Temperature effects on female maturation in a temperate marine fish

The ability to disentangle phenotypic plasticity from genetic contribution is important in understanding the factors that influence life history traits. Size and age at maturity have decreased in many fish stocks at a time when sea temperatures have generally increased. Whilst the role of fishery-induced selection in this decrease has been widely proposed, little is known about the importance of temperature as a direct driver of change. This study investigated the influence of temperature during the maturation “decision” period in haddock (Melanogrammus aeglefinus L.), an exploited species that has exhibited a long-term trend towards decreasing size at maturity. Wild-caught 1-year old fish were held during the maturation “decision” period from June to November under three temperature regimes: 8, 10 and 12 °C. Individual growth was monitored monthly to account for any temperature–growth interaction over the maturation “decision” period. Temperature explained most of the accountable variation in maturation, with the proportion maturing by November in the 12 °C treatments being over twice that of the 8 °C treatment. The effect of body size and energetic accumulation on maturation was greatest early in the “decision” process. This is the first demonstration that temperature can directly influence the physiological “decision” to mature in a temperate fish species.

Research Highlights
► Effects of temperature on maturation were examined under controlled experimental conditions in the haddock, Melanogrammus aeglefinus.
► A substantial growth independent temperature effect was demonstrated over the natural range experienced by this species.
► Rising sea temperatures would therefore be expected to influence the proportion maturing at a given size and age.
► This is relevant to the debate about the causes of long term change in maturation reaction norms.