Deep-sea crabs tracked with Argos!
Deep-sea species are scarcely known. However, a team at the University of Windsor in Canada has devised a means of tracking porcupine crabs living at 900 m depth. Pop-up archival tags programmed to release at regular intervals emitted data, collected by Argos, resulting in a better view on this species’ movements.
Photo: a porcupine crab with its harness (Credit University of Windsor)
Deep-sea crab tracked
The porcupine crab (Neolithodes grimaldii) is a deep-sea king crab. This family of crabs are expected to expand and establish in new areas due to climate change. However, like most deep-sea animals, porcupine crab space-use is difficult and expensive to study, and therefore, knowledge about their population in the Eastern Canadian Arctic is scarce. Bycatch by fisheries show a seasonality of crab presence on some sites, and research on other related crab species shows a similar behavior pattern; further motivating this study. In particular, it is predicted that porcupine crabs would move as a group, in a linear pattern, staying at similar depths and temperatures.
Pop-up archival tags (mrPATs and miniPATs) were fitted on 18 porcupine crabs captured in Davis Strait at ~900 m depth. The equipped crabs ranged in size from 54 to 110 cm (total length) and 0.4–2.1 kg (total weight). Expecting that the crabs will move together, the idea was to program the tags to be released at regular interval (every 6 days) during the period July-October, thus tracking the whole group since the position of one crab would be representative of the group’s position.
The results show that porcupine crabs are capable of moving long distances, but do not always do so, since six of them moved from 3.1 to 33 km away from the place they were dropped on, but the rest moved less than 1 km.
Several explanations are possible and will require further studies.
A new technique to investigate deep-sea species movements
All temperature and depth values confirmed that the porcupine crabs remained within very close depth and thermal range during the whole period. The miniPATs recorded an average temperature of 3.7°C (standard deviation 0.1) and an average depth of 994.5 m (standard deviation 3.4) over the 6 months of the study.
It must be noted that estimating the location of the crabs both when they reach the seafloor at the release and when the tag released is not an easy task. They drifted (vertically and horizontally) from the surface point of release and, most importantly from the seafloor (“release initiated”) to the first Argos location respectively. Therefore, a drift error buffer was applied to the first reported location and the best location post release.
“This study is the first to administer pop-up archival tags on porcupine crabs, revealing a new technique to investigate their spatiotemporal movements” say the authors. The results should help in assisting in the development of appropriate fishery access regulations, since the species is now envisioned as potentially fishable.
- E.R. Davidson, N.E. Hussey, 2019: Movements of a potential fishery resource, porcupine crab (Neolithodes grimaldii) in Northern Davis Strait, Eastern Canadian Arctic, Deep-Sea Research Part I (In Press), https://doi.org/10.1016/j.dsr.2019.103143