The way an animal moves from place to place can inform us about its life and environment. In this lesson, students examine the travel patterns of juvenile flatfishes in an estuary. The process of sampling bottom-dwelling fishes is explained, and data from a university-based marine science laboratory are evaluated. Students compare the distance traveled by juvenile fish to human movement by determining their own average step length. Comparing step length to the distance-to-body-length traveled by flatfish enables students to put in perspective the journey taken by the fish.

Important information about an animal’s life and ecosystem can be ascertained by the way it moves from place to place. Key factors regarding how and why certain animals change location include the need for food, protection from predators, and reproduction. Environmental factors must be considered as well, including food quantity, presence of shelter, and temperature. Not all fish species migrate, and there are large potential costs to migrating. Migrating organisms are exposed to unfamiliar areas that may have more or different predators. Studying animal movement therefore leads to a broad consideration of the survival strategies of a species.

Tracking animal movement can be difficult, and understanding travel patterns of marine organisms presents the particularly daunting challenge of mapping underwater movement. For commercial species, considerable information is collected by fishermen. Visual underwater census counts are possible for some species, especially shallow-water reef fish such as angelfish, as well as certain benthic crustaceans and mollusks (Paddack & Estes, 2000; Samoilys & Carlos, 2000; Hereu et al., 2008; Kendall et al., 2009). It is even possible to conduct visual surveys using submersibles or remotely operated vehicles for deeper-water fish (Willis et al., 2000; Yoklavich et al., 2007). Tagging fish with darts, coded wire tags, or acoustic transmitters is becoming more common and can provide information not only on long-distance migration patterns but also on fish growth (Holland et al., 1993; Heupel et al., 2006; Holm et al., 2007). Finally, species abundance can be estimated through sampling by trawl nets, and data on fish movement into and out of a region can be obtained by repeated trawling of a given area (Pihl, 1989; Cabral et al., 2007).

Here, we present actual data collected from repeated trawls of Wylly Creek, a shallow tidal creek in Savannah, Georgia. The objective of the research is to profile the use of a shallow estuarine tidal creek by flatfish species. Flatfishes are intriguing animals that undergo extreme metamorphosis. Many species, such as southern flounder and halibut, are important sources of food. In this middle school lesson, students review the data set and infer what it tells us about the behavior of different flatfish species. On the basis of these data, students discover that even though flatfishes are members of the same taxonomic order, they move into and out of a tidal creek in different ways. Students then use a map of the area to plot an example of the distance traveled by a particular species of flatfish, the southern flounder (Paralichthys lethostigma), and calculate the relationship between this distance and the size of the fish. The resulting distance-to-body-length ratio is then multiplied by the student’s average step length, so that a comparable estimate of how far a human would have to walk to mirror the southern flounder’s movement is determined. This exercise demonstrates how far these fish travel, considering their small size.

In addition to learning about animal movement patterns, students will also become more ocean literate. A recent definition of ocean literacy was developed through a consensus-building process involving many marine science and educational organizations, including the National Geographic Society, the National Oceanic and Atmospheric Administration (NOAA), the Centers for Ocean Sciences Education Excellence, and the National Marine Educators Association (Cava et al., 2005). This lesson on flatfishes addresses Principle 5 of Ocean Literacy (The ocean supports a great diversity of life and ecosystems), Concept j: Coastal estuaries (where rivers meet the ocean) provide important and productive nursery areas for many marine species.

Background

Flatfishes are bottom-dwellers with particular adaptations for life spent lying on or in sand or mud. Their bodies are flattened, with oval or elongated shapes. In adults, both eyes are on the upper side of the fish and protrude from the body to allow vision in many directions. Flatfishes undergo a most unusual physical metamorphosis that students find fascinating. Larval flatfish are not one-sided like the adult but have eyes on both sides of their body. As the fish matures, the eye on one side of the body migrates over to the other side (for illustrations of the metamorphosis, see Martinez & Bolker, 2003; Ramos et al., 2010). Which side becomes the upper side with eyes is used to categorize flatfish as “left-eyed” or “right-eyed.” Changes in swimming technique reflect these morphological changes. As a larva, the flatfish swims like a round fish (think about how a goldfish swims). As an adult, the flatfish swims on its side, with its eyed side on top. Short video clips of these two swimming patterns can be found at http://www.ssufisheries.com/main/outreach.html.

