Age of most marine fishes (except sharks and rays) is estimated from examinations of the otoliths (earbones) that are located beneath the brain and function much like the human inner ear (balance and detection of vibrations). After cutting a thin cross-section from the center of the otolith, inspection under a microscope reveals concentric dark growth rings that are akin to the growth rings seen in trees (see figure below). One ring equals one year of life.

Photomicrograph of a cross-section of a red snapper otolith with 30 dark annual growth rings. (Image by A. J. Fischer, Dept. of Oceanography and Coastal Sciences, Louisiana State University)

As recently as 20 years ago, red snapper from the Gulf of Mexico (GOM) were thought to live only about 10-15 years; we now know them to be significantly long-lived compared to many familiar marine fishes. Spotted seatrout (specks) in Louisiana seldom survive past age 5, tunas are old at age 12, and redfish may live about 40 years at the maximum. The oldest red snapper reported in the scientific literature is an individual sampled in February 1991. This specimen, a female 53.6 years of age at time of capture, was actually hatched before World War II and survived to “see” the dawn of the atomic age, the first man on the moon, and the technological boom of the late 20th century. However, an even older specimen, almost 59 years of age, was sampled from the commercial harvest by LSU biologists some years later. This potentially long lifespan complicates management of red snapper; the species must be managed more like a forest than an annual crop like shrimp. Very old individuals have been rarely encountered in the various research projects that have sampled either the commercial harvest or the recreational harvest and they have become increasingly more uncommon in the last decade or so. The vast majority of the red snapper harvested by both the recreational and commercial fisheries are in the range of 2-6 years of age.

Age frequency of red snapper harvested by the commercial fishery off Louisiana, 1995-2004. (Modified from: Nieland, D. L., A. J. Fischer, M. S. Baker, Jr., and C. A. Wilson. Red snapper in the northern Gulf of Mexico: Age and size composition of the commercial harvest and mortality of regulatory discards. Pages 301-310 in W. F. Patterson, III, J. H. Cowan, Jr., G. R. Fitzhugh, and D. L. Nieland, editors. Red snapper ecology and fisheries in the U.S. Gulf of Mexico. American Fisheries Society, Symposium 60, Bethesda, Maryland.)

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Red snapper grow in length relatively fast during their first 10 years or so of life reaching, on average, a length of about 30 inches. Growth rate decreases drastically thereafter as they shift more energy into reproduction and less energy into growth. This growth strategy also allows them to get big quickly, an advantage in both avoiding and deterring predators. However, there is great variety in individual growth rates among red snapper; size is little indication of age (see figure below). For instance, a 5 year old red snapper may range in length from as little as 13 inches to as large as 32 inches (average = 25 inches) and a 32 inch long specimen may range from 5 to 50+ years of age. Interestingly, old individuals are seldom very large and large individuals are seldom very old. The 53.6 year old female referenced above was a mere 33.5 inches long and weighed only 17.5 pounds. Conversely, the world angling record red snapper (caught in the GOM off Louisiana by Doc Kennedy of Grand Isle, LA on 23 June 1996) was 41 inches long and weighed 50.25 pounds, yet was only 20 years old!

Age-length relationship for red snapper from the Gulf of Mexico off Louisiana. (Modified from: Wilson, C. A., and D. L. Nieland. 2001. Age and growth of red snapper Lutjanus campechanus from the northern Gulf of Mexico off Louisiana. Fishery Bulletin 99:653–664.)

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The red snapper spawning season in the northern Gulf of Mexico begins in May and ends in late September (about 120 days); peak spawning months appear to be May, June and July. Unlike many fish species that spawn between dusk and midnight, red snappers begin their spawning activities in the early afternoon and stop at dusk. There is no evidence that red snappers form spawning aggregations at specific sites year after year as do some other species of snappers and many species of groupers. Red snappers seem to spawn wherever and whenever they are capable of doing so.

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Almost all female red snappers in the GOM off Alabama become spawning-capable (reproductively mature) at age 2 and at a total length of about 13 inches. In the GOM off Louisiana, however, while many females become spawning capable at age 2, some female red snappers do not start spawning until they are age 6 and almost 27 inches in length. This is likely due to differences in population sizes between the two areas (more fishing pressure and fewer red snappers off Alabama). This process of maturing at younger ages and smaller sizes, called juvenescence, is usually a compensatory response to diminishing numbers within a population of fishes.

Age at maturity (able to produce and spawn eggs) for female red snapper captured off Alabama (purple) and Louisiana (green), 1999-2001. (Modified from: Woods, M. K. 2003. Demographic differences in reproductive biology of female red snapper (Lutjanus campechanus) in the northern Gulf of Mexico. Master’s thesis. University of South Alabama, Mobile, Alabama.)

