The patterns in variation in RPS and maturity meant that periods of high and low productivity were not the same for the two species. Warm_1 was a period of high productivity for cod with high RPS leading to a very high G0 despite lower weight and maturity at age. This same period was one of very low productivity for plaice, arising from low RPS, weights and maturity at age. Cold_2 was a period of low productivity for cod with very low RPS leading to limited potential for population growth. For plaice on the other hand, Cold_2 was a period of high RPS and high maturity at age leading to high productivity (under the assumption of M = 0.2). The impact of factors other than temperature on RPS and maturity meant that the association of productivity with temperature period was not consistent. For example, while Warm_1 had a very low G0 for plaice, the shift to maturation at an earlier age meant that Warm_2 had average G0 despite low RPS. Previous studies have examined the impact of changes in temperature on productivity and reference points in the context of climate change ( Cook and Heath, 2005 and Kell et al., 2005). The results here show that the impact of drivers other than temperature may make it difficult to predict how productivity will change as temperature changes.