Analysis of Catch Length Limit Regulations for Nahuel Huapi Lake, Northern Patagonia, Argentina

Nahuel Huapi Lake is a 554 km² deep ultraoligotrophic lake located in the center of the National Park in Northern Patagonia. Its fish community is composed of five native species (Percichthys trucha, Galaxias platei, Galaxias maculatus, Olivaicthys viedmensis, Odontesthes hatcheri) and three salmonids species introduced at the beginning of the 20th century (Oncorhynchus mykiss, Salmo trutta and Salvelinus fontinalis). Only the salmonids and the native perch are subject to sport fishing. While National Park objectives are centered on conservation of native species, sport fishery supporters advocate fisheries development. Management of the sport fishery has been historically based on regulations copied from other parts of the world without scientific data or monitoring programs to support their validity. For the past 15 years, catch-and-release of native species has been mandatory, allowing the retention of one salmonid per species per fisher with no size limit. Outcomes of this regulation have not been assessed. An ongoing evaluation program of the fish community of the lake using gill nets and hydroacoustics provided the opportunity to evaluate the state of the sport fishery and to simulate varying catch and size limit regulations under increasing fishing pressure. The software program FAST developed by Slipke and Maceina (2001) was used to analyze size population structure through proportional stock density and relative stock density indexes and to simulate the responses of salmonid and perch populations to increased fishing and varying size limit increments of 100 mm starting at 250 mm TL. Results suggest that from the sport fishery perspective, under increasing exploitation, a 350 mm TL size limit for all species would be preferable to the actual no size limit. This regulation should result in a declining numerical catch; however, the mean weight of fish harvested would increase while maintaining an acceptable catch rate. The native perch constitutes a special case; some fishers prefer to keep perch which are more desirable to eat than salmonids. However, the species has a protected status within the National Park which makes its present fishing mortality close to null. The model simulations suggest that the native perch population of Nahuel Huapi Lake would not be endangered by implementing catch size limit regulations similar to those suggested here for salmonids.