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Red snappers, like many other marine fish species, are batch (or serial) spawners. This means they are capable of repeatedly spawning batches of eggs every few days over the course of the entire spawning season, a strategy that allows them to produce and spawn many times more eggs than if they only spawned a single time per season. The number of eggs spawned in each batch varies with the size of the individual and can be as few as a 1000 for a small female to as many as 2.5 million for a large, healthy female. Given that the average time between successive spawning is four days, female red snappers will spawn about 30 times (some more, some fewer) during the spawning season. Even a small red snapper will produce a seemingly respectable 30,000 eggs in a season while a large female might spawn an incredible 75 million or more eggs each season! And if it should survive to the known maximum of its longevity, a female could potentially spawn nearly 4 billion eggs in her lifetime. Naturally, with all these red snapper eggs being spawned, it must be incredibly difficult to survive from egg to spawning adult or the GOM would be wall to wall red snappers! However, with the bulk of the recreational and commercial harvests consisting largely of individuals 2-6 years of age (see above), most females spawn only a couple of times and are harvested well before they achieve their maximum spawning potential.

Photomicrograph of red snapper oocytes (immature eggs). The smaller dark oocytes are not yet developed enough to be spawned; the larger, clear oocytes would have been part of the next batch of eggs spawned. (Photomicrograph by David L. Nieland)

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Red snapper are pelagic spawners, that is, the males and females simultaneously release their eggs and sperm up in the water column and allow the fertilization of the eggs to the whims of the ocean. The eggs hatch after about a day and the larvae are dispersed by the currents and tides of the GOM. After a month or two of feeding, growing, and being carried by the currents, the young red snapper take up residence on low-relief, inshore or offshore, sand or mud habitats where they will spend the next year or two. It is while inhabiting these areas that they are most susceptible to being caught in shrimp trawls.

Shortly before they reach 2 years of age, most red snappers move to areas of cover and high relief such as natural and artificial reefs, shipwrecks and petroleum platforms, where these structures afford both food and protection from predators. Surprisingly, little of their food comes directly from the structure itself; rather they forage at night for shrimp, worms and crabs that live on the seabed as much as several hundred yards away from the structure. While resident on these structures, red snapper are quite safe from shrimp nets, but they become vulnerable to both commercial and recreational fishermen. It is thought by some that, after several (5-10) years of residency on either reefs or rigs, red snapper migrate away from these structures to remote, more isolated habitats in the deeper waters of the GOM.

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The red snapper in the GOM is currently managed under the “unit stock hypothesis;” this generally implies that there is both a great deal of long-distance movement by individuals and little genetic difference among individuals and populations throughout the GOM. Management of red snapper under the unit stock hypothesis also has the advantage of simplicity in both the application and enforcement of regulations. Tagging studies (in which fish are caught, tagged, released and hopefully re-caught at a later time) have shown that red snapper are indeed capable of movements as much as 350 miles, especially when motivated to do so by tropical storms and hurricanes. However, in these same studies, the vast majority of tagged red snappers are recaptured within a few miles of their initial tagging sites, even after several years of post-tagging freedom. Genetic studies analyzing both nuclear DNA and mitochondrial DNA have generally been unable to refute the unit stock theory; however, they have shown that there are minor, yet very consistent, differences in the genetic makeup of red snapper populations across the GOM. Also certain demographic differences, such as the variations in lengths/ages (see above) at maturity in Alabama and Louisiana red snapper, indicate that local populations of red snapper are largely isolated from neighboring populations.

Recapture locations of red snapper initially caught and tagged off Alabama. Note that almost all of the movement by these red snappers is to the east. (Source: J.H. Cowan, Jr.)

All of the above suggest that red snapper in the GOM may indeed have become structured into a series of semi-isolated, largely independent populations that perhaps should be managed each as its own unit stock. Application of region-specific regulations (quotas, minimum sizes, daily bag limits, etc.) in different areas of the GOM may be a more appropriate approach to management of the species, if not more complicated for management and enforcement personnel.

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Minimum size regulations have been applied to both the recreational and the commercial red snapper fisheries since 1984. The purpose of minimum sizes was to increase the yield of the fisheries and to enhance the likelihood of female red snapper spawning at least once before being harvested. Both fisheries started with a 13 inch minimum, but over the years the minimum allowable length for harvest increased to 15 inches in the commercial fishery and 16 inches in the recreational fishery. Just recently the minimum size for the commercial fishery has reverted to 13 inches.

For years there have been anecdotal reports of great numbers of dead, discarded, undersized red snappers floating off from behind fishing boats, both commercial and recreational. The ascent from depth to the water’s surface often produces injury to hooked red snappers due to hydrostatically-induced barotrauma (eyes bulging, intestine protruding from anus, air bladder distended and stomach protruding from mouth, etc.). What are the probabilities of an undersized red snapper surviving catch and release?

