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.

Early development of eel-tailed catfish, Tandanus tandanus (Mitchell) (Teleostei : Plotosidae), with validation of daily otolith increment formation

Eel-tailed catfish, Tandanus tandanus, have recently experienced widespread population declines in eastern Australia; with some southern populations facing the risk of extinction, the management and conservation of Queensland populations should be considered a priority. There is a lack of sound, scientific knowledge surrounding the species’ reproductive patterns and early life-history requirements. To assist in clarifying the influence of changes to the natural environment on the reproductive ecology of T. tandanus, we investigated their early life history using naturally fertilised eggs and larvae from a wild population. Nest depth ranged from 0.20 m to 1.35 m, with in situ temperatures between 15.1°C and 29.9°C, and in situ velocities from 0.00 to 0.52 ms–1. Eggs ranged in diameter from 2.6 to 4.0 mm throughout development, and preservation of eggs in ethanol caused significant shrinkage (mean 18.9%). Hatching took 4–7 days (mean 5.29 days; 15.7–28.0°C). Larvae collected from nests ranged in length from 5.1 mm to 15.3 mm SL, and in age from one day old to 16 days old. Larvae are likely to actively disperse from their nest at ~16 days old, as they approach juvenile metamorphosis. Daily otolith increment formation was validated up to 28 days after hatching; and sagittal otoliths were used to develop an age–length relationship for larvae. These results can assist researchers in estimating the timing of critical recruitment events, and investigating how the species’ early life history is influenced by environmental conditions.

Impact of hatch date on early life growth and survival of Mueller’s pearlside (Maurolicus muelleri) larvae and life-history consequences

Growth and survival of Maurolicus muelleri larvae in Herdlefjorden, Norway, were investigated by daily otolith increment analysis. While high egg densities were generally observed throughout the spawning season, three cohorts each with a narrow window of hatching dates were identified. The first of these cohorts was characterized by low growth and poor morphometric condition and disappeared from the fjord during autumn. High-resolution drift modeling indicated that Herdlefjorden had a net export of larvae and negligible import in the period cohort 1 disappeared. Yet, the advective loss rate of larvae was not considered high enough to explain the near complete disappearance of the first cohort. An otolith-based growth chronology indicated that growth conditions in Herdlefjorden improved noticeably around mid-September and remained favorable the following month. The analysis of daily otolith increments could thus be used to document within-season variability in larval growth and survival. The low and variable survival due to short-term fluctuations in environmental conditions indicate that multiple batch spawning is an adequately evolved life-history strategy for marine planktivorous fish such as M. muelleri.