DOI: 10.7291/d1109b
title: Black rockfish otolith and early life history data

description: Understanding how future ocean conditions will affect populations of
 marine species is integral to predicting how climate change will impact
 both ecosystem function and fisheries management. Fish population dynamics
 are driven by variable survival of the early life stages, which are highly
 sensitive to environmental conditions. As global warming generates extreme
 ocean conditions (i.e., marine heatwaves) we can gain insight into how
 larval fish growth and mortality will change in warmer conditions. The
 California Current Large Marine Ecosystem experienced anomalous ocean
 warming from 2014-2016, creating novel conditions. We examined the otolith
 microstructure of juveniles of the economically and ecologically important
 species black rockfish (Sebastes melanops) collected from 2013-2019 to
 quantify the implications of changing ocean conditions on early growth and
 survival. Our results demonstrated that fish growth and development were
 positively related to temperature, but survival to settlement was not
 directly related to ocean conditions. Instead, settlement had a
 dome-shaped relationship with growth, suggesting an optimal growth window.
 Our results demonstrated that the dramatic change in water temperature
 caused by such extreme warm water anomalies increased black rockfish
 growth in the larval stage; however, without sufficient prey or with high
 predator abundance these extreme conditions contributed to reduced
 survival.
description: <em>Fish collection</em> Juvenile black rockfish were
 collected in standard monitoring units for the recruitment of fishes
 (SMURFs; Ammann 2004). These SMURFs were located in nearshore waters 16 km
 north of Newport, OR between Cape Foulweather and Otter Rock (see Ottmann
 <em>et al.</em>, 2018). Eight SMURF moorings were deployed in
 ~15 m of water and SMURFs were attached 1 m below the surface. SMURF
 moorings were anchored in sandy habitat &gt;390 m from shore and well
 offshore of rocky reefs and kelp canopy habitats to ensure fish collected
 in the SMURFs were those transitioning from their pelagic to nearshore
 life stage. Each mooring was a minimum of 300 m apart and sampled every
 ~14 days. Fish were collected by two snorkelers using a benthic
 ichthyofauna net for coral and kelp ecosystems (BINCKE, Anderson &
 Carr 1998) to engulf a SMURF, remove it from the mooring, and bring the
 sample to a boat where fishes were rinsed out of the SMURFs. Fish were
 euthanized with a lethal dose (2 mM) of tricaine methanesulfonate (MS-222)
 buffered with sodium bicarbonate (6 mM), placed on ice, and transported to
 the lab for measurement and dissection. For the purposes of determining
 age-at-settlement, we assumed fish that appeared in SMURFS arrived the day
 they were collected. <em>Sample
 Processing</em> Juvenile black rockfish were
 distinguished from similar looking yellowtail rockfish using pectoral fin
 ray counts, pectoral fin pigmentation, and dorsal coloration patterns
 (Laidig & Adams, 1991). We used digital calipers to measure each
 fish to the nearest 0.1 mm standard length (SL) before otoliths were
 dissected and removed for microstructure analysis. To
 examine interannual variability of early life history traits we dissected
 and processed the otoliths of up to n = 34 juveniles per year (Table I).
 Recruitment was very low in 2015 such that only 1 black rockfish recruited
 to the SMURFs deployed near Newport, OR. We used all (n=5) black rockfish
 that recruited to SMURFs in southern Oregon (233 km away; see Ottmann
 <em>et al.</em>, 2018) to increase our sample size for this
 year. Daily growth increments have been validated for juvenile black
 rockfish (Yoklavich & Boehlert, 1987), so otolith increment counts
 can be used to estimate age, and widths between successive otolith
 increments can be used as a proxy for somatic growth (Miller &
 Shanks, 2004; Wheeler <em>et al.</em>, 2016). We embedded
 sagittal otoliths in Crystalbond thermoplastic resin (Electron Microscopy
 Science) and used lapping paper to polish otoliths along the sagittal
 plane. Otoliths were read at 400x using a compound microscope equipped
 with polarized transmitted light, and increments were interpreted using
 image analysis software (ImagePro v.9.0). Following standard procedures
 (Miller & Shanks, 2004; Sponaugle, 2009), we obtained otolith
 increment counts and measurements of daily increment widths to estimate
 the age and daily growth of each individual. Additionally, we used the
 presence of secondary growth primordia to determine the initiation of
 metamorphosis from the larval to pelagic juvenile stage (Laidig
 <em>et al.</em>, 1991). Because juvenile black rockfish were
 frequently older than 100 days, it was difficult to completely encompass
 the core and the edge of the otolith in the same plane. We captured two
 otolith images: the first included the edge of the otolith with a little
 material remaining above the plane of core, after which the otolith was
 polished to the plane of the core, producing the second image.
 Occasionally, this final polishing resulted in the loss of some edge
 material, but the use of both images during microstructure reading
 minimized the loss of information. We created transects from the core to
 the edge of each of these images aligning these transects by otolith
 landmarks. This allowed us to combine the two transects and create
 complete core-to-edge increment counts. Each otolith was read blind two
 independent times by the same person (HWF) and if the ages differed by
 &gt;5%, it was read a third time. If no two reads were within 5% of
 one another, the otolith was excluded from further analysis. For reads
 within 5% of each other, one read was randomly selected for further
 analysis. There was a significant positive relationship between the
 residuals of the radius-at-age and size-at-age of surviving rockfish
 (<em>F</em><sub>1,173</sub> = 128.7, p
 &lt;0.0001, R<sup>2</sup> = 0.42), confirming that otolith
 radius and otolith increment width could be used as proxies for size and
 growth, respectively (see Thorrold & Hare, 2002).
description: There are missing values in these two data sets. These are
 indicated by "0".