IGFA Briefs
The following are excerpts from "International Angler", a bimonthly publication printed by the International Game Fish Association.
Conservation Notes
To Vent of Not to Vent? Does Venting Promote Survival of Released Fish?
Before we can answer that question, we need to understand some basic physics concepts.
Imagine that you have two glasses, one is empty and the other is half filled with water. Which glass weighs more? The glass that is half filled with water. Now if you fill that glass to the top, it will be even heavier, right? Because water has weight, it exerts pressure. In the ocean, the greater amount of water that is above a given point, the greater the pressure being exerted on that point. So, in other words, an increase in depth is an increase in pressure.
Fish that are caught and rapidly brought up to the surface can be affected by the decrease in pressure from depth to the surface and face risk of barotraumas. Barotraumas are the physical damages that the body tissues endure when the fish can not slowly adapt to the change in pressure from deeper water to shallower water. Some barotraumas can be easily identified in fish with swim bladders because the air in the swim bladder over-expands, sometimes to the point of rupture, forcing the eyes to bulge from the head and forcing the stomach to protrude from the mouth. In addition to the damages caused by the over-expanded swim bladder, almost every organ in the body is affected, regardless of the presence of a swim bladder.
In an attempt to relieve barotrauma symptoms specifically associated with an expanded swim bladder, some anglers will use a venting tool or other sharp object to pierce the swim bladder and/or body cavity to release the pressure and essentially ‘deflate’ the fish. This is commonly known as “venting a fish”. Whether or not to vent the fish when suspected barotraumas have occurred is a controversial topic among anglers and fishery management agencies.
Those who promote the practice of venting the fish, such as the US National Marine Fisheries Service and various angler groups, believe that it highly increases their chance of survival. This seems evident in fish that are unable to leave the surface of the water due to an over-expanded swim bladder, leaving them highly susceptible to surface predators such as birds, high surface water temperature, sun exposure, and the risk of being hit by a boat. It is widely assumed that if a fish can swim away it is considered to have survived, although this has not been proven.
Likewise, most Canadian provincial and many US state fishery management agencies are now discouraging anglers from venting fish, believing that it does not increase the fish’s chance of survival. Although venting relieves the pressure from the swim bladder or body cavity, it does not aid in any of the other injuries potentially accrued to the rest of the body. Furthermore, improper venting techniques can result in additional injuries to internal organs and result in an increase in mortality.
Venting is controversial, largely due to the variety of conclusions from venting studies. Some studies have demonstrated that there are benefits to venting while others prove the practice is ineffective in increasing the survival of the fish.
While this is probably not the end of the venting debate, results from the compiled studies are strongly against the practice of venting. The next question is: will anglers and fisheries managers follow?Weighing Your Fish Properly Can Increase the Survival of Released Fish
IGFA is very pleased to see that more and more anglers are opting to release fish after they are weighed and documented for record purposes. IGFA rules do not require that a fish be killed to be eligible for a record, only that they are not weighed on a boat (Junior Anglers may weigh the fish on the boat).
With a number of high-quality, certifiable hand scales now affordable to anglers, it’s easier than ever to document a fish for a record and release it in good health. Nevertheless, there are a few things that you need to do to ensure that your catch swims away healthy.
Most hand scales utilize a hook or lip-gripping device to secure the fish so that it hangs vertically during the weighing. However, hanging a fish vertically, especially large ones, can cause damage to muscle, bone, and internal organs. This damage may not be visible to the angler and the fish may even swim away after release, but many of these fish may be permanently injured and succumb to delayed or cryptic mortality.
The reason for this is simple. Fish have evolved in a buoyant environment (i.e., water), which does not necessitate the heavy skeletal systems and strong mesenteries (membranes that keep organs in place) that terrestrial animals have. So, taking a fish out of water and suspending it vertically can damage connective tissue and muscle in the jaw and also displace organs within the fish’s abdominal cavity.
Fortunately, there are several easy ways to avoid harming fish while weighing them. By far the easiest is to weigh them in the net you landed them in. IGFA strongly recommends anglers use knotless rubberized nets to reduce the amount of slime loss. Simply weigh your catch in the net, record the weight of the empty net and subtract the two. For larger fish that do not fit in nets, many anglers are using slings to weigh fish. There are several models that are commercially available and anglers can even make their own from a variety of materials.
We all know that the more fish we release today means the more available to us and our children in the future. By taking a few extra steps while weighing your fish, you will be doing your part to ensure that your catch will live to reproduce and be enjoyed by other anglers.
Did You Know?
The Food and Agriculture Organization of the United Nations Fisheries and Aquaculture Department has just released The State of the World Fisheries and Aquaculture 2008. Some interesting facts from the recent report (all values / annual totals are for the year 2006)
Catch – Global capture fisheries production was about 92 million tons.
Calculations indicate that is the equivalent to the weight of 18.4 million elephants or 46 million SUV’s (all these SUVs’ lined up would stretch five times around the earth at the equator).
Value – Global fish capture production first sale value is estimated at US$91.2 billion.
Countries – Top five countries world capture production
China
Peru
United States of America
Indonesia
Japan
*Asian countries accounted for 52% of global capture production.
People – 43.5 million people are directly engaged, part time or full time, in primary production of fish (including fish capture from the wild and aquaculture) with an additional 4 million people engaged on an occasional basis.
For each person employed in the primary sector, it is estimated there are four employed in the secondary sector (fish processing, marketing, and service industries) indicating employment of about 170 million people in the industry as a whole.
If you consider the number of dependants, about 520 million people could be dependant on the sector. This is about 8% of the world population.
Species / Stocks – The top five species for capture production:
Anchoveta
Alaska Pollock
Skipjack Tuna
Atlantic Herring
Blue Herring
Overall, 80% of the world fish stocks for which assessment information is available are reported as fully exploited or overexploited.
Quote from text: “As stated before in The State of World Fisheries and Aquaculture, the maximum wild capture fisheries potential from the world’s oceans has probably been reached, and a more closely controlled approach to fisheries management is required, particularly for some highly migratory, straddling, and other fishery resources that are exploited solely or partially in the high seas.”
For more information about the IGFA contact them at: HQ@igfa.org or at www.igfa.org.
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