The bottom line: Coral reef fishes move different distances. The first comprehensive review of larval dispersal and movement patterns of coral reef fish species shows how we can use this information to improve marine reserve design so they actually work!
When you swim around a coral reef it is easy to believe that the fishes that you see have spent their whole lives there.
But in fact, that is seldom the case because most species have a two-stage life history, where they live on reefs as adults and juveniles and float around in the plankton as larvae.
Understanding how fish move at different times in their lives is critical for designing marine reserves so they actually work.
In fact one of the biggest problems that we have is that marine reserves are often too small for the species that they are trying to protect.
Ideally, marine reserves should be larger than the movement patterns of the adults and juveniles of the species that you want to protect. That way, they are likely to stay inside the reserve where they are protected from fishing so that they can grow big and fat and make lots of babies to export to other reserves and fished areas.
Marine reserves should also be close enough to each other so that the larvae from one reserve can replenish another reserve if it is wiped out by a disturbance (such as a hurricane).
Reserves should also be located close to fishing areas so that the fishery can benefit from the increased number of adults and larvae coming from the reserve.
While we’ve known that we should use this approach for years now in theory, we couldn’t actually apply it with any rigor because the information that we needed on fish movement was not available in a format that we could use.
Recent scientific advances have also redefined our understanding of how far fish move, which meant that we had to rethink our recommendations for marine reserve network design.
A recent paper appearing in the journal Biological Reviews provides a comprehensive review of larval dispersal and movement patterns of 34 families (representing 210 species) of coral reef fishes.
This paper provides, for the first time, species specific advice for the size, spacing and location of marine reserves in tropical marine ecosystems to maximize the benefits for conservation and fisheries management.
Scientists with The Nature Conservancy and several partner organizations (the Australian Research Council Centre of Excellence for Coral Reef Studies, the Coastal Conservation and Education Foundation, the Laboratoire d’Excellence ‘CORAIL’, The University of Hawaii at Hilo, Silliman University and the University of Queensland) completed the analysis.
Their paper finds that fish movement patterns (including home ranges and spawning migrations) vary among and within species and are influenced by a range of factors.
For example some species move <0.1–0.5 km (e.g. some surgeonfishes and grouper), <0.5–3 km (e.g. most parrotfishes and goatfishes) or 3–10km (e.g. large parrotfishes and wrasses), while others move tens to hundreds (e.g. some groupers, snappers and jacks) or thousands of kilometres (e.g. some sharks and tuna).
Therefore marine reserves should be more than twice the size of the home range of focal species. So reserves of different sizes will be required depending on which species require protection and how far they move.
Mean larval dispersal distances of coral reef fishes also tend to be <5–15 km, so reserves should be spaced less than 15 kilometers apart, and isolated populations that are more than 20 km from their nearest neighbour may require greater protection.
This information has been enthusiastically received by field managers, and is already being used to improve the design of marine reserves in many coral reef areas around the world, including in the West Indian Ocean, Southeast Asia, the Pacific Islands, the Caribbean and Latin America.
Read the paper – it is free at http://onlinelibrary.wiley.com/doi/10.1111/brv.12155/abstract
Go deep: Read more about the design of marine protected area networks for fisheries, climate change and biodiversity objectives (including extensive primary literature) visit the Conservation Gateway.