Two studies, one off Texas and one off Louisiana, simulating techniques used in the red snapper recreational fishery have estimated mortality of regulatory discards to range between 1% and 44% and increasing with depth of capture. In the relatively shallow waters off Alabama, another study calculated a discard mortality of 13% for red snapper caught with recreational gear. Among red snapper less than 18 inches released from headboats in Texas waters, 15.2% floated off and 1.4% were discarded dead.

Given the gamut of life-threatening circumstances that a red snapper regulatory discard must face, it may not be unreasonable to expect a near 100% mortality of discards in the commercial fishery. In a study conducted on commercial fishing boats off Louisiana, 69% of undersized red snapper returned to the water were either near death (as evidenced by their failure to resubmerge) or dead. Additional mortality due to either fish (sharks, barracudas, groupers, jacks) or mammalian (dolphins) predators may occur on specimens that are trying, perhaps struggling, to return to depth. Should an individual survive the catch and release experience and should it avoid the various predators as it swims down, there is also the possibility of long-term mortality due to barotrauma-induced internal injuries. Additional studies are needed to determine the level of, as well as spatial and temporal patterns in, both short-term and long-term mortality of discarded red snapper.

Fates of under-sized red snapper captured with commercial gear from the Gulf of Mexico off Louisiana, 2002 and 2003. 1 = fish oriented toward the bottom and swam down vigorously, 2 = fish appeared disoriented upon entering the water, but soon oriented toward the bottom and swam down slowly, 3 = fish appeared very disoriented upon entering the water and remained at the surface, and 4 = fish was either unresponsive or dead upon entering the water. (Modified from: Nieland, D. L., A. J. Fischer, M. S. Baker, Jr., and C. A. Wilson. Red snapper in the northern Gulf of Mexico: Age and size composition of the commercial harvest and mortality of regulatory discards. Pages 301-310 in W. F. Patterson, III, J. H. Cowan, Jr., G. R. Fitzhugh, and D. L. Nieland, editors. Red snapper ecology and fisheries in the U.S. Gulf of Mexico. American Fisheries Society, Symposium 60, Bethesda, Maryland.)

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For additional information, please go to these primary sources of information on red snapper:

Patterson, W. F., III, J. H. Cowan, Jr., G. R. Fitzhugh, and D. L. Nieland, editors. 2007. Red snapper ecology and fisheries in the U.S. Gulf of Mexico. American Fisheries Society, Symposium 60, Bethesda, Maryland. See particularly:

Fischer, A. J. An overview of age and growth of red snapper in the Gulf of Mexico. Pages 189-200

Gold, J. R., and E. Saillant. Population structure of red snapper in the northern Gulf of Mexico. Pages 181–195.

Hood, P. B., A. J. Strelcheck, and P. Steele. A history of Red Snapper Management in the Gulf of Mexico. Pages 267-284.

McCawley, J. R., and J. H. Cowan, Jr. Seasonal and size specific diet and prey demand of red snapper on Alabama artificial reefs. Pages 77-104.

Nieland, D. L., A. J. Fischer, M. S. Baker, Jr., and C. A. Wilson. Red snapper in the northern Gulf of Mexico: Age and size composition of the commercial harvest and mortality of regulatory discards. Pages 301-310.

Nieland, D. L., A. J. Fischer, and C. A. Wilson. Declining size at age among red snapper in the northern Gulf of Mexico: Recovery or collapse? Pages 329-335.

Patterson, W. F. A review of movement in Gulf of Mexico red snapper: Implications for stock structure. Pages 245-261.

Rummer, J. L. Factors affecting catch and release (CAR) mortality in fish: Insight into CAR mortality in red snapper and the influence of catastrophic decompression. Pages 123-144.

Wilson, C. A., and D. L. Nieland. 2001. Age and growth of red snapper Lutjanus campechanus from the northern Gulf of Mexico off Louisiana. Fishery Bulletin 99:653–664.

Woods, M. K. 2003. Demographic differences in reproductive biology of female red snapper (Lutjanus campechanus) in the northern Gulf of Mexico. Master’s thesis. University of South Alabama, Mobile, Alabama.

The Magnuson-Stevens Fishery Conservation and Management Act: Reauthorization Issues.

Congressional Research Service, February 7, 2005. E. H. Buck. http://digital.library.unt.edu/govdocs/crs/permalink/meta-crs-10098:1

The Magnuson-Stevens Fishery Management and Conservation Act of 1996 www.nmfs.noaa.gov/sfa/magact/

The Magnuson-Stevens Fishery Management and Conservation Act of 2007 www.gulfcouncil.org/Beta/GMFMCWeb/downloads/MSA07.pdf

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