Did you ever wonder, after all the aerial leaps, power dives, and resistance, when a billfish is brought boat-side for a release, how long it takes to recover – if they do recover?
Several studies have been conducted to determine both the mortality rate, as well as the time it takes for various species to recover from encounters with a rod and reel. Recently, a new study by the Guy Harvey Research Institute at Nova Southeastern University's Halmos College of Arts and Sciences used remote tracking sensors to better understand the health and behavior of two popular billfish species- blue marlin and sailfish.
The research team attached remote sensing tags to the fish after they were caught with a rod and reel, and then released them back into the ocean. These newly designed tags and are similar to homemade “Fitbits for fish” and equipped to log acceleration, depth, light and temperature. The tag’s sensors record every single tail beat, body orientation, and swimming patterns that the fish experiences right after release.
For the angler, a fight with a billfish consists of a fast-paced, high-energy battle that hopefully culminates with a leader grab and a safe release of the fish – some high-fives, rehydration, and re-setting the spread for the next one. For the fish, this is a fight for its life using a tremendous amount of energy. It’s those high-speed runs and aerial acrobatics that make us wonder how long it will take them to physically recover from that fight after being “released.”
The answer varies depending on the species. The “man in the blue suit” (blue marlin) is larger, stronger, and, perhaps, meaner than a sailfish due to its size and bulk. Accordingly, they fight harder and longer than their smaller “spindle-beak cousins.” A study on this topic revealed that the average “fight time” for a sailfish was about 7 minutes, compared to 45 minutes on average for a successful blue marlin release.
For the blue marlin, size, and strength come at a cost. The study found that it took a blue marlin an average of 9 hours, to fully recover after its release. Sailfish, on the other hand, being smaller and easier to reel in, recovered in around 6 hours. The research also indicated both species swam much harder right after they were released. This response might seem unexpected as humans and other mammals need to rest after running or exercising.
Since fish breathe by running water through their gills, swimming harder and faster is their way of catching their breath. Because marlin and sailfish have to continuously swim to breathe, this faster-than-normal swimming behavior is likely a way for them to increase the amount of oxygen moving over their gills, facilitating recovery. Interestingly, immediately after a blue marlin is released, it dives to the thermocline depth and will remain there for an extended period, typically somewhere between one and ten hours.
The study found that the length of the period for recovery largely depends on how long the fight was. While they are down there (in a cooler temperature zone) they are swimming faster than normal and beating their tail harder and faster than normal. Sailfish, on the other hand, do not always dive to the depths, but they do beat their tail faster. It’s important to note that all of the fish during the study remained in the water during tagging and were released as quickly as possible.
Removing any billfish from the water is not recommended (and a violation in some countries) because it has been shown to drastically increase stress levels and the probability of mortality. Mortality rates vary depending on several factors, including the length of the fight, the age of the fish, and whether the fish was caught on a circle vs “J” hook. How the fish is released is also a factor. It is proven that circle hooks provide a 17% higher survival rate per species of billfish, over conventional “J” hooks that are not swallowed.
One study showed successful releases of blue marlin at 86% from rod & reel vs 77.8% from commercial long-liners. Another study showed a survival rate for white marlin released from rod & reel at 89% vs 74% from long-liners. A study by Dr. Michael Musyl and colleagues published in the Canadian Journal of Fisheries and Aquatic Sciences compiled the results of 49 independent studies into a single “meta-analysis” to estimate post-release survival in six species of billfish. “This study included billfish that were caught on both recreational and commercial fishing gear (longline). The authors’ meta-analysis reported 41 instances of post-release mortality, with 90% of mortalities occurring within 10 days of release.
Taken collectively, post-release survival was calculated among all species at roughly 86%. Results for individual species are as follows:
Blue Marlin (12 studies): Seven mortalities out of 142 tags, or roughly 90% survival.
Black Marlin (three studies): Three mortalities out of 26 tags, or roughly 86% survival.
Striped Marlin (seven studies): 14 mortalities out of 108 tags, or roughly 85.5% survival.
Sailfish (seven studies): 7 mortalities out of 85 tags, or roughly 90% survival.
White Marlin (six studies): 9 mortalities out of 94 tags, or roughly 89% survival.
Spearfish (one study): 2 mortality out of 2 tags, or roughly 50% survival.”
The IGFTO is dedicated to the conservation of billfish. We applaud and participate in industry release programs. From the studies above, the numbers are encouraging. Care of the resource cannot be preached enough to ensure successful fishing for our descendants. Gone are the days when boats boasted of their “kill rate” on billfish, whose only worth was a picture of a dead fish on a scale somewhere. Times have changed, definitely, for the betterment of both fish and angler.
Story by Art McDonald, VP Emeritus, IGFTO