Seasonality in the deep sea and tropics revisited: what can otoliths tell us?

Abstract

The accepted idea that fish otoliths from supposedly aseasonal environments, such as the deep sea and tropics, do not present seasonal growth increments is questioned and re-evaluated. The main seasonal fluctuation in deep seas is a result of the transfer of organic material from the productive upper layers to the abyssal depths. There is some evidence for seasonal patterns of otolith growth, although the validation of seasonal structures is limited owing to the difficulties inherent in deep-water studies. Tropical regions have an extremely high diversity of aquatic environments but in fact very few are aseasonal, and almost all areas have strong hydrological seasons, mainly annual, interacting with temperature variations. These climatic fluctuations have undoubtedly an effect on otolith growth, therefore leading to a succession of different incremental zones. The lack of previous knowledge on this impact of seasonality is probably a result of the previous low level of exploitation or economic interest of target species, and consequently the absence of age-based assessments. This trend has now changed possibly as a result of the increased exploitation of the resources, and to the greater involvement of international and national fishery management bodies. The number of studies showing apparent or validated seasonal marks has recently increased for these environments.Extra keywords: aseasonality, deep-sea environment, seasonal increment, state of the art, tropical environment, validation.

The use of otolith shape analysis for ageing juvenile red snapper, Lutjanus campechanus

“…However, the current ageing technique of counting annual growth increments on sectioned otoliths is often difficult and subjective in young red snapper. In particular, identification of the first annulus (typically diffuse and non-distinct) is subject to reader interpretation and is a source of considerable error in ageing of young fish (Holt and Arnold 1982;Wilson and Nieland 2001;Rooker et al 2004;Allman et al 2005;Morales-Nin and Panfili 2005). Difficulty in identifying annual growth increments in sectioned otoliths leads to reduced accuracy and precision by otolith readers.…”

Otoliths as individual indicators: a reappraisal of the link between fish physiology and otolith characteristics

“…Annual increments are found in species living at depths where light and temperature are unlikely to function as zeitgebers for an endogenous circadian rhythm (Stewart et al 1995;Allain and Lorance 2000;Morales-Nin and Panfili 2005) and daily increment formation has been observed in laboratory experiments without cyclical variation in feeding, light and temperature . Neat et al (2008) summarised the processes proposed to be responsible for the formation of otolith zones as follows: (1) physiological changes related to growth and reproduction; (2) environmental change that acts independently of somatic and reproductive processes; and (3) an endogenous biological rhythm.…”

Difficulties associated with modeling growth in the Atlantic angel shark (Squatina dumeril)

“…otolith) that can be used for ageing analysis is rare among fishes, but is more common among deep water, and especially slow-growing species (Treble et al, 2008). However, more species are being aged in what are commonly thought to be 'aseasonal' environments, such as the deep sea and tropical areas, as sampling and ageing techniques become more sophisticated (Morales-Nin and Panfili, 2005). Laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) is a relatively new method for assessing the spatial distribution of elements in cartilage of elasmobranchs, and has been demonstrated to effectively elucidate band counts for round stingrays with fewer than five band counts (Hale et al, 2006).…”