Sex-biased mortality of marine threespine stickleback (Gasterosteus aculeatus L.) during their spawning period in the White Sea
Golovin, P. V., Bakhvalova, A. E., Ivanov, M. V., Ivanova, T. S., Smirnova, K. A., Lajus, D. L.
Golovin, P. V., Bakhvalova, A. E., Ivanov, M. V., Ivanova, T. S., Smirnova, K. A., & Lajus, D. L. 2019. Sex-biased mortality of marine threespine stickleback (Gasterosteus aculeatus L.) during their spawning period in the White Sea. Evolutionary Ecology Research, 20(1–3), p. 279–295.
The selective mortality of threespine stickleback in the White Sea has been studied as the reason for the shift in the sex ratio of stickleback in favor of females on spawning grounds. The study was conducted in the Kandalaksha Bay of the White Sea in the period from June to August 2012-2018. The following sampling methods were used: beach seining to determine adult threespine stickleback density and local population size, hand collection of dead fish on the spawning grounds, gill netting of predatory fishes, analysis of predatory fish (Atlantic cod (Gadus morhua), shorthorn sculpin (Myoxocephalus scorpius), and fourhorn sculpin (Myoxocephalus quadricornis)) stomach contents to determine the sex of wellpreserved stickleback, and morphological analysis of stickleback spines to determine the sex of decomposed stickleback. The dynamics of stickleback abundance in the lagoon is explained by inshore migration of the fish to the spawning area at the beginning of the spawning period, and their subsequent departure at the end of the spawning season, with females leaving the grounds earlier than males. During spawning (5–30 June), total stickleback mortality reaches about 0.1%; the difference in the relative mortality rates of 0.0044% per day for males and 0.0030% for females is statistically significant. Mortality increases in the post-spawning period, when fish abundance in the inshore zone falls considerably, but remains at a very low level. Because of the low level of non-predation mortality, it cannot be the cause of the female-biased sex ratio observed in the White Sea stickleback population. Predation-associated mortality caused by Atlantic cod and sculpins was male-biased. Based on the stomach contents of predatory fish, the sex ratio of stickleback prey was as follows: cod, 61% males/39% females; sculpins, 82% males/18% females, which was significantly different from the population at sea (35% males/65% females). This factor alone, however, is unlikely to explain the prevalence of female stickleback in the lagoon. The eventual offshore male-biased mortality, caused by increased depletion of energy reserves during the spawning period, is probably the main reason for the observed female-biased sex ratio.
Keywords: Atlantic cod, fourhorn sculpin, Gasterosteus aculeatus, mortality, population dynamics, predation, sex, sexual dimorphism, shorthorn sculpin, spawning, threespine stickleback, White Sea.