While most tagging studies rely on numbered artificial tags that are attached to fishes and then later either recaptured by anglers or recorded by remote sensing, sometimes scientists can use aspects of the biology of fishes to keep track of them. As you will see below, spot patterns, seawater chemistry and genetics can all be used as tags to keep track of certain individuals or even groups of fishes.
Whale Shark Photo Identification
The spot pattern of whale sharks is like a finger-print or a “natural tag” because it does not change over time and can be used to identify individuals. The same pattern-matching algorithm that NASA uses to search for stars in the night sky is used to map the spots of a whale shark and identify individuals. Wildbook for Whale Sharks photo-identification library is a global database used by marine biologists to collect and analyze whale shark sighting data in order to study these animals over their entire range. The Wildbook uses photographs of the skin patterning behind the gills of each shark, as well as scars or other diagnostic features to distinguish between individual animals. Cutting-edge software supports rapid identification using pattern recognition and photo management tools. Additionally, “citizen scientists” can submit their photographs if they encounter a whale shark in the wild. In areas where large ecotourism industries exist for whale shark snorkel tours (such as Utila, Honduras; Gladden Spit, Belize; and along the Yucatan Peninsula of Mexico), “citizen scientists” have provided a vast amount of natural tagging data. In the northern Gulf of Mexico, most submissions to date have come from scientific encounters.
As part of the northern Gulf of Mexico Whale Shark Research Program, LDWF biologists prioritize photo-capture of the target area of the “natural tag” during field efforts. Out of 200 photos submissions to the Wildbook photo-identification library, 64 new sharks have been identified. Only six of those sharks have documented movement throughout the Gulf of Mexico and Caribbean Sea. One of the most interesting sharks we’ve encountered is known as H-021 in the WildMe database, which has been tracked for 14 years. H-021 was first documented in Belize in 2000. It was seen again in both 2005 and 2006 in the Caribbean Sea between Honduras and Belize. In 2010 it was first documented in Mexican waters near the Yucatan Peninsula, where it was seen repeatedly for several years. The last and most recent encounter with this shark was in July 2014 on Ewing Bank in the north-central Gulf of Mexico, where LDWF researchers were able to attach a pop-off tag to it. The tag stayed on the animal for 47 days, during which the animal moved south to the Bay of Campeche at a rate of about 22 kilometers per day.
Yellowfin Tuna Chemical Tags
LDWF has been working with scientists at Texas A&M University at Galveston to develop natural tags for yellowfin tuna. The idea behind this work is that since there are differences in the seawater chemistry in different parts of the ocean, those differences should be reflected in the composition of hard parts formed by fishes from different geographic locations. Unlike other bones, the ear bones, otoliths, of fishes do not get resorbed and therefore they represent a sealed record of the sea water chemistry individual fish experience throughout their lifetime. In the current study, “young of the year” yellowfin tuna are being collected from sites throughout the Atlantic Ocean including here in the Gulf of Mexico off of Louisiana. Because tuna are capable of traveling such great distances, it is important to collect the smallest individuals possible for this study to work, so that there is no chance that the fish came from another location. The chemical tags from these tiny tunas are then compared to the center part of the ear bone from adult yellowfin tuna, and researchers are then able to make an educated guess about where the adults may have spent the early part of their lives.
To get the samples required for this Atlantic-wide project, LDWF is collecting ear bones from adult tuna caught by recreational fishermen here in Louisiana as well as catching baby tuna from this region. TAMUG researchers have been able to get young tuna from both the western (Brazil, Martinique, Dominican Republic) and eastern (Gulf of Guinea and Cape Verde, Africa) Atlantic Ocean. Results from this on-going work will likely have profound implication for how yellowfin tuna are managed in the future.
Tarpon Genetic Tagging
DNA provides another type of natural tag that can be used to identify specific individuals. In this tagging scenario, mucous swabs or scale samples are taken from fish that are subsequently released. DNA profiles are generated and stored and are compared to samples collected throughout the fishery for many years. While this approach requires significant public outreach and lab costs, it also has the potential to track fish over great distance and time and also allow for multiple recaptures. This approach is best suited for a fishery that is largely catch and release.
Beginning in 2006, the Florida Fish and Wildlife Conservation Commission and Florida’s Fish and Wildlife Research Institute began a genetic tagging study for Atlantic tarpon. This program has been gathering tarpon DNA “fingerprints” using non-invasive, harmless “tagging” that involves scraping skin cells from the outer jaw or other bony surface of captured tarpon using a small abrasive sponge. A tarpon of any size can be left in the water while taking the sample and the technique can be used on dead fish from tournaments. This material is used to provide DNA for fingerprinting individual fish and can also identify particular fish in the genetic database that have been previously caught and sampled. DNA provides a natural tag that lasts as long as the tarpon is alive and is used to track the movements and habits of tarpon in coastal waters. The FWRI study has collected an amazing 24,323 DNA samples as of the end of the 2014 sampling season.
In order to encourage tarpon anglers from Louisiana to get involved in the biological tarpon tagging project, LDWF began supplying sampling kits and outreach materials to Louisiana tarpon anglers in 2010. Last year, 82 samples were submitted from Louisiana as part of this effort.
Largemouth Bass Genetics
Genetic analysis is also used to help manage Louisiana’s freshwater fisheries. LDWF uses the introduction of Florida-strain largemouth bass to increase the potential for anglers to catch Louisiana bunkers. Not all Florida bass grow to trophy size, but they do all have a genetic signature that can be used as an indicator of stocking success.
Bass are favorite targets for anglers, and trophy-sized bass are often the source of lifetime memories. LDWF biologists often use bass produced in our freshwater fish hatcheries as a management tool to increase the proportion of Florida bass genetics in Louisiana bass populations. With a limited supply of Florida bass available for stocking each year, it is important to stock in waterbodies that provide good conditions for survival and rapid growth. As part of the assessment process, Louisiana bass populations are monitored through genetic analysis of fish tissue. The presence of Florida bass genes is an indicator of stocking success. The degree to which Florida genetic material is incorporated into a bass population determines if Florida bass will continue to be stocked in that particular waterbody.
Take for instance the Atchafalaya Basin. Hurricanes and other weather-related events have caused massive fish kills in the past. In response, LDWF stocked large numbers of Florida bass into the basin over multiple years. With few predators surviving the storm, Florida bass fingerlings should have become established as the dominant species of bass. That did not happen at all. Native bass proved they were far more adapted to the basin’s dynamic aquatic habitat. Despite stocking efforts, genetic indicators for Florida bass were not observed in LDWF samples. The conclusion is that the native bass are more suitable than Florida bass in the Atchafalaya Basin. Florida bass should be stocked into other water that are more conducive to their size and growth.
The program is working to great success. Since the initiation of the Florida bass stocking program in the 1980s, the record books have been completely rewritten.
Florida bass integration works at a few different levels. Native bass do not tend to get as large or grow as fast, but they are eager to bite lures. Florida bass have the potential to get huge, but sometimes keep their lips tight for anglers. It is actually the hybrid of the two that offers anglers the best of both worlds – eager to bite and able to become the next potential Louisiana trophy bass.
Using the genetic analysis of largemouth bass allows LDWF to continue to make wise management decision to benefit Louisiana anglers.
