenotes) in addition to rivers, backwaters, and bays (Vega-Cendejas et al. 2013).  The Pike Killifish are tolerant of low dissolved oxygen, high salinity, and high temperature (Turner and Snelson 1984; Kerfoot et al. 2011)   
Range map of the Pike Killifish.  Source
Males mature at 6 cm and females at 8 cm. Breeding is year-round.  The male has a modified anal fin that serves as an intromittent sex organ, aka gonopodium.  Males repeatedly conduct ritualistic behavioral acts when in the presence of females.  The courting male fans his fins and gonopodium in her direction (Horth 2004).  Fertilization is internal and large clutches (100-300) may be produced every 6-7 weeks.  Newly born Pike Killifish are approximately 15 or 16mm at birth.   All reproductive traits contribute to a high reproductive rate.
Large adult Pike Killifish. Photo by Kenneth Tse Photography
From a single introduction in Miami-Dade County in 1957, the Pike Killifish became established in south Florida
(Schofield et al 2017).  Pike Killifish are common from central western Florida to the Florida Everglades.   Pike Killifish adapted to the physical conditions of Florida because of their wide tolerance for temperature, salinity, and oxygen levels. In the Everglades, the Pike Killifish persisted in several canals east of the Everglades for more than 20 years before expanding dramatically in the 1980s and 1990s; however, no coincidental changes in indigenous fishes were noted (Trexler et al. 2000).  Admittedly, few investigations have examined effects of Pike Killifish in Florida.  One challenge to evaluating the effects of fish introductions is the lack of before-introduction community data.  Greenwood (2012) examined effects of the Pike Killifish on indigenous fishes of the Tampa Bay in Florida.  Here, the Pike Killifish first occurred in 1994 and pre-invasion monitoring data were available.  Pike Killifish reduced the abundance of small resident, indigenous fishes, namely the Eastern Mosquitofish Gambusia holbrooki , Goldspotted Killifish Floridichthys carpio, Sheepshead Minnow Cyprinodon variegatus, and Sailfin Molly Poecilia latipinna.   
Trend in the biomass of Pike Killifish in the Everglades (Trexler et al. 2000)
It is likely the Pike Killifish will persist and spread.  Perhaps it will be accommodated without major effects. It’s too early to know if the Frankenstein Effect (i.e., new invasions are likely to have unexpected consequences) will emerge.  Though most successfully invasive fish are euryphagous, the feeding behavior of the Pike Killifish, though optimized for specialized feeding on fishes, is just as effective for capturing a variety of elusive prey. If there are no fish prey, the Pike Killifish switches to shrimp prey (Harms and Turingan 2012).  

Ornamental and aquaria are growing industries. Photo by Dan Woudenberg/LuCorp Marketing
Florida is home to more non-indigenous fishes than any state due to historic practices. Tropical ornamentals industry contributes $28M per year to Florida’s economy, and ornamental fish farms must be licensed by the Florida Department of Agriculture and Consumer Services.  Best practices can and do minimize the escape, if implemented (Tuckett et al. 2016), and that can reduce the likelihood of invasion success.      

