There two main categories of harvest control measures (HCM): input controls and output controls (See Tables 1 and 2 below).
Input Controls:
Input controls are aimed at controlling fishing mortality indirectly, by reducing the efficiency with which fishermen can catch fish. They are often relatively easy to implement (because they require less monitoring, i.e. you don’t have to count all the fish that are caught), so they are often more appropriate for small scale fisheries that don’t produce much revenue (and hence have limited funding for monitoring and administration).
However, input controls may make it easier for fishermen to get around them, which works against the achievement of fishery goals. Input controls sometimes also cause other problems both ecological and socioeconomic in nature. For example, size limits are quite common in many fisheries but can result in discarding the undersized fish at sea to avoid prosecution, which in turn results in higher but undocumented fishing mortality, leading to overfishing. Gear restrictions such as a minimum mesh sizes are often used to prevent this, but if fishermen are motivated to maximize their catch, illegal gear is sometimes deployed resulting in catch of the prohibited size classes.
Other examples of input controls include: restrictions on engine horsepower, which can be circumvented by using multiple engines; restrictions on vessel size, which can be circumvented by increasing the number of fishing trips and the effectiveness of the gear; the implementation of fishing seasons, which can be rendered ineffectual by increases in fishing effort, either from existing fishermen fishing harder or from the entry of more fishermen; and spatial controls such as Marine Protected Areas (MPAs), which are often either too small to protect enough of the stock to control fishing mortality to a meaningful degree or so large that the boundaries are difficult to enforce. Good governance such as the allocation of secure catch or fishing territory privileges, including monitoring and accountability measures, can prevent these kinds of problems. In principle, any governance system that is very effective at controlling actual fishing effort and preventing gaming behavior (i.e., clever ways to get around the regulations) should enable adjustment of fishing mortality using input controls.
Output Controls:
Output controls, often called catch limits, directly control the amount of fish that are caught. They are generally more effective at controlling fishing mortality than input controls but are typically more difficult to implement than input controls because the fish have to be counted through one or various monitoring and/or catch accounting efforts. This can be challenging if fishermen land fish at multiple sites and/or discard fish at sea. Output controls can also be ineffective in a number of ways. For example, if catch limits are imposed on large groups of fishermen, it is very challenging to count the number of fish that are caught rapidly enough to ensure that the catch limit is not overshot, resulting in too much fishing mortality. If catch limits are imposed on individual fishermen and incentives to maximize catch persist, violations of the individual and aggregate catch limits (or “quotas”) can become commonplace, again resulting in too much overall fishing mortality. As is the case for input controls, output controls can also be made more effective through good governance (e.g., effective ways to hold fishermen accountable to catch limits, participatory decision-making processes, etc.) which generates incentives for fishermen to comply with the catch limit.
Step 11, Table 1. Description of common harvest control measures in fisheries. BMSY is the biomass associated with maximizing sustainable yield. FMSY is the fishing mortality associated with maximizing sustainable yield. SSB is the spawning stock biomass. (Table adapted from Liu et al 2016).
| Example Harvest Control Rule (HCR) | Type of Harvest Control Measure (HCM) | Method | Description |
|---|---|---|---|
| Maintain BMSY/ Preserve Target SSB | Output Control | Catch Limit | Sets an upper limit on how many fish can be removed by a fishery in a given time |
| Escapement Threshold | Allows a certain number of fish to escape a fishery before harvest | ||
| Bag or Trip Limit | Limits the number of fish that can be landed by an individual fisher or vessel on a single day or fishing trip | ||
| Size Limit | Sets minimum and/or maximum bounds on the size of fish that can be legally landed in a fishery | ||
| Sex-specific Limit | Similar to catch limits, but broken down by sex within a target species | ||
| Fish at FMSY | Input Control | Temporal Limit | Restricts the time period over which a fish can be legally landed |
| Gear/ Vessel Restrictions | Restricts the dimensions and characteristics of a gear or vessel allowed to participate in a fishery. May also restrict the quantity of gears allowed | ||
| Deployment Limit | Places a cap on the individual fishers' use of fixed gears |
Step 11, Table 2. Harvest control control measures. Here we list the major types of fishing control measures that are used to achieve various kinds of fishery management objectives. The symbols indicate the degree to which each control measure is useful for achieving a specific objective.
Combining HCMs:
Harvest Control Measures (HCMs) can be combined to better achieve the goals of a given fishery management system. Figure 1 shows some common incentives and management challenges that may result from the application of a single HCM, as well as some potential solutions to those challenges, which often involve combining HCMs.