There are several hundred species of flatfish in the order Pleuronectiformes (Robins & Ray, 1986). Some left-eyed flatfishes are in the family Bothidae or the family Paralichthyidae, which includes many commercially important species of flounder, such as the southern flounder. Some right-eyed flounders are in the family Pleuronectidae. Other types of flatfish include sole (family Soleidae) and tonguefishes (family Cynoglossidae). Flounder, sole, plaice, and halibut are important for both commercial and recreational fishing throughout the world.

Flatfishes eat smaller fish, crustaceans, and mollusks (Topp & Hoff, 1972; Carpenter, 2002). They tend to be ambush predators, lying camouflaged and partially buried in sand or mud (Figure 1). Their coloration may change in as little as 2–8 seconds to blend in with the bottom (Carpenter, 2002). Flatfishes may have a mottled pattern of coloration, with spots and ocelli, depending on the species. The blind side that rests on the bottom is often pale white or yellowish (Carpenter, 2002).

Figure 1.

This southern flounder on a light mottled substrate may be hard to see.

Figure 1.

This southern flounder on a light mottled substrate may be hard to see.

Most flatfish species inhabit temperate and tropical coastal waters, although some species are found in polar waters (Robins & Ray, 1986). Certain species, such as the hogchoker (Trinectes maculatus) and southern flounder, are also common in fresh water (Dahlberg, 1972). Adult flatfish are typically found from coastal areas through the continental shelf; tonguefishes can even reach depths up to about 1500 m (Carpenter, 2002). For many species, breeding adults are found in offshore waters, and spawning appears to be triggered by temperature changes (Smith et al., 1975). Most species release eggs into the water column (Gibson, 1997). After hatching, the larvae are usually carried by tidal currents or wind to estuaries (Gibson, 1997). The larvae then undergo metamorphosis; most species, including the summer flounder (P. dentatus), southern flounder, and bay whiff (Citharichthys spilopterus) then settle to the bottom of shallow creek nursery areas (Burke et al., 1991; Reichert & van der Veer, 1991; DuBeck & Curran, 2007). As the fish grow larger, they may move into deeper, cooler waters, as seen in the bay whiff (Reichert & van der Veer, 1991). The seasonal occurrence of these life stages varies by species, as shown in the data that follow.

Introducing the Lesson

The movement or migration patterns of animals can be specific to their life stage, reflect survival adaptations, and indicate habitat quality or changing animal requirements. We introduce students to the concept of animal travel from place to place through a class discussion (Figure 2); however, questions could be posed to students individually as part of an activity at the beginning of class.

Figure 2.

Student orientation questions, with possible answers.

Figure 2.

Student orientation questions, with possible answers.

Seasonal Use of a Shallow Creek by Flatfish Species

The abundance of flatfishes in Wylly Creek, GA has been studied every year since 2004, ensuring that we have replicate data across multiple years. In research funded by the NOAA Living Marine Resources Cooperative Science Center, scientists at Savannah State University conduct monthly sampling with a beam trawl that is 1 m wide (Figure 3). To fulfill the scientific requirement for replicate samples, three bottom trawls of 2 minutes each are performed for each sampling event. Contents are placed in separate buckets (Figure 4) and the flatfishes are taken back to the laboratory for identification and measurement. This lesson’s companion presentation, with pictures from a trawl, is included at http://www.ssufisheries.com/main/outreach.html.

Figure 3.

A 1-m beam trawl net used to collect flatfish samples.

Figure 3.

A 1-m beam trawl net used to collect flatfish samples.

Figure 4.

Sample collected with 1-m beam trawl net in Wylly Creek, GA.

Figure 4.

Sample collected with 1-m beam trawl net in Wylly Creek, GA.

The purpose of the research is to understand the seasonal use of shallow creeks as nursery areas for flatfishes where they grow during their juvenile stage. We ask students to predict which season of the year they would expect to find young, small flatfish in the shallow creek. We then review some of the actual data presented for a 13-month period in Table 1.

Table 1.

Total number of flatfishes, by species and average length, collected in 3 same-day trawls per month at Wylly Creek from December 2004 through December 2005 (DuBeck & Curran, 2007).

