Juvenile Fish

Survey Methods

Juvenile fish communities in the Tolo area were surveyed using:

Beach seining
Purse seining

Beach seining

A total of 3 soft shores without mangroves and 4 mangrove mudflats inside the Tolo area were chosen for beach seining surveys. Two replicates were conducted in each site in the dry (December to March) and wet seasons (June to September), and one replicate in each transitional season (April to May, and October to November). Sampling of all sites was conducted during daytime, with additional night-time surveys at two selected sites (i.e., Ting Kok and Starfish Bay) to allow day and night comparison. The surveys were conducted during ebb tides.

The dimension of the beach seine net was 10 m in width × 1.5 m in depth with mesh size of 1 mm. The length of each haul was set to 50 m in maximum, whenever possible, perpendicular to the shoreline. During each haul the net was pulled towards the shore along a transect set perpendicular to the shoreline.

Purse seining

2 sites were selected in each section for this approach. At each study site, hauls of 3 minutes of the seine net were conducted from a licensed P4 fishing boat at a speed of 0.5 knots. The purse seine net used was 11 m in width, 10 m in depth and 15 m in purse length, and with a mesh size of 6 mm. The same fishermen and fishing boat from Sam Mun Tsai were hired throughout the whole study period to maintain consistency of sampling method. Two sites near the shore of approximately 2 m depth were chosen in each section for sampling based on the fishermen’s experience in capturing juvenile fishes and 3 hauls were conducted in each site.

In order to collect representative samples of each species for estimates of biomass and length all the
large and rare species were collected after on-board and on-site sorting, and the remaining abundant species were sub-sampled for further species identification and measurement back in the laboratory. Species of special conservation concern, such as seahorses (Hippocampus spp.) were released after species identification, measurement of length and being photographed on site. If too much fish were caught in a haul, a portion if the fish caught will be collected as sub-samples and the remaining will be released immediately during the survey.