Abstract
AbstractSpreading the offspring in space and time may offer bet‐hedging benefits by buffering environmental influences on parts of the offspring distribution. It has previously been shown that high mean age and size of spawners in the Northeast Arctic stock of Atlantic cod (Gadus morhua) is positively associated with high abundance and wide spatiotemporal distribution of eggs. However, little support has been found for a wide egg distribution acting as a buffer against environmental influences by leading to higher mean or less variable recruitment. The lacking relation between egg distribution and recruitment can be due to data limitation or alternatively that wide egg distributions may be of limited relevance for survival in later stages. To investigate these two alternatives, we analysed the output from a mechanistic coupled physical–biological drift model that projected the abundance of juvenile cod on the nursing grounds in the Barents Sea from empirically estimated egg distributions. The projections were performed with initial egg distributions reflecting the expected distributions at high and low mean weight of the spawners. We found that the extended distribution at the fringes only marginally contributed to recruitment, as a large proportion of the extra eggs at high mean age and size of spawners did not reach suitable nursing areas or failed to grow to a suitable size by the end of the season. In conclusion, our results suggest that the buffering effect of a geographically wide distribution of spawning products is insignificant compared to other effects on recruitment.
Highlights
Fishing may, in addition to causing mortality and removal of biomass, alter demographic structure of harvested populations through truncation of the age and/or size structure (Charbonneau et al, 2019; Hutchings & Myers, 1994; Law, 2000)
The surplus abundance at high mean weight of spawners (MWS) was reduced from 48% to 26% when removing the contribution from offspring that did not reach the Barents Sea, and further reduced to 5% when removing the particles that did not reach a size of 50 mm by early October (Figure 3)
Local density dependence increased the importance of wide egg distribution from 5% to about 12% higher recruitment at high MWS compared to low MWS (Figure S2)
Summary
In addition to causing mortality and removal of biomass, alter demographic structure of harvested populations through truncation of the age and/or size structure (Charbonneau et al, 2019; Hutchings & Myers, 1994; Law, 2000). Offspring at the fringes of the distribution may experience more adverse environmental conditions than individuals in core areas, as proposed by the density-dependent basin model (MacCall, 1990), or have lower chances of being advected into favourable nursery areas, as proposed by the aberrant drift (Hjort, 1914) and the member-vagrant hypotheses (Iles & Sinclair, 1982; Sinclair & Iles, 1989) It is unknown whether reduced age- and size-diversity in fish stocks generally leads to reduced spatial distribution of the offspring, and if it does, how a narrow offspring distribution influences the recruitment to the adult stock
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