The potential of beaks as a valuable tool for age estimation and growth studies in Southern Ocean squids

Squid species in the Southern Ocean play a crucial role in the ecosystem by acting as a link between lower trophic levels and top predators. Despite their importance, there have been limited studies on the abundance, age, and growth of Southern Ocean squid. Traditional methods of studying age and growth in cephalopods require capturing live individuals, which is challenging for highly mobile oceanic squid. However, cephalopod beaks, which grow throughout an individual’s life, can be easily sampled from predators’ stomachs and used to study age and growth patterns.

The authors focus on the giant warty squid Moroteuthopsis longimana, which is a major prey for Southern Ocean predators and has been previously studied for its age and growth using different techniques. The study aims to evaluate the feasibility of using beaks collected from predators’ stomachs, such as the Antarctic toothfish (Dissostichus mawsoni) to determine the age and growth of M. longimana and estimate the age and growth patterns of this species in different areas of the Southern Ocean.

The study found that beaks collected from predators’ stomachs can be used to study the age of Southern Ocean squids, specifically M. longimana. The rostrum sagittal section (RSS) of the lower beak was found to be the most reliable section for age estimation (Fig.1), as it had readable micro-increments that could be counted while the upper beaks presented highly compacted increments with many of them being indistinguishable. Also, it was estimated that M. longimana can live up to 820 days and may hatch throughout the year. This species showed a consistent growth rate from hatching to death with at least one period of faster growth. A novel pattern of regular cycles, composed of 7-10 lighter increments followed by a darker one, was found in the medium-anterior region of the RSS (Fig.2b). Differences in growth rate and size reached at the same age were observed between individuals from the Pacific and Atlantic sectors of the Southern Ocean, suggesting the influence of different environmental conditions.

Fig. 1: Moroteuthopsis longimana beaks and analyzed sections. Dashed lines are the expected format of the increments in the reading zones of the lateral wall surface (LWS) and rostrum sagittal section (RSS).
Fig. 2: Growth increments in the beaks of Moroteuthopsis longimana. (a) composition image of the increments on the rostrum sagittal section (RSS) of lower beaks; (b) lower beaks RSS with cycles of 7–10 light increments followed by a dark increment; (c) lateral wall showing a zone with regular increments; (d) lateral wall with only one increment.

Therefore, beaks collected from predators’ stomachs can be used to study the age and growth of Southern Ocean squid, specifically Moroteuthopsis longimana. However, the authors highlighted the need for future research to validate the periodicity of increment formation in cold-water and deep-sea squid and to consider the impact of environmental conditions on the growth of M. longimana.

Reference: Queirós, J. P., Bartolomé, A., Piatkowski, U., Xavier, J. C., & Perales-Raya, C. (2022). Age and growth estimation of Southern Ocean squid Moroteuthopsis longimana: can we use beaks collected from predators’ stomachs? Marine Biology, 170(1).

Author: Diogo Francisco