Seasonal trends in mortality and growth of cod and haddock larvae result in an optimal window for survival

Abstract

Changing climate and global depletion of fish stocks have added urgency to the centuryold quest to understand the factors controlling fish production. The leading hypotheses advanced to explain the large (orders of magnitude) inter-annual variability in recruitment of young fish emphasize rapid growth and a match to prey production in the first weeks after hatching, although avoiding predators may be of equal or greater importance. Here we show for 2 important North Atlantic groundfish (Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus) that seasonal patterns in growth (G) and mortality (M) rates of young larvae combine in some years to yield a window of opportunity when M falls below G within days after hatching and cohort biomass increases rapidly possibly leading to high recruitment. Contrary to expectations, this window occurs early in the seasonal production cycle (February to March) when temperatures are near their annual minimum, fish larvae and their prey are relatively scarce, and G is low. In most cases examined, later, faster-growing cohorts appear to be rapidly lost to a suite of vertebrate and invertebrate predators whose abundance, metabolism, and consumption increase through the spring with increasing water temperature. In this seasonally varying environment, size on year day may be critical to minimizing M/G. Our data demonstrate the importance of rapid growth throughout the season cycle, but particularly early in the season when temperatures, potential prey, and predators are at seasonal low levels. These findings reinforce the importance of management practices protecting larger, older females that begin spawning earlier in the season and produce larger, more viable eggs and larvae.

Reconsidering the impossible — linking environmental drivers to growth, mortality, and recruitment of fish

“…However, comparative approaches face important hurdles because the potential advantages of the similarities of location and environmental variability can be trumped by the differences in behavior or life histories among focal species. For example, Georges Bank cod (Gadus morhua) and haddock (Melanogrammus aeglefinus), despite taxonomic closeness, demonstrated significant differences in growth and mortality rate and their relationship to environmental conditions (Buckley et al 2010;Mountain and Kane 2010). Although identifying the importance of the differences represents an advancement in knowledge, whether in the case of Georges Bank cod-haddock or in other regions (e.g., Möllmann et al 2005Möllmann et al , 2008, the sum of the differences can also limit the identification of common principles that can serve to explain variations year-class strength.…”

On the edge of death: Rates of decline and lower thresholds of biochemical condition in food-deprived fish larvae and juveniles

“…In a recent study, Huwer et al (in press) utilized sRD measurements to identify Baltic cod larvae in poor nutritional condition within areas having low concentration of the preferred prey, Pseudocalanus acuspes. In the Northwest Atlantic, Buckley et al (2010) identified 'windows for survival' of Atlantic cod and haddock larvae based upon seasonal and inter-annual differences in larval RD condition and prey abundance. Voss et al (2006) utilized sRD measurements to reveal size-specific 'windows of survival' for Baltic sprat larvae that were linked to the availability of suitable prey.…”

Incorporating temperature-driven seasonal variation in survival, growth, and reproduction into population models for small fish

“…The inclusion of seasonal variations in demographic rates increases the realism of population models, but is generally lacking in application for fish management despite its well-documented occurrence (Post & Parkinson 2001, Shoji & Tanaka 2007, Buckley et al 2010. The model presented here incorporates temperature-driven growth rate, mortality, and reproduction for a small fish species, Cyprinodon variegatus, and is used to compare projections using seasonally varying and constant parameters.…”

“…Seasonal variation in natural mortality and reproduction is well documented for fish species (Nordlie 2000, Shoji & Tanaka 2007, Buckley et al 2010. With the exception of overwinter mortality for commercially important stocks (e.g.…”

“…Directly, temperature increases fish growth rate which can result in higher mortality from increased energetic costs (Savage et al 2004, McCoy & Gillooly 2008. Indirectly, small fish in warmer water are at greater risk of predation because predators eat more to meet higher metabolic demands, which has been demonstrated both geographically (Pauly 1980) and seasonally (Buckley et al 2010). Conversely, faster growth rates can reduce mortality by decreasing the duration of vulnerable life stages (Takasuka et al 2004).…”