MonthTemperature (°C)Bay whiffBlackcheek tonguefishOcellated flounderSouthern flounder
  No. Average length (mm) No. Average length (mm) No. Average length (mm) No. Average length (mm) 
Dec 14  51.6   
Jan 11 103 14.8    
Feb 12 24 19.0 23.5   
Mar 12 34 38.9 49.3 77.5  
Apr 24  25 53.8 20 55.9 10 65.9 
May 18  77.6 60.7 87.7 
Jun 30  76.6 86.5 172.0 
Jul 32     
Aug 30  45.3   
Sep 27  55.3  171.0 
Oct 16 102.7 58.0   
Nov 17 106.0 47.0   
Dec 11  32.7 55.0  
MonthTemperature (°C)Bay whiffBlackcheek tonguefishOcellated flounderSouthern flounder
  No. Average length (mm) No. Average length (mm) No. Average length (mm) No. Average length (mm) 
Dec 14  51.6   
Jan 11 103 14.8    
Feb 12 24 19.0 23.5   
Mar 12 34 38.9 49.3 77.5  
Apr 24  25 53.8 20 55.9 10 65.9 
May 18  77.6 60.7 87.7 
Jun 30  76.6 86.5 172.0 
Jul 32     
Aug 30  45.3   
Sep 27  55.3  171.0 
Oct 16 102.7 58.0   
Nov 17 106.0 47.0   
Dec 11  32.7 55.0  

After reviewing the data table together, each student prepares a summary of the data (Table 2). The students must consider how to define “season” and evaluate the advantages of using traditional descriptions (e.g., summer is June, July, and August) versus defining the seasons by quarter or according to trends in water temperature. In addition, students could be required to graph the data in Table 1, providing a visual depiction of the seasonal patterns. Graphs could be generated with abundance or size on the y-axis and month on the x-axis for each species.

Table 2.

Summary data chart for students to complete, with analysis questions.

Season with:Bay whiffBlackcheek tonguefishOcellated flounderSouthern flounder
Most fish     
Largest fish     
 
Analysis Questions: 
Does the size of the fish species always increase over time? If so, why? If not, what could that indicate? 
When would be the best season for finding bay whiff in Wylly Creek? 
When would you expect to find ocellated flounder in Wylly Creek? 
What life stage do you think the bay whiff might be in during the winter months? 
Which two fishes appear to have similar movement patterns into and out of the creek? 
Describe the use of the creek by the blackcheek tonguefish. 
Consider the trend for the southern flounder. After 2 months with no southern flounder found in the creek, a large one is found in September. Can you think of a reason why? 
Overall, which species is most abundant in Wylly Creek, and during what season? 
Is there a relationship between size and abundance for each species? 
Season with:Bay whiffBlackcheek tonguefishOcellated flounderSouthern flounder
Most fish     
Largest fish     
 
Analysis Questions: 
Does the size of the fish species always increase over time? If so, why? If not, what could that indicate? 
When would be the best season for finding bay whiff in Wylly Creek? 
When would you expect to find ocellated flounder in Wylly Creek? 
What life stage do you think the bay whiff might be in during the winter months? 
Which two fishes appear to have similar movement patterns into and out of the creek? 
Describe the use of the creek by the blackcheek tonguefish. 
Consider the trend for the southern flounder. After 2 months with no southern flounder found in the creek, a large one is found in September. Can you think of a reason why? 
Overall, which species is most abundant in Wylly Creek, and during what season? 
Is there a relationship between size and abundance for each species? 

In summary, bay whiffs seemed to use the creek in the winter months. They are small and may have settled out of the water column while undergoing metamorphosis from the larval to the juvenile phase. The ocellated flounder and southern flounder also exhibited seasonal use of the creek, but in the springtime. The large southern flounder that was found in the creek in September may have been a predator looking for a meal. The blackcheek tonguefish (Symphurus plagiusa) appeared to be a year-round resident species in the creek. These patterns illustrate typical estuarine use, with some species found on a seasonal basis and others found consistently.

