Otolith increment width-based chronologies disclose temperature and density-dependent effects on demersal fish growth

Climate change and fishing are drastically impacting marine ecosystems. Comprehending the biological consequences of these effects on commercially exploited fish is especially challenging. Here, we developed a 43-year otolith increment width-based growth chronology for one of the most important commercially exploited fish species in the Northeast Atlantic (European hake, Merluccius merluccius). Increasingly complex linear mixed-effects models were used to partition growth variation into intrinsic (age, sex, and age-at-capture) and extrinsic (environmental and biotic variables) factors, allowing age interaction with extrinsic variables to assess age-dependent responses in growth. Our results provided strong evidence that European hake growth is impacted by ocean temperature, namely sea surface temperature and temperature at depth, and species abundance (recruitment), with different responses depending on fish age. We found evidence that increasing ocean temperature could be highly detrimental for species growth especially during the first years of life. We provided insights into the effects of environmental and biotic factors on species growth variation. Such information is key to recognize the sensitivity of European hake growth to climate change, which may contribute to sustainable management policies for this valuable resource.

Planktonic duration in fourteen species of intertidal rocky fishes from the south-eastern Pacific Ocean

The planktonic duration (PD) was determined in fourteen intertidal rocky fishes from the south-eastern Pacific Ocean by counting the otolith micro-increments from hatch check to a transition mark (TM). TMs were validated by comparing the PDs estimated from post-settlers with the total increment counts from otoliths of more recent (new) settlers. In 11 species (79%), the most common TM corresponded to a notable decrease in increment width after settlement. The PDs ranged from 45 days in the kyphosid Girella laevifrons to 135 days in the labrisomid Auchenionchus variolosus, and eight species (57%) had mean PDs of longer than three months. The mean observed size-at-settlement (SASM) values ranged from 17.5 ± 7.2 mm TL in Gobiesox marmoratus (Gobiesocidae) to 40 ± 5.5 mm TL in Calliclinus geniguttatus (Labrisomidae) and showed low variability within species of the same family. PDs were markedly longer in intertidal rocky fishes than in other littoral and reef fishes in tropical and temperate waters. A lengthy and variable duration of the pre-settlement phase, along with a relatively consistent size-at-competence within closely related species, are suggested as mechanisms through which these fishes may increase their probability to settle in the spatially restricted habitat of exposed rocky pools.

Daily growth patterns of six species of young-of-the-year of Chilean intertidal fishes

Otolith microstructure analysis was used to reveal daily growth patterns of young-of-the year (YOY) of six species of perciform fishes, Bovichtus chilensis (Bovichtidae), Girella laevifrons and Graus nigra (Kyphosidae), Helcogrammoides chilensis (Tripterygiidae) and Hypsoblennius sordidus and Scartichthys viridis (Blenniidae). YOY collected in intertidal pools from June to December 2008 in Central Chile, ranged from 24 to 76 mm total length and from 25 to 390 days of age. In the six species, sagittal otoliths showed a slightly oval shape, symmetrical and laterally compressed and showed micro-increments distinguishable after a two-side polishing. Increment width of sagittae showed two patterns irrespective of hatch month and species: (i) a parabolic growth with wider increment widths (during the first 150 of YOY life, e.g. B. chilensis, G. nigra and G. laevifrons); and (ii) a more irregular pattern with lower increment widths during most of the seasons in H. chilensis and H. sordidus. Further results were: (i) a unique central primordium enclosed by two checks after which distinctive increments were deposited; (ii) low instantaneous growth rates estimated through the slope of the length-at-age relationship (range 0.1–0.21 mm d−1); and (iii) a linear fish size–otolith size relationship.

Otolith shape analysis: its application for discriminating between stocks of Irish Sea and Celtic Sea herring (Clupea harengus) in the Irish Sea

Burke, N., Brophy, D., and King, P. A. 2008. Otolith shape analysis: its application for discriminating between stocks of Irish Sea and Celtic Sea herring (Clupea harengus) in the Irish Sea. – ICES Journal of Marine Science, 65: 1670–1675. The extensive movement of Celtic Sea juvenile Atlantic herring (Clupea harengus) during the first year of life into the Irish Sea results in two stocks of herring living together on Irish Sea nursery grounds: the resident autumn-spawned juveniles that originate in the Irish Sea, and the winter-spawned juveniles that hatch in the Celtic Sea and drift into the Irish Sea as larvae. Measurements of otolith increment width can be used to distinguish between the fast-growing winter-spawned and the slow-growing autumn-spawned stocks, but this method can be time-consuming. Otolith shape analysis is investigated as an alternative method for discriminating between seasonal spawning stocks. Juvenile herring collected from nursery grounds in the Irish Sea in 2006 were classified as autumn- or winter-spawned using increment width measurements. Otolith shape was defined using shape indices and Fourier descriptors. Juveniles were classified successfully to hatch type with a high degree of accuracy (86–87%) using shape variables. The potential use of otolith shape analysis for identifying Celtic Sea juvenile herring in the Irish Sea and its possible use for other mixed-herring stock assessments are discussed.

Interpretation of statolith microstructure in reared hatchling paralarvae of the squid Illex argentinus

To identify sub-daily or aperiodic increments of statolith growth in the ommastrephid squid Illex argentinus, we examined statolith microstructure, especially with regard to the natal ring, where counting of daily growth increments should begin, and the widths of subsequent daily increments. Paralarvae obtained by artificial fertilisation were incubated on board at different temperatures ranging from 11.4 to 25.4°C, and were starved throughout the experiments. We observed statolith growth from newly hatched to 10-day-old paralarvae and used alizarine complexone staining to attempt validation of the growth. The maximum statolith radius (MSR) of newly hatched paralarvae was constant at 21.1 μm across the full range of temperatures, with the exception of 25.4°C. Daily growth of MSR was analysed separately in two phases, the pre-yolk-absorption phase (i.e. yolk sac still present) and the post-yolk-absorption phase. During the pre-yolk-absorption phase, the daily growth rate (DGR, y) of the MSR varied from 3 to 7 μm day–1 depending on rearing temperature (x) and was expressed as y = 0.37x – 1.77. We concluded that the natal ring forms at 21 μm MSR. The initial increment width obtained from the DGR of MSR seems applicable for distinguishing daily rings from sub-daily rings, although this application should be limited to hatchling paralarvae in the pre-yolk-absorption phase.

The role of measurement error on the interpretation of otolith increment width in the study of growth in larval fish

Patterns in increment widths and the associated measurement error were studied in the otoliths of radiated shanny (Ulvaria subbifurcata) larvae sampled from the field. Mean increment widths increased with larval age, whereas the relative measurement error decreased. Furthermore, the level of serial correlation in increment widths showed a clear increase with age. When measurement error was taken into consideration, the pattern of serial correlation indicates that an individual's growth increments did not show the effect of changes in local environmental conditions for at least 3 days, independent of age. Only after that period can we hope to detect the effect of environmental influences on increment widths (and by inference growth rates). The patterns of measurement error and serial correlation will have direct impacts on our ability to find the influence of environmental conditions on growth rates of individual larvae and determine patterns of selective loss in a population of larval fish.