Young-of-the-year spot (Leiostomus xanthurus) intra-annual demographics and growth during estuarine residency

Young-of-the-year spot ( Leiostomus xanthurus ) intra-annual cohort growth rates are influenced by the timing of their arrival to and environmental conditions within estuaries. Fish growth rates while in estuaries positively affect juvenile emigration to deeper estuarine and offshore habitats as well as the resulting potential year class strength as age 1 subadults. Spot from North Inlet estuary, South Carolina, USA, were collected from an intertidal creek pool biweekly during 2020 to evaluate potential effects of the seasonal arrival timing and water temperature, chlorophyll, and salinity during residency on standard length (mm), biomass (g dry tissue), and related growth rates including the transition from isometric to allometric growth. Representatives from three young-of-the-year spot cohorts ( n = 974 fish) entered the estuary during early December 2019 (11–16 °C), early February 2020 (10–14.9 °C), and mid to late April 2020 (20–24.9 °C). Water temperature experienced during intertidal creek use as indicated by degree days positively influenced fish growth in length and biomass for all three 2020 cohorts more strongly than either chlorophyll or salinity. The April cohort increased in length while using the intertidal creek pool at a much faster rate (0.29 mm/d) than the December and February cohorts (0.22 and 0.25 mm/d, respectively). However, the April cohort increased in biomass in the intertidal creek pool more slowly than the other cohorts and generally had lower weights than fishes in the earlier cohorts at the same standard lengths. All cohorts transitioned from isometric to allometric growth between 59 and 61 mm ± 2 mm standard length at 0.44–1.35 g dry tissue weight. The February cohort that arrived in the intertidal creeks just before the spring bloom and moved to deeper habitats in early fall had the largest biomass at the end of intertidal creek residency which might enhance future survival and reproduction success.