Effects of species interactions on pre- and post-harvest size distribution in size-selective fisheries

Background/Question/Methods

Empirical observations and theoretical predictions show that fisheries can truncate target species size distribution by selectively removing larger individuals.  It is less clear, however, how quickly populations revert to pre-harvest distributions after implementation of no-take policies by fisheries managers.  In particular, the presence of a strongly interacting size-specific predator may interfere with the recovery of a targeted prey species.  We used a two-species size-structured model to examine how gape-limited predation alters post-harvest recovery for three example species, cod, haddock, and whiting.  

Results/Conclusions

We found that there was little difference in recovery time between the generalist predation and no-predation models.  However, gape-limited obligate predation delays the recovery of large prey individuals to pre-harvest abundance, even for sizes not targetable by the predator.  In addition, the obligate predator lowers the relative abundance of smaller vulnerable individuals, delays the shift to pre-harvest size distribution, and can complicate post-harvest monitoring through the presence of population cycles.  We conclude that the presence of a strong dynamically-linked predator can interfere with the rapid recovery predicted from single-species management models, particularly for smaller-bodied fish with greater lifetime exposure to predation.