Effects of the Winter 2000–2001 Freezes on Common Snook in Florida

Numerous common snook were affected by one of the coldest Florida winters ever recorded.

Weather Observations
The first cold fronts of winter 2000-2001 reached Tampa Bay the week of November 23rd, dropping air temperatures into the 40s and 50s and chilling bay waters to 65-68° F. This first front was followed closely by several more with air temperatures in the 40s; by the third week in December, water temperatures had dropped to 62° F. Because snook are tropical fishes at their northernmost limits here in southern Florida, cold is a threat; 54° F is considered the lowest they can tolerate.

The morning of December 22 brought the first freeze of the winter, with air temperatures of 29° F recorded at Palmetto. Bay waters dropped to 55.8-59° F.

Early on December 31st, the air temperature again dropped below freezing and the water temperature in Tampa Bay fell to the critical 54° F. Water temperatures in the shallow flats were as low as 52° F. At this juncture, we expected to receive reports of stunned, dying, and dead snook, especially in the more northern reaches of our area. We solicited the help of fishing guides, park rangers, and outdoor writers to gather accounts of any stressed or dead snook, but no sightings were reported.

During the first three days of the new year, overnight air temperatures remained in the mid to low 30s and daytime highs did not exceed 55° F. On the morning of January 5th, the air temperature at Palmetto dropped to 28° F and remained below freezing for about seven hours. The freeze dropped bay water temperatures to 49.1-50.2° F across Pinellas and Manatee Counties. Reports of stunned, dying, and dead snook began to come in.

Field Observations
The following notes are taken from our field journal for the three days following the first reports of cold-stunned snook. Our notes are similar to reports received from cooperating individuals across the state.

January 5, 2001
We marshalled three teams to collect dead snook for aging purposes and to describe conditions in the field. Matt McGlothlin, Dan Carlson, and I covered Port Manatee and Bishop's Harbor. We went first to the Port, arriving at Berth 12 about 12:30 p.m. There we found 1,200-1,500 snook of all sizes milling about at the surface in the sunlight. We collected about 10 dead fish at that site and saw about as many dead snook out of our reach on the bottom. Beneath the large milling schools were many of the largest snook I have ever seen on Florida's west coast. We estimated these at a total length of 42 to 45 inches; they were very obviously longer than the one meter (40") measuring board used to size large fish. The schools of distressed snook spilled out of Berth 12 and onto the nearby flats around the large spillway pipes. Water temperatures were 51.4° F at the surface, 50.7° F in mid-water, and 50.2° F at the bottom. We checked the entire area and found most of the dead snook in Berth 12; only two or three were found in other areas of the Port.

We then went to Bishop's Harbor and searched the entire bay. We found snook only in the canals along the southeast shore near the ramp. In the first canal, there were about 500 live snook that appeared to be in better shape than those in the Port. However, we found more snook dead here than in the Port and collected about 25 for aging studies. Water temperatures in the first canal were 53.9° F at the surface and 53.6° F at the bottom. In the second canal we found another 300 to 500 live snook in similar condition to those in the first canal and we recorded similar water-temperature readings. We collected another ten dead snook here. We then went into the adjoining creeks thinking we would find dead fish that had been trapped in these shallow areas, but we didn't find any.

Two suppositions are apparent from this trip: 1) If water temperatures drop gradually, snook leave the shallow flats for deeper water and appear to become acclimated to colder temperatures. The minimum of 54° F is reported to be the lethal low, but we found snook alive and doing well in 50-51° F water this winter. 2) Following periods of extreme cold, snook come to the surface to benefit from the warmth of the sun. Almost all the snook we saw were in sunny, quiet, protected areas.

January 7, 2001
I spent the entire day on the water with Kevin Kish exploring the canals from Pinellas Point north to Gandy Bridge. Water temperatures near the St. Pete Pier were at the critical 54° F point. We left a grouper hole and looked in Bayou Grande, Smacks Bayou, Coffeepot Bayou, and the Coquina Key canals. Water temperatures in the protected bayous and canals ranged from 55.5° F to 58° F. In the sun and the warmer waters, we always found snook. Many fish of legal catch-size were seen throughout the Pinellas County areas. We found many dead and dying jacks, lookdowns, sand bream, tilapia, and mullet, but no dead snook. The snook were all at the surface sunning and were usually in the same areas where they are normally found in the summer.

January 9, 2001
Minimum temperatures for the last two days have been in the mid-upper 40s, but bad news.... the forecast is for another freeze tonight. The prospect of yet another freeze is worrisome. Many snook are already badly debilitated by the cold weather of last week and now carry large patches of fungus and bacteria. We estimate that 25% of the total local population are affected. The debilitated fish have been severely stressed, probably have not eaten, and are extremely weak. Following tonight's forecasted freeze, we expect to receive reports of dead snook killed by secondary effects, much like humans succumb to infectious pneumonia following some other debilitating condition.

We walked the shorelines around Bayboro Harbor, Weedon Island and Bishop's Harbor. There were still hundreds of lethargic snook milling at the surface in sunny, sheltered coves. Forty to 50 percent had patches of fungal and bacterial infections and frayed bloodshot fins, however they were responsive and actively moved off as we came into view or caused a shadow to pass over them. We did not locate any dead snook still floating in the bay; though, there were several hundred decaying and half-eaten carcasses along the shoreline.

