Population structure and morphology of South African deep‐water parapagurid hermit crabs

An experiment to investigate the potential of a trap-fishery for deep-water rock lobster Palinurus delagoae was conducted off the east coast of South Africa between 1994 and 1996. The 75–425 m depth interval between 27°S and 32°S was stratified according to depth and latitude, and three regions (North, Central and South) were sampled systematically over the three years. Sampling by commercial vessels operating long-lines and traps included an experimental phase (fixed fishing positions) and a commercial phase (no restriction on fishing location). Generalized linear models were used to investigate the influence of year, region, sampling phase, month and soak time. Sampling phase was significant, with traps set during the commercial phase catching more than those set in the experimental phase. The effect of soak time on catch rates was not significant. The almost-50% decrease in the combined abundance index combined with a marked decrease in mean lobster size over the study period suggests a relatively low fisheries potential for this species in South African waters; this may be attributable to the relative scarcity of suitable habitat in the area.

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Connectivity and population structure of albacore tuna across southeast Atlantic and southwest Indian Oceans inferred from multidisciplinary methodology

Scientific Reports ◽

10.1038/s41598-020-72369-w ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Natacha Nikolic ◽

Iratxe Montes ◽

Maxime Lalire ◽

Alexis Puech ◽

Nathalie Bodin ◽

...

Keyword(s):

Population Structure ◽

South African ◽

Species Dispersal ◽

Commercial Catch ◽

Albacore Tuna ◽

Particle Drift ◽

Dispersal Potential ◽

Thunnus Alalunga ◽

Tuna Fisheries ◽

Drift Models

Abstract Albacore tuna (Thunnus alalunga) is an important target of tuna fisheries in the Atlantic and Indian Oceans. The commercial catch of albacore is the highest globally among all temperate tuna species, contributing around 6% in weight to global tuna catches over the last decade. The accurate assessment and management of this heavily exploited resource requires a robust understanding of the species’ biology and of the pattern of connectivity among oceanic regions, yet Indian Ocean albacore population dynamics remain poorly understood and its level of connectivity with the Atlantic Ocean population is uncertain. We analysed morphometrics and genetics of albacore (n = 1,874) in the southwest Indian (SWIO) and southeast Atlantic (SEAO) Oceans to investigate the connectivity and population structure. Furthermore, we examined the species’ dispersal potential by modelling particle drift through major oceanographic features. Males appear larger than females, except in South African waters, yet the length–weight relationship only showed significant male–female difference in one region (east of Madagascar and Reunion waters). The present study produced a genetic differentiation between the southeast Atlantic and southwest Indian Oceans, supporting their demographic independence. The particle drift models suggested dispersal potential of early life stages from SWIO to SEAO and adult or sub-adult migration from SEAO to SWIO.

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