Jetski-based plankton towing as a new method of sampling larval fishes in shallow marine habitats

Abstract

I tested jetski-based plankton towing as a new method of sampling larval fishes in a shallow marine environment in warm temperate South Africa. Larval fishes were collected by towing a stainless-steel ring net behind a three-man jetski. The sampling technique was designed and tested to overcome problematic sampling of shallow sandy beach surf zones and the adjacent, shallow nearshore immediately seaward of the surf zone (behind the breaker line) with the same type of equipment. The composition, density, stage of development, estuary association, and length frequency of larval fish catches obtained by the new sampling method in the surf zone and in the adjacent shallow nearshore were compared. The success of the technique was evaluated by determining the extent of replication of known trends observed in other surf studies in the same climatic region of South Africa using either a seine or pushnet. Preflexion and postflexion larval fishes were collected. Larvae of the family Sparidae dominated the catches. Trends in catch composition, estuary association, and length frequency of the larvae were similar to those found in other studies of warm temperate South African surf zones. Density of larvae varied depending on the type of equipment used, although these results are tentative given the subjectivity of calculation of the water volume sampled and the extent of nursery use by larvae in the habitats sampled in each study. Increased towing times are recommended. Jetski-based plankton towing is a useful alternative technique for sampling larval fishes in shallow habitats and can easily be applied in surf zones, shallow nearshore areas, and estuaries. The technique greatly increases sampling agility in previously problematic sampling areas.