When bigger is not better: selection against large size, high condition and fast growth in juvenile lemon sharks

Abstract

Selection acting on large marine vertebrates may be qualitatively different from that acting on terrestrial or freshwater organisms, but logistical constraints have thus far precluded selection estimates for the former. We overcame these constraints by exhaustively sampling and repeatedly recapturing individuals in six cohorts of juvenile lemon sharks (450 age‐0 and 255 age‐1 fish) at an enclosed nursery site (Bimini, Bahamas). Data on individual size, condition factor, growth rate and inter‐annual survival were used to test the ‘bigger is better’, ‘fatter is better’ and ‘faster is better’ hypotheses of life‐history theory. For age‐0 sharks, selection on all measured traits was weak, and generally acted against large size and high condition. For age‐1 sharks, selection was much stronger, and consistently acted against large size and fast growth. These results suggest that selective pressures at Bimini may be constraining the evolution of large size and fast growth, an observation that fits well with the observed small size and low growth rate of juveniles at this site. Our results support those of some other recent studies in suggesting that bigger/fatter/faster is not always better, and may often be worse.

Plant and Animal Reproductive Strategies: Lessons from Offspring Size and Number Tradeoffs

“…Therefore, the widely-accepted model of offspring fitness increasing monotonically with size may not be universal (Hendry et al, 2001). Aquatic animals provide notable empirical examples of costs of larger size during particular developmental stages (Hendry et al, 2001;Dibattista et al, 2007;Sun et al, 2015).…”

Intraspecific variation in physiological performance of a benthic elasmobranch challenged by ocean acidification and warming

“…In elasmobranch fishes, the effect of warming and acidification on predator escape performance, especially for juveniles, may pose additional challenges because they grow slowly, thus increasing and prolonging the chance of being predated upon before reaching sexual maturity (DiBattista et al, 2007). Although the consequences of rapid ocean acidification and warming on escape performance could be high, no studies to date have evaluated their combined effect on an elasmobranch fish.…”

Diversity in young shark habitats provides the potential for portfolio effects

“…In one such lagoon, Jennings et al (2008) reported a 23.5% reduction in juvenile survival in the year following localised dredging activities and associated declines in seagrass coverage. Negligible migration between N. brevirostris nurseries appears to be the norm (Gruber et al 1988, Morrissey & Gruber 1993a, 1993b, DiBattista et al 2007, Jennings et al 2008, and this strong site attachment may have precluded movement away from the degraded habitat. In contrast, C. leucas move out of their usual young shark habitats and into adjacent embayments in response to low salinity events (Simpfendorfer et al 2005, Heupel & Simpfendorfer 2008.…”