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Western Dry Rocks Research

 A school of fish swim together underwater near the ocean bottom.

In Florida Keys waters, various fish species gather each year to reproduce in known areas and form what are called spawning aggregations. These aggregations can be predictable in time and location and can be negatively impacted by high fishing pressure. In 2021, the FWC enacted a seasonal closure from April 1st through July 31st to protect a known multi-species spawning aggregation site. This area is approximately 10 miles southwest of Key West on an offshore bar near a reef known as Western Dry Rocks. The newly established spatial closure includes one square mile of habitat that protects multiple recreationally and commercially important fish species that reproduce at that location.

Why Western Dry Rocks?

Learn more about why Western Dry Rocks is a special place and the research being conducted there by FWC.

Research Objectives

Science conducted by the FWC Finfish Research Team in the Florida Keys will monitor how reef fish communities change over time due to this new spatial closure. We are using a variety of tools and methods over multiple years to create a holistic monitoring program. This research will be used to inform managers and stakeholders about the effects of this management decision and is focused on three core objectives.

Objective 1

Documenting changes in reef fish behavior, abundance, and size structure in and around Western Dry Rocks over time.

Why it is important: By monitoring reef fish communities, we can understand the changes of the aggregations. Understanding trends over time in the abundance of fish and their size structure is one part of understanding the effectiveness of this management action. 

FWC scientists have several projects that collect information to monitor these changes: 

A diver underwater writes on a clipboard.

Underwater fish counts allow us to understand changes in reef fish communities. We conduct these surveys both inside the seasonal closure and in surrounding waters. When conducting these surveys, we record the number and species of fish present, lengths of fish, and habitat measurements.  

What this will tell us: 

  • Changes in reef fish communities over time, both inside and outside of the seasonal closure. 
  • The timing of the reef fish aggregation formations. 
  • Patterns of habitat use within the seasonal closure area.
A man holds a tagged fish in water inside of a large plastic tote container.

Acoustic telemetry is when animals tagged with special transmitters are tracked through the environment using an array of listening devices. We use these transmitting tags to follow reef fish over several years to evaluate the effect of the spatial closure on their movement patterns. 

What this will tell us:

  • The timing of reef fish movements in the Western Dry Rocks area.
  • The range of habitats that the reef fish use.
  • When they arrive at a spawning site.
  • How long they stay.
  • How often they come back.
Flyer with two fish and two black cylinder tag drawings. The fish drawings show where the tags are located in the stomach.

Angler Participation Program

When fishing near Western Dry Rocks, be on the lookout for tagged grey snapper and mutton snapper. They can be identified by an orange external tag located near their dorsal fin and/or by a black internal acoustic tag located inside their belly. If you catch one of these fish, report your findings to (786) 647-8908 or and collect your reward.

Using different types of sonar equipment, we conduct surveys that record not only the habitat but also any masses of fish in the water column. This equipment works similarly to the fish finder on a recreational boat. A sound signal is sent towards the ocean floor from a transducer, the signal strikes an object, and is returned. Depending on how quickly a signal is returned, we can tell where an object was in the water column. One tool we use for biomass surveys is the autonomous underwater vehicle (AUV) which maps the ocean floor and contains a mobile transceiver that can record acoustically tagged fish nearby. Additionally, the AUV contains high-definition cameras that will be able to identify what reef fish species are in any recorded biomasses in the water column. 

What this will tell us:  

  • How large the fish aggregations are within the seasonal closure.
  • What habitat features they are using.
  • What species are present within the aggregations.
An image capture from an underwater camera showing fish swimming around an underwater hydrophone.

We have built specialized underwater cameras that can be deployed for weeks at a time at specific known spawning locations. These cameras have an extended battery life that allows them to capture multiple weeks of video when divers are not present.  

What this will tell us:  

  • Capture behaviors associated with these aggregations.
  • Document timing of spawning events.
  • Quantify numbers of fish associated with these aggregations.
A metal device with a covered blade floats underwater.

Current speed, direction, and temperature, can influence reef fish behavior at spawning aggregation sites. To better understand how the currents within the seasonal closure influence reef fish behavior we deploy current meters during the time of the closure.   

What this will tell us:  

  • The current speed and direction associated with reef fish behaviors.
  • Water temperature influencing presence of reef fish.
  • This information, coupled with acoustic telemetry data, can verify the timing of spawning aggregations. 

To learn more about this research from our scientists, view the video Western Dry Rocks Research: Current Meter.

Objective 2

Determining changes in age and reproductive output from Western Dry Rocks aggregations over time. 

