Hydrodynamic insights into designing and locating effective MPAs

 

 Image: Tom Adams

New research has found that fish populations within the majority of marine protected areas (MPAs) studied are not significantly different to fish populations in unprotected waters. The study looked at a total of 964 sites in 87 marine protected areas (MPAs) across 40 different countries (including both tropical and temperate waters).  It also found that only 10% of those sites studied are ‘effective’ in meeting their conservation goals. ‘Effective’ MPAs were defined as those meeting at least four out of five management and planning criteria:

·      No-take (no fishing permitted)

·      Enforced well (MPA boundaries and restrictions complied with)

·      Old (more than ten years old)

·      Large (more than 100km squared)  

·      Isolated (by deep water or sand)

This latest research is likely to add fuel to an already raging debate (discussed in an earlier post on this blog) on the designation of areas to create an ecologically coherent network of MPAs in the UK. Indeed, the study (discussed by the lead author here) has already been picked up on in this context in another recent article in The Conversation which takes the view that:

‘Evidence from UK waters may be poor, but there is ample information available from the rest of the world to provide a guide for the best way to build a biologically functional MPA…. The challenge to conservation planners, in Britain and elsewhere, is to build a series of protected areas that fulfil the criteria for successful conservation. It would help to have clearly stated biological goals for these parks that would provide a basis for their location and design.'

The problem (or one of the many problems) is that locating and designing effective MPAs is not as simple as having clearly stated biological goals. Scientific research uses mathematical models (which are informed by huge amounts of scientific data) to predict, for example, the likely changes to fish populations in an area over time. While models of both population dynamics (eg changes to fish populations) and hydrodynamic processes (such as the effects of ocean currents) are now well developed, studies that combine both are rare. Yet accounting for hydrodynamic processes is a crucial part of understanding population processes in specific environments, such as larval dispersal and settlement. If such processes are not understood, it is difficult to predict whether a designated area will be effective in maintaining or (ideally) increasing the fish population within that area.

The science of where to situate MPAs in temperate waters is still very much developing and studies have, to date, been largely based on estimated tidal movements (see here for an example). However, the situation is a lot more complex. Estimated tidal movements alone do not provide the full picture in relation to, for example, how larval dispersal takes place in a particular environment. Recent research on larval dispersal of intertidal organisms shows that differing roles of particular sites as larval ‘sinks’ and ‘sources’ need to be taken into account in order to fully understand dispersal patterns. Understanding such dispersal patterns is necessary to accurately design and locate networks of MPAs so that the biological goals of such MPAs (which will include the recovery or maintenance of fish stocks) can be achieved. However, studies such as this research have not generally been taken into consideration for MPA design and location up to now. An exception is a recent study by Marine Scotland Science. While this is a positive step forward, such work is still in its infancy and needs further refinement to work well in coastal areas.

Is this an excuse to ignore the alarming decrease in the biodiversity of the world’s oceans and to throw the precautionary principle out of the window? Not at all. The authors of the recent MPA research underline the seriousness of this decline:

‘By using effective MPAs as an unfished standard, our study allows the first global assessment of the magnitude of fishing effects on temperate as well as tropical reef communities. Fish biomass was greatly reduced overall, with 63% of all fish biomass, 80% of large fish biomass, 93% of sharks, 84% of groupers and 85% of jacks apparently removed.’ 

What I am highlighting is the need to acknowledge the complexity of designing and locating networks of effective MPAs, and to enable and encourage emerging science around population dynamics and hydrodynamic processes to be taken into account by, and incorporated into, the social, cultural, economic and political contexts which shape, and are themselves shaped by, the creation of these networks.

I am grateful to Dr Tom Adams for comments on this piece.