Why You Need Granders in a Blue Marlin Fishery
The capture of a marlin greater than 500 kg represents a major life achievement for billfish anglers, and fishers refer to marlin of that size using colloquial descriptors such as “Grander” or “Big Julie” depending on location and species. However, their presence in a fishery is valuable, not only for the excitement and interest they create, but because how often fishers encounter granders can tell resource managers about the status of the fishery.
C. Phillip Goodyear modeled hypothetical Atlantic Blue Marlin Makaira nigricans populations under varying rates of fishing mortality and found that sample sizes required to detect large fish increased disproportionally with increased fishing. The number of observations required to detect a 350 cm individual increased by 43% when the population was depressed by only 25%, and the value rose 50-fold when the population was reduced below 10%. In contrast, mean lengths decreased by only 2 to 14%, and mean weights decreased by 5 to 45%. This suggests that frequency of trophy catches (individuals greater than a species-specific threshold) may be a good indicator of stock health and can be used as an early warning of overfishing or even a clear end point denoting stock recovery. That metric, defined by Goodyear as NZ50, seemed far more useful than traditional indicators, such as mean length or weight. And while his study focused on Blue Marlin, the idea may be transferable to other species. We urge readers to examine this article for possible applications in other fisheries.
See original article here:
Prager, M.H. and Goodyear, C.P., 2001. Effects of mixed-metric data on production model estimation: simulation study of a blue-marlin-like stock. Transactions of the American Fisheries Society, 130(5), pp.927-939. dx.doi.org/10.1577/1548-8659(2001)130%3C0927:EOMMDO%3E2.0.CO;2
