Young-of-year (YoY) Atlantic silversides were collected from Mumford Cove (41.32N, 72.02W), a small, salt-marsh dominated embayment in eastern Long Island Sound (Connecticut USA, 0.5 km\u00b2, 1-3 m depth). From a biweekly beach seine survey (30\u00d72m seine with 3mm mesh), three samples on 23 October, 20 November, and 18 December 2015 were used. On each date, samples were pooled from two independent seine casts. All silversides were euthanized, enumerated, measured for total length (TL) to the lower 5 mm and preserved frozen (-20\u00b0C). From each collection, ~100 individuals were selected for otolith microstructure analysis using a TL-stratified random sampling design. For each individual, we again measured TL (nearest 0.1 mm) and determined its sex via visual inspection of gonads, before extracting both sagittal otoliths. Sagittae were mounted on microscope slides using CrystalBond 509 thermoplastic cement. If equally suitable, the left or right sagitta was randomly chosen for analysis. Otoliths were hand-polished using 9 \u00b5m then 3 \u00b5m lapping films (3M) until daily increments along the entire reading axis were clearly visible under 400x magnification (Nikon Eclipse E400 compound microscope). Otoliths were measured and read across the sagittal plane from the nucleus to the dorsal or ventral otolith edge, because the more conventional core to post-rostrum axis proved to be too curved to be reliably interpretable. Increments were enumerated and measured using Image Pro Premier (V9.1) connected to a Luminera Infinity2-2 digital camera. For each otolith section, multiple focal planes were captured and merged into multi-layer images to aid the reader interpreting the otolith microstructure. The radius of the hatch-check (\u00b5m) was measured. The last growth increment was presumed to be incomplete and thus excluded from growth analyses. Increment number was assumed to correspond to an individuals\u2019 age in days post hatch (dph). Hatch date was calculated by subtracting age from the date of collection, while the formation date of each increment was calculated by adding the increment number to the hatch date.
\nTo estimate the thermal history of October YoY we used continuous temperature data recorded by a Manta Sub2 probe (Eureka\u00a9 Water Probes) at our study site. Three small gaps in the record (<8 days) were linearly interpolated. Daily temperatures during a larger data gap (34 days, 18 June - 22 July) were estimated via linear regression between the Mumford Cove dataset and temperatures in nearby Niantic Bay (2015-2016) that were strongly correlated (TMumford= 1.07*TNiantic \u2013 0.54 r\u00b2= 0.92, F = 6024.9, p < 0.001). Average daily temperatures were then linked to the corresponding day of increment formation for each individual. To quantify the thermal dependency of larval growth in October YoY, we calculated the mean experienced temperature during the first 30 dph for each individual and correlated it to its mean daily growth rate over the first 30dph (GR30) and its back-calculated TL at day 30 post hatch (TL30, a proxy for the end of the larval stage).
Back-calculated age, hatch date, length-at-age, growth rate, and experienced temperature of young-of-year Atlantic silversides (Menidia menidia) collected during 3 successive collections in Mumford Cove, CT in fall 2015.
Data Processing:
\nThe proportion of females (Nfem/Nfem+male) per 10 mm TL class in the otolith sample was used to derive sex-specific TL distributions of the population sample (beach seine), assuming sexes being randomly sampled within each TL class. Similarly, otolith-derived hatch distributions were scaled to population by applying a scale factor (SF) to each individual based on the relative frequencies (RF) of each 10 mm TL class in the population vs. otolith sample for each collection (SF = RFpopulation/RFotolith).
Only for YoY survivors from October, individuals were grouped into each of four bi-weekly hatch intervals that were chosen based on sample size and the known semi-lunar spawning periodicity of silversides. TL-at-age was back-calculated for each individual over the entire increment record (99-148dph) with the biological intercept method and an assumed length at hatch of 5 mm.
\nProblem Report:
\nAs detailed in the corresponding publication, a central objective was to determine whether ages in older young-of-year Atlantic silversides could be reliably determined. Because this was found to be the case only for individuals sampled during October, but not during subsequent collections in November and December, back-calculated ages, hatch dates, length-at-age, or growth rates are only given for individuals collected in October.
BCO-DMO Processing:
\n- formatted all dates to yyyy-mm-dd;
\n- modified parameter names (replaced spaces w/ underscores; removed parens & units);
\n- filled in blanks with \"nd\" (\"no data\").