Most people who love a bit of big game fishing unfortunately know that in order to catch many really big fish one must…travel back in time.
Sadly due to commercial overfishing during the last century, we have seen a dramatic reduction in the size of large predatory fish (Jackson et al, 2001). Selection of the larger fish by the fishing industry is of course the most economically profitable, giving you more bang for your buck. The result, however, means today there is a lot less big fish in the sea (Jackson et al, 2001). Now this is not a problem just for big game fishermen or the commercial fishing trade, this “fishing down of the food web” (see figure 1) has many direct and indirect effects on marine environments and everything living within them (Jackson et al,2001). Figure 2 illustrates the trophic cascade of effects that fishing can have on predators, their prey and plant life. Marine ecosystems are often complex, dynamic and interconnected functioning systems. Changing any aspect of the system can have impacts on the rest of the system (Madin et al, 2010).
In a recent seminar Professor Robert Warner, University of California, brought to light a very important aspect of marine ecosystems that is often overlooked in marine conservation research…fish behaviour. Professor Warner discussed many examples of how changing the pressure of predation can alter the behaviour of prey.
For example research by Munoz and colleagues (2010) revealed how social life of the hogfish (Lachnolaimus maximus) in protected no fishing zones can be very different to sites where fishing is still permitted. Specifically they found fish only reproduced in the protected reserve and not in the area being fished. Researchers suggest a perceived increase in risk of capture may affect where and when these fish choose to mate and produce offspring (Munoz et al, 2010).
An unlikely comparison of shark and wolf research also revealed common effects prey animals can show in response to the presence of predators (Wirsing & Ripple, 2011). Sharks and wolves, while in very different ecosystems are both top predators and as a consequence the other animals on the menu have adapted behaviours to avoid being eaten by them. Avoiding encountering, escaping effectively and being on the lookout for predators are all common strategies prey animals use (Wirsing & Ripple, 2011). Professor Warner used research such as this to illustrate how connected life is between predator and prey and how changing predator numbers within an area can affect not on the abundance of prey animals, but also how they behave.
The good news is governments, the fishing industry and the general public are all reasonably aware of the need to reduce fishing in order to restore natural marine ecosystems. This is owed, in part, to the wealth of researched done looking at the effects of predator loss from fishing (Madin et al, 2012).
The significance of Warners most recent research lies in his unique attempt to answer the unresolved question; how much of the pristine environment functioning (pre human disruption) can be recovered after the ecosystem is restored (Madin et al, 2012) Warner revealed that while most of the research in this area looked at the effects of predator loss from fishing, his research would be the first to investigate the effects of predator recovery after fishing has ceased (Madin et al, 2012).
Specifically, Warner and colleagues (2012) looked at how returning predators to an area that was previously fished can impact the foraging behaviour of prey animals further down the food web. This was done by comparing the foraging behaviour of two prey fish species (damselfish Plectroglyphidodon dickii & parrotfish Chlorurus sordidus) across areas (Line islands and Great Barrier Reef) that had never been fished (pristine), recently stopped being fished and was currently fished (Madin et al, 2012). Foraging behaviour of prey fish included measuring how far they would travel from safe areas to feed, for example. The results revealed that bringing back top predators can indeed restore foraging behaviour of prey to levels seen in pristine environments (Madin et al, 2012). Unlike previous studies, Warner and colleagues (2012) show for the first time how restoring predator populations can have important effects on returning the feeding behaviour of prey animals to a more natural level.
This research not only reveals the necessity to reduce fishing in order to restore natural marine food webs, it exposes the reality that behaviour of fish in response to reduced fishing needs consideration in marine conservation and management.
So it seems the moral of this fishy story may be; while we can hope reducing fishing pressure may help return all those big fish to the sea, the story is probably just is not that simple.
Jackson, J. B., Kirby, M. X., Berger, W. H., Bjorndal, K. A., Botsford, L. W., Bourque, B. J., Bradbury, R. H., Cooke, R., Erlandson, J., Estes, J. A., Hughes, T. P., Kidwell, S., Lange, C. B., Lenihan, H. S., Pandolfi, J. M., Peterson, C. H., Steneck, R. S., Tegner, M. J. & Warner, R. R. 2001. Historical overfishing and the recent collapse of coastal ecosystems. Science, 293, 629-37.
Madin, E. M., Gaines, S. D., & Warner, R. R. 2010. Field evidence for pervasive indirect effects of fishing on prey foraging behavior. Ecology, 91(12), 3563-3571.
Madin, E. M., Gaines, S. D., Madin, J. S., Link, A. K., Lubchenco, P. J., Selden, R. L., & Warner, R. R. 2012. Do behavioral foraging responses of prey to predators function similarly in restored and pristine foodwebs?. PloS one, 7(3), e32390.
Muñoz, R. C., Burton, M. L., Brennan, K. J., & Parker, R. O. 2010. Reproduction, habitat utilization, and movements of hogfish (Lachnolaimus maximus) in the Florida Keys, USA: comparisons from fished versus unfished habitats. Bulletin of Marine Science, 86(1), 93-116.
Wirsing, A. J. & Ripple, W. J. 2011. A comparison of shark and wolf research reveals similar behavioral responses by prey. Frontiers in Ecology and the Environment, 9, 335-341.
Professor Bob Warner, University of California, Santa Barbara- webpage
Video about sharks as a top predator and how they impact food webs.
Video explaining trophic food pyramid