Century-long cod otolith biochronology reveals individual growth plasticity in response to temperature

Abstract

Otolith biochronologies combine growth records from individual fish to produce long-term growth sequences, which can help to disentangle individual from population-level responses to environmental variability. This study assessed individual thermal plasticity of Atlantic cod (Gadus morhua) growth in Icelandic waters based on measurements of otolith increments. We applied linear mixed-effects models and developed a century-long growth biochronology (1908–2014). We demonstrated interannual and cohort-specific changes in the growth of Icelandic cod over the last century which were mainly driven by temperature variation. Temperature had contrasting relationships with growth—positive for the fish during the youngest ages and negative during the oldest ages. We decomposed the effects of temperature on growth observed at the population level into within-individual effects and among‐individual effects and detected significant individual variation in the thermal plasticity of growth. Variance in the individual plasticity differed across cohorts and may be related to the mean environmental conditions experienced by the group. Our results underscore the complexity of the relationships between climatic conditions and the growth of fish at both the population and individual level, and highlight the need to distinguish between average population responses and growth plasticity of the individuals for accurate growth predictions.

Larger but younger fish when growth outpaces mortality in heated ecosystem

“…Our study provides strong evidence for warming-induced differentiation in growth, mortality, and size-structure in a natural population of an unexploited, temperate fish species exposed to an ecosystem-scale experiment with 5-10 ℃ above normal temperatures for more than two decades. While it is a study on only a single species, these features make it a unique climate change experiment, as experimental studies on fish to date are much shorter and often on scales much smaller than whole ecosystems, and long time series of biological samples exist mainly for commercially exploited fish species (Thresher et al 2007;Baudron et al 2014;Smoliński et al 2020) (in which fisheries exploitation affects size-structure both directly and indirectly by selecting for fast growing individuals). While factors other than temperature could have contributed to the observed elevated growth and mortality, the temperature contrast is unusually large for natural systems (i.e., 5-10 ℃, which can be compared to the 1.35 ℃ change in the Baltic Sea between 1982 and 2006 (Belkin 2009)).…”

“…Several factors likely contribute to this pattern, such as increased allocation to reproduction (Wootton et al 2022) and larger individuals in fish populations having optimum growth rates at lower temperatures (Lindmark et al 2022). Empirical support in fishes for this pattern seem to be more consistent for increases in size-at-age of juveniles (Thresher et al 2007;Rindorf et al 2008;Huss et al 2019) than declines in adult size-at-age (but see (Baudron et al 2014;Smoliński et al 2020;Oke et al 2022)), for which a larger diversity in responses is observed among species (Barneche et al 2019;e.g., Huss et al 2019). However, most studies have been done on commercially exploited species (since long time series are more common in such species), which may confound effects of temperature plastic and/or genetic responses to size-selective mortality on growth and size-at-age (Audzijonyte et al 2016).…”

Differences in metabolic rate between two Atlantic cod (Gadus morhua) populations estimated with carbon isotopic composition in otoliths

“…The first and last increment widths were excluded from further analysis since they may not reflect a whole year of growth. Further details on the otolith sampling, processing, and measurement can be found in [ 25 , 26 ].…”

Otolith “spawning zones” across multiple Atlantic cod populations: Do they accurately record maturity and spawning?

“…ICE cod otoliths were selected and processed as described in Smoliński et al . [ 28 ]. NCC otoliths from Porsangerfjord were selected from a collection of sections partly described in Andrade et al .…”

“…A large collection of NEA cod otoliths was retrieved, processed and imaged at the Institute of Marine Research (Norway), the full methodology is available in Denechaud et al [27]. ICE cod otoliths were selected and processed as described in Smoliński et al [28]. NCC otoliths from Porsangerfjord were selected from a collection of sections partly described in Andrade et al [29] and were imaged similarly to the NEA cod otoliths.…”