Enhancing marine fisheries
Fish stock are released into the wild.
Courtesy of UNSW, Australia
The production of the marine wild stocks is oscillating around its feasible maximum of 80-100 million tonnes and improvements, if any, can only come from sustainable enhancements of the habitat (e.g. through artificial reefs), productivity (providing for limiting elements such as iron) or recruitment (e.g. through restocking/ranching). However, while experience in fisheries enhancement is already well established in inland fisheries, it is still in its infancy and raising issues in the marine environment.
For various reasons, the effectiveness of human enhancements in an open environment are still very uncertain. For decades, emphasis was put on the politically rewarding action (e.g. of putting reefs or fingerlings in the ocean) and on the successful rearing of the animals in captivity for release, little has been done to effectively demonstrate the biological or economic performance of the interventions. Indeed, the late discovery of the inefficiency of many such operations have tended to discredit the whole field as a waste of public resources.
Interest might be renewed because:
With the progress now at hand in rearing marine animals, the potential is growing but the experience, protocols, guidelines, etc., on how to combine fisheries enhancement and management are still missing.
Improvements in productivity may come, inter alia, from sustainable enhancements of the habitat (e.g. through artificial reefs), primary productivity (providing for limiting elements such as iron) or recruitment (e.g. through artificial propagation and restocking/ranching).
Artificial propagation would be a solution to consider: (i) for areas in which a species cannot reproduce naturally due to irremediable loss of critical habitat; (ii) to maintain fisheries despite recruitment overfishing in places and situations where conventional management do not work; or (iii) to boost stock rebuilding.
Physical modifications are likely to be acceptable when they aim in fact at re-establishing natural conditions (e.g. reopening coastal lagoons and wetlands, replanting mangroves or seagrass beds).
Artificial reefs made with using redundant vessels, old tyres, quarry rocks and concrete structures may might be adequate to create additional habitats (e.g. in soft bottoms ecosystems) in order to increase biodiversity; attract predators; develop refuges for adults and juveniles; provide reproductive, feeding or nursery space; or establish biofilters (e.g. with oyster or mussels to re-establish water quality when nutrient loads are too high). Artificial reefs have also been used as “anti trawl” devices.
Potential sources of failure
A strong risk exist that enhancements be considered as a “cool” quick fix to long standing fisheries problems. At best, the technology could find its place into a well implemented ecosystem approach to fisheries. At worst, it will be paying lip service to sustainability at high cost to society, delaying real management action.
To develop a sound marine stock-enhancement, a number of considerations are essential.
First, as a premise, be doubtful about the efficiency of enhancement in general and take “successful” experiments with a grain of salt, examining the claims in light of the steps suggested below.
Second, recognize from the onset that the number of species and individuals released or the extent of artificial reefs built are irrelevant without a detailed assessment of the impact.
Third, when considering the possibility to integrate stock enhancement in the fishery management package:
It is not easy to foresee the future of marine fisheries enhancement. The demand for it should be expected to increase steadily with the growth and development of the world population. Progress in the area is likely to be slow considering the inherent difficulties and the strong a priori dubious or negative attitude of many fishery scientists, ecosystem specialists and environmental NGOs in relation to large scale ecosystem modifications. Considering in particular the complex nature of social-ecological systems, assessing, ex ante, or demonstrating at pilot scale, the expected effects remains a high order challenge.