Changes in the timing of spawning of Baltic cod: possible causes and implications for recruitment

Abstract

Interannual variations in spawning time, defined as the peak in egg abundance, of cod (Gadus morhua) in the Bornholm Basin, Baltic Sea, were analysed. Effects of water temperature, size and age structure of the spawning stock, abundance of food, and timing of spawning in preceding years were studied as possible determinants of annual spawning time. During the 1970s and late 1980s, peak spawning took place between the end of April and mid-June. A remarkable shift in the timing of spawning to the end of July was observed in the 1990s. The key factors governing the timing of spawning are water temperature during the period of gonadal maturation, density-dependent processes related to the size of the spawning stock, and food availability. The age structure of the spawning stock is suggested to have an additional effect. A high proportion of first-time spawners and decreasing water temperature have caused progressively delayed spawning since the early 1990s. Late spawning involves several processes that are detrimental to the survival of the early life stages. Recruitment in the mid-1990s was below what could be expected from spawning stock biomass and favourable hydrographic conditions. It is therefore suggested that the rebuilding of the Baltic cod stock could be improved by reduced fishing pressure in spring on early spawners. 2000 International Council for the Exploration of the Sea

Linking lipid dynamics with the reproductive cycle in Baltic cod Gadus morhua

“…Experimental results for Atlantic cod report a delay in spawning time by 8 to 10 d with a decrease in temperature of 1°C (Kjesbu 1994), and cod kept at low temperatures (4°C below ambient) showed a delay in spawning of 1 mo compared to cod kept at ambient temperatures (Kjesbu et al 2010). Seasonal peak egg abundance in Baltic cod was also negatively associated with ambient water temperature in January to April in the period from1986 to 1996, but only at low levels of cod spawning biomass (Wieland et al 2000). In the succeeding period of 1996 to 2005, spawning stock biomass was low and temperature relatively stable (ICES 2007).…”

“…A remarkable shift in the peak spawning time of cod in the central Baltic Sea (ICES subdivisions 25 to 32) was observed in the 1990s: peak egg abundance changed from April-June to end of July (Wieland et al 2000, Kraus et al 2002, Karasiova et al 2008. Later spawning has consequences for several processes influencing survival of early life stages (MacKenzie et al 1996, Støttrup et al 2008.…”

Reproductive output traits of the simultaneous hermaphrodite <I>Serranus scriba</I> in the western Mediterranean

“…If nutritional status is only appreciable at extreme values, manipulative experiments that control condition of individuals in order to achieve a suitable range of condition values may help us to better evaluate how nutritional status affects egg production. However, condition may also act on other reproductive aspects, such as length of the spawning season (Wieland et al 2000).…”

Developing Baltic cod recruitment models. II. Incorporation of environmental variability and species interaction

“…Mean annual egg and larval abundance values are available for the different subdivisions from ichthyoplankton surveys in (Appendix Tables A1 and A2) based on data compiled by Karasiova (1995), E.M. Karasiova (Atlantic Scientific Research Institute of Marine Fisheries and Oceanography, Kaliningrad, Russia, personal communication), MacKenzie et al (1996), Makarchouk (1997), A. Makarchouk (Latvian Fisheries Research Institute, Riga, Latvia, personal communication), R. Voss (Institute of Marine Sciences, Kiel, Germany, personal communication), and Wieland et al (2000). Egg abundance estimates are based on a 3-month period encompassing the main spawning period, i.e., AprilJune up to 1989 and successively shifted to May-June (1990 and June-August (1993 to take into account a shift in the spawning period in recent years .…”

“…As a result, several new time series are becoming available for variables relating to these processes. In particular, data series have been compiled for egg production (including sex-specific maturity ogives, Tomkiewicz et al 1997; individual fecundity, Kraus et al 2000), egg characteristics (buoyancy and viability; Nissling et al 1998), abiotic factors affecting egg survival (Plikshs et al 1993;Wieland et al 1994;MacKenzie et al 2000), estimates of egg and larval abundances in spawning areas (e.g., Plikshs et al 1993;Wieland et al 2000), hydrographic processes affecting larval and 0-group distribution (Voss et al 1999;Hinrichsen et al 2001), predation on early life history stages (Köster and Möllmann 2000a), and cannibalism (Sparholt 1996;Neuenfeldt and Köster 2000).…”