How is our garrick/leervis stock doing? Results of a recent stock assessment conducted by ORI.

By Bruce Mann and Daniel Smith

The limited distribution range of garrick or leervis (Lichia amia), its popularity as a gamefish to all sectors of the recreational fishery and the degradation of many estuaries which function as important nursery areas for this species, has aroused concern by anglers, fishery managers and scientists about the stock status of this species. Other than a preliminary investigation conducted by ORI in 1992 into the age, growth and stock status of L. amia (van der Elst et al., 1993), surprisingly little research has been undertaken on this important angling species. Considering the value of garrick and the need to provide a scientific basis for its future management, a comprehensive stock assessment was recently undertaken by Daniel Smith, a MSc student from the University of KwaZulu-Natal under the supervision of Bruce Mann and Rudy van der Elst from ORI. The focus of this study was to investigate the age, growth, movement and stock status of garrick in South African waters.

Some of the key findings of this research project were as follows:

• Based on ageing of otoliths and analysis of growth rate determined from tag-recapture data, garrick was found to be a relatively fast growing species reaching a maximum age of 10+ years.
• Based on tag-recapture data, movement behaviour of garrick consists of a resident, estuarine dependent juvenile phase and a highly migratory adult phase with adults migrating to KZN to spawn during the winter months and returning to cooler Cape waters in early summer.
• Trends in catch rates of garrick were determined from the analysis of data stored on the National Marine Linefish System (NMLS) and the Boat Launch Site Monitoring System databases. This analysis showed a decreasing trend in catch per unit effort (CPUE) of garrick along the KZN coast over time for all sectors of the KZN marine recreational linefishery (i.e. shore fishing, recreational skiboat fishing and spearfishing).
• Growth parameter estimates and catch data were used in undertaking a per-recruit assessment of the garrick stock in South African waters. The spawner-biomass-per-recruit (SBPR) model indicated that the garrick stock is currently at approximately 14% of its unfished level!

These results came as a shock to scientists who had previously determined that the garrick stock was in relatively good shape due to is fast growth rate. In terms of the Linefish Management Protocol, this means that the garrick stock has collapsed (i.e. there may now be too few adult fish left to ensure successful spawning and recruitment of juveniles to sustain the population). Appropriate management action is therefore urgently needed to help rebuild the stock. There are a number of management options available which could be used to achieve this. These include one or more of the following: reduce the daily bag limit to one fish/angler/day; increase the minimum size limit to 90 cm TL; introduce a slot size limit with a minimum size of 80 cm TL and a maximum size limit of 100 cm TL; introduce a closed season from 1 October to 30 November; establish estuarine protected areas where juveniles of this species are fully protected.

The decision, on which of the above management options should be implemented, needs to be taken by the responsible government scientific and management working groups at Marine & Coastal Management (MCM). These decisions should then be passed through a forum fully representative of all user groups such as the South African Marine Linefish Management Association (SAMLMA) to ensure user endorsement before legislation is implemented.
References cited:
VAN DER ELST, R.P., GOVENDER, A. and S.A. CHATER 1993 - The biology and status of the garrick (Lichia amia). In Fish, Fishers and Fisheries. Proceedings of the Second South African Marine Linefish Symposium. Beckley, L.E. and van der Elst R.P. (Eds.).