Fish Facts

FISH FACTS: What happens when the line parts?

HAVE you ever wondered what happens to those fishing lures or hooks that are left in fish after they break off? Perhaps you’ve caught an undersized fish while baitfishing and it swallowed the hook right down, forcing you to leave the hook in it as you cut the line prior to release. In either case, there was little scientifically proven data available on the subject. Fortunately, fisheries scientists are an inquisitive lot, and over the last decade or so this subject has been researched fairly well, and we now know a little of what goes on after the line parts.

For some time now it has been well established that if you hook a fish deep in the mouth, throat, gills, or gut, it reduces its survival chances quite a bit. This is because of the increased risk of damage to vital organs and/or bleeding. Of course this means if you are releasing lots of fish you should try to eliminate deep hooking by fishing actively and using, for example, circle hooks or lures, both of which promote more superficial hookups. However, its also now well established that leaving the hook in deep hooked fish and cutting the line will greatly increase their chances of survival compared to the alternative of the angler exercising a little amateur surgery to try to regain a hook. For example, one study found that 77% of deep hooked snapper (Pagrus auratus) released with embedded hooks survived, with most shedding their hooks on average around 9 days later. In contrast, the same researchers found 0% survival for snapper on which amateur piscatorial surgery was undertaken to remove the hook. Another study found 85% of deep hooked yellowfin bream survived if they were released after cutting the line, with 76% of fish shedding the hook between 6 and 56 days after release. Unfortunately, despite this I have seen anglers sacrifice a fish just to get their hook back, which is a sad and sorry state of affairs when hooks are, in the whole scheme of things, the cheapest bit of fishing gear in your whole tackle box.

This x-ray of a healthy yellowfin bream showed it was surviving and feeding voraciously while possessing a 2/0 sized hook, which had worked its way out of the stomach to lie loose inside its peritoneal cavity. Image: Ben Diggles

Even though survival chances of deep hooked fish are much improved when the line is cut, the presence of the hook may not be completely benign, as studies have shown yellowfin bream which carry ingested hooks long term gained weight at slower rates than normal. Fortunately, anglers can improve the hook shedding rate for fish that are released even further by using hook materials that will corrode (as opposed to stainless steel hooks that do not), and by going barbless. Data from sharks hooked as bycatch in Pacific longline fisheries (where they bite through monofilament droppers set for tunas) found that stainless steel hooks of size 10/0 and upwards persisted in shark mouths for around 3 times longer (up to 7.6 years) than did plated corrodible hook types. Despite this, there was no detectable influence of hook type on shark survival, regardless of whether the sharks were trailing line or not (trailing line persisted as long as hooks were embedded). These results are not surprising when you consider that an embedded hook is very similar to injuries obtained from eating sharp natural prey items, while trailing line is similar in many ways to certain natural copepod parasite infections (which of course sharks and other fishes are naturally resilient to).

The influence of corrosion appears to be consistent across various hook types, but of course smaller thinner hooks corrode faster, and for the ultimate in hook shedding, barbless is best. Studies on much smaller (size 2) hooks retained by yellowfin bream have found that plated hooks quickly corrode and are shed by fish usually within the first 2 weeks post release, but up to 9 times faster if they are rendered barbless. This is because the corrosion originates from the area under the damaged barb (which if the hook remains in the fish for long enough), eventually causing the hook point to fall off allowing the hook to be shed.

So what about lures? Recent studies of largemouth bass, and European pike suggest all of the above in relation to hook materials and barbless also applies to lures. A telemetry study of European pike simulated breakoffs using lures manufactured with radio telemetry transmitters inside them. Of over 50 pike hooked and broken off, only one died and all fish except for one shed the lures within 14 days of release. Again, use of barbless hooks significantly reduced the time required for pike to shed lures, while another finding was those fish that were hooked more deeply tended to be not as active as those hooked superficially. These results were similar to those found for largemouth bass in North America, which demonstrated that bass which had ingested soft plastic lures typically expelled the lure within 9 d of ingestion, either by spitting it out or defecating it. The main detrimental effect that was noted for bass which ingested lures was a temporary reduction in growth rate, due to a temporary reduction in feed intake.

So now we know more about what happens when the line breaks. Its encouraging to know that fish can cope with shedding hooks and lures reasonably well, but of course as noted by the scientists in each of these studies, anything anglers can do to firstly rig up to help the fish shed the hooks (i.e. using non-stainless hooks, and going barbless), then avoid breakoffs or deep hooking in the first place, will also help.

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