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Management of Common Snook in Florida

The common snook, Centropomus undecimalis, is a popular game fish in Florida. Snook have presented challenges to management because of complex life history and distribution.

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INTRODUCTION
The common snook, Centropomus undecimalis, is a popular gamefish in Florida that has presented challenges to management because of its complex life history and distribution. Because snook may reach maturity between the ages of 4 an 6 and may live more than 20 years, they may be easily overfished. In addition to the mortality associated with exploitation, snook are vulnerable to water temperatures less than 55–56 degrees Farenheit; episodic, massive kills have occurred during severe winters. Snook populations on the two coasts of Florida have significantly different growth patterns and different reproductive schedules. Common snook are protandric hermaphrodites, i.e., some portion of male snook reverse sex and become females between the ages of one and seven years (Taylor et al. 1993). Additionally, Atlantic-coast snook are genetically different from gulf-coast snook (Tringali and Bert 1996). Because snook support one of the largest and most popular fisheries in Florida and because of their complex biology and susceptibility to low water temperatures, managers have promulgated strict regulations that emphasize low bag limits, closed seasons, and the value of catch-and-release fishing in an effort to ensure high levels of abundance.

Historical levels of abundance
Prior to World War II, human consumption of snook was low because the fish developed a "soapy" taste as a result of cleaning practices that left the skin attached to the fillet. Snook were considered "cat food," and commercial fishermen were paid between $0.025–0.04 per pound (Marshall, 1958). As demand increased during the protein-short war years, techniques for using large, shore-based haul-seines and gill-nets were developed that allowed harvesters to catch from 5,000 to 20,000 lbs. of snook per set. Annual landings of snook in Florida during 1941–1955 averaged 498,492 lbs. and ranged between 374,312 and 800,698 lbs. at prices of $0.14–0.25per pound. Harvest peaked in 1948, followed by annual declines until 1957; these declines were partially due to decreased demand and partially to the prohibition of haul seines in Lee County in 1947 and throughout the state in 1951. During the mid-fifties, anglers reported declines in abundance at the same time steady decreases in commercial landings were reported, and the Florida legislature passed stricter regulations in 1957. These rules made it illegal to buy or sell snook, set the bag limit at four snook per day, and made legal capture of snook by "hook and line" only.

Between 1957 and 1976, there was a hiatus in research and technical information regarding snook abundance; although, fishing guides and members of conservation organizations continued to report that snook populations were declining (Bruger and Haddad, 1986). In 1976, biologists from the Florida Department of Natural Resources, Marine Research Laboratory, (later known as, Department of Environmental Protection, Florida Marine Research Institute, DEP, FMRI)* began a mark-recapture study in the Naples–Marco Island area to determine annual estimates of abundance of snook populations in southwest Florida. Snook were collected in a 100-m beach seine each summer from 1976 through 1987. The area was sampled again in 1994, and another estimate of the population was made.

Current levels of abundance
Results of the tagging program indicated that snook abundance in the Naples area had declined by approximately 70% between 1977 and 1981 (Fig. 1a.), presumably because of the effects of increased exploitation and a disastrous freeze in January 1977 (Gilmore et al., 1978). As a result of these findings, the legislature, in 1981, set possession limits at two snook per day with the provision that no snook longer than 18 inches fork length could be kept during June or July 1982–1986. In 1982, the snook fishery was closed January, February, June, and July during 1982–1986. These rules were intended to halt the decline in abundance by eliminating the take during the winter months, when snook become lethargic in the cold water and so can easily be harvested in dip nets, and by eliminating the take during the summer spawning season, when catch rates were the highest. Despite these added restrictions, snook abundance remained low in the Naples area during 1983–1986.

In 1985, the newly created Florida Marine Fisheries Commission (FMFC) permanently closed the snook fishery during the months of January, February, June, July, and August; increased the minimum legal size to 24 inches total length; and established a daily bag limit of two snook, only one may exceed 34 inches total length. The Naples index for 1987 indicated that the levels of snook abundance were still depressed but that they approximated the levels of 1981, reflecting an improvement. The tagging study was conducted again in the summer of 1994, and that estimate was also greater than the yearly estimates for the period 1981-1986. Although it is difficult to make conclusions from these data because of the large error associated with the prior estimates, the estimates of 1987 and 1994 indicate that the decline has abated and that the snook populations in the Naples area may have stabilized or may have increased to the levels of the early eighties.

