By Sascha Clark Danylchuk

Finsights #8 - Science to help you catch more fish. Bryan Huskey photo.

Finsights #8 - Science to help you catch more fish. Bryan Huskey photo.

I want to introduce a new type of scientific paper, called a review paper.  So far, the literature I have used has been based on single studies.  Every once in a while, however, scientists will gather together much of the literature about a given topic, summarize it, and be able to draw new or stronger conclusions due to the support of multiple studies.  While review papers often lack the detail of papers based on individual studies, they are very helpful in advancing a discipline or subject area.  

Just a couple months ago there was a review paper published on what makes fish vulnerable to capture by hooks.  Because fishing is not a random process, some species or individuals within a species are more likely to be caught by anglers than others.  Likewise, at any given moment some fish may be in a vulnerable state while others are less vulnerable.  There are many, many factors that influence fish vulnerability and as anglers we know that what worked yesterday to catch a fish may not work today. The authors of the review paper have used a three-part framework to discuss the various aspects of vulnerability - represented by the yellow triangle in Figure 1.  There is also a video accompanying this paper.

"Vulnerability of fish conceptualized as a dynamic state-switching process in which fish transition into states of vulnerability as a function of the internal state, the encounter with the predator (i.e., fisher), and the selectivity of the gear. We also show how vulnerability is modified across axes of life history and environments and how it can be modulated by management actions such as fishing restrictions. Fish vulnerability is only observable insofar as the fish is captured, making it difficult to empirically quantify. Nevertheless, these concepts are the foundational mechanisms driving vulnerability." 

"Vulnerability of fish conceptualized as a dynamic state-switching process in which fish transition into states of vulnerability as a function of the internal state, the encounter with the predator (i.e., fisher), and the selectivity of the gear. We also show how vulnerability is modified across axes of life history and environments and how it can be modulated by management actions such as fishing restrictions. Fish vulnerability is only observable insofar as the fish is captured, making it difficult to empirically quantify. Nevertheless, these concepts are the foundational mechanisms driving vulnerability." 

Internal state
What is going on inside an individual fish and the factors that influence a fish to eat and strike comprise its internal state.  While the need to eat in fish is controlled by metabolism (just like in humans) there are many environmental factors that play into this, especially as fish are cold blooded.  The abiotic factors are those that are non-living such as physical (temperature, light, lunar phase) and chemical (dissolved oxygen, pH, salinity) properties of the environment.  The biotic environmental factors are the other living organisms including other fish of the same species, as well as predators and prey.  

Predatory encounter
When a fish is hungry or motivated to feed, you can think of it as a predator looking for prey.  The chance that the prey will be the hook on the end of your fishing line is the “predatory” encounter.  The probability of hooking a fish depends where a hungry fish is as well as where your fishing gear is – you will never catch a fish if there aren’t fish close to you to be caught.  Predatory encounter relates to the spatial components of vulnerability including fish and human movement patterns.  

Gear selectivity
The type of fishing gear we use, either by choice or regulation, ultimately determines whether you will catch a fish that is hungry and in the right place at the right time.  Fishing gear is selective, meaning it works better on certain (sized, shaped, or species of) fish.  Incorrectly selected gear (e.g. the wrong species of fly) can turn a vulnerable fish back to the invulnerable state.  Similarly, the ability of fish to learn in catch and release situations also influences gear selectivity.  

Why is this important for anglers?
As anglers, we talk and think about fish vulnerability constantly.  We talk about the bite being on or off, which flies or lures work, what moon phase is best for fishing, where the secret spots are, and on and on and on. There are books and magazines and blogs devoted to the topic.  Likewise, there are at least as many fishing theories out there as there are anglers.  While some of the factors that influence fish vulnerability are in an angler’s control, many are not.  Thinking systematically and using this mechanistic approach to vulnerability just might help you have more success the next time you are on the water.  

Read the entire review paper here.

Happy Fishing!
Sascha Clark Danylchuk

Fish vulnerability by Robert Lennox.

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