Ferry-Graham LA, Hernandez LP, Gibb AC, Pace C, 2010. Unusual kinematics and jaw morphology associated with piscivory in the poeciliid, Belonesox belizanus. Zoology  113:140-147.
Greenwood, M.F.D.  2012.  Assessing the effects of the nonindigenous pike killifish on indigenous fishes in Tampa Bay, Florida, using a weighted-evidence approach.  Transactions of the American Fisheries Society 14(1):84-99
Greven, H., and M. Brenner. 2008. Further notes on dentition and prey capture of the Pike killifish Belonesox belizanus (Poeciliidae). Bulletin of Fish Biology 10(1/2):97-103.
Harms, C.A., and R.G. Turingan. 2012.  Dietary flexibility despite behavioral stereotypy contributes to successful invasion of the pike killifish, Belonesox belizanus, in Florida, USA.  Aquatic Invasions 7:547-553.
Horth, L, 2004. A brief description of the courtship display of male pike killifish (Belonesox belizanus). Florida Scientist 67:159-165.
Kerfoot, J.R., Jr. 2012. Thermal tolerance of the invasive Belonesox belizanus, pike killifish, throughout ontogeny. Journal of Experimental Zoology Part A: Ecological Genetics and Physiology 317(5):266-274.
Kerfoot J.R., J.J. Lorenz, and R.G. Turingan RG, 2011. Environmental correlates of the abundance and distribution of Belonesox belizanus in a novel environment. Environmental Biology of Fishes 92:125-139.
Kerfott, J.R., and R.G. Turingan.  2011.  Similarity and disparity in prey-capture kinematics between the invasive pike killifish (Belonesox belizanus) and the native Florida largemouth bass (Micropterus floridanus).  Florida Scientist 74:137-150
Marchio, E.A., and K.R. Piller. 2013. Cryptic diversity in a widespread live-bearing fish (Poeciliidae: Belonesox). Biological Journal of the Linnean Society 109:848-860.
Schofield, P.J., L. Nico, and M. Neilson 2017. Belonesox belizanus.  USGS Nonindigenous Aquatic Species Database, Gainesville, Florida.   Website [accessed 8 February 2017]
Trexler J.C., W.F. Loftus, F. Jordan, J.J. Lorenz, J.H. Chick, and R.M.Kobza. 2000. Empirical assessment of fish introductions in a subtropical wetland: an evaluation of contrasting views. Biological Invasions 2:265-277.
Tuckett, Q.M., J.L. Ritch, K.M. Lawson, and J.E. Hill. 2016. Implementation of best management practices for Florida ornamental aquaculture with an emphasis on non-native species. North American Journal of Aquaculture 78: 113-124.
Turner, J.S., and F.F. Snelson. 1984. Population structure, reproduction and laboratory behavior of the introduced Belonesox belizanus (Poeciliidae) in Florida. Environmental Biology of Fishes 10:89-100.
Vega-Cendejas, M.E., M.H. de Santillana,  and S. Norris. 2013. Habitat characteristics and environmental parameters influencing fish assemblages of karstic pools in southern Mexico. Neotropical Ichthyology 11(4):859-870.

Tuesday, January 31, 2017

Puzzling Over Large Aggregations of Sharks, by Don Orth

Ecological principles should guide the wise use and management of fisheries. However, occasionally it appears at first glance that some principles don't apply. My example today is the extreme inverted pyramid.  Animal ecologist, Charles S. Elton,  introduced the pyramid of numbers in 1927 and coined the term “food chain.”  Later we would adopt the term “food webs” (May 1983).  But Eltonian pyramids would remain as characteristics of ecosystems. Pyramids of numbers and biomass were replaced by energy pyramids (Lindeman 1942) where organism biomass is constrained into rigidly delineated trophic levels. Early work by Elton and Lindeman did not include coral reef ecosystems; however, recently investigators have revealed the shapes of pyramids in coral reef ecosystems where shark are apex predators.
Gray Reef Shark Carcharhinus amblyrynchos was one of several sharks studied by Mourier et al. (2016). Photo by Albert Kok  Source
Basically, energy pyramids graphically depict the declining energy as one moves up the trophic levels in a community.  The producers derive and transfer energy from nonliving sources into the biotic community. 
(i) Bottom-heavy pyramids of numbers (N), (ii) bottom-heavy pyramid of biomass (B), and  (iii)   inverted biomass pyramid.  From Tribelco et al. (2013).
Elton observed a strong relation between the trophic level organisms in food chains and their body sizes.   Consequently, we would expect to see a decline in biomass (abundance) with corresponding increase in body mass.  This is called the biomass size spectrum. It makes intuitive sense and complies with the laws of thermodynamics.  Numerous investigators have explored the application of the biomass spectrum to identify constraints on the structure of aquatic communities and as an indicators of perturbation (Jung and Houde 2005; Sprules and Barth 2016).      
Example biomass size spectrum    Source
A recent investigation of a biosphere reserve located in French Polynesia, largely protected from human influences, revealed a unique energy pyramid and size spectrumInvestigators used a series of video-assisted underwater visual census surveys across the entire shark school to provide precise estimates of shark numbers.  Here the density of apex predator, the Gray Reef Shark, averaged of 600 reef sharks, two to three times the biomass per hectare documented for any other reef shark aggregations!  Imagine 14 to 40 sharks per hectare.  It is unexpected for the largest apex predators to be so abundant. 
Gray Reef Shark aggregations in Fakarava Pass, in the Tuamotu Archipelago of French Polynesia.   Source: Mourier et al. (2016).
So, how is it that we observe cases of extreme inverted pyramids?  The extreme reef shark densities do not make ecological sense.  The observation was made in a biosphere reserve where human impact was negligible.  Is this what we expect in pristine reefs?

