Selective Pressures Impact on Fisheries Management Reference Points

Fisheries management is a diverse field, essentially reliant on ecological reference points as proxies for fisheries stability and sustainability. Reference points are generally based on population dynamics such as maximum sustainable yield (MSY), spawning stock biomass (SSB), fishing mortality (F), and yield-per-recruit relationships among others. Heino et al (2013) defined fisheries-induced evolution (FIE) as a selective mechanism ,which can impact the stock population characteristics and life history traits through the shifting of reference points. Although it has been theorized that fisheries-induced evolution is taking place in various fish stocks, predominantly seen through reduced fish sizes, quantitative evidence for FIE actually occurring in the wild is still unavailable. Nonetheless, the authors conclude that reference points are shifting due to FIE, climate change, or other environmental and ecological factors, and emphasize that reference points must be re-evaluated and adjusted to be current and effective for fisheries management and conservation. – Hannah Tannenbaum

Heino, M. et al. 2013. Can Fisheries-induced Evolution shift Reference Points for Fisheries Management? ICES Journal of Marine Science 70, 707 – 721.

                  Marine fisheries management uses reference points as a means of establishing targets to both maximize potential catches for food, employment and otherwise, but also to maintain the sustainability of fish populations. Therefore the accuracy of the reference points is paramount to effective fisheries management and prevention of over-exploitation. The authors conducted this study under the overall hypothesis that fishing is a selective pressure that can influence evolution in fish stocks in relation to their development, body size, fecundity and general life histories. They also emphasize that the accuracy or appropriateness of any reference point is limited by the data used to establish it; therefore, the impacts of fisheries-induced evolution must be evaluated to understand how reference points may need to be amended for effective management.
                  In order to evaluate the impact of FIE, the authors analyze a variety of source material on selective pressures affecting individual-level, population-level, and fishery-level properties. For the individual-level, other research was synthesized to bring the conclusion that FIE leads to earlier maturation, and overall smaller body size, due to fishing increasing mortality of both immature and mature fish, and investment trade-offs between growth and reproduction. Population-level consequences of FIE were less concrete, and again based on the synthesis of others’ research. The authors hypothesized that FIE would affect populations in two ways: 1. Populations that are fished can maintain a higher population biomass, or carrying capacity, and 2. If fishing drives stocks towards faster life histories, there will be an initial increase in maximum population growth rate. They came to these hypotheses based on research done on life-history theory and dynamics as well as population demography, which is essentially all theoretical. Lastly, the authors examine the fishery-level impacts due to FIE, namely potentially shifting reference points. Reference points for fisheries management can be based on a variety of different dynamic parameters, including productivity, yield-recruit relationships, or biomass. While reference points can be quantitative values, they are still theoretical measures based on the available data.

                  Through the analysis of potential FIE effects on the various levels of fisheries dynamics, the authors conclude that FIE is likely shifting reference points. It is emphasized that reference points should not be static quantities, but indeed, must shift and be constantly re-evaluated in order to remain effective and relevant.

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