Stable ocean hypothesis

The stable ocean hypothesis (SOH) is one of several hypotheses within larval fish ecology that attempt to explain recruitment variability (Figure 1; Table 1). The SOH is the notion that favorable and somewhat stable physical and biological ocean conditions, such as the flow of currents and food availability, are important to the survival of young fish larvae and their future recruitment. In the presence of stable ocean conditions, concentrations of prey form in stratified ocean layers; more specifically, stable ocean conditions refer to “calm periods in upwelling ecosystems (sometimes called 'Lasker events')” that cause the water column to become vertically stratified. The concept is that these strata concentrate both fish larvae and plankton, which results an increase of the fish larvae feeding because of the density-dependent increase in predator-prey interactions. Lasker is attributed with constructing this hypothesis in the late 1970s by building on previous larval fish research and conducting his own experiments. He based the SOH on case studies of clupeid population fluctuations and larval experimentation.

Author	Year	Name	Summary	Comments
Hjort	1914	Critical period hypothesis	Larval survival pivots on whether or not a larval fish successfully feeds during the “critical period” when it transitions from relying on its yolk sac to exogenous food sources	Myopic view of larval starvation being the primary factor in larval recruitment variability
				Cites marine fisheries of northern Europe
	1926	Aberrant drift hypothesis	Larval recruitment is affected by winds and ocean currents which cause dispersal of eggs and larvae, removing them from essential larval and juvenile habitat	Provided the foundation for future larval recruitment paradigms, but was under-tested until recently, when both starvation and oceanographic movements have been recognized as important factors
				Also cites marine food fisheries of northern Europe, like cod
Cushing	1974; 1990	Match-mismatch hypothesis	Success of larval recruitment is linked to a temporal alignment of fish reproducing, larvae hatching, and plankton (prey) blooming (generally associated with spring)	An evolved hypothesis combining both of Hjort's founding concepts
				Cites Atlantic cod
Lasker	1978	Stable ocean hypothesis	When tranquil ocean conditions occur in upwelling systems, the water column becomes stratified in layers that concentrate larvae and plankton, which increases successful larval feeding, which increases larval recruitment and contributes to year class strength	Relevant to larval survival, but does not correlate strongly to variations in recruitment (Peterman and Bradford 1987)
				Cites northern anchovies in the Pacific
Cury and Roy et al.	1989; 1992	Optimal environmental window	In upwelling systems, wind, storm, and other energetic events cause turbulence that, within an optimal range, increase larval recruitment; dependent upon the presence/absences of Ekman transport	Builds upon Lasker's Stable Ocean hypothesis
		Hypothesis		Cites Peruvian anchoveta, Pacific sardines, and West African sardines
Iles and Sinclair	1982	Stable retention hypothesis	Prey availability is not as critical to recruitment as the physical retention of the larvae, so spawning events must coincide with suitable wind and current conditions	Adaptation of and forward progress on Hjort's aberrant drift hypothesis
				Cites Atlantic herring

Sale	1978; 1991	Lottery hypothesis	Variability in tropical fish recruitment is dependent on pre- and post-settlement dynamics	Contrasts Hjort's original perspectives
				Supported by modern research (Doherty, 2002; Cowen 2002)
				Cites tropical reef fish