Diversity, distribution patterns and recruitment of fish in the Lake Kohangatera catchment and the implications of breaching to sea : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Conservation at Massey University
The fish fauna of a relatively unmodified coastal lake, Lake Kohangatera situated 11km south east of Wellington, was investigated as well as the impact of a large scale and prolonged breaching event that occurred in February 2004. A total of ten native species; inanga (Galaxias maculatus), giant kokopu (Galaxias argentus), banded kokopu (Galaxias fasciatus), koaro (Galaxias brevipinnis), longfin eel (Anguilla dieffenbachii) shortfin eel (Anguilla australis), common bully (Gobiomorpus cotidianus), redfin bully, (Gobiomorphus huttoni), smelt (Retropinna retropinna) and lamprey (Geotria australis) and one introduced species; brown trout (Salmo trutta) were found within the catchment. The majority of these fish are diadromous, spending part of their life cycle at sea. Some are able to form land locked populations while others are obligatory migrators. Lake Kohangatera occasionally breaches to sea during high flows. Historical records of the fish assemblage indicate that some of those species which depend on access to the sea periodically disappear from the fauna for periods of time, presumably when breachings do not coincide with their migratory phase. In February 2004 a severe storm caused the lake to breach for a prolonged period of time. Observed changes in the fish fauna following this breaching were the reappearance of redfin bully (Gobiomorphus huttoni) after an absence of several years, smelt (Retropinna retropinna) were recorded for the first time in the catchment, and recruitment of giant kokopu, (Galaxias argentus) banded kokopu (Galaxias fasciatus) and longfin eel (Anguilla dieffenbachii) improved. The diversity of fish species within Gollans Valley, the catchment of Lake Kohangatera. decreased with distance from the sea. Some species exhibited very defined distributions. Eight species were found in the lower catchment and just two or three in the headwaters. Some species were very low in abundance e.g. redfin bully or were restricted to a particular stretch or tributary e.g. koaro and banded kokopu, while others were widespread throughout the catchment e.g. longfin eel.