In 1984, FMRI biologists began to monitor levels of snook abundance annually along the southeast coast of Florida using similar mark-recapture procedures to those used in Naples. The capture gear was hook and line instead of seines. This research was conducted through 1997 which provided continuous estimates of the abundance of common snook in the Jupiter-Palm Beach area. Even though 95% confidence limits overlap for most estimates, the mean abundance indices increased during the late eighties (Fig.1b.). Mean east-coast estimates were lower, though not significantly, during 1991-1994, perhaps because of increased fishing effort combined with the effects of the severe winter of 1989–1990.

Biologists from DEP, FMRI began monitoring levels of snook abundance in two micro-habitats of Tampa Bay in the summer of 1990 using a trammel net as the capture gear and the Petersen one-time mark-recapture technique to make annual population estimates. Current levels of abundance in both the upper bay MacDill site and the lower bay Port Manatee site are significantly higher than levels determined at the beginning of the study (Figs. 2 a. and b.). These increases may be the result of increased recruitment after the depletion of Tampa Bay stocks during the extreme winter of 1989–1990. We cannot estimate either the total snook mortality sustained during this cold-kill event or the levels of abundance in Tampa Bay prior to 1990; however, more than 60,000 adult snook were estimated to have been killed in the Manatee and Little Manatee rivers in December 1989.

The National Marine Fisheries Service, Marine Recreational Fisheries Statistical Survey (MRFSS) landings summary has been recorded since 1982 and provides other fishery data used to assess the status of snook stocks in Florida. The number of intercepts has increased annually on both coasts from about 55 in 1982 to more than 900 in 1995 (Figs. 3a. and b.). Effort increased from fewer than 100,000 trips on each coast in 1982 to more than 700,000 trips on the Atlantic coast and more than 800,000 on the gulf coast in 1995. Effort and catch-per-unit-effort (CPUE) have increased significantly. The number of snook harvested increased from about 5,000 fish on the Atlantic coast and about 20,000 on the gulf coast in 1982 to about 44,000 snook on each coast in 1995. The simultaneous increase in effort and CPUE indicates that current levels of abundance have surpassed the levels of the early eighties. The actual harvest represents only six and eight percent of the total snook caught on the Atlantic and gulf coast, respectively, demonstrating that the snook fishery in Florida has primarily become a catch-and-release fishery.

Spawning potential ratios

The strategy for managing snook in Florida has been to maintain very high standing stocks by instituting low bag limits, closed seasons, and slot limits and by encouraging catch-and-release fishing. In 1993, the FMFC adopted the concept of spawning potential ratios (SPR) as the primary method with which to assess snook populations in Florida. In 1991, using catch-curve information from known ages of female snook collected during a previous life-history study, FMRI biologists determined that SPR values for Atlantic and gulf coast snook populations were 48% and 38%, respectively. In 1993, the FMFC established a management goal of maintaining a minimum SPR of 40% for snook populations on both coasts of Florida. This level is higher than the levels adopted for other inshore species in Florida e.g., red drum, spotted seatrout, and mullet, but it is warranted because snook are vulnerable to cold kills coupled with the uncertainties associated with managing a protandric hermaphrodite.

All available information indicates that the current snook management strategy is viable and has achieved the intended results. It appears that stringent management measures, combined with recent mild winters, have allowed snook abundance to rise to high levels (Nelson, 1993). The estimated SPR values for Atlantic stocks in 1996 and 1997 were 44 and 40%, respectively, while these values for the gulf stocks were 41 and 40%, respectively (Muller and Murphy, 1998). The weakness inherent in using the SPR analyses to assess fish stocks is the assumption that natural mortality remains constant. Random catastrophic cold kills and red tide events render that assumption invalid. This weakness and the reluctance to independently sample adults of a popular gamefish may provide the impetus to manage snook by using other techniques, such as CPUE, abundance indices, survival rates derived from tag-recovery studies, or angler satisfaction ratings.

