The vulnerability of fish to hook-and-line capture has become a hot topic among fisheries scientists. 

A recent technical article in fisheries literature provided a rigorous review of what biologists know about why a fish gets caught on hook-and-line. In many ways, the long and heavily researched article was overkill, because it covered a diversity of fish species and fishing situations. It also tried to partition the complex issue into more narrow topics that could be studied. But the article left me with two significant take-home messages: 

- Catching fish isn’t easy and;

- Successful anglers are very accomplished predators.

You can only catch a fish if it is there to be caught. Fish are not randomly distributed. Habitat and forage affect where you are more likely to encounter a fish. Fish that are move mobile are more likely to be caught, and anglers who cover more water are more likely to have more encounters.


Gear Selectivity

Although we’ve all caught fish on a lure that was too big to actually be consumed, generally fish can only be caught on a hook or lure that fits into their mouth. Fish with small mouths require smaller baits. Larger fish can feed on a spectrum of sizes of lure or baits. For those fish, like bass, that feed on fish that vary widely in size, larger lures or bait tend to catch bigger fish. Of course, the choice of bait or lure may change seasonally. What a lure resembles, its color and where it is presented also determines what you catch.

A premise of catching fish is that any point in time, an individual fish or a bunch of individual fish are either vulnerable or non-vulnerable to capture. Anglers can only catch fish that are vulnerable. The idea of “triggering a reaction bite” touted by successful tournament bass anglers may challenge the simple dichotomy of vulnerable or non-vulnerable, such that there may be levels of non-vulnerable. Nevertheless, what affects fish being vulnerable is quite complex.


Externals

Factors such as temperature, wind, water current, light levels — often referred to as the abiotic environment — affect catchability. Many anglers believe that lunar phase and barometric changes also affect catchability.


Internal State

The internal state of the fish will affect vulnerability. Some individuals are more bold or aggressive than others. This can be a function of size, but it also can vary among individuals of the same size. Substantial evidence exists for group effects on the internal state. For example, competition may trigger aggression — or one fish feeding may excite others to feed. Abiotic conditions affect internal conditions. Fish stressed by poor environmental conditions, like toxic chemicals or low dissolved oxygen, won’t bite. Temperature (an external condition) affects metabolism, which in turn affects hunger (an internal state).


Life History

Some fish have predictable behaviors tied to completing their life cycle. Many fish spawn in shallow water at certain narrow ranges of water temperature. Others make spawning migrations. These genetically programmed behaviors concentrate the fish or place them in predictable locations, but they may also change the fish’s vulnerability to capture, such as bluegill on a spawning bed.


Learning

Much of what fish do is a consequence of what has conveyed fitness — what kept the species surviving and reproducing — over eons. Maladaptive behaviors are filtered out, effective behaviors are passed on across generations. Fish, however, do learn, and there is ample evidence that they can learn to avoid capture.  


Sensory Ecology

Fish use their senses of sight, touch, smell, taste, hearing, detection of water movement, and, for catfish, electroreception to detect, capture, and accept or reject food. Whether fishing live bait, dead bait or lures, anglers exploit these senses to attract fish, make them bite, and not reject the offering.

Each of the above topics of what affects fish biting could be expanded into pages of greater detail and examples. Regardless of what you fish for or how you fish, the simple outcome of catching fish is far from a simple process. Anglers who consistently catch fish, whether they are aware of it or not, know a lot about the fish they pursue. 


Vulnerable?

A prespawn smallmouth bass is vulnerable to capture for a number of reasons. It is in a predictable place, allowing anglers to more easily locate it. Internal factors cause it to take in more food for its reproductive function. And its sense of sight can be fooled by a lure of the proper size and coloration for conditions.