An ichthyologist tags and releases 200 fish in a reef ecosystem. Later, she collects a sample of 150 fish and finds that 30 are tagged. Using the capture-recapture method, estimate the total fish population in the reef.

Sun, 10 May 2026 10:43:44 +0000

**Why Counting Fish Matters: The Science Behind an ichthyologist’s Reef Study** Marine scientists are quietly tracking ecosystem health with precision—sometimes with something as simple as a tag. When an ichthyologist tags 200 fish in a vibrant coral reef and later samples 150 fish, discovering 30 tagged among them, she’s not just tagging fish. She’s applying a proven method rooted in ecological science: the capture-recapture technique. This approach offers a powerful way to estimate population sizes—information critical for conservation, tourism, and marine research. With rising interest in ocean sustainability and visible shifts in reef ecosystems, this kind of discovery sparks real curiosity and concern across the US. **The Capture-Recapture Method: How Population Estimates Are Born** The process is elegant in its simplicity. By tagging 200 fish and releasing them, researchers create a small but measurable group representing a cross-section of the reef’s population. After some time, a second sample of 150 fish is collected, and 30 are found with tags. Mathematically, this ratio helps scientists infer the total number of fish: if 30 out of 150 are tagged, and 200 were originally tagged, the estimated reef population is calculated by assuming proportional representation. The formula—(tagged in first sample / total population) ≈ (tagged in second / second sample size)—yields an estimate that balances fieldwork with data science. This method is trusted across ecology and wildlife studies because it reflects real-world movement and mixing within populations.