Future considerations
Future snook management must be tempered with the realization that during the past 50 years in Florida, more than half of the snook's principal habitat, mangrove shoreline, has been lost (Bruger and Haddad, 1986). Marshall (1958) stated that closing the commercial fishery for snook and imposing size restrictions had done little to halt the population declines that began in the fifties and that these declines were more likely due to alterations of the habitat than to fishing. Because of habitat reduction, increased exploitation, and sporadic cold kills, it is prudent to maintain strict regulations on the fishery to ensure high levels of stock abundance. However, high levels of snook abundance may not be sustainable unless the habitat critical to this species is managed as well.

Common snook is an economically valuable resource to the state of Florida; enthusiasts generate large revenues in pursuit of this "species of special concern." Anecdotal reports and scientific data indicate that snook abundance has increased over the last ten years as a result of mild winters, restrictive management, and angler conservation. Even though it may not be possible to restore the populations to levels of the pre-World War II era because of the changes in habitat and increased fishing effort, it may be possible in the short term, to maintain or even increase, levels of abundance if harvest remains low.

* The FMRI's name changed again in July 2004 to Florida Fish and Wildlife Conservation Commission (FWC), Fish and Wildlife Research Institute (FWRI).

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References
Bruger, G. E., and K. D. Haddad. 1986. Management of tarpon, bonefish and snook in Florida. In R. H. Stroud (ed.) Multi-jurisdictional management of marine fishes: Marine Recreational Fisheries II. Proceedings of the eleventh annual marine recreational fisheries symposium. Tampa, FL. May, 1986. National Coalition for Marine Conservation, Inc. Savannah, GA.

Gilmore, R. G., L. H. Bullock, and F. H. Berry. 1978. Hypothermal mortality in marine fishes of south-central Florida: January, 1977. NE Gulf. Sci. 2(2):77–97

Marshall, A. N. 1958. A survey of the snook fishery of Florida, with studies of the biology of the principal species, Centropomus undecimalis (Bloch). Fla. Board Conserv. Mar. Res. Lab. Tech. Ser. No. 22.

Muller, R. G., and M. D. Murphy. 1998. A stock assessment of common snook, Centropomus undecimalis. Dept. Env. Prot. Fl. Mar. Res. Inst. 100 Eighth Ave. SE, St, Petersburg, FL. 33701.

Nelson, R. 1993. A review of snook management: current status and potential issues. Florida Marine Fisheries Commission Staff Report. May 27, 1993. Tallahassee, FL.

Taylor, R. G., J. A. Whittington, and H. J. Grier. 1993. Biology of common snook from the east and west coasts of Florida. Study 3, Sect. 1. In Investigations into nearshore and estuarine gamefish distributions and abundance, ecology, life history, and population genetics in Florida.R. E. Crabtree, T. M. Bert, and R. G. Taylor, eds. FDNR/FMRI Rep. No. F0165-F0296-88-93-C. U. S. Department of the Interior, Fish and Wildlife Services, Washington, D. C. Pp 1–51.

Tringali, M. D., and T. M. Bert. 1996. The genetic stock structure of common snook Centropomus undecimalis. Can. Jour. Fish Aquat. Sci. 53 (5): 974–984.

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A Historical Review of Snook Regulations in Florida:

1947

Snook haul seines made illegal in Lee County

1951

Snook haul seines made illegal in Collier County

1953

Minimum size set at 18 inches fork length

1957

Snook made illegal to buy or sell

Capture by hook and line only

Bag limit set at four snook per day, eight snook possession limit

1981

Bag limit reduced to two snook per day, two snook possession limit

No snook less than 26 inches fork length may be taken in June or July during 1982–1986

1982

June and July of 1982 closed to snook possession.

1983

January and February 1983–1986 closed to snook possession

June and July 1983–1986 closed to snook possession

1985

January, February, June, and July closed permanently to snook possession

August 1985–1986 closed to snook possession

Minimum size increased to 24 inches total length

Only one snook may be greater than 34 inches total length

1987

All species of the Genus Centropomus covered by the regulations

August closed permanently to snook possession

All snook to be landed whole

Use of treble hooks prohibited with natural baits

1994

Closed winter season changed to 15 December through January 31

1999

Slot limit set at 26 inches minimum–34 inches maximum total length

To view the most current regulations on snook, please visit the Florida Administrative Code Web site—Chapter 68B-21.