One of the most common topics I have been asked about over the years is the question of survival of released fish. These days, as more and more anglers become conservation oriented, catch-and-release and tag-and-release are becoming part and parcel of fishing all over the world. The huge support received by organized tagging programs in Australia and other areas shows just how ethical fishing has become. Size limits on most species also mean that many undersized fish are released, and more recently, several states in Australia have introduce a wide range of bag limits, again leading to more and more fish being released after being hooked and landed. How many survive? What can be done to maximize survival? Is tag and release, or clean release a waste of time, or are we really being effective in trying to conserve our limited fish stocks?

Experiments have been done which measure mortality of fish after hooking. An overview of these studies was recently publish, and it is worth going into a little detail here about the findings of that review.

Titled "Hooking Mortality : A Review for Recreational Fisheries", and publishd in volume 2 of reviews in Fisheries Science, two Texan biologists, Maurice Muoneke and Michael Childress, amassed details of some 132 studies which were relevant to hooking mortality, and summarised them in a number of ways. It is important to realise that most of the studies were conducted in North America on salmonids (trout, salmon), with smaller numbers on other freshwater fishes such as catfish, pike, bass, crappies and walleye. Very few studies were found for saltwater fish and most of those were confined to members of the striped bass family and the drum family.

Most of the studies have been carried out by catching fish on angling gear, confining them for a period of time, and measuring the resultant mortality, although recapture rates of tagged fish are also important sources of information. Sometimes the fish have been caught by anglers under normal fishing conditions, sometimes by scientists using carefully replicated techniques. Numbers of fish per experiments are variable, and the lengths of the experiments in terms of days also have varied greatly. Nevertheless, in summarising this large amount of information, some generalisation seem to be able to be stated:

Combining all result, 41% of studies showed mortslity due to hooking to be 5% or less, 52% showed mortality at 10% or less and 70% of studies showed hooking mortality at less than 20%. These figures varied little amongst types of fish, but in general, were consistent enough to be pretty confident that those sorts of mortality rates are the 'ball park' figures in most situations. Some of the variables which affect mortality due to hooking and releasing were covered too. A few studies have looked at effects of catching fish from different depths and have suggested that deflating the swim bladder may indeed increase survival. On the other hand, trying to deflate popped eyes by inserting a sharp object into the eyes cavity of the skull resulted in greater mortality than non deflation (ouch!).

While a lot of the studies quoted only lasted for a few days after capture, a resonable number of experiments conducted over longer periods suggest that most of the mortality happens within 24 hours of hooking and release, and that mortality is substantially complete after about 6 days. (I would like to see more of this work done, but long term experiments are very costly).

Single or Treble hooks?

Should we use single or treble hooks; barbed or barbless hooks if release is intended? Perhaps not surprisingly, barbless hooks have usually been shown to cause less mortality than barbed, but not in all cases. On the other hand, it may come as some surprise to find that treble hooks are not as bad as singles. Trebles tend to cause less deep-tissue damage (fish usually can't swallow them) but this may sometimes be conteracted by the longer handling times in unhooking fish caught on trebles.

Concern has sometimes been shown for non lethal effects of catch and release, such as on growth rate or reproduction. Most of the studies on trout have shown that reproduction is not affected by prior hooking, but one Australian study on red bream was quoted as indicating that hooking-related stress may impair their reproductive development, although this effect may have been due to the combined effects of angling stress and subsequent confinement.

Quite a lot of studies strongly suggest that removing hooks from deeply hooked fish is not a good idea. This tend to tear vital organs and increases mortality, so the advice if a hook has been swallowed is to cut the line or leader.

Unfortunately, little light was shed on the tissue of live bait versus dead bait versus lures and the stainless versus galvanised hook debates, mainly because few, if any studies have yet been done to try to answer these difficult questions. There is still a lot of work to be done on hooking mortality, but we at least now have an excellent summary of what has already been done.