Dear MPA News:
I was surprised by the Georges Bank scallop example cited by both Halpern and Agardy (MPA News 6:9) in their recent pieces on the fisheries benefits of marine reserves. At first I thought I had missed something, so I looked at the evidence Halpern cited (MPA News 2:3). The cited article specifically says the jury was (is?) still definitely out on whether the observed year/s of high recruitment in areas around the Georges Bank closures are really due to the closures or just happened to be good recruitment periods (for example due to climate, etc). That is consistent with what I also remember having heard from scientists who work on Georges Bank. Recruitment is notoriously variable, and the stock-recruitment relationship notoriously weak, so can we attribute scallop recruitment variability in this case to a single cause - even when there are good reasons to expect enhanced recruitment such as increased spawner biomass and Allee effects? I would like to hear from the experts on Georges Bank about what is really happening.
Halpern and Agardy are not the only ones citing this as an example, and I think it is important that we have an open discussion about how we deal with this type of phenomenon (I won't yet say evidence). The precautionary principle does not apply equally in the worlds of management and science. If the evidence is equivocal, as MPA News 2:3 states, what research can be done to provide a clear answer to this question?
PO Box 5 Wembley, 6913 WA, Australia. Tel: +61 8 93336535; E-mail: russ.babcock [at] csiro.au