Manatee Synoptic Surveys

The word "synoptic" means presenting a general view of the whole. The current manatee synoptic survey is a count of manatees over a broad area. The Florida Fish and Wildlife Conservation Commission (FWC) uses these surveys to obtain a general count of manatees statewide. The FWC coordinates an interagency team that conducts the synoptic surveys from one to three times each year (weather permitting). The synoptic surveys are conducted in winter and cover all the known wintering habitats of manatees in Florida. The survey is conducted to meet Florida state statute 379.2431(4)(a), which requires an annual, impartial, scientific benchmark census of the manatee population. From 1991 through 2019, the counts have been conducted 33 times.

These statewide, interagency surveys are currently conducted during the coldest weather of the year (January through March) when manatees move to warm-water sites, such as natural springs, thermal discharges from power and industrial plants, and deep canals. The ideal conditions for the current synoptic survey are cool weather, following a prolonged period of cold weather (usually following multiple cold fronts), low winds and bright sunshine. Weather conditions and manatee behavior during the survey have a large effect on the synoptic counts. Counts can vary depending on whether it is warm or cold, sunny or cloudy, calm or windy. For that reason, the counts are not suitable for assessing long-term population trends. Manatees are more easily counted a few days after a cold front when it is slightly warmer, clear and windless. A warming trend with sunny, windless conditions following cold weather increases the likelihood that manatees will be resting at the water's surface, where observers can easily spot them.

Although there is no single formula for predicting the best days to conduct the current synoptic survey, FWC scientists use a list of minimum criteria to help predict the most appropriate day to conduct a survey.

Minimum Criteria for Conducting the Current Synoptic Survey

1. Air temperatures forecast to be less than or equal to 49° F near most major manatee aggregation sites* on at least 3 of 5 days before the survey
2. Water temperature below 68° F near most major manatee aggregation sites
3. On the survey days, no winds forecasted above 15 knots in the entire survey area
4. On survey days, no sky conditions forecasted as "mostly cloudy" or "rainy" in the entire survey area

Surveys will only be scheduled if all of these minimum requirements are met simultaneously.

There are unfavorable weather conditions that cause poor short-term water clarity:

1. Absence of sunny and clear skies
2. Heavy rain in previous 48 hours
3. High winds in previous 48 hours (above 20 knots)

Forecasts that include such conditions may be sufficient to postpone a survey.

Sometimes weather conditions meet the criteria in some parts of the survey area but not in others - especially while a cold front is slowly passing through - or a cold front may fail to reach the southern part of the state - causing warm weather in some survey areas. Although conditions may be excellent for surveying in some areas, they may not be appropriate statewide, and the survey may be delayed until the weather is more appropriate in all parts of the state (from the Big Bend area to the Florida Keys).

Constraints:

• Weather forecasts are now widely available on TV, radio, newspapers, and the Internet, but those forecasts are usually highly variable and inconsistent for events 4-5 days in advance. Surveys are not scheduled based on the single lowest temperature forecast available or the single best forecasted weather conditions. Instead, researchers use a representative forecast that is typical of the range of forecasts available.
• Many weather forecasts are available 4-5 days in advance, but most do not give the projected wind speeds more than 2-3 days in advance. No water temperature forecasts are available. The common forecasts do not address many of the factors needed to make the proper decision (for example, wind speed and water temperature).
• Often cold fronts fail to drop to the south (over Florida) or will be less severe than forecasted.

Timing a synoptic survey is not an easy task, given the unpredictable nature of Florida weather and the logistics involved in organizing a survey of this magnitude on short notice. Synoptic surveys are scheduled about 5 to 7 days in advance, which gives staff members time to notify the proper authorities such as power plants, the Federal Aviation Administration, local sheriff and police departments, and airport towers. Because the surveys are organized many days in advance, sometimes weather conditions are not perfect on the day of the survey. However, with each season, staff members become better at predicting the best time to count manatees, and the higher counts in recent years are, in part, reflective of improved knowledge.

On Florida's east coast, counts using current synoptic methods are made at sites from Jacksonville to the Florida Keys. On the west coast, counts are made at sites from the Wakulla River to the Everglades. The 2021 survey will not be conducted due to safety precautions related to the COVID-19 pandemic.

Improvements to the Synoptic Survey

The current synoptic survey method provides a minimum count of manatees in the survey area, but because the number of manatees missed during the survey is not known, it does not provide us with a population estimate. In addition, not all Florida waters are included in the that survey. Survey flights concentrate on areas where manatees are known to gather in large groups during cold weather, but do not cover other areas like the Florida Panhandle or deeper, colder waters like the center of Tampa Bay. Therefore, an unknown number of manatees in these areas are not counted.

Biologists at the FWC's Fish and Wildlife Research Institute have developed a new survey method to estimate abundance. This new abundance survey method differs from the older synoptic survey method in several key ways: 1) it takes place over the course of a week or more for each coast (the two coasts are flown in consecutive years); 2) it is scheduled for a time of year when all Florida manatees should be in the state but are more spread out instead of congregated at warm water and winter habitats; 3) instead of a prescribed flight path, we sample thousands of locations that are randomly selected (within guidelines) by a computer; and 4) two observers on each flight each independently count the number of manatees they see at each location. This method is preferable because: 1) it samples all likely manatee habitat in the State of Florida including the Florida Panhandle; 2) it accounts for important sources of error, such as manatees that are not seen and detected by observers during the survey; and 3) it provides a statistically sound framework for estimating statewide manatee abundance.

*The manatee warm-water aggregation sites are listed in the United States Fish and Wildlife Service Florida Manatee Recovery Plan: U.S. Fish and Wildlife Service 2001 Florida Manatee Recovery Plan, (Trichechus manatus latirostris), Third Revision. U.S. Fish and Wildlife Service. Atlanta, Georgia. 144 pp. + appendices.

*The Florida Fish and Wildlife Conservation Commission (FWC) did not conduct the annual statewide manatee synoptic survey in winter 2008, 2012, 2013 and 2020 because of warmer than average weather. The 2021 survey will not be conducted due to safety precautions related to the COVID-19 pandemic.

Researchers need specific weather conditions to successfully conduct these surveys. The state developed these requirements because surveys conducted in less than favorable conditions produce low counts, as many animals may be missed. Conditions these winters never met the state's minimum requirements.

The FWC will only conduct the survey if conditions meet all of the following requirements simultaneously:

1. Air temperatures forecast to be less than or equal to 49 degrees Fahrenheit near most major manatee aggregation sites on at least three of five days prior to the survey.
2. Water temperatures below 68 degrees Fahrenheit near most major manatee aggregation sites.
3. No winds forecast above 15 knots (17 mph) in the entire survey area on survey days.
4. No sky conditions forecast as "mostly cloudy" or "rainy" in the entire survey area on survey days.