This large shark aggregation would need 147-350 kg of fish per day --  that is 91 tonnes per year. Yet, the fish production is only 17 tonnes per year.  The math doesn't work here.  The extreme inverted pyramid is a paradox.  It cannot exist, unless there is a subsidy from outside the area.  Either the sharks move out of the area to feed or else fish enter the area from elsewhere and become shark food.   Investigators tagged the sharks and tracked their movements.  Predators typically make foraging excursions to enable them to feed on multiple pyramids.  However, that was not the whole story.
Examples of shark foraging in the pass at night on the Camouflage Grouper Epinephelus polyphekadion (A, B, and C) and the Whitemargin Unicorn fish Naso annulatus (D).  Source:  Mourier et al. (2016)
What Mourier et al. (2016) discovered were large aggregations of groupers (17,000 were counted in one aggregation) that moved into the area during the grouper spawning season.  This migration brought in 31 tonnes of shark food that was produced elsewhere.  Other fish also migrate in large aggregations, thereby transferring fish production from elsewhere.  These spawning aggregations provide the energy subsidies needed to support large aggregations of sharks.  When the spawning aggregations became scarcer, the sharks shifted to making foraging excursions.  For a quick video review of this work, click here

The full potential of the size spectrum theory approach linked to energy pyramids has yet to be realized as more studies must be done from a wide range of ecosystems (Tribelco et al. 2013).  It is a data-hungry approach, but few worthwhile scientific investigations are data free.  Our challenge is finding study regions not heavily influenced by the removal of the top predators. 

This story about super abundant shark aggregations and their reliance on spawning aggregations of groupers for energy subsidies is an important discovery for fisheries management.  It illustrates the futility of single species fisheries management.  Sharks cannot be managed via harvest regulations alone.  Even if no sharks were harvested from this population, the population may decline depending on conditions for other fishes outside the biosphere reserve. Conservation of fish spawning aggregations, which are often targets of exploitation (Sadovy and Domeier 2005), can help conserve shark populations, especially if combined with shark fishing bans.  Simpfendorfer and Heupel (2016) emphasized the critical need for managers to protect the areas over which the sharks disperse to feed, which requires a better understanding of the movement patterns to inform management plans.  Fisheries managers cannot draw boundaries in open ecosystems without knowing the actual movement patterns of all elements of the community.    

Elton, C. S. 1927. Animal Ecology. The Macmillan Company, New York. 260 pp.
Jung, S., and E.D. Houde. 2005.    Fish biomass size spectra in Chesapeake Bay. Estuaries 28:226-240.
Lindeman, R. L., 1942. The trophodynamic aspect of ecology. Ecology 23: 399–418.
May, R. M. 1983. The structure of food webs. Nature 301: 566–568.
Mourier, J., J. Maynard, V. Parravicini, L. Ballesta, E. Clua, M.L. Domeier, and S. Planes.  2016.  Extreme inverted trophic pyramid of reef sharks supported by spawning groupers.  Current Biology 26(15):2011-2016.  DOI:
Sadovy, Y., and M. Domeier. 2005.  Are aggregation-fisheries sustainable? Reef fish fisheries as a case study. Coral Reefs 24:254. doi:10.1007/s00338-005-0474-6
Simpfendorfer, C.A., and M.R. Heupel.  2016.  Ecology: The upside-down world of coral reef predators.  Current Biology 26:R701–R718,
Sprules, W.G., and L.E. Barth. 2016.  Surfing the biomass size spectrum: some remarks on history, theory, and application.  Canadian Journal of Fisheries and Aquatic Sciences 73(4): 477-495, 10.1139/cjfas-2015-0115
Trebilco, R., J.K. Baum, A.K. Salomon, and N.K. Dulvy.   2013.  Ecosystem ecology: size-based constraints on the pyramids of life.  Trends in Ecology & Evolution 28(7):423-431.

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:
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 
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. 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
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