Striped Marlin Mortality Study
One of the greatest thrills for a recreational fisherman is to catch a large marlin. The chance to battle a fish five times your weight and watch them dance across the water's surface sends fishermen to the far corners of the globe. Over the years, the tag and release approach for sport fishing, particularly billfish, has been encouraged as a conservation measure. There has been some concern, however, that there may be significant billfish mortality associated with the tag and release approach, despite the best intentions of recreational fishermen.
As marlin populations in the Atlantic drop far below historic levels, tensions are rising between commercial and recreational fisherman. To date, mostly anecdotal evidence fuels the controversy because there is little scientific research to substantiate the levels of mortality associated with tag and release.
In November 2000, PIER researchers initiated a study of striped marlin in Magdalena Bay, Baja California, Mexico to address the questions of mortality associated with tag and release. Fish were caught using typical recreational fishing methods to compare the mortality of fish caught with two types of gear - circle hooks and J hooks.
Thirty-nine pop-up tags were deployed in 2000 and 41 in 2001 with a special link designed to release the tag if the fish dies and sinks below 1000 meters. Also, if the fish sinks to a depth less than 1000 meters and remains with no change in depth for a set period of time - another indication of mortality - the tag software will release the tag.
The observations resulting from this study allow for the suggestion of some guidelines that would reduce mortality of striped marlin and may help sustain this important fishery:
- When fishing with live or dead bait, anglers should be encouraged to use circle hooks. They are equally effective and far less likely to cause serious injury.
- Striped marlin that are bleeding from the gill chamber should be retained and consumed; in our study fish in this condition did not survive.
- Caution should also be taken when handling marlin at the leader; fish brought in too soon will be more prone to mortal injury as a result of striking the side of the boat.
An intriguing observation that has emerged from this study is that the Mexican striped marlin do not range far from Mexican waters, at least for as long as
we have been able to track them (up to nine months, November through July). The red line in the map below encompasses the tracks of 115 striped marlin that have been satellite tagged off the coast of Mexico. This has huge implications for fisheries management. It simplifies management by allowing a local governments, like Mexico, to effectively manage a stock of striped marlin without having to enter into any international treaties.
The results from this study were published in Marine and Freshwater Research.
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