Marlins are a group of 5 species of fish that are categorized as billfish- Makaira mazara, Makaira nigricans, Istiompax indica, Tetrapturus albidus, and Kajikia audax. Unlike many species of fish targeted by anglers, we don’t know that much about Marlins. This is most likely because they are pelagic fish, that is to say, fish who spend much of their lives swimming around in the open ocean. They reside in the Atlantic, Pacific, and Indian oceans. They are fast swimmers, averaging 50 mph but have been recorded swimming 82 miles per hour! While we know about where the different species of marlin live around the world, how fast they can swim, and what their diet consists of, we don’t know all that much about their behaviors. This is why it is so important to tag marlin; to learn more about their patterns and movements. Marlin aren’t the first fish to be studied utilizing tags. In fact numerous other species are studied using the help of tags. While the term tag might seem vague, there's a reason. There are several different types of tags that are available for researchers to use, each of them providing different kinds of data. Tagging Marlin is an important tool to understanding their behavior and once we are able to understand that, we can better protect the habitats they live in.

Despite what little we know about individual species of marlins, researchers have learned enough to classify a few species within the IUCN Red List’s 9 categories. Among them, two are listed as ‘Least Concern’, while two are classified as ‘Vulnerable’ and there is so little known about the species fifth, it is listed as ‘Data Deficient’ on the IUCN Red List. The White Marlin (Kajikia albida) and Striped Marlin (Kajikia audax) are both listed as species of least concern, however due to decreasing population numbers, there is the potential for the Striped Marlin to be reclassified in the future. Blue marlin, made up of the Makaira mazara and Makaira nigricans species which live in the Pacific and Atlantic Oceans, respectively, are both listed as ‘vulnerable’ species. They are threatened by fishing pressure from both sport fisheries, artisanal fisheries, Fish Aggregating Devices (FADS), and as the bycatch from long lining for tuna and swordfish.

While the Black Marlin (Istiompax indica) is listed as “Data Deficient”, it is very likely that it should be listed as “Threatened” as it is also a discarded product of bycatch from purse seines, longlines, trolling, and gill nets, in addition to being targeted by artisanal and sport fisheries. If we don’t know much about these fish, how do we know enough about their populations to list them in the first place? Bycatch mortality only gives us a certain number of the population, but there are other methods to study population size.

Tagging fish as a method to study them has been around for more than 100 years. In fact the earliest known fish to be tagged in the United States were Atlantic salmon in 1873 in Maine. By tagging fish we can learn all sorts of information about the individuals and their populations. We are able to define their stocks, determine if they migrate, conduct age and growth studies, and determine population estimates. By tagging fish in different areas, researchers can better identify the population. Take for example the Blue Marlin- M.mazara and the M. nigricans -where there has been debate as to whether or not they are the same or different species. In tagging them, we have been able to identify two unique habitats- the Atlantic and Pacific oceans. The M. nigricans is native to the Atlantic ocean, which is a pretty broad area to study. Tagging once again offers a solution to determine the migration patterns of species. According to marlinmag.com’s Conservation Director, Jason Schratwieser “During a tagging event that took place in San Juan, Puerto Rico, in 2011, a blue marlin traveled an amazing 4,776 nautical miles before the tag popped off near the coast of West Africa.”. It would have been nearly impossible to collect that information without the help of tags. In addition to illuminating migration pathways and potential spawning grounds, the tags also teach us about the Marlin’s rate of travel, and the time of year during which they travel. When a fish is tagged, certain data is collected. If a tagged fish is released and then recaptured, new data can be collected and compared against the existing data. From this, the age and growth of the fish is able to be determined so that information can be applied to other individuals in the population. Population numbers can also be estimated with tagging fish and then comparing the ratio of future fish caught with and without tags. It should be noted that fish population estimates are easier to do with coastal species. With all the knowledge that tagging brings, we get a step closer to understanding Marlin behavior and protecting their habitats.

As you can probably imagine, there is more than just one type of tag that is used to study all of these different aspects of a fish's life. Tags can be broken down into three different categories- conventional, natural, and telemetry. Each type of tag gives us different information, and some of them are more invasive than others. Natural tags are an example of a tag that isn’t that invasive for the animal. Natural tags are markers on or in the animal itself. While they are alive their body patterns can be uniquely identified, and repeated spottings can give us information about the individual over time. Examples of this are the flukes of whales, spots on Whale sharks, and the spots on Giant Sea Bass. If an individual is deceased, things like scales and otoliths (ear bones) can tell us the age of the fish and a bit about its growth rate over time.

One of the most common and frequently used tags are conventional tags. According to the Louisiana Wildlife and Fisheries Department, “A conventional tag is marked with an identification number as well as contact information for reporting the fish when it’s caught.”. Sometimes referred to as Tag and Release tags, they are compact, and easy to quickly attach. They are made of plastic, are around a few inches long, and are usually printed with a code and a number to call if the individual is recaptured. Because they are small and made of affordable materials, these are used in large numbers. The only problem with this type of tag is that unless the fish is caught a second time or its body is found, there isn’t a lot of data collected about them. That said, The Billfish Foundation sends out a lot of these tags for anglers to use, and since 1990, they have assisted in tagging more than 260,000 individual fish which provide important information for Marlin and billfish conservation!

The real data intensive type of tags are the telemetry tags, which are made up of internal, acoustic, and satellite tags. These tags allow us to measure and collect data about the fish from a distance, but each works a little bit differently.

First is the internal tag. As the name suggests, these tags are surgically implanted inside of the fish and depending on the tag can last for several years before they stop collecting data. While they are implanted, they collect data like depth, temperature, and location. The downside to these tags is that you have to recapture the fish, or seek out the tag to access the data that has been collected by them.

The second type of telemetry tag are the acoustic tags. These are also tags that are implanted in the body of the fish, are powered by batteries, but they also need a receiver to work. As the fish swims around the tag transmits information about the fish’s location, depth, water temperature, time, and other information about the specific fish that was collected when it was tagged, to the receivers. Over time the data has to be collected from the receivers (if they are stationary). If the fish swims outside of the area of the receiver, no information is collected and the tag is potentially lost. Acoustic tagging is great for studying specific habitats, and highly traveled areas.

Of all the types of tags, satellite, or SAT tags are the most high tech and the most costly of the tags. These tags-PSAT and SPOT- can tell us about the temperature, depth, and location of the fish during the course of its life. PSAT tags or Pop-off Satellite tags will eventually detach and float to the surface, and transmit collect data to a satellite. While the PSAT only transmits data at the end of its stay with the fish, the SPOT or Smart Position Only Tags will transmit data every time the fish is at or near the surface. Since they don’t require you to be within a certain radius of the fish to collect the data, they are great for use with highly migratory species like marlin.

Although telemetry tags provide us with a plethora of data in a somewhat real time fashion, they are expensive and it's not realistic to use them in every application. Sometimes getting out thousands of smaller conventional tags, can give a better overall picture of the catchable population. The Billfish Foundation says it best when they stated “Both types of tagging are vital to creating a robust, full understanding of billfish to be used for management and conservation.”. The more we know about marlin and their behavior patterns, the better we are able to protect their habitat, and one way we can do that is through tagging. If you would like to learn more about the tagging efforts of the R/V Pilar, make sure to follow us on social media.

Tagging Marlin: A Key Tool for Understanding their Behavior and Protecting their Habitat