Modelling fish attraction to artificial reefs – not always a fatal attraction

The debate on whether artificial reefs produce new fish or simply attract existing fish biomass continues, and there remains considerable doubt as to whether artificial reefs are a harmful form of habitat modification. The... [ view full abstract ]

The debate on whether artificial reefs produce new fish or simply attract existing fish biomass continues, and there remains considerable doubt as to whether artificial reefs are a harmful form of habitat modification. The harm typically associated with fish attraction is that fish will be easier to exploit due to the existing biomass aggregating at higher densities on an artificial reef. This outcome of fish attraction has never developed past an anecdotal form, however, and is always perceived as a harmful process. We present a numerical model that simulates the effect that a redistributed fish biomass, due to an artificial reef, has on fishing catch per unit effort (CPUE). This model can be used to identify the scenarios (in terms of reef, fish and harvest characteristics) that pose the most risk of exploitation due to fish attraction.

Simulations revealed that attraction is not always harmful, because it does not always cause increased fish density. Rather, attraction sometimes disperses existing fish biomass, making them harder to catch. Therefore some attraction can be ideal, with CPUE lowest when attraction leads to an equal distribution of biomass between natural and artificial reefs. Simulations also showed that the outcomes from attraction depend on the characteristics of the target fish species, such that transient or pelagic species run a higher overall risk of ‘concentration by attraction’ than resident species. Although great progress is being made on estimating fish production from artificial reefs, production remains a very uncertain metric, and models such as this can be used to highlight the most risky scenarios that should be avoided when knowledge of fish production is scarce. This study also highlights that the redistribution of fishing effort is as important as the redistribution of fish biomass for estimating the risk, effects, and impacts of artificial reefs.