Page 92

Bisbees Conservation Journal Q2 2015

While much research has been conducted on the effects of using circle hooks on the post release mortality of billfish, there is little analyzing the effects of fight times and other sources of stress from recreational fishing such as handling (i.e. whether or not the fish was removed from the water). Existing studies however do shed some light on the matter, revealing interesting trends that may indicate removing a billfish from the water is much more damaging than an angler may suspect. In studies conducted by students at the Virginia Institute of Marine Science (VIMS) 22 pop-up satellite archival tags (PSATs) were deployed in white marlin caught using circle hooks. As part of the study, blood samples were also taken from the fish which required removing the marlin from the water. Data from the PSATs indicated that 21% of the white marlin died immediately after release. In a separate, similar study also conducted by VIMS, 30 white marlin were tagged without being removed from the water resulted in only 2% post release mortality. It was hypothesized that the significantly different mortality rates could be due the additional stress put on the white marlin caused when the fish was removed from the water. It’s also interesting to note that the white marlin that did not survive did not have the longest fight times. While a person might think that a longer time fight time and exerting more energy would cause more stress on the fish it turns out that it is the. Researchers hypothesize that a short fight time before being removed from the water for blood samples may be equivalent to a person sprinting for as long and hard as possible then being forced to hold their breath! Regardless of how conclusive the science may or may not be, it holds up to simple logic that it’s just not a good idea to remove a billfish from the water. It is well known that stress caused by fighting a fish makes a fish more vulnerable to predation and commercial fishing pressure. Results from PSATs studies show that it can take billfish as long as 14 days to recover and resume normal behavior. The welfare of the billfish is always paramount, but especially when deploying a $4,000 PSAT, to ensure survival and the invaluable data from the tag. With that in mind, these scientists took every precaution to ensure the survival of the fish; it could perhaps have been the additional stress of being hauled aboard a boat and being deprived of oxygen that resulted in mortality. Billfish already face a gauntlet of threats from natural predators, artisanal and commercial fishing so why would anyone want to inflict even more strain and risk needlessly killing the fish? 92 BISBEE’S CONSERVATION JOURNAL Q2 • 2015


Bisbees Conservation Journal Q2 2015
To see the actual publication please follow the link above