Census Information

Census 2006

2006

Using a sampling design-based approach in 2006 we conducted a research cruise to the Dry Tortugas that resulted in 1,344 scientific dives in the region monitoring reef fish, benthic habitats, and spiny lobster, with 817 dives occurring the DRTO. We compared these data to a series of synoptic research cruises with over 4,000 research dives to survey reef fish populations and habitats in the Dry Tortugas before and three years after the NTMRs were implemented. We recorded the presence, abundance and size of 267 fish species from eight reef habitats in three management areas offering different levels of resource protection: the Tortugas North Ecological Reserve (a NTMR), Dry Tortugas National Park (recreational angling only), and southern Tortugas Bank (open to all fishing under regional regulations).  Species richness and composition remained stable between 1999–2000, 2004, and 2006, within the overall survey domain. Greatest reef fish biodiversity was found in the more rugose habitats. We detected significant domain-wide increases in abundance for several exploited and non-exploited species, while no declines were detected. In the Tortugas Bank NTMR, we found significantly greater abundances and shifts in length composition structures towards a higher proportion of exploited phase animals in 2004 and 2006 compared to 1999-2000 for some species (e.g., black grouper and red grouper). Consistent with predictions from marine reserve theory, we did not detect any declines for exploited species in the NTMR, while for non-target species we detected both increases and declines in population abundance in the NTMR for non-target species. The observed upsurge in exploited populations, however, may have also been influenced by other factors including past or recent fishery management actions that increased minimum sizes or reduced fishing mortality rates; the passage of recent hurricanes; and, the occurrence of good recruitment year classes. Although still early in the recovery process, our results after three years are encouraging and suggest that no-take maritime zones (NTMRs), in conjunction with traditional management, can potentially help build sustainable fisheries while protecting the Florida Keys coral reef ecosystem.

Also in 2006 we developed a pilot study using state-of-theart acoustic telemetry technology to track real-time movements of groupers in key habitats of DRTO to precisely estimate population flux rates in fully-protected areas free from exploitation. Rosenstiel School fisheries researchers tracked red and black grouper in the Dry Tortugas National Park to develop a better understanding of species’ movement and habitat requirements, so they can help more efficiently design and assess future marine-protected areas.

The following points summarize our findings:

  1. reef fish within Dry Tortugas National Park are capable of, and do, cross reserve boundaries;
  2. red grouper demonstrated relatively high site;
  3. red grouper seldom moved across large expanses of sand and all movements out of the Research Natural Area (RNA) occurred across contiguous reef habitat;
  4. red grouper are apparently crepuscular feeders as frequency of detections increased during dawn-dusk.

The results of this pilot study have provided us with previously unavailable insights into grouper movements that are critical towards improving the experimental ethodology to better address the goal of quantifying the rate of flux across reserve boundaries for these important species, a focus of our current research. Ultimately, these data will be used to parameterize a spatially explicit model that provide insights into how flux of exploited species across reserve boundaries will impact NTMR effectiveness as a fisheries management tool and help ensure sustainable fisheries in the Dry Tortugas and Florida Keys ecosystems.

Please click here for a complete report of the 2006 Dry Tortugas Expedition.