Otolith Shape and Fish Movement

Hey there fishheads!

So as we learned in Joy’s post on the FACT array, tracking fish movements is an important part of fisheries science. In particular, it is important to know whether fish from different places are mixing or remaining geographically isolated (why? see below); however, this can often be a tricky thing to figure out. With this in mind, today I want to introduce a method I think is pretty darn cool…(cue drum roll)…otolith shape analysis! Now, for anyone who may be thinking oto-what now?, fear not! First, watch this handy 1:30 video, and then we can all share in the excitement-

Awesome, right? As a technique, otolith shape has been used to look at stock structure in a whole variety of different species, from goatfish to cod to king mackerel down here in Florida. I used otolith shape in my master's degree to look at stock structure of greater amberjack in the Gulf of Mexico (results coming soon). Now, otolith shape analysis doesn't always work or lend conclusive results (as can happen with any scientific method), but it is a nice technique that can be used to supplement tagging or genetic analysis methods, and as it is relatively simple and inexpensive (once the otoliths are collected, the analysis is essentially free), it can be a quick first step into examining stock structure. 

Where did my fish go? Using collaborative processes to enhance tracking of aquatic animals

           Understanding the spatial and temporal use of habitats by animals is critical to resolving their role in the environment and formulating sound management plans. Fish movement data can be used to measure response to harmful environmental events (e.g. red tide events), water temperature, salinity, no or reduced fishing zones, and movement of other species (e.g. known predators). For tracking of aquatic animals acoustic telemetry has several benefits over traditional radio and satellite telemetry. Radio waves cannot transmit through saltwater, and given the very salty nature of Florida including tidally influenced creeks and rivers, radio telemetry is very limiting. Satellite telemetry, while very informative and functions well in saltwater, is also very expense. Financial constraints may limit the number of animals in a study. Acoustic telemetry is the best of both worlds, it works equally well in salt and freshwater and is cost effective.

Several companies including Vemco, Sonotronics and Lotek produce the hardware needed for tracking animals with acoustic technology. While most tracking equipment in Florida is purchased from Vemco, Sonotronics and Lotek offer compatible tags and receivers. Acoustic tags transmit an underwater sound aka ping that uniquely identifies an animal. When in range, the pings are registered on an underwater device called a receiver that also records the date and time. Multiple animals can be tracked at once with little effort on behalf of the scientists. After the original start-up of tag and receiver deployment, effort is only needed to download and service receivers at the leisure of the scientists (but at least once a year).  

A Goliath grouper poses next to an underwater
 receiver.

Lemon sharks circle around an underwater receiver.