Determining the size of caging mesh:

Because this study is designed to keep predators out, it was very important to take data regarding the smallest possible mesh size that could be accommodated without limiting goby movement. This would, in effect, reduce as many predators as possible. As we did not want to limit goby movement at all, it was necessary to accept the possible entrance of some small predators such as small lizardfish (see below). If, during the study, these small lizardfish are a significant predator on the gobies, it is assumed that they will be seen at some point during the population counts. If they are not seen, their threat can be seen as minimal if any.

During mid September, data was taken on the size of shrimps versus the size of gobies. This data is as follows:

Table 1: Size of shrimp vs. Size of Goby.

The size range we found through this analysis was from 1.23 cm to 4.5cm. Gobies have been recorded in other studies to 5.8cm. The smallest goby I’ve recorded was 1.23 cm. Therefore the upper limit of a fish that needs to enter a hole is 5.8cm. I estimated from photographs that the shrimp-goby’s width is about 0.15 of the length. Thus, a 5.8 cm goby is approximately 0.87 cm long or 0.34 inches. Therefore, I estimate the smallest sized fencing that I could use to make sure the fish can swim through easily is … ½ inch fencing.

To make sure gobies have no problem swimming through this size fencing I conducted observations on gobies in the bay. I began by closing their holes with the edge of a hand shovel. I then held the fencing in a semicircle around them and proceeded to encourage them with my finger to swim away from me. From my perspective they showed no sign of avoiding the fence. It seemed to posse no obstacle to them in the process of my encouragement. The results were as follows.

Table 2.The size of gobies tested for fence detection.
Size of Goby (cm) Direction change because of fence.

As a fence size of ½ inch is the preferred size to make sure gobies can swim freely through, I wanted to determine the size of any particular predator that could swim through a mesh size such as this. I calculated a table of a 0.45 inch predator (the actual size of the opening; ½ inch is how the mesh is laid. The interior is smaller), calculated the width to length ratio and finally came up with a number of the standard length of a fish (Table 3).

Table 3: Predators of shrimp gobies showing the maximum length of a predator that could fit through a ½ inch mesh cage relative to the smallest length of predator recorded to have eaten a goby.

For goatfish, jacks and hammerheads the maximum size of fish that can get through the cage is significantly smaller than the largest fish that has been recorded to have eaten a goby. For the lizardfish, however, it seems impossible to exclude the smallest predators. Predators down to 6.4cm will be excluded. For the lizardfish gut contents, only 2 out of 15 lizardfish captured on a North West Hawaiian Island cruise that ate gobies were smaller than or equal to 6.4 cm (Parrish unpublished).