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Critical habitat characterized for juvenile Nassau grouper

After 43 scouting expeditions, we were able to identify and characterize the critical habitat of juvenile Nassau grouper on the east coast of Puerto Rico. This information now rounds out our understanding of the habitats this threatened fish uses throughout its lifecycle. Specificially for Puerto Rico, our results can be used to locate other similar habitat around the island where juvenile Nassau grouper potentially recruit.

Shoreline view of the Las Cabezas de San Juan in Fajardo

Nassau groupers can be found in a wide variety of habitats (submerged vegetation like seagrass beds and hardbottom structure like coral reefs) in a diversity of environments like lagoons, shelfs and banks. However, information on the distribution of the juvenile phases of this species was lacking. Understanding habitat use through ontogeny (a fancy word for development) helps resource management identify the different habitats that the Nassau grouper uses throughout its lifecycle, and what types of habitats may require extra protection or care to sustain Nassau grouper in this delicate life phase. The identification of such habtats are essential for continuing conservation efforts for rebuilding populations of Nassau grouper to historical levels.

The search is on

Part of this project involved tagging juvenile Nassau grouper to see if we could recapture them at a later date. Our research partner, Capt Marcos Hanke of 787Fishing, helped us locate areas where he often found juvenile Nassau grouper. Tagging studies are useful to answer questions about site fidelity (how long does a fish stay in the same place?), growth over time, and movement patterns within the study sites. However, only five juvenile Nassau grouper were successfully tagged with internal and external tags, which means the sample size was a bit too small to answer the question concerning population size. But, these fish are likely still out there so there is a chance they could still be reported to our project.

Above: Evan Tuohy inserts an internal tag into the grouper. Below: a juvenile Nassau grouper showing off its external tag

Where do juvenile Nassau grouper live?

With the help of 787Fishing, we surveyed over 40 sites during June to October 2020 in the areas of Fajardo and Ceiba on the northeast coast of Puerto Rico. Twenty-three Nassau grouper were sighted at 15 of these locations. Interestingly, the total area surveyed in habitats located in bank/shelf zones was three times greater than in bay/lagoon environments, however, the mean density of Nassau grouper was 11 times greater in the latter.

The team readied for site surveys

Smaller juveniles (6-15 cm) were found in shallower, nearshore vegetated habitats while large juveniles (15-30 cm) were found further offshore and in deeper coral reef habitats, hence an developmental shift in habitat use occurred for larger individuals. This means that they used different habitats throughout their lifecycle as they grew from juveniles to adults. In other words, we will not expect to find adult Nassau grouper in seagrass beds but there is a good chance we could come across their offspring here!

Size Matters

The above photos show examples of the habitat where juvenile Nassau grouper were most often found. In this case, size does matter in terms of how we classify habitat. At the largest spatial scales, juvenile Nassau grouper were found in seagrass beds, patch and linear reefs. At smaller spatial scales, they occupy hardbottom surrounded by loose sand and sediment that is colonized by seagrass. At the finest spatial scale, these habitats can be defined as patch reefs colonized by macro- and turf algae, and bare substratum (rubble, pavement, or sand) located within 25 m or less from continuous/dense seagrass beds. Notably, other commercially important groupers and reef fishes were observed at these sites in much greater densities than those of Nassau grouper.

The following infographic summarizes the main results of the project. Feel free to share this infographic and link back to our report. You can find the report here to download and read.

Want to get involved?

We created two virtual ways that you get involved with this project! We have a web-based app called iMero where you can report your grouper sightings. We are particularly interested in knowing about Goliath and Nassau grouper!

We also created a bilingual website called MerosPR where you can find details about this project, important groupers in Puerto Rico and their regulations, and loads of answers to all your favorite grouper questions!


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