Female Length and Mass Quantify the Difference between Atlantic Salmon Ova Fecundity and Ova Deposition

Abstract

The population status of salmonids is often assessed as ova deposition relative to “ova conservation densities.” Traditional approaches to assessing ova deposition predict log(ova numbers) from log(female length) for Atlantic salmon Salmo salar based on calibrations for unspawned females. Better ova deposition predictions are obtained by using both female length and female mass, especially when part‐spawned females arrive at or leave local study sites, which are crucial to parameterizing such relationships. Improved estimates of ova deposition could help reduce the noise in crucial stock–recruitment relationships and thus improve both mortality estimates at other life stages and management understanding.Received August 23, 2011; accepted January 12, 2012

Ova fecundity in Scottish Atlantic salmon Salmo salar: predictions, selective forces and causal mechanisms

“…As the North Esk River is the key monitored river for Scottish S. salar, the implications will be appreciable irrespective of the outcome. In any such co-ordinated future study of ova production (not reliant on historical data) it would be desirable to record both body length and body mass per female (Bacon et al, 2012). Furthermore, measuring the sizes (diameters) of a sample of some 30 individual ova per female might elucidate the currently poorly predicted (only 31% of variance) average ovum volume per female.…”

Do trends in the size of wild female Atlantic salmon have a substantial effect on egg deposition?

“…However, there were no significant trends in the length–weight relationships over this shorter time period (unpublished data), and Bacon et al. () showed that this relationship was constant for early running upland fish between two datasets collected 40 years apart. Despite the limited additional effect of declining spawner size on egg deposition, accounting for long‐term trends in size will improve estimates of egg deposition.…”

“…It is therefore possible that the current analysis underestimates the effects of size if reductions in fish weight have exceeded those in length; that is, if the fecunditylength relationship has not been constant. However, there were no significant trends in the length-weight relationships over this shorter time period (unpublished data), and Bacon et al (2012) showed that this relationship was constant for early running upland fish between two datasets collected 40 years apart. Despite the limited additional effect of declining spawner size on egg deposition, accounting for long-term trends in size will improve estimates of egg deposition.…”

“…Bacon et al. () provided length–fecundity relationships for early running upland spring fish from which egg deposition can be estimated.…”

“…The body size of salmonids is an important characteristic, frequently linked to their reproductive success (Dickerson, Quinn & Willson, 2002). This is particularly true for female salmon where size determines the number (and often size) of eggs spawned (Bacon, Malcolm, MacLean, McLaren & Thorne, 2012;Berg et al, 2001;de Eyto et al, 2015). Salmon management often relies on ova deposition targets (ova per unit area) estimated from spawner numbers assuming established sex ratios and mean fish sizes (e.g.…”