The hypothesis written here is not very clear; however, it is possible to answer your question as it is asking for what the independent and dependent variables are. The independent variable is the variable that the experimenter has control over. If "I" am doing the experiment, "I" have control over the "I"ndependent variable. In the case of your roughed out experiment, the independent variable is going to be either the time of year or the location. Two hypothesis are stated, and the first hypothesis mentions time of year, and the other hypothesis says "time/area." It would be beneficial to the hypothesis and entire experimental setup if one independent variable could be determined. "Good" experiments have one independent variable, and everything else should be controlled for.
The dependent variable is the variable that changes because of the changing independent variable. The dependent variable is the result of the experiment. It depends on the independent variable. Based on the information given in the prompt, the dependent variable is the number of shark attacks.
The data collection of this study is going to be difficult. I would imagine that the area being studied is quite large. The study is also likely to take a long time as it is dependent on migration patterns which are seasonal. Furthermore, you do not want to base your results on a single season. That's not enough credible data. If this is just a hypothetical exercise, then the data that you are monitoring and recording is seal population numbers and numbers of shark attacks. Ideally, you are likely looking for a positive correlation. Increased seal numbers result in increased shark attacks.