|Description||The naked goby (Gobiosoma bosc) is a small benthic fish that inhabits western Atlantic estuaries, where it ranges from Massachusetts to Mexico. Previous work has found limited gene flow between and among populations of G. bosc in western Atlantic estuaries; however, between the benthic nature of the adult organisms and the high winds driving currents in the area, it is thought that the gene flow is likely accounted for by larval dispersal. It is because of their benthic nature that it is assumed that adult naked gobies do not travel far beyond areas with complex microhabitat, but this hypothesis has not yet been tested in the field. Ultimately, we hope to be able to perform a mark-recapture study using visual implant elastomer (VIE) tags as a marking agent in order to evaluate the range of adult naked gobies. According to available literature, VIE has never been used to mark naked gobies in this manner. Therefore, we must first evaluate the effect (if any) that the VIE tag has on the behavior of G. bosc before it can be used reliably in a mark-recapture setting. More specifically, our goal is to examine any possible differences in structured habitat affiliation and movement ability as a result of the subcutaneous injection of a VIE marking tag. The implications of this behavioral analysis could allow the movement of naked gobies, as well as other benthic fish species, to be monitored at a landscape scale.
A total of 383 G. bosc were collected from Mallard Creek at Goose Creek State Park (along the Pamlico River near Washington, NC) throughout the summer of 2018. In order to see what part of the tagging process causes a potential behavior shift, different treatments were designed to evaluate potential behavioral effects from the tagging process, ranging from unhandled (control) to undergoing a full tagging procedure to both the caudal and dorsal regions, with each treatment introducing an additional stressor. In all, seven different treatment types were used during this study with each treatment having three replicates containing ten individuals. Each treatment type had one day replicate, one night replicate and the third replicate was randomly assigned to a day or night observation.
Behavior was observed by means of video recording in order to eliminate the effects of having an observer present in the room. Replicates were video recorded in randomly assigned pairs over a period of several hours only a sample of footage being used for analysis. Footage was stopped every 30 seconds and the apparent behavior that each individual displayed at that moment was recorded using a pre-established behavioral ethogram.
A statistical test of the count data showed no significant effect of treatment type on shelter affinity, indicating that the subcutaneous injection of VIE tags in G. bosc had no differential effect on their perching behaviors compared to all other treatments, and particularly the unhandled controls. This result is vital to the eventual mark-recapture study because it indicates that a major aspect of G. bosc behavior (i.e., its structure affiliation) is unaffected by the introduction of VIE material. However, the results did indicate a significant overall effect of behavior regardless of treatment, which, upon post-hoc pairwise analysis, was revealed to be driven by the darting behavior, which was displayed consistently less than the perching behaviors. This observation is consistent with what is known about adult G. bosc behavior, in that they are usually associated with having strong interactions with the benthos instead of moving constantly throughout the water column.
A separate analysis revealed a significant effect of time of day on the exhibited behaviors (i.e., a significant interaction between behavior and time of day). In other words, the time of day in which the observation took place had a significant influence on the likelihood of certain behaviors being displayed. During the day trials, the perching shelter behavior was displayed more often on average while at night the perching shelter behavior was displayed significantly less often during the observation period. Conversely, the perching exposed behavior was displayed on less often on average during day trials and more often on average during the night trials. This inversion of exposed vs shelter behavior between day and night observations is consistent with what is known about their hunting behavior as these fish are primarily diurnal hunters, hunting their polychaetae and isopod prey within structured habitat (such as oyster shell) throughout the day. At night, it is thought that G. bosc take advantage of the lack of light to avoid their visually based predators in order to venture between structured microhabitats in search of food.
It is also relevant to note that the darting (movement) behavior was displayed much less than that other two behaviors on average despite the time of day in which the trial occurred. This evidence, further supported by the internal behavior effect mentioned earlier, supports the notion that these organisms spend most their time associated with the benthos as opposed to moving throughout their environment.
Overall, this study supports the claim that the introduction of VIE tagging material into G. bosc specimens does not significantly affect their behavior in terms of association with shelter or movement ability regardless of the time of day or the tagging location. Based on these findings, a mark-recapture study will be attempted in the field following the evaluation of the potential change in predator susceptibility as a result of the implantation of VIE material.||