Size limits are placed on different kinds of fish for different reasons. Some size limits are set to allow fish to grow old enough to reproduce. Others are in place to allow the harvest of smaller fish but protect bigger fish that spawn. And some special limits are set to encourage fishermen to remove fish of a certain size to improve the population dynamics of a body of water.
Minimum Size Limits
A minimum size limit is the most common one in most areas. Bass have minimum size limits in most states and some states have a lake-by-lake size limit on bass, usually somewhere between twelve and sixteen inches. Some saltwater fish also have minimum size limits that can be surprising to freshwater fishermen, ranging from twelve inches for fish like Spanish mackerel and bluefish to almost five feet for fish like tarpon.
Bass tournaments usually have a minimum size limit of twelve inches unless the local limit is higher. This is to ensure fishermen bring in bigger fish, and to protect the resource. Most bass tournaments also have a five-fish creel limit, usually lower than the local creel limits, for the same reasons.
Minimum size limits make you release fish shorter than that limit. This ensures a good population of fish below a certain size for slow-growing or hard-fished species. The minimum size is often just above the size where that species starts spawning. Some fisheries have a minimum size set on certain species to allow fish to grow to trophy size. Those waters usually have a very low creel limit, allowing only one fish, if any at all, to be kept.
Maximum Size Limits
Some species of fish don't reproduce until they get very big, so a maximum size limit is often set for them. This allows larger fish a better chance to survive and spawn, ensuring more fish for the future. Redfish often have a maximum size as well as a minimum size, ensuring some fish reach a quality size before being harvested and also protecting the bigger spawning-age fish. Striped bass are another species that often has a maximum size limit.
Bodies of water sometimes have unbalanced populations of fish where it's beneficial to try to increase the numbers of fish in a certain size range. To do this, slot limits are set, allowing anglers to keep fish under and above a set size, but requiring the release of all fish in the slot size. This can stockpile fish of a specific age and size range while reducing fish that are smaller.
On lakes with slot limits, too many fishermen do not keep smaller fish below the slot size, but keep only the larger fish over the slot size. This defeats the purpose of the slot limit and hurts the lake in the long run. Keep the smaller fish as the fisheries biologists recommend.
Bass are one of the most managed fish in fresh water and they often have slot limits placed on them. A lake that has a slot limit of eleven to fourteen inches would mean you could keep bass shorter than eleven inches and longer than fourteen, but those in the slot must be released. On lakes with high reproduction rates but slow growth rates for bass, this would allow thinning the numbers of small fish while protecting a group of a size that could take advantage of bigger prey fish.