Estimates of Fatalities
The summary below lists the estimated fatalities reported during the first three weeks of January 2001.

                          Atlantic Coast
Date Area Number of Fatalities
1/2/01 Mosquito Impoundment 50
1/4/01 Mosquito Impoundment 30
1/4/01 New Smyrna 50
1/5/01 Sebastian 100
1/9/01 Daytona 40
1/9/01 Melbourne 25
1/13/01 Oak Hill 1
Gulf Coast
Date Area Number of Fatalities
1/3/01 Estero 20
1/4/01 Clearwater 30
1/4/01 Manatee River 4
1/4/01 MacDill 1
1/5/01 Lowry Park 1
1/5/01 Port Manatee 200
1/5/01 Bishop's Harbor 300
1/5/01 SERF 20
1/7/01 Clearwater 54
1/8/01 Cockroach Bay 50
1/8/01 Dunedin 30
1/11/01 Peace River 400
1/12/01 Myakka River 150
1/16/01 Palma Sola 100
1/17/01 Simmon's Park 100
1/17/01 Fort DeSoto 30
1/19/01 St. Joe Sound 10
1/23/01 Pinellas Point 60
1/23/01 Tarpon Springs 100

It is difficult to arrive at a final estimate of snook killed by the 2000-2001 winter freezes because of lag-time between the actual freeze and when fish are discovered and reported. Additionally some dead snook are never counted because they sink from view, float away with the tides and winds, or are eaten by scavengers like raccoons, buzzards, gulls, and ospreys. Thus the estimates above are minimum numbers. If we assume that roughly an equivalent number of dead snook were lost to observation as were counted, then the best estimate of snook killed this past winter is about 1,500 snook on the Atlantic coast and about 3,300 on the gulf coast, or about 5,000 for a statewide total. Two weather conditions kept the mortality from being higher than it was. First,the initial freeze of the winter was not a sudden drop in temperature but was preceded by days of gradual cooling that allowed the snook to acclimate. Second, the days following a freeze event were usually sunny, allowing some cold-stunned fish to recuperate.

Comparison to Past Losses from Winter Freezes
Although the loss of any snook is regrettable, the reduction in abundance in 2001 as a result of the severe winter will be negligible compared to estimated populations of 1.2 million snook on the Atlantic coast and 0.7 million on the gulf coast. Past freezes have had much greater impact on snook populations in Florida. In 1989, an estimated 200,000 snook were lost statewide. No statewide estimate was made in 1977, but over 20,000 snook died in Lake Okeechobee alone. Because they are tropical and at the limits of their natural range, snook will continue to be susceptible here to episodic kills from winter water temperatures below 54° F.

Condition of the Fish and Fishery
Evidence of the severe winter will be apparent in the snook fishery in 2001. Scars, missing scales, and frayed fins will be seen into the summer on fish in the Melbourne-Daytona Beach areas on the Atlantic coast and the Tampa and Sarasota Bay areas on the gulf coast. Body weight and total length may be lower than normal due to the debilitating effects of reduced feeding, fungal, and bacterial infections, and the rigors of surviving a severe winter. Springtime fishing may be different; the normal seasonal distribution patterns may be disrupted as a result of the freezes and by the cold fronts that have continued into late March. Snook normally found on the flats in the spring may not be there.

Length-frequencies of common snook killed in Florida during the winter of 2000-2001.
Fig. 1. Length-frequencies of common snook killed in Florida during the winter of 2000-2001.

The prediction for 2001 is that snook stocks on both coasts will be robust. Reports persist of reduced numbers of large (> 34") snook in the Charlotte Harbor area, but there are indications that the stock in Charlotte Harbor contains as many, if not more, larger snook than does the Tampa Bay stock. We measured 161 cold-killed snook from Charlotte Harbor and compared them to 222 on the Atlantic coast and 61 from Tampa Bay. We found that about 30% of the fish in Charlotte Harbor were larger than 26", while only 11% on the Atlantic coast and 13% in Tampa Bay were 26" or larger (Fig. 1). Moreover, the comparison between snook in Charlotte Harbor and Tampa Bay is a straightforward one because the two estuaries are much alike. Both are large, open systems, and both have deep areas that snook can use for a thermal refuge. Freezes do not selectively kill either larger or smaller snook. Many of the snook killed on the Atlantic coast were the younger, smaller individuals only because they had entered mosquito-control structures as juveniles and had become trapped in these shallow impoundments. When water temperatures dropped, they could not retreat to the thermal protection of deeper, warmer waters.

Future Considerations
It is illegal to harvest any snook at all from December 15-January 31, and it is illegal to cast-net or gig snook at any time. Respecting and adhering to the regulations will benefit all anglers! The State of Florida is unique in that it has a large variety of tropical and subtropical fish species, snook being one of them. To sustain healthy stocks of this highly prized game fish, we must foster a sound and conservative fishing ethic and observe all fishing regulations. rt

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