Saturday, September 26, 2020

Listening for Sharks at Rookery Bay

COASTAL CONNECTIONS


Intern Kaylee Smith records data as Pat O’Donnell prepares to deploy one of the acoustic receivers. Submitted Photos

Intern Kaylee Smith records data as Pat O’Donnell prepares to deploy one of the acoustic receivers. Submitted Photos

Sharks are top-level predators that play a key role in our ecosystem by keeping prey populations healthy. They also contribute to estuarine research since they can feely move along the coast in response to shortterm environmental cues, food availability or changes in their habitat.

At least five species of shark are known to use estuaries in South Florida as nurseries: bull, blacktip, bonnethead, lemon and nurse sharks. The presence of newborn or juvenile sharks in an estuary can indicate that the water chemistry conditions are favorable for breeding. Generally speaking, if several species are found using the same estuary as a nursery, the water chemistry can be considered healthy and ideal.

Pat O’Donnell releases a tagged shark.

Pat O’Donnell releases a tagged shark.

In 1999, biologists with Rookery Bay National Estuarine Research Reserve (RBNERR) began studying sharks in the Ten Thousand Islands because of a hydrologic restoration in the adjacent area known as Picayune Strand State Forest. The restoration aims to improve the distribution of fresh water flowing across the land by plugging canals and leveling roads built in the 1960’s for a development that was never finished.

The study intended to show how sharks respond to changes in freshwater flows to the estuaries downstream. The research team uses gill nets and baited lines to catch sharks in three bays each month. These bays are directly downstream of the canal system currently in the process of being restored. In Faka Union Bay, the bay that receives the most canal discharge, the salinity, or salt concentration in the water, is very diluted, especially in the summer rainy season. Bull sharks are the most commonly caught species in Faka Union Bay because they can easily adapt to lower salinities.

Pat O’Donnell takes GPS coordinates for the acoustic receiver he has just submerged.

Pat O’Donnell takes GPS coordinates for the acoustic receiver he has just submerged.

Volunteers provide important logistic assistance to this study by helping to retrieve the sharks from the gear, weighing and measuring the fish while the Reserve’s biologist, Pat O’Donnell, characterizes and tags each one. The sharks are then quickly released to help minimize stress. The tags help O’Donnell or other researchers to continue to learn about a shark’s use of habitat as it grows, if it is caught again.

 

 

When a shark of the appropriate species and age class is brought onboard, O’Donnell also now implants a small transmitter in the shark’s belly before releasing it. The transmitter sends a signal made up of acoustic pulses, or “pings,” with information about the transmitter to acoustic receivers recently deployed in the area. The receivers record the presence of any sharks, sawfish or other implanted fish if they swim within a certain distance of a receiver.

Information collected from the sharks, including length, weight, age and gender, is compiled to produce a baseline database about community composition. This long-term dataset can be used as a bench-

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