The effects of appendage loss on growth of South African west coast rock lobster Jasus lalandii

Abstract

Capture by traps, sorting by fishers and discard of lobsters smaller than a minimum legal size (MLS) may induce physical injuries, such as loss of appendages, which can reduce somatic growth rates and population productivity. Heavily fished populations of rock lobster Jasus lalandii off western South Africa are prone to physical injuries, we investigated the extent of and effects on growth of various degrees of appendage loss. Lobsters injured by removal of legs, feeding legs or antennae were kept in cages at sea until moulting, and their subsequent growth and recovery of appendages monitored. Incidence of injury in wild populations was recorded by observers on lobster fishing vessels at sea. Growth decreased significantly following the loss and re-growth of ≥3 appendages, mortality rate increased, and injured lobsters moulted earlier than uninjured individuals. Five to 9% of trap-caught lobsters had missing appendages, although most of these (80%) had only one or two missing appendages. Most multiple injuries were found in lobsters larger than the MLS. The proportions of injured male and female lobsters in commercial catches declined sharply during the moulting season, but increased gradually thereafter coincident with rising cumulative fishing effort. The low relative estimate of appendage loss suggests that regulations to reduce injuries are effective.