Final answer:
The precautionary principle applied to a declining fishery would lead to decreased fishing efforts, aiding in the recovery of fish populations and improving marine ecosystem health. Such measures are designed to prevent overharvesting, a problem historically exemplified by the collapse of the western Atlantic cod fishery.
Step-by-step explanation:
The application of the precautionary principle to a commercial fishery whose primary catch species is in decline would result in decreased fishing efforts. This approach is anticipated to allow for the rebound of fish populations and lead to healthier marine ecosystems. When fisheries are managed as common resources, they often fall victim to the 'tragedy of the commons', where individual fishers have little incentive to practice restraint. This results in overharvesting, which can decimate fish stocks and lead to ecological imbalances, as seen in the historic collapse of the western Atlantic cod fishery.
Implementing a precautionary approach would likely involve establishing networks of large marine protected areas and reducing fishing effort, for example, by creating dedicated access privileges such as those for adjacent small scale fisher communities. This can help avoid a 'race for fish' and the overcapitalization that often leads to resource depletion.