“Travel Like a Fish” Activity

Considering their size, some juvenile flatfish travel long distances between shallow nursery areas and deeper tidal rivers and sounds. Students use the map in Figure 5 to calculate the distance a juvenile southern flounder might travel from Wylly Creek to location A. Location A is not based on actual trawling data, but on logical suppositions based on other studies of movement of southern flounder (Wenner & Archambault, 2005). Using a ruler to determine the shortest path between the points is not representative of how fish must travel. Therefore, a piece of string should be used to plot the path, via creeks and rivers, between the points. Students then divide the distance traveled by the size of the southern flounder, which equals the number of body lengths traveled. This is a common technique that scientists use to consider the speed a fish travels given its size (if time is recorded), but it can also be used to put in perspective the distance traveled. The students compute the ratio of the distance traveled in meters to the average size of the southern flounder in meters using the average length for juvenile fish in May (when we see a decrease in the number of southern flounder in Wylly Creek) from Table 1 (approximately 14,700 m/0.0877 m = 167,617).

Figure 5.

“Travel Like a Fish” activity sheet. Hatched areas are land.

Figure 5.

“Travel Like a Fish” activity sheet. Hatched areas are land.

To appreciate the absolute magnitude of the distances these small animals travel, students then calculate what it would mean in human terms if they traveled as far as the juvenile southern flounder. Rather than wiggling our whole body to travel, as a fish does, we humans use our legs to take steps. Mark off a 30-m track, either outside or in the hallway. Have students conduct two replicate trials of the number of normal steps they take in the 30 m (usually around 40–45 steps). If available, pedometers are a great tool to introduce in this lesson. Health or physical education teachers may have some to lend. Show students how to use the pedometers and some other features of the tool (many have estimates of calories burned). Students then compute the average length of their step from the two trials (usually about 0.7 m/step) and multiply this average step length by the juvenile distance-to-body-length ratio. This calculation yields how far the proportional distance traveled would be in human terms (Figure 5).

Lesson Extensions

Students are amazed at how far they would have to travel to move as far as a juvenile southern flounder does in proportion to its size. Estimated distances are around 115,000–120,000 m, which is about twice the distance from Washington, D.C., to Baltimore, Maryland. If the Google Earth program is available, the distance of about 120 km from any location could be shown (change the ruler from miles to kilometers). In concluding the lesson, it is important to discuss the risks that might be present as a flatfish makes the journey, including such human-generated hazards as fishing and water pollution. A possible extension activity could be to pose a possible disaster scenario (e.g., an oil spill). If the southern flounder can swim at a speed of 1 body length per second, use the map to determine how far the fish can move in a given period from its spring location, assuming that currents and tides do not help or hinder its movements. Or, based on the size of the spill, calculate how long it would take them to pass through it.

The basic structure of this lesson could be used to study travel patterns of freshwater fishes. Analysis questions could focus on how and why the fish move through the freshwater environment. If data can be found on movement patterns of local fish, the lesson might be more meaningful for students and would help them better understand fish in their region.

To incorporate physical activity into the lesson or to engage younger pupils, students can act out the various life-history stages of flatfish and learn about their feeding habits (see Schaffner & Curran, 2005). An example of the role of fish in an estuarine food web can be found in Aultman and Curran (2008). A hands-on activity about flatfish sampling can also be incorporated (see Schaffner & Curran, 2007). Other ways to use fish research in math-oriented activities can be found in Curran (2003).

In this lesson, students consider what it must be like to be a different animal. Asking students to think outside the box of human experience helps build an appreciation for the environment that we live in. Many students savor the challenge of analyzing real-world data and truly enjoy learning about these uniquely shaped fish.

Acknowledgments

We thank the students, interns, and technicians of Dr. Curran’s laboratory at Savannah State University (SSU) for their assistance and for reviewing this lesson. Special thanks for help in demonstrating flatfish sampling and identification go to Michael Partridge and Benjamin Maher, and we also thank Michael Partridge for the videos of the swimming fish. Our sincere appreciation goes to Robert Kiser and Sigourney Bain for their assistance in field-testing this lesson. Funding for the research this lesson was based on was provided by the NOAA Office of Education through the Living Marine Resources Cooperative Science Center (award no. NA050AR4811017). The opportunity to develop this lesson was provided through funding by the National Science Foundation GK–12 teacher intern program (award no. DGE-0841372). The lesson was tested at the 2010 SSU Coast Camp, supported by the NOAA LMRCSC (award no. NA06OAR4810163). This is Contribution Number 1635 of the Belle W. Baruch Marine Field Laboratory of the University of South Carolina. All photographs by Terry Aultman.

References

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