THE POINT OF HOOKS

The point of hooks

By Sascha Clark Danylchuk

Hooking damage is the the number one cause of mortality for fish that are caught-and-released. That’s not a surprising statement since hooks are the only commonality for all fish caught by recreational anglers. But what that statement doesn’t address is how and why fish die from hooking damage. If every fish that is landed has a hook wound, what is it that makes some fish die and others live? How much damage do hooks actually cause? Does it matter what type of hook you use? What other factors come in the play to determine if a fish lives or dies after being hooked?

This paper looks at hooks and specifically hooking mortality in many different studies. It’s called a meta-analysis, which is a statistical analysis that combines the results of multiple scientific studies. It’s also a great introduction to Dr. Robert Arlinghaus, our newest science ambassador. Robert’s work is often based a social-ecological systems approach, which means that he looks at fisheries issues through the lens of both fish ecology and social science. You can learn more about Robert here.

What did they do?

Looked at hooking mortality studies for fishes that are important in European freshwater recreational fisheries. All species in a genus were included, even if the species were not found in Europe. Studies conducted anywhere in the world were included in the study.

• 107 studies on 8 European species and an additional 10 species from the same genus.

• Extracted what caused mortality from each study:

Water temperature

Fish length

Hook type (singe vs. treble)

Existence of a barb (barbed vs. barbless)

Type of bait (natural vs. artificial)

What did they find?

Across all studies and species:

• Mean hooking mortality was 15.9%, with a range of 0 to 88.5%.

• Half of the studies reported hooking mortality of less than 10%. Only a few studies reported mortality levels over 50%.

• Factors that are important for hooking mortality:

1. Water temperature (higher water temperatures lead to higher mortality rates).

2. Bait type (average mortality for artificial baits was 11.4%, average mortality for natural bait was 25%)

3. Existence of a barb (average mortality for barbless hook was 8.2%, average mortality for barbed hooks was 14.6%).

For Salmonids:

• Results for trout and salmon species was similar to the overall results.

• Factors that were important for hooking mortality:

1. Water temperature (higher water temperatures lead to higher mortality rates).

2. Bait type (average mortality for artificial baits was 11.6%, average mortality for natural bait was 27%)

3. Existence of a barb (average mortality for barbless hook was 8.6%, average mortality for barbed hooks was 15.1%).

Takeaways:

• The good news is that most of the reported hooking mortality rates were very low (less than 10%).

• High mortality was most often due to deep hooking or when fish were caught at high water temps.

• There are several reasons why barbed hooks could lead to higher mortality rates than barbless hooks: barbed hooks have been known to cause more injury and bleeding, they also take longer to remove which often increases handling time and air exposure (both things known to lead to worse outcomes for fish), and either or both of these could increase stress levels in fish which also leads to poorer outcomes for fish after release.

• Despite the fact that in this study hook type (single vs. treble hooks) did not turn out to be significant, the authors think that hook type is a species specific issue and likely dependent on hook size as well as the mouth morphology of the fish, and the type of fishing. All these factors could not be teased out in the present study, but are likely important on a species by species basis.

Lip Grippers

Lip gripping devices and your catch. Tiger fish. Dave McCoy photo.

Sport Fishing Magazine recently published an article on A Guide to Lip Grippers. The very last paragraph of the article touches on how lip gripping devices can impact fish and the author states “Many of the lip-grip manufacturers interviewed independently stated that they believe their weight scales do not cause physical damage to fish or inhibit future feeding ability — when the fish is hung vertically”.  I decided to dig through the scientific literature to see if anyone had looked at this at this and found only three studies that focused on lip gripping devices, each on different species.

 
Bonefish The first study looked at if lip-gripping devices caused injury to bonefish.  They compared bonefish held vertically in the air with a lip gripper to those held horizontally in the water with a lip gripper, all compared against a ‘control group’ where bonefish were handled only with bare hands   Bonefish held with a lip-griping device either vertically or horizontally were prone to injury – 90% of fish had at least minor injuries (which included holes through the tissue of the lower jaw where the lip gripping device was placed) and 35% of fish had major injuries (including broken mandible and separated tongue).  Conversely, only one of the fish held by hand had a minor injury and none had major injuries.  All fish survived for 48 hours after being handled, but the authors did not monitor for long-term survival or feeding ability.  

Injuries sustained to bonefish using a mechanical lip-gripping device. Link to report.

Barramundi In 2009, a different group of scientists looked at how lip grippers compared to nets for holding barramundi (an Australian sportfish).  They compared barramundi held in a net with those held vertically by a lip gripper, as well as those held horizontally with a lip gripper and one hand supporting the midsection of the fish.  They found that all fish held vertically and 81% of fish held horizontally had holes in their lower jaws.  However, no fish had severe injuries as was seen with bonefish.  Furthermore, all fish resumed feeding within 3-5 days and all holes healed within three weeks.  The scientists also took x-rays of some of the barramundi to see if holding them with lip grippers had any effect on their vertebral alignment.  They found that holding barramundi vertically, and to a lesser extent holding them horizontally with the lip gripper causes vertebral separation.  None of the vertebrae separations recovered after three weeks. Being water dwellers where the water supports much of their body weight, holding fish in the air has the possibility of causing damage or separation to vertebrae.

Florida Largemouth Bass The most recent study on lip grippers was conducted on Florida largemouth bass and examined the differences between holding largemouth bass vertically with a lip gripper, by hand on the lower jaw using a tilted grip, and using a two-handed hold.  They found no difference in feeding behavior, survivorship, or rates of injury between any of the three methods of holding bass.  They did, however, find that largemouth bass that were held with the lip-gripping device took longer to recovery than other fish.

Why are these studies important to anglers?
    •    These three studies constitute a start to the much-needed research on lip-gripping devices, and given the diversity of these devises and the species they are used on, clearly there is more work to be done.
    •    What these studies do show is that there is a wide variation in how lip-gripping devices affect the incidence of injury on different fish species.
    •    What I could not find are any studies that examine repeated use of lip grippers, long-term affects on fish, or compare injuries from lip grippers to those caused by nets.  
    •    If tackle manufactures want to make claims that their lip grippers and other fish handling products do not harm fish, they should consider independent testing.

Happy Fishing!
Sascha Clark Danylchuk