Why it is important: By protecting an aggregation, reef fish spawn without being harvested which can increase reef fish young in surrounding waters. Additionally, older individuals can produce more eggs, therefore we are interested in knowing if the age of reef fish in these aggregations change and if the number of eggs released increases. 

FWC scientists have several projects that collect information to help us monitor these changes: 

White whole ear stones on a brown background.

Otoliths from a mutton snapper

Otoliths are the inner ear bones of fish and can be used to age an animal similarly to the way the rings in a tree trunk can age a tree. Species of snapper otoliths are being collected in and around the Western Dry Rocks seasonal closure to understand how the ages of reef fish change with this management decision.  

What this will tell us: 

  • The ages of the fish collected.
  • How these ages change over multiple years at these aggregation sites.
Two pink colored bean-shaped organs are on a white table.

Female snapper reproductive organs

The reproductive organs of sampled fish are removed and preserved. These tissues are used to create microscope slides that we study to understand their stages of sexual maturity. We are interested in tracking how reproduction and egg quality and quantity change over time.. 

What this will tell us: 

  • How many of the collected fish are actively spawning.
  • What is the timing of their spawning.
  • If reef fish at these aggregations are able to spawn multiple times in a season.
  • If the total egg output of individuals changes over time.

To learn more about this research from our scientists, view the video Western Dry Rocks Research: Life History.

Objective 3

Quantifying how the Western Dry Rocks seasonal closure is affecting stakeholders.  

Why this is important: Understanding reef fish community changes is only one piece of the puzzle. The regulations enacted at Western Dry Rocks has the potential to affect a wide range of stakeholders. FWC is documenting changes in perception and the economic implications for managers and stakeholders due to this policy change.  

FWC scientists have several projects that collect information to help us monitor these changes: 

Economic Studies

At a marina, a woman in an orange FWC shirt is pointing to a clipboard being held by a man in a blue shirt.

We are using in-person surveys and fish harvest data to document any economic changes for various user groups, such as: commercial fishers, charter boat operators, and recreational anglers. This information will be collected again several years from now to better understand these changes over time. 

What this tells us: 

  • Costs of associated fishing.
  • Effects of the seasonal closure on fishing habits.
  • Participants’ knowledge of Western Dry Rocks.

Social Science Interviews

We are using anonymous in-depth interviews with members of key stakeholder groups (i.e., charter fishers, commercial fishers, dive shops, NGOs, general public) to gain insights in their awareness, opinions, and anticipated impacts of the seasonal closure. In addition, qualitative information gathered and collected from the public prior to the closure will be analyzed to assess changes over time.

What this tells us: 

  • People’s awareness of the closure.
  • Their viewpoints regarding this regulation, their opinion about the process by which the closure was established, their perception of the anticipated/realized impacts of the closure, and more.
  • How these perceptions might change over time.

The Florida Keys Reef Tract is a heavily used marine ecosystem. Protecting multi-species spawning aggregations will encourage resilience for reef fish communities. Understanding how boating pressure changes due to the seasonal closure will provide information for how the closure will affect the broader ecosystem.  

FWC scientists have several projects that collect information to help us monitor these changes:

Passive Acoustic Hydrophones

A microphone attached to a box sits underwater on the ocean floor.

Passive acoustic hydrophones are large microphones that record underwater sound. These hydrophones can be deployed for several months at a time and can detect not only fish sounds but also boat traffic. Boats that are rapidly moving through the area sound different than boats that are slowly maneuvering. We have placed several hydrophones within the Western Dry Rocks seasonal closure throughout the year. This will provide information on how boating patterns change during and after the closure.  

What this will tell us: 

  • This will give us an understanding of relative boat activity in the Western Dry Rocks area. 
  • How this boating activity changes during the months of the closure and other times of the year. 
  • This will give managers an understanding of how boat traffic is changing and a relative estimate of compliance to the regulations. 

To learn more about this research from our scientists, view the video Western Dry Rocks Research: Passive Acoustic Hydrophones.

Aerial Surveys

A woman and man wearing headsets with microphones are sitting inside a small airplane.

We conduct two aerial surveys a month from April – July to record boat locations throughout the Lower Florida Keys reef tract. We collect data during the aerial survey using a specialized app. With this app we can record the number of boats at a location, document the GPS location of boats, as well as categorize the activity of those boats. 

What this tells us:  

  • These surveys can provide understanding of boating pressure during the months of the closure and determine if pressure shifts to other sites when the closure is in effect. 

To learn more about this research from our scientists, view the video Western Dry Rocks Research: Aerial Surveys.