An extreme climate event and extensive habitat alterations cause a non-linear and persistent decline to a well-managed estuarine fishery

Theoretical, field-based, and experimental research all suggest that animal populations remain relatively stable under increasing habitat alteration until a critical threshold is reached, after which small changes to habitats result in large negative responses. However, there are few empirical examples demonstrating this in marine fishes, making identification of such thresholds difficult. Here, we synthesized long-term (25 + year) fisheries and habitat datasets across four estuaries in Florida (USA) to examine the combined effects of a once in ninety-year cold spell and habitat alterations on populations of an estuarine dependent fish, common snook ( Centropomus undecimalis ). In Florida, common snook support an important recreational fishery where harvest is well-managed. Common snook populations in three estuaries with less severe habitat alterations recovered to pre-disturbance levels within 4 years of the cold spell. However, in the estuary with the most extensive habitat alteration—including 34% loss of mangrove habitats, near complete loss or fragmentation of saltmarsh habitats, a 65,000 acre seagrass die-off, and eutrophication—the common snook population had yet to recover 8 years after the cold spell. Using a life-stage explicit approach, habitat alterations affecting early life history processes (i.e., juvenile survival and larval settlement) may be responsible for decreased resilience. This study highlights the need for fisheries management to consider habitat loss and disturbance, along with harvest in stock assessment and management processes. Adopting policies to protect and restore habitats will improve fish population resiliency to disturbance, thereby mitigating non-linear and costly declines to fisheries.