Timing of cod reproduction: interannual variability and the influence of temperature

Abstract

We examined interannual variability in the timing of spawning of female cod Gadus rnorhua from 1947 to 1992 in 3 regions off Newfoundland, Canada, in the northwest Atlantic. Maturity data, assessed by visual examination of dissected gonads of cod collected by research trawls, were analysed with probit regressions to identify the day of each year on which 50% of females had ceased spawnlng (which we refer to as spawning time) on northern [Northwest Atlantic Fisheries Organisation (NAFO) Division 3L] and southern (3NO) Grand Bank and on St. Pierre Bank (3Ps). We minimized the bias in our estimates by separating sampling variability and interannual variation in age structure from true interannual variability in reproduction. Among regions, average spawning time (mean -t SD) varied from Days 157 + 18 (June 6 ) and 139 * 16 (May 19) on northern and southern Grand Bank, respectively, to Day 135 2 24 (May 15) on St. Pierre Bank. Interannual differences in spawning time were significant within 3L (1948-1991), 3 N 0 (1947-1992), and 3Ps (likelihood ratlo tests; p < 0.001). Interannual variation in spawning time was significantly associated wlth variation in water temperature prior to spawning in 3L and in 3Ps although the signs of the associations differed between regions, casting doubt on the hypothesis that the timing of cod reproduction represents an adaptive response to temperature change. The negative correlation between temperature and spawning time in 3L can be explained by the positive influence of temperature on gonad development. In 3Ps, we attribute the early spawning dates in years characterized by cold bank temperatures to (1) a thermal barrier Imposed by sub-zero temperatures on spawning migrations from the continental slope to the shelf, and to (2) increased rates of gonad development, and an earlier readiness to spawn, experienced by cod 'forced' to prolong their residence in warm slope waters. Our analyses indicate that cod spawning time varies significantly among years, demonstrate how the effects of temperature on cod reproduction depend on regional hydrography, and underscore the importance of separating variation in sampling protocol and age structure from true interannual variability in spawning time.

Bottom-up effects of climate on fish populations: data from the Continuous Plankton Recorder

“…In addition, factors not considered here may also play an important role. Among such factors are spawning stock size, reproduction, including spawning location and time (Ellertsen et al 1989, Hutchings & Myers 1994, transport of eggs and larvae outside their spawning/nursery grounds (Hinrichsen et al 2001, Ottersen et al 2004a), predation on eggs and larvae (Bailey & Houde 1989, Kempf et al 2009) and competition between species for limited food resources (Kane 1984). These results further illustrate the complexity of the mechanisms involved in the appearance and survival of fish larvae.…”

On the prediction of short term changes in the recruitment of North Sea cod (<i>Gadus morhua</i>) using statistical temperature forecasts

“…metabolic rates, growth rates, swimming rates, oxygen consumption and spawning (Brown et al, 1989;Blaxter, 1992;Hutchings and Myers, 1994;Brander, 1995;Rideout et al, 2000), and at the community level, e.g. geographical distributions and predation rates (Heessen and Daan, 1994;Ottersen et al, 1998;van der Veer and Witte, 1999).…”

Reproductive investment in Atlantic cod populations off Newfoundland: Contrasting trends between males and females

“…Even though some interannual variability has been reported in the spawning time of cod (Hutchings and Myers 1994;Morgan et al 2013), this variability seems to be captured by the various individual characteristics (e.g., relative liver index) or sampling characteristics (e.g., longitude) we have considered. As a consequence, the interaction between sampling day and CIL area or water temperature anomaly appears not to bring any additional information, and hence, has never been retained in any of the 12 best models.…”

“…However, in Subdivision 3Ps, CIL area has a positive effect on the gonadal investment of females, which suggests a different mechanism linking oceanographic conditions and reproductive investment. For example, Hutchings and Myers (1994) found a positive effect of cold water on spawning time and attributed this to cold on-shelf conditions in the area forcing the fish to stay in deeper warmer waters. Water temperature anomaly and CIL area do not have a large influence on our results.…”