Romaleon setosum

Romaleon setosum is a crab of the family Cancridae that lives in the Humboldt Current and is known in Peru as cangrejo peludo ^[1],[2]. Its range runs from Guayaquil, in Ecuador, to the Taitao Peninsula, in Chile, and it is a commercial resource of the artisanal fisheries of both countries ^[3],[4].

Its distribution is described as running from Guayaquil, in Ecuador, to the Taitao Peninsula, in Chile, which amounts to about 5000 km of coastline ^[3]. A Peruvian study places it from 2°S in Peru to 46°S in Chile and describes the species as adapted to the cold, nutrient-rich waters of the Humboldt Current ^[4].

In Chile, an analysis of 256 individuals from 10 areas along 2700 km of coast, using 2383 genetic markers, found no genetic structure: all of them belong to a single population ^[3]. The egg-bearing females used to compare its reproduction were collected in shallow water across 21 degrees of latitude ^[5].

The planktonic larva lasts 55 to 60 days and reaches its last stage, zoea V, at temperatures of 13.5 to 14.6 °C; the reproductive cycle changes with latitude, from several cycles a year in the north to a single one in the south, and eggs are larger towards the south ^[3].

Among five brachyuran crabs studied in Chile, Romaleon setosum (reported as Cancer setosus) had the highest mean number of embryos per brood, 1381867, and the lowest mean dry weight per embryo, 0.009 mg; embryo loss during development was 3.6 % in its case, and females from the far north of Chile laid lighter egg masses than those from the centre and south ^[5].

In Peru, the carapace width of females at the end of the first year was estimated at 58 mm in Lima, 51 mm in Ica and 76 mm in Moquegua, and at 113-145 mm by the third year; the estimated asymptotic maximum size was 173 to 179 mm depending on the region, and the analysis took as the maximum size observed in the fishery the 172 mm of a female from Callao ^[4]. Males reach larger sizes than females ^[4].

It feeds on other crustaceans, bivalves and gastropods, and is regarded as one of the most important predators of subtidal environments in northern and central Chile ^[3].

In turn it is prey for coastal fishes such as Paralabrax humeralis and Pinguipes chilensis and for the cephalopod Robsonella fontaniana ^[3]. Its growth and longevity in Peru do not rise steadily with latitude, which the authors attribute probably to local upwelling regimes and to interannual thermal variability linked to El Niño ^[4].

The authors note that this crab lacks stock assessments in Peru and that estimates of parameters such as growth are needed to design precautionary fishing strategies ^[4].

In Chile the law sets a minimum catch size of 12 cm and bans the capture of egg-bearing females; the genetic study shows that the most heavily fished area supplies the highest proportion of migrants to the others, and the authors stress the urgency of managing source populations locally and of controlling the fishery by size and sex ^[3].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

In 15 hairy crabs bought between December 2020 and January 2021 at the Ventanilla wholesale fish market, in Callao, all had microplastics in the muscle, the gills and the digestive tract, with more particles in the digestive tract than in the gills and the muscle ^[2].

The hairy crab is the most important crustacean in Peruvian waters after shrimp ^[4]. The largest landings are recorded in the regions of Lima, Ica and Moquegua ^[4].

Because males are larger, the trade prefers them, and so large males are scarce in the fishery ^[4]. In Chile artisanal fishers take it with traps or by scuba diving, and the landing for human consumption is 218 tonnes a year, from 1 tonne at 18°S to 109 tonnes at 35°S ^[3].

The literature on Peru does not describe places to observe it; it says only that the artisanal fishing zones with the largest landings are in the regions of Lima, Ica and Moquegua, with sampling data from 2010-2011 in Lima, 2014-2015 in Ica and 2018-2019 in Moquegua ^[4].