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Dr. Phillip Goodyear TBF scientist, Dr. Phillip Goodyear’s most recent Atlantic blue marlin research focused on the effect fishing has on the number of the largest fish (“granders”) in a population. His research is published by the American Fisheries Society, the oldest, largest and most influential association of fisheries professionals in the world. Typically, fishing reduces the number of fish that survive to old age, which also reduces the average age of fish available to be caught. With most species this also significantly reduces the average size of the catch, which is an important indicator of stock health. However, in earlier research Goodyear discovered that average size is a poor indicator of population health in fast-growing species like blue marlin. This is a consequence of the fact that the fast growth of young fish reduces the difference between the size of the very old and young fish. Hence the average size can’t change very much when fishing removes most of the old, large fish from the population. This phenomenon lessens the utility of average size as a population standard of measurement (metric) for stock assessments. Still, the abundance of the oldest and very largest fish does decline even in fast growing species, but there has been no statistic to quantify this fact for use in stock monitoring or assessments. Goodyear’s research developed a new statistical measure (NZ50) to fill this gap and showed it to be a sensitive indicator of excessive fishing. NZ50 is the smallest number of observations required from the catch or population to include at least one fish of some particular large size half of the time. Think of it as the statistical measure of the number of fish an average angler would have to catch to have a 50-50 chance of catching a “grander” at different population levels of abundance. Goodyear illustrated the statistic with data from a simulated hypothetical population modeled after Atlantic blue marlin. The results showed NZ50 to be a much more responsive indicator of the decline in abundance than the use of average size for judging population status. He concluded that this new statistical measure would be useful for monitoring stock recovery and should be routinely included in stock assessments. TBF’s Grander Release Club TBF’s “conservation and responsible use” philosophy applauds anglers big enough to release the big marlin girls that are estimated at boat side to weigh 750 pounds and up. To honor the anglers, captains and mates who release these very large, female marlin, TBF created the Grander Release Club. If a safe tagging opportunity is available when a decision is made to release the big marlin, tagging would be appreciated for it can generate needed recapture data. Reports of the grander releases should be submitted with a photo to tag@billfish.org. In recognition of releasing the marlin, a newly designed TBF certificate will be sent to each team member, with their names entered into the Grander Release Club section on TBF’s website. Only with smart release investments will granders grow and be available for generations to come. In Addition As with many fish species, the number of eggs released during spawning increase exponentially with the weight of the fish. For instance, an Atlantic blue marlin of 90” (approximately 350 lbs.) is estimated to release 3,6000,000 eggs versus close to 7,000,000 eggs from a 114” fish (approximately 500 lb.). Not only are the big girls more fecund, they are also passing along the DNA and any genetic advantages that allowed them to successfully grow to such a large size. 48 BISBEE’S CONSERVATION JOURNAL Q1/